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1 Status of the Main Report World’s Soil Resources © FAO | Giuseppe Bizzarri INTERGOVERNMENTAL INTERGOVERNMENTAL TECHNICAL PANEL ON SOILS TECHNICAL PANEL ON SOILS

2 Status of the World’s Soil Resources Main report Prepared by Intergovernmental Technical Panel on Soils (ITPS) Luca Montanarella (Chair), Mohamed Badraoui, Victor Chude, Isaurinda Dos Santos Baptista Costa, Tekalign Mamo, Martin Yemefack, Milkha Singh Aulang, Kazuyuki Yagi, Suk Young Hong, Pisoot Vijarnsorn, Gan Lin Zhang, Dominique Arrouays, Helaina Black, Pavel Krasilnikov, Jaroslava Sobocá, Julio Alegre, Carlos Roberto Henriquez, Maria de Lourdes Mendonça-Santos, Miguel Taboada, David Espinosa Victoria, Abdullah Alshankiti, Sayed Kazem Alavi Panah, Elsiddig Ahmed El Mustafa El Sheikh, Jon Hempel, Dan Pennock, Marta Camps Arbestain, Neil McKenzie. Luca Montanarella (Chair), Victor Chude (Africa), Kazuyuki Yagi (Asia), Pavel Krasilnikov Editorial board: (Europe), Seyed Kazem Alavi Panah (Near East and North Africa), Maria de Lourdes Mendonça-Santos (Latin America and the Caribbean), Dan Pennock (North America), Neil McKenzie (SW Pacific). Managing editor: Freddy Nachtergaele Coordinating Lead Authors and Regional Coordinators/Authors: Mubarak Abdelrahman Abdalla, Seyed Kazem Alavipanah, André Bationo, Victor Chude, Juan Comerma, Maria Gerasimova, Jon Hempel, Srimathie Indraratne, Pavel Krasilnikov, Neil McKenzie, Maria de Lourdes Mendonça- Santos, Chencho Norbu, Ayo Ogunkunle, Dan Pennock, Thomas Reinsch, David Robinson, Pete Smith, Miguel Taboada and Kazuyuki Yagi. Reviewing Authors : Dominique Arrouays, Richard Bardgett, Marta Camps Arbestain, Tandra Fraser, Ciro Gardi, Neil McKenzie, Luca Montanarella, Dan Pennock and Diana Wall. : Lucrezia Caon, Nicoletta Forlano, Cori Keene, Matteo Sala, Alexey Sorokin, Isabelle Verbeke, Editorial team Christopher Ward. GSP Secretariat : Moujahed Achouri, Maryse Finka and Ronald Vargas. Other contributing Authors: Adams, Mary Beth Balyuk, Svyatoslav Cerkowniak, Darrel Adhya Tapan, Kumar Bardgett, Richard Charzynski, Przemyslaw Agus, Fahmuddin Basiliko, Nathan Clark, Joanna Al Shankithi, Abdullah Batkhishig, Ochirbat Clothier, Brent Alegre, Julio Bedard-Haughn, Angela Coelho, Maurício Rizzato Aleman, Garcia Bielders, Charles Colditz, Roland René Alfaro, Marta Bock, Michael Collins, Alison Alyabina, Irina Bockheim, James Compton, Jana Anderson, Chris Bondeau, Alberte Condron, Leo Anjos, Lucia Brinkman, Robert Corso, Maria Laura Arao, Tomohito Bristow, Keith Cotrufo, Francesca Asakawa, Susumu Broll, Gabrielle Critchley, William Aulakh, Milkha Bruulsma, Tom Cruse, Richard Ayuke, Frederick Bunning, Sally da Silva, Manuela Bai, Zhaohai Bustamante, Mercedes Dabney, Seth Baldock, Jeff Caon, Lucrezia Daniels, Lee Balks, Megan Carating, Rodel de Souza Dias, Moacir Status of the World’s Soil Resources | Main Report II

3 Dick, Warren Leys, John Seneviratne, Sonia Dos Santos Baptista, Isaurinda Lobb, David Shahid, Shabbir Drury, Craig Ma, Lin Sheffield, Justin El Mustafa El Sheikh, Ahmed Macias, Felipe Sheppard, Steve Elsiddig Maina, Fredah Sidhu, Gurjant Elder-Ratutokarua, Maria Mamo, Tekalign Sigbert, Huber Elliott, Jane Mantel, Stephan Smith, Scott Espinosa, David McDowell, Richard Sobocká, Jaroslava Fendorf, Scott Medvedev, Vitaliy Sönmez, Bülent Ferreira, Gustavo Miyazaki, Tsuyushi Spicer, Anne Flanagan, Dennis Moore, John Sposito, Garrison Gafurova, Laziza Morrison, John Stolt, Mark Gaistardo, Carlos Cruz Mung'atu, Joseph Suarez, Don Govers, Gerard Muniz, Olegario Takata, Yusuke Grayson, Sue Nachtergaele, Freddy Tarnocai, Charles Griffiths, Robert Nanzyo, Masami Tassinari, Diego Grundy, Mike Ndiaye, Déthié Tien, Tran Minh Hakki Emrah, Erdogan Neall, Vince Toth, Tibor Hamrouni, Heidi Noroozi, Ali Akbar Trumbore, Susan Hanly, James Obst, Carl Tuller, Markus Harper, Richard Ogle, Stephen Urquiaga Caballero, Segundo Harrison, Rob Okoth, Peter Urquiza Rodrigues, Nery Havlicek, Elena Omutu, Christian Van Liedekerke, Marc Hempel, Jon Or, Dani Van Oost, Kristof Henriquez, Carlos Roberto Owens, Phil Vargas, Rodrigo Hewitt, Allan Pan, Genxing Vargas, Ronald Hiederer, Roland Panagos, Panos Vela, Sebastian House, Jo Parikh, Sanjai Vitaliy, Medvedev Huising, Jeroen Pasos Mabel, Susana (†) Vrscaj, Boris Ibánez, Juan José Paterson, Garry Waswa, Boaz Jain, Atul Paustian, Keith Watanabe, Kazuhiko Jefwa, Joyce Pietragalla, Vanina Watmough, Shaun Jung, Kangho Pla Sentis, Ildefonso Webb, Mike Kadono, Atsunobu Polizzotto, Matthew Weerahewa, Jeevika Kawahigashi, Masayuki Pugh, Thomas West, Paul Kelliher, Frank Qureshi, Asad Wiese, Liesl Kihara, Job Reddy, Obi Wilding, Larry Konyushkova, Maria Reid, D. Keith Xu, Renkou Kuikman, Peter Richter, Dan Yan, Xiaoyuan Kuziev, Ramazan Rivera-Ferre, Marta Yemefack, Martin Lai, Shawntine Rodriguez Lado, Luis Yokoyama, Kazunari Lal, Rattan Roskruge, Rick Zhang, Fusuo Lamers, John i Rumpel, Cornelia Zhou, Dongme Lee, Dar-Yuan Zobeck, Ted Rys, Gerald Lee, Seung Heon Schipper, Louis Lehmann, Johannes Schoknecht, Noel FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Rome, 2015 Status of the World’s Soil Resources | Main Report III

4 Disclaimer and copyright Recommended citation: FAO and ITPS. 2015. Status of the World’s Soil Resources (SWSR) – Main Report. Food and Agriculture Organization of the United Nations and Intergovernmental Technical Panel on Soils, Rome, Italy The designations employed and the presentation of material in this information product do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations (FAO) concerning the legal or development status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. The mention of specific companies or products of manufacturers, whether or not these have been patented, does not imply that these have been endorsed or recommended by FAO in preference to others of a similar nature that are not mentioned. The views expressed in this information product are those of the author(s) and do not necessarily reflect the views or policies of FAO. ISBN 978-92-5-109004-6 © FAO, 2015 FAO encourages the use, reproduction and dissemination of material in this information product. Except where otherwise indicated, material may be copied, downloaded and printed for private study, research and teaching purposes, or for use in non-commercial products or services, provided that appropriate acknowledgement of FAO as the source and copyright holder is given and that FAO’s endorsement of users’ views, products or services is not implied in any way. All requests for translation and adaptation rights, and for resale and other commercial use rights should be www.fao.org/contact-us/licence -request or addressed to [email protected] . made via FAO information products are available on the FAO website www.fao.org/publications [email protected] . and can be purchased through Status of the World’s Soil Resources | Main Report IV

5 Table of contents Disclaimer and copyright | IV | V Table of contents Foreword | XIX Preface | Scope of The State of the World’s Soil Resources | XXI Acknowledgment | XXII List of abbreviations | XXIV List of tables | XXXIII List of boxes | XXXIV List of figures | XXXV Preface | 1 Global soil resources | 3 1 | Introduction | 4 1.1 | The World Soil Charter | 4 1.2 | Basic concepts | 7 Sustainable soil management | 8 Soil degradation and threats to soil functions | 8 Soil functions and ecosystem services | 9 Soils and natural capital | 9 Planetary boundaries and safe operating space for humanity | 9 Biodiversity | 10 2 | The role of soils in ecosystem processes | 13 2.1 | Soils and the carbon cycle | 13 | 14 2.1.1 | Quantitative amounts of organic C stored in soil Status of the World’s Soil Resources | Main Report V

6 2.1.2 | Nature and formation of soil organic C | 15 | 16 2.1.3 | Soil C pools 2.1.4 | Factors influencing soil C storage | 17 2.1.5 | Carbon cycle: knowledge gaps and research needs | 18 2.1.6 | Concluding remarks | 18 2.2 | Soils and the nutrient cycle | 18 2.2.1 | The nutrient cycle: knowledge gaps and research needs | 21 2.3 | Soils and the water cycle | 21 2.4 | Soil as a habitat for organisms and a genetic pool | 24 3 | Global Soil Resources | 31 3.1 | The evolution of soil definitions | 31 3.2 | Soil definitions in different soil classification systems | 32 3.3 | Soils, landscapes and pedodiversity | 32 3.4 | Properties of the soil | 33 3.5 | Global soil maps | 33 | 34 3.6 | Soil qualities essential for the provision of ecosystem services 3.6.1 | Inherent soil fertility | 35 3.6.2 | Soil moisture qualities and limitations | 37 3.6.3 | Soils properties and climate change | 37 3.6.4 | Soil erodibility and water erosion | 38 3.6.5 | Soil workability | 39 3.6.6 | Soils and ecosystem goods and services | 40 3.7 | Global assessments of soil change - a history | 43 3.7.1 | GLASOD: expert opinion | 43 3.7.2 | LADA-GLADIS: the ecosystem approach | 45 3.7.3 | Status of the World’s Soil Resources | 46 4 | Soils and Humans | 50 Status of the World’s Soil Resources | Main Report VI

7 4.1 | Current land cover and land use | 50 | 53 4.2 | Historical land cover and land use change 4.3 | Interactions between soils, land use and management | 54 4.3.1 | Land use change and soil degradation | 54 4.3.2 | Land use intensity change | 60 4.3.3 | Land use change resulting in irreversible soil change | 65 4.4 | Atmospheric deposition | 72 4.4.1 | Atmospheric deposition | 72 4.4.2 | Main atmospheric pollutants: Synopsis of current state of knowledge | 73 4.4.3 | Knowledge gaps and research needs | 76 Global Soil Change Drivers, Status and Trends | 88 5 | Drivers of global soil change | 89 5.1 | Population growth and urbanization | 89 5.1.1 | Population dynamics | 89 5.1.2 | Urbanization | 91 | 91 5.2 | Education, cultural values and social equity 5.3 | Marketing land | 92 5.4 | Economic growth | 94 5.5 | War and civil strife | 94 5.6 | Climate change | 96 6 | Global soil status, processes and trends | 100 6.1.1 | Processes | 100 6.1.2 | Status of Soil Erosion | 101 6.1.3 | Soil erosion versus soil formation | 103 6.1.4 | Soil erodibility | 104 6.1.5 | Soil erosion and agriculture | 104 6.1.6 | Soil erosion and the environment | 105 Status of the World’s Soil Resources | Main Report VII

8 6.1.7 | Effects of hydrology and water | 106 | 107 6.1.8 | Vegetation effects 6.1.9 | Alteration of nutrient and dust cycling | 107 6.1.10 | Trends in soil erosion | 108 6.1.11 | Conclusions | 108 6.2 | Global soil organic carbon status and trends | 109 6.2.1 | Introduction | 109 6.2.2 | Estimates of global soil organic carbon stocks | 109 6.2.3 | Spatial distribution of SOC | 111 6.2.4 | Spatial distribution of carbon in biomass | 113 6.2.5 | Distribution of terrestrial carbon pool by vegetation class | 114 6.2.6 | Historic trends in soil carbon stocks | 116 6.2.7 | Future loss of SOC under climate change | 118 6.2.8 | Conclusions | 118 6.3 | Soil contamination status and trends | 119 | 119 6.3.1 | Introduction 6.3.2 | Global status of soil contamination | 119 6.3.3 | Trends and legislation | 121 6.4 | Soil acidification status and trends | 122 6.4.1 | Processes and causes of acidification | 122 6.4.2 | Impact of soil acidification | 123 6.4.3 | Responses to soil acidification | 123 6.4.4 | Global status and trends of soil acidification | 123 6.5 | Global status of soil salinization and sodification | 124 6.5.1 | Status and extent | 124 6.5.2 | Causes of soil salinity | 126 6.5.4 | Trends and impacts | 126 Status of the World’s Soil Resources | Main Report VIII

9 6.5.5 | Responses | 126 | 127 6.6 | Soil biodiversity status and trends 6.6.1 | Introduction | 127 6.6.2 | Soil biota and land use | 128 6.6.3 | Conclusions | 129 6.7 | Soil sealing: status and trends | 130 6.8 | Soil nutrient balance changes: status and trends | 132 6.8.1 | Introduction | 132 6.8.2 | Principles and components of soil nutrient balance calculations | 133 6.8.3 | Nutrient budgets: a matter of spatial scale | 134 6.8.4 | Nutrient budgets: a matter of land use system, land use type, managementand household equity | 135 6.8.5 | What does the future hold? | 136 6.9 | Soil compaction status and trends | 137 6.9.1 | Effect of tillage systems on compaction | 138 | 139 6.9.2 | What is the extent of deep soil compaction? 6.9.3 | Solutions to soil compaction problems | 139 6.10 | Global soil-water quantity and quality: status, processes and trends | 140 6.10.1 | Processes | 140 6.10.2 | Quantifying soil moisture | 142 6.10.3 | Status and trends | 143 6.10.4 | Hotspots of pressures on soil moisture | 144 6.10.5 | Conclusions | 146 Soil change: impacts and responses | 168 7 | The impact of soil change on ecosystem services | 169 7.1 | Introduction | 169 7.2 | Soil change and food security | 172 Status of the World’s Soil Resources | Main Report IX

10 7.2.1 | Soil erosion | 175 | 178 7.2.2 | Soil sealing 7.2.3 | Soil contamination | 178 7.2.4 | Acidification | 178 7.2.5 | Salinization | 178 7.2.6 | Compaction | 179 7.2.7 | Nutrient imbalance | 179 7.2.8 | Changes to soil organic carbon and soil biodiversity | 179 7.3 | Soil change and climate regulation | 181 7.3.1 | Soil carbon | 181 7.3.2 | Nitrous oxide emissions | 183 7.3.3 | Methane emissions | 184 7.3.4 | Heat and moisture transfer | 185 7.4 | Air quality regulation | 188 7.4.2 | Ammonia emissions | 188 | 188 7.4.3 | Aerosols 7.5 | Soil change and water quality regulation | 189 7.5.1 | Nitrogen and phosphorous retention and transformation | 190 7.5.2 | Acidification buffering | 191 7.5.3 | Filtering of reused grey water | 192 7.5.4 | Processes impacting service provision | 192 7.6 | Soil change and water quantity regulation | 194 7.6.2 | Precipitation interception by soils | 194 7.6.3 | Surface water regulation | 195 7.7 | Soil change and natural hazard regulation | 195 7.7.1 | Soil landslide hazard | 197 7.7.2 | Soil hazard due to earthquakes | 198 Status of the World’s Soil Resources | Main Report X

11 7.7.3 | Soil and drought hazard | 198 | 199 7.7.4 | Soil and flood hazard 7.7.5 | Hazards induced by thawing of permafrost soil | 199 7.8 | Soil biota regulation | 199 7.9 | Soils and human health regulation | 201 7.10 | Soil and cultural services | 203 8 | Governance and policy responses to soil change | 223 8.2 | Soils as part of global natural resources management | 224 8.2.1 | Historical context | 224 8.2.2 | Global agreements relating to soils | 225 8.3 | National and regional soil policies | 228 8.3.1 | Sustainable soil management – criteria and supporting practices | 228 8.3.2 | Education about soil and land use | 229 8.3.3 | Soil research, development and extension | 229 | 229 8.3.4 | Private benefits, public goods and payments for ecosystem services 8.3.5 | Intergenerational equity | 230 8.3.6 | Land degradation and conflict | 230 8.4 | Regional soil policies | 231 8.4.1 | Africa | 231 8.4.2 | Asia | 232 8.4.3 | Europe | 232 8.4.4 | Eurasia | 232 8.4.5 | Latin America and the Caribbean (LAC) | 233 8.4.6 | The Near East and North Africa (NENA) | 233 8.4.7 | North America | 234 | 234 8.4.8 | Southwest Pacific Status of the World’s Soil Resources | Main Report XI

12 8.5 | Information systems, accounting and forecasting | 235 | 236 8.5.1 | Soil information for markets 8.5.2 | Environmental accounting | 236 8.5.3 | Assessments of the soil resource | 237 9 | Regional Assessment of Soil Changes in Africa South of the Sahara | 242 9.1 | Introduction | 243 9.2 | Stratification of the Region | 244 9.2.1 | Arid zone | 244 9.2.2 | Semi-arid zone | 246 9.2.3 | Sub-humid zone | 246 9.2.5 | Highlands zone | 247 9.3 | General soil threats in the region | 247 9.3.1 | Erosion by water and wind | 247 9.3.2 | Loss of soil organic matter | 248 9.3.3 | Soil nutrient depletion | 249 | 250 9.3.4 | Loss of soil biodiversity 9.3.5 | Soil contamination and pollution | 251 9.3.6 | Soil acidification | 252 9.3.7 | Salinization and sodification | 252 9.3.8 | Waterlogging | 252 9.3.9 | Compaction, crusting and sealing | 252 9.4 | The most important soil threats in Sub-Saharan Africa | 253 9.4.1 | Erosion by water and wind | 254 9.4.2 | Loss of soil organic matter | 258 9.4.3 | Soil nutrient depletion | 260 9.5 | Case studies | 263 9.5.1 | Senegal | 263 Status of the World’s Soil Resources | Main Report XII

13 9.5.2 | South Africa | 266 | 275 9.6 | Summary of conclusions and recommendations 10 | Regional Assessment of Soil Change in Asia | 287 10.1 | Introduction | 288 10.2. Stratification of the region | 288 10.2. 1 | Climate and agro-ecology | 288 10.2.2 | Previous regional soil assessments | 289 10.3 | General threats to soils in the region | 291 10.3.1 | Erosion by wind and water | 291 10.3.2 | Soil organic carbon change | 291 10.3.3 | Soil contamination | 291 10.3.4 | Soil acidification | 293 10.3.5 | Soil salinization and sodification | 293 10.3.6 | Loss of soil biodiversity | 294 10.3.7 | Waterlogging | 295 | 295 10.3.8 | Nutrient imbalance 10.3.9 | Compaction | 296 10.3.10 | Sealing and capping | 297 10.4 | Major threats to soils in the region | 297 10.4.1 | Erosion | 297 10.4.2 | Soil organic carbon change | 299 10.4.3 | Soil salinization and sodification | 301 10.4.4 | Nitrogen imbalance | 302 10.5 | Case studies | 304 10.5.1 | Case study for India | 304 10.5.2 | Case study for Indonesia | 307 10.5.3 | Case study for Japan | 310 Status of the World’s Soil Resources | Main Report XIII

14 10.5.4 | Case study of greenhouse gas emissions from paddy fields | 314 | 315 10.6 | Conclusion 11 | Regional assessment of soil changes in Europe and Eurasia | 330 11.1 | Introduction | 331 11.2 | Stratification of the region | 331 11.3 | General threats to soils in the region | 335 11.4. Major threats to soils in Europe and Eurasia | 338 11.4.1 | Soil contamination | 338 11.4.2 | Sealing and capping | 339 11.4.3 | Soil organic matter decline | 339 11.4.4 | Salinization and sodification | 341 11.5 | Case studies | 344 11.5.1 | Case study: Austria | 344 11.5.2 | Case study: Ukraine | 350 11.5.3 | Case study: Uzbekistan | 353 | 356 11.6 | Conclusion 12 | Regional assessment of soil changes in Latin America and the Caribbean | 364 12.1 | Introduction | 365 12.2 | Biomes, ecoregions and general soil threats in the region. | 366 12.3. General soil threats in the region | 371 12.3.1 | Erosion by water and wind | 371 12.3.2 | Soil organic carbon change | 372 12.3.3 | Salinization and sodification | 372 12.3.4 | Nutrient imbalance | 372 12.3.5 | Loss of soil biodiversity | 372 12.3.6 | Compaction | 373 12.3.7 | Waterlogging | 373 Status of the World’s Soil Resources | Main Report XIV

15 12.3.8 | Soil acidification | 373 | 373 12.3.9 | Soil contamination 12.3.10 | Sealing | 373 12.4 | Major threats to soils | 374 12.4.1 | Soil erosion | 374 12.4.2 | Soil organic carbon change | 375 12.4.3 | Soil salinization | 380 12.5 | Case studies | 382 12.5.1 | Argentina | 382 12.5.2 | Cuba | 386 12.6 | Conclusions and recommendations | 388 13 | Regional Assessment of Soil Changes in the Near East and North Africa | 399 13.1 | Introduction | 400 13.2 | Major land use systems in the Near East and North Africa | 402 13.3 | Major threats to soils in the region | 404 | 404 13.3.1 | Erosion 13.3.2 | Soil organic carbon change | 406 13.3.3 | Soil contamination | 406 13.3.4 | Soil acidification | 406 13.3.5 | Soil salinization/sodification | 407 13.3.6 | Loss of soil biodiversity | 407 13.3.7 Waterlogging | 408 13.3.8 | Nutrient balance change | 408 13.3.9 | Compaction | 409 13.3.10 | Sealing/capping | 409 13.4 | Major soil threats in the region | 411 13.4.1 | Water and wind erosion | 411 Status of the World’s Soil Resources | Main Report XV

16 13.4.2 | Soil salinization/sodification | 416 | 417 13.4.3 | Soil organic carbon change 13.4.4 | Soil contamination | 420 13.5 | Case studies | 423 13.5.1 | Case study: Iran | 423 13.6.2 | Case Study: Tunisia | 426 13.6 | Conclusions | 430 14 | Regional Assessment of Soil Changes in North America | 442 14.1 | Introduction | 443 14.2 | Regional stratification and soil threats | 443 14.2.1 | Regional stratification and land cover | 443 14.3 | Soil threats | 447 14.3.1 | Soil acidification | 447 14.3.2 | Soil contamination | 448 | 450 14.3.3 | Soil salinization 14.3.4 | Soil sealing/capping | 452 14.3.5 | Soil compaction | 453 14.3.6 | Waterlogging and wetlands | 454 14.4 | Major soil threats | 454 14.4.1 | Soil erosion | 455 14.4.2 | Nutrient imbalance | 456 14.4.3 | Soil organic carbon change | 457 14.4.4 | Soil biodiversity | 459 14.5 | Case study: Canada | 460 14.5.1 | Water and wind erosion | 460 | 463 14.5.2 | Soil organic carbon change Status of the World’s Soil Resources | Main Report XVI

17 14.5.4 | Nutrient imbalance | 464 | 467 14.6 | Conclusions and recommendations 15 | Regional Assessment of Soil Change in the Southwest Pacific | 476 15.1 | Introduction | 477 15.2 | The major land types in the region | 477 15.3 | Climate | 480 15.4 | Land use | 480 15.4.1 | Historical context | 480 15.4.2 | Nineteenth and twentieth centuries | 481 15.4.3 | Contemporary land-use dynamics | 482 15.5 | Threats to soils in the region | 485 15.5.1 | Erosion by wind and water | 485 15.5.2 | Soil organic carbon change | 487 15.5.1 | Soil contamination | 490 15.5.2 | Soil acidification | 492 15.5.3 | Salinization and sodification | 494 15.5.4 | Loss of soil biodiversity | 495 15.5.5 | Waterlogging | 496 15.5.6 | Nutrient imbalance | 496 15.5.7 | Compaction | 497 15.5.8 | Sealing and capping | 498 15.6 | Case studies | 498 15.6.1 | Case study one: Intensification of land use in New Zealand | 498 15.6.3 | Case study two: Soil management challenges in southwest Western Australia | 500 | 504 15.6.2 | Case study three: Atoll Islands in the Pacific 15.6.4 | Case study four: DustWatch – an integrated response to wind erosion in Status of the World’s Soil Resources | Main Report XVII

18 Australia | 505 15.7 | Conclusions | 507 16 | Regional Assessment of Soil Change in Antarctica | 520 16.1 | Antarctic soils and environment | 521 16.2 | Pressures/threats for the Antarctic soil environment | 521 16.3 | Response | 523 Annex | Soil groups, characteristics, distribution and ecosystem services | 527 1 | Soils with organic layers | 528 2 | Soils showing a strong human influence | 530 3 | Soils with limitations to root growth | 534 4 | Soils distinguished by Fe/Al chemistry | 544 5 | Soils with accumulation of organic matter in the topsoil | 561 6 | Soils with accumulation of moderately soluble salts | 569 7 | Soils with a clay-enriched subsoil | 575 8 | Soils with little or no profile development | 585 9 | Permanently flooded soils | 593 Glossary of technical terms | 599 Authors and affiliations | 602 Status of the World’s Soil Resources | Main Report XVIII

19 Foreword This document presents the first major global assessment ever on soils and related issues. Why was such an assessment not carried out before? We have taken soils for granted for a long time. Nevertheless, soils are the foundation of food production and food security, supplying plants with nutrients, water, and support for their roots. Soils function as Earth’s largest water filter and storage tank; they contain more carbon than all above-ground vegetation, hence regulating emissions of carbon dioxide and other greenhouse gases; and they host a tremendous diversity of organisms of key importance to ecosystem processes. However, we have been witnessing a reversal in attitudes, especially in light of serious concerns expressed by soil practitioners in all regions about the severe threats to this natural resource. In this more auspicious context, when the international community is fully recognizing the need for concerted action , the Intergovernmental Technical Panel on Soils (ITPS), the main scientific advisory body to the Global Soil Partnership (GSP) hosted by the Food and Agriculture Organization of the United Nations (FAO), took the initiative to prepare this much needed assessment. The issuance of this first “Status of the World’s Soil Resources” report was most appropriately timed with the occasion of the International Year of Soils (2015) declared by the General Assembly of the United Nations. It was made possible by the commitment and contributions of hosts of reputed soil scientists and their institutions. Our gratitude goes to the Lead Authors, Contributing Authors, Editors and Reviewers who have participated in this effort, and in particular to the Chairperson of the ITPS, for his dedicated guidance and close follow up. Many governments have supported the participation of their resident scientists in the process and contributed resources, thus also assuring the participation of experts from developing countries and countries with economies in transition. In addition, a Technical Summary was acknowledged by representatives of governments assembled in the Plenary Assembly of the GSP, signaling their appreciation of the many potential uses of the underlying report. Even more comprehensive and inclusive arrangements will be sought in the preparations of further, updated versions. The report is aimed at scientists, laymen and policy makers alike. It provides in particular an essential benchmark against periodical assessment and reporting of soil functions and overall soil health at global and regional levels. This is of particular relevance to the Sustainable Development Goals (SDGs) that the international community pledged to achieve. Indeed, these goals can only be achieved if the crucial natural resources – of which soils is one – are sustainably managed. The main message of this first edition is that, while there is cause for optimism in some regions, the majority of the world’s soil resources are in only fair, poor or very poor condition. Today, 33 percent of land is moderately to highly degraded due to the erosion, salinization, compaction, acidification and chemical pollution of soils. Further loss of productive soils would severely damage food production and food security, amplify food-price volatility, and potentially plunge millions of people into hunger and poverty. But the report also offers evidence that this loss of soil resources and functions can be avoided. Sustainable soil management, using scientific and local knowledge and evidence-based, proven approaches and technologies, can increase nutritious food supply, provide a valuable lever for climate regulation and safeguarding ecosystem services. Status of the World’s Soil Resources | Main Report XIX

20 We can expect that the extensive analytical contents of this report will greatly assist in galvanizing action at all levels towards sustainable soil management, also in line with the recommendations contained in the updated World Soil Charter and as a firm contribution to achieve the Sustainable Development Goals. We are proud to make this very first edition of the Status of the World’s Soil Resources report available for the international community, and reiterate once again our commitment to a world free of poverty, hunger and malnutrition. JOSÉ GRAZIANO DA SILVA FAO Director-General Status of the World’s Soil Resources | Main Report XX

21 Preface | Scope of The State of the World’s Soil Resources The main objectives of are: (a) to provide a global scientific The State of the World’s Soil Resources assessment of current and projected soil conditions built on regional data analysis and expertise; (b) to explore the implications of these soil conditions for food security, climate change, water quality and quantity, biodiversity, and human health and wellbeing; and (c) to conclude with a series of recommendations for action by policymakers and other stakeholders. The book is divided into two parts. The first part deals with global soil issues (Chapters 1 to 8). This is followed by a more specific assessment of regional soil change, covering in turn Africa South of the Sahara, Asia, Europe, Latin America and the Caribbean, the Near East and North Africa, North America, the Southwest Pacific and Antarctica. (Chapters 9 to 16). The technical and executive summaries are published separately. In Chapter 1 the principles of the World Soil Charter are discussed, including guidelines for stakeholders to ensure that soils are managed sustainably and that degraded soils are rehabilitated or restored. For long, soil was considered almost exclusively in the context of food production. However, with the increasing impact of humans on the environment, the connections between soil and broader environmental concerns have been made and new and innovative ways of relating soils to people have begun to emerge in the past two decades. Societal issues such as food security, sustainability, climate change, carbon sequestration, greenhouse gas emissions, and degradation through erosion and loss of organic matter and nutrients are all closely related to the soil resource. These ecosystem services provided by the soil and the soil functions that support these services are central to the discussion in the report. In Chapter 2 synergies and trade-offs are reviewed, together with the role of soils in supporting ecosystem services, and their role in underpinning natural capital. The discussion then covers knowledge - and knowledge gaps - on the role of soils in the carbon, nitrogen and water cycles, and on the role of soils as a habitat for organisms and as a genetic pool. This is followed in Chapter 3 by an overview of the diversity of global soil resources and of the way they have been assessed in the past. Chapter 4 reviews the various anthropogenic and natural pressures - in particular, land use and soil management – which cause chemical, physical and biological variations in soils and the consequent changes in environmental services assured by those soils. Land use and soil management are in turn largely determined by socio-economic conditions. These conditions are the subject of Chapter 5, which discusses in particular the role of population dynamics, market access, education and cultural values as well as the wealth or poverty of the land users. Climate change and its anticipated effects on soils are also discussed in this chapter. Chapter 6 discusses the current global status and trends of the major soil processes threatening ecosystem services. These include soil erosion, soil organic carbon loss, soil contamination, soil acidification, soil salinization, soil biodiversity loss, soil surface effects, soil nutrient status, soil compaction and soil moisture conditions. Chapter 7 undertakes an assessment of the ways in which soil change is likely to impact on soil functions and the likely consequences for ecosystem service delivery. Each subsection in this chapter outlines key soil processes involved with the delivery of goods and services and how these are changing. The subsections then review how these changes affect soil function and the soil’s contribution to ecosystem service delivery. The discussion is organized according to the reporting categories of the Millennium Ecosystem Assessment, including provisioning, supporting, regulating and cultural services. Status of the World’s Soil Resources | Main Report XXI

22 Chapter 8 of the report explores policy, institutional and land use management options and responses to soil changes that are available to governments and land users. The regional assessments in Chapters 9 to 16 follow a standard outline: after a brief description of the main biophysical features of each region, the status and trends of each major soil threat are discussed. Each chapter ends with one or more national case studies of soil change and a table summarizing the results, including the status and trends of soil changes in the region and related uncertainties. Status of the World’s Soil Resources | Main Report XXII

23 Acknowledgments The Status of the World’s Soil Resources report was made possible by the commitment and voluntary work of the world’s leading soil scientists and the institutions they are affiliated with. We would like to express our gratitude to all the Coordinating Lead Authors, Lead Authors, Contributing Authors, Review Editors and Reviewers. We would also like to thank the editorial staff and the GSP Secretariat for their dedication in coordinating the production of this first seminal report. Appreciation is expressed to many Governments who have supported the participation of their resident scientists in this major enterprise. In particular, our gratitude to the European Commission who financially supported the development and publication of this report. Status of the World’s Soil Resources | Main Report XXIII

24 List of abbreviations AAFC Agriculture and Agri-Food Canada Arab Centre for the Study of Arid Zones and Dry Lands ACSAD Anno Domini AD AEZ Agro-Ecological Zones Association Française Pour L’étude Du Sol AFES African Soil Information Service AFSIS AGES Austrian Agency for Health and Food Safety AGRA Alliance for a Green Revolution in Africa AKST Agricultural Knowledge Science and Technology ALOS Advanced Land Observation Satellite AMA Agencia De Medio Ambiente AMF Arbuscular Mycorrhizal Fungi ANC Acid-Neutralising Capacity AOAD Arab Organization for Agricultural Development AOT Aerosol Optical Thickness APO-FFTC Asian Productivity Organization- Food & Fertilizer Technology Center ARC Agricultural Research Council ASGM Artisanal and Small-Scale Gold Mining Advanced Science Institutesseries ASI Asia Soil Partnership ASP ASSOD Assessment of Human-Induced Soil Degradation in South and Southeast Asia African Union AU Biome of Australia Soil Environments BASE BC (1) Black Carbon; (2) Before Christ BD Biodiversity BDP Bureau for Development Policy BIH Bosnia And Herzegovina BMLFUW Austrian Federal Ministry of Agriculture, Forestry, Environment and Water Management BNF Biological Nitrogen Fixing BOM Bureau of Meteorology BP Before Present (1 January 1950) C:N Carbon To Nitrogen Ratio CA Conservation Agriculture CAAA Clean Air Act Amendments Comprehensive Africa Agriculture Development Programme CAADP Status of the World’s Soil Resources | Main Report XXIV

25 CACILM Central Asian Countries Initiative for Land Management Council of Arab Ministers Responsible For the Environment CAMRE Central Arid Zone Research Institute CAZRI CBD Convention on Biological Diversity CBM-CFS Carbon Budget Model of the Canadian Forest Sector CCAFS Climate Change, Agriculture and Food Security CCME Canadian Council Of Ministers of the Environment CE Common Era (Also Current era or Christian era) CEC (1) Cation Exchange Capacity; (2) Commission of the European Communities CECS Chemicals of Emerging Concern CEPAL Comisión Económica Para América Latina Y El Caribe CF Commercial Farming CGIAR Global Agricultural Research Partnership CIAT International Center for Tropical Agriculture CIFOR Center for International Forestry Research CITMA Ministerio De Ciencia, Tecnologia Y Medio Ambiente CLIMSOIL Review of Existing Information on the Interrelations between Soil and Climate Change CLM Contaminated Land Management CMIP 5 Coupled Model Intercomparison Project Phase 5 COM Commission Working Documents Comision Nacional Para El Conocimiento Y Uso De La Biodiversidad CONABIO Comisión Nacional Forestal CONAFOR COSMOS Cosmic-Ray Soil Moisture Observing System CRC Risk of Colorectal Cancer CRP Conservation Reserve Program CSA Climate-Smart Agriculture CSIF-SLM Country Strategic Investment Framework for Sustainable Land Management CSIRO Commonwealth Scientific and Industrial Research Organisation CSM-BGBD Conservation and Sustainable Management of Below-Ground Biodiversity CSSRI The Central Soil Salinity Research Institute CSWCR&TI Central Soil & Water Conservation Research & Training Institute (India) DAFWA Department Of Agriculture and Food, Western Australia DBC Dissolved Black Carbon DDT Dichlorodiphenyltrichloroethane DEA Deliberate Evacuation Area DECA Department Of Environment and Conservation, Australia DED Dust Event Days Department Of Environment and Natural Resources DENR Status of the World’s Soil Resources | Main Report XXV

26 DEST Australian Government Department of Education, Science and Training Dynamic Global Vegetation Models DGVMS Dissolved Inorganic Carbon DIC DLDD Desertification, Land Degradation and Drought DNA Deoxyribonucleic Acid DOC Dissolved Organic Carbon DOI Digital Object Identifier DPYC Dissolved Pyrogenic Carbon DSEWPAC Department Of Sustainability, Environment, Water, Population and Communities DSI Dust Storm Index DSMW Digital Soil Map of the World EA-20km Twenty Km Evacuation Area EAD Environment Agency Abu Dhabi EC DG ENV European Commission Directorate-General for Environment EC European Commission EEA European Environment Agency EEAA Egyptian Environmental Affairs Agency EEZ Exclusive Economic Zone ELD Economics of Land Degradation EM-DAT Emergency Events Database El Niño Southern Oscillation ENSO Encyclopedia of Life Support Systems EOLSS United States Environmental Protection Agency, Comprehensive Environmental EPA CERCLIS Response, Contamination and Liability Information System E PA United States Environmental Protection Agency ERW Explosive Remnants of War ES Ecosystem Services ESA United Nations Economic and Social Affairs Department ESAFS East and Southeast Asia Federation of Soil Science Societies ESCWA United Nations Economic and Social Commission for Western Asia ESDB European Soil Database ESP Exchangeable Sodium Percentage ESRI Environmental Systems Research Institute EU SCAR European Standing Committee on Agricultural Research EU European Union FAO Food and Agriculture Organization of the United Nations FAO S TAT Food and Agriculture Organization Corporate Statistical Database Food and Agriculture Organization World Reference Base FAO-WRB Status of the World’s Soil Resources | Main Report XXVI

27 FDNPS Fukushima Dai-Ichi Nuclear Power Station Farmer Field School FFS Forest Inventory and Analysis FIA FSI Forest Survey in India FSR Fund-Service-Resources GAP Southeast Anatolia Development Project Region GDP Gross Domestic Product GEF Global Environment Facility GEO Global Environmental Outlook GHG Greenhouse Gases GIS Geographic Information System GIZ Deutsche Gesellschaft Für Internationale Zusammenarbeit (GIZ) Gmbh GLADA Global Land Degradation Assessment GLADIS Global Land Degradation Information System GLASOD Global Assessment of Human-Induced Soil Degradation GLC 2000 Global Land Cover 2000 Project GLC-SHARE Global Land Cover SHARE GLRD Gender and Land Rights Database GRACE Gravity Recover and Climate Experiment GRID Global Resource Information Database Global Soil Biodiversity Initiative GSBI Global Soil Map GSM GSP Global Soil Partnership Horticulture New Zealand HORTNZ Hemispheric Transport of Air Pollution HTAP HWSD Harmonized World Soil Database HYDE History Database of the Global Environment International Assessment of Agricultural Knowledge, Science and Technology for IAASTD Development IAATO International Association of Antarctic Tour Operators ICAR Indian Council of Agricultural Research ICARDA International Center for Agriculture Research In The Dry Areas ICBA International Center for Biosaline Agriculture ICBL International Campaign to Ban Landmines ICRAF International Center for Research in Agroforestry IDP Internally Displaced Peoples IFA International Fertilizers Association International Fund for Agricultural Development IFAD Status of the World’s Soil Resources | Main Report XXVII

28 I FA DATA International Fertilizer Industry Association Database International Food Policy Research Institute IFPRI Instituto De Geografía Tropical Y La Agencia De Medio Ambiente IGT-AMA IIASA International Institute for Applied Systems Analysis ILCA International Livestock Centre for Africa IMAGE Integrated Modelling Of Global Environmental Change IMBE Mediterranean Istitute of Biodiversity and Ecology IMF International Monetary Fund IMK-IFU Institute of Meteorology and Climate Research Atmospheric Environmental Research INIA Instituto De Investigaciones Agropecuarias (Chile) IPBES Intergovernmental Panel on Biodiversity and Ecosystem Services IPCC Intergovernmental Panel on Climate Change IRENA International Renewable Energy Agency IROWC-N The Indicator of Risk of Water Contamination by Nitrogen IROWC-P Indicator of Risk of Water Contamination by Phosphorus ISA Impervious Surface Area ISAM Integrated Impacts of Climate Change Model ISBN International Standard Book Number ISCO International Soil Conservation Organization ISCW Institute for Soil, Climate and Water Integrated Soil Fertility Management ISFM International Standards Organization ISO ISRIC International Soil Reference and Information Centre ISS-CAS Institute of Soil Science – Chinese Academy of Sciences ISSS International Society for the Systems Sciences ITPS Intergovernmental Technical Panel on Soils IUSS International Union of Soil Sciences IW International Waters JRC Joint Research Centre (European Commission) LAC Latin America and the Caribbean LADA Land Degradation Assessment in Drylands LCCS Land Cover Classification System LD Land Degradation LDCS Least Developed Countries LPFN the Landscapes for People, Food and Nature LPJ-GUESS Lund-Potsdam-Jena General Ecosystem Simulator LRTAP Long-Range Transboundary Air Pollution Topographic Factors LS Status of the World’s Soil Resources | Main Report XXVIII

29 LU Land Use Millennium Ecosystem Assessment MA Ministère De l’Agriculture Du Développement Rural et Des Pêches Maritimes MADRPM MAF New Zealand Ministry of Agriculture and Forestry MAFF Ministry of Agriculture, Forestry and Fishery of Japan MDBA Murray–Darling Basin Authority (Australia) MDGS Millennium Development Goals MENARID Integrated Natural Resources Management in the Middle East And North Africa MGAP Ministry of Livestock, Agriculture and Fisheries MNP Netherlands Environmental Assessment Agency MODIS Moderate Resolution Imaging Spectroradiometer NAAS National Academy of Agricultural Sciences of India NAIP National Agricultural Investment Plan NAMA Nationally Appropriate Mitigation Action NAP (1) National Action Programme; (2) National Action Plan NAPA National Adaptation Programme of Action NBSAP National Biodiversity Strategy and Action Plan NBSS&LUP National Bureau Of Soil Survey And Land Use Planning NDVI Normalized Difference Vegetation Index NENA Near East And North Africa Region The New Partnership for Africa’s Development NEPAD Nigerian Environmental Study Action Team NEST NGO Non-Governmental Organization NISF National Institute for Soils And Fertilizers NLWRA National Land and Water Resources Audit NOAA National Oceanic and Atmospheric Administration - Advanced Very High Resolution AVHRR Radiometer NPK Nitrogen (N), Phosphorus (P) and Potassium (K) NPL National Priorities List NRC National Research Council USA NRCAN Natural Resources Canada NREL National Resource Ecology Laboratory NRI National Resources Inventory Program NRM Natural Resources Management NRSA National Remote Sensing Agency (India) NSW New South Wales NT No-Tillage Nitrogen Use Efficiency NUE Status of the World’s Soil Resources | Main Report XXIX

30 OECD Organization for Economic Co-Operation And Development Organic Matter OM National Standard Published By the Austrian Standards Institute ÖNORM ÖPUL Austrian Environment Programme for Agriculture ORNL-CDIAC Oak Ridge National Laboratory-Carbon Dioxide Information Analysis Center OSWER Office of Solid Waste and Emergency Response PA H Polycyclic Aromatic Hydrocarbon PA M Polyacrylamide PCB Polychlorinated Biphenyl PCM Pyrogenic Carbonaceous Matter PEA Participatory Expert Assessment PHC Petroleum Hydrocarbon PL Plastic Limit PLAR Participatory Learning-Action-Research PMID Pubmed Identifier PNUD Programa De Las Naciones Unidas Para El Desarrollo POC Particulate Organic Carbon POP Persistent Organic Pollutant PVC Polyvinyl Chloride Radar- Radar-Automated Meteorological Data Acquisition System AMEDAS Regional Office for Asia and the Pacific RAPA Sida’s Regional Land Management Unit RELMA ROTA P Review Of Transboundary Air Pollution Residual Soil Nitrogen RSN Revised Universal Soil Loss Equation RUSLE SAGYP-CFA Secretaría De Agricultura, Ganadería Y Pesca – Consejo Federal Agropecuario SAV Submerged Aquatic Vegetation SCAN Soil Climate Analysis Network SCARPS Salinity Control and Reclamation Projects SCWMRI Soil Conservation and Watershed Management Research Institute SD Soil Degradation SDGS Sustainable Development Goals SEC Staff Working Documents of European Commission SEEA System of Environmental Economic Accounting SEED Sustainable Energy and Environment Division SF Subsistence Farming Stock-Flow-Resources SFR Status of the World’s Soil Resources | Main Report XXX

31 SKM Sinclair Knight Merz Sustainable Land and Agro-Ecosystem Management SLAM Soil Landscapes of Canada SLC SLM Sustainable Land Management SMAP Soil Moisture Active Passive SMOS Soil Moisture Ocean Salinity SOC Soil Organic Carbon SOE State of the Environment SOER European Environment State and Outlook Report SOLAW State Of Land and Water SOM Soil Organic Matter SOTER Soil and Terrain Database SOW-VU Centre for World Food Studies of the University Of Amsterdam SPARROW Spatially Referenced Regressions on Watershed Attributes SPC Secretariat of the Pacific Community SPI Science-Policy Interface SRI Salinity Risk Index SSA Sub-Saharan Africa SSM Sustainable Soil Management SSR Shift Soil Remediation Soil Science Society of America SSSA Soil Taxonomy ST STATSGO 2 Digital General Soil Map of the United States STEP-AWBH Soil, Topography, Ecology, Parent Material – Atmosphere, Water, Biotic, Human Model SWC Soil and Water Conservation SWSR Status of the World’s Soil Resources TEEB Economics of Ecosystems and Biodiversity TEOM Tapered Element Oscillating Microbalances TOC Total Organic Carbon TOMS Total Ozone Mapping Spectrometer TOT Transfer of Technology TSBF Tropical Soil Biology and Fertility UN United Nations UNCCD United Nation Convention to Combat Desertification UNCED United Nations Conference on Environment And Development UNDCPAC United Nations Desertification Control Program Activity Center UNDESA United Nations Department of Economic And Social Affairs United Nations Development Program UNDP Status of the World’s Soil Resources | Main Report XXXI

32 United Nations Environment Programme and Department of Early Warning and UNEP DEWA Assessment UNEP United Nations Environment Programme UNESCO United Nations Educational, Scientific and Cultural Organization UNFCCC United Nations Framework Convention on Climate Change United Nations Population Fund (Formerly the United Nations Fund for Population UNFPA Activities) UNISDR United Nations Office for Disaster Risk Reduction UNSO United Nations Development Programme - Office to Combat Desertification and Drought USDA United States Department Of Agriculture USEPA United States Environmental Protection Agency USGS United States Geological Survey USLE Universal Soil Loss Equation UXO Unexploded Ordnance WANA West Asia-North Africa WCED World Commission on Environment and Development WFP United Nations World Food Programme WMO World Meteorological Organization WOCAT World Overview of Conservation Approaches and Technologies WOTR Watershed Organization Trust WRB World Reference Base for Soil Resources WRI World Resources Institute World Wildlife Fund WWF Status of the World’s Soil Resources | Main Report XXXII

33 List of tables Table 1.1 | 7 | Chronology of introduction of major concepts in pedology and holistic soil management | Ecosystem services provided by the soil and the soil functions that support these services. Table 1.2 | 11 Table 2 | Soil functions related to the water cycle and ecosystem services | 22 Table 2.2 | Examples of global trends in soil management and their effects on the ecosystem services mediated by water. | 24 | Generalized ecosystem service rating of specific soil groups (WRB) 7 Table 3.1 | 42 Table 4.1 | Soil carbon lost globally due to land use change over the period 1860 to 2010 (PgC) | 58 Table 4.2 | Threats to soil resource quality and functioning under agricultural intensification | 64 Table 4.3 | Artificial areas in Corine Land Cover Legend | 65 Table 4.4 | Artificial areas in Emilia Romagna according to the Corine Land Cover Legend and sealing index | 66 Table 5.1 | 90 | World population by region Table 5.2 | The ten most populous countries 1950, 2013, 2050 and 2100 | 90 Table 6.1 | Distribution of Soil Organic Carbon Stocks and Density by IPCC Climate Region | 112 Table 6.3 | Estimate of the historic SOC depletion from principal biomes. Source: Lal, 1999. | 116 Table 6.4 | Estimates of historic SOC depletion from major soil orders | 117 Table 6.5 | Estimates of historic SOC loss from accelerated erosion by water and wind | 117 Table 6.6 | Distribution of salt-affected soils in drylands different continents of the world | 125 Table 6.7 | Major components of soil nutrient mass balances for N, P and K | 134 Table 7.1 | Erosion and crop yield reduction estimates from post-2000 review articles | 177 | Recent Milestones in soil governance and sustainable development Table 8.1 | 227 Table 8.2 | The 5 Pillars of Action of the Global Soil Partnership. | 227 Table 9.1 | Characteristics and distribution of agro-ecological zones in Africa | 245 | Classes of nutrient loss rate (kg ha-1 yr-1) Table 9.2 | 260 Table 9.4 | Definitions of the five land-cover classes on which the land-cover change study was based | 274 Table 9.5 | Summary of soil threats status, trends and uncertainties in Africa South of the Sahara. | 277 Table 10.1 | Soil organic carbon change in selected countries in Asia | 299 Table 10.2 | Harmonized area statistics of degraded and wastelands of India | 306 Table 10.3 | Emission factors of drained tropical peatland under different land uses and the 95 percent confidential interval | 309 Table 10.4 | Summary of Soil Threats Status, trends and uncertainties in Asia | 318 Table 11.1 | The percentage of agricultural land area of total land area in the countries of the European | 332 Table 11.2 | The areas of saline soils in the countries with major extent of soil salinization in the European region | 342 Table 11.3 Types and extent of soil degradation in Ukraine | 352 Table 11.4 | Summary of soil threats status, trends and uncertainties in Europe and Eurasia | 358 Table 12.1 | Summary of Soil Threats Status, trends and uncertainties in in Latin America and the Caribbean | 389 Status of the World’s Soil Resources | Main Report XXXIII

34 Table 13.1 | 404 | Land degradation caused by water erosion in the NENA region (1000 ha) Table 13.2 | Soil degradation caused by wind erosion in the NENA region (1000 ha) | 405 Table 13.3 | Summary of soil threats: Status, trends and uncertainties in the Near East and North Africa | 432 Table 14.1 | Summary of soil threats status, trends and uncertainties in North America | 469 Table 15.1 | Summary of current primary drivers of land-use and the associated implications for soil resources in the Southwest Pacific region | 484 Table 15.2 | Current population, project population (UNDESA, 2013) and Gross Domestic Product per capita (World Bank, 2014) for countries of the region. | 484 Table 15.3 | Estimated annual land–atmosphere (net) carbon (C) exchange rate for New Zealand’s major vegetation types | 489 Table 15.4 | Summary of soil threats status, trends and uncertainties in the Southwest Pacific | 509 List of boxes Box 1.1 6 | Guidelines for Action | Box 5.1 | Minefields | 95 Box 5.2 | Migration/Refugee Camps | 95 Box 5.3 | Combined effects of war and strife on soils | 95 Box 6.1 | Livestock-related budgets within village territories in Western Niger | 135 Box 6.2 | Nutrient balances in urban vegetable production in West African cities | 137 | The catastrophe of the Aral Sea | 354 Box 1 Status of the World’s Soil Resources | Main Report XXXIV

35 List of figures Figure 2.1 | 14 | Overview of ecosystem processes involved in determining the soil C balance. | Global (a) nitrogen (N) and (b) phosphorus (P) fertilizer use between 1961 and 2012 split for Figure 2.3 the different continents in Mt P per year. Source: FAO, 2015. | 19 | Applied and excess nitrogen and phosphorus in croplands. Nitrogen and phosphorus Figure 2.4 inputs and excess were calculated using a simple mass balance model, extended to include 175 crops. To account for both the rate and spatial extent of croplands, the data are presented as kg per ha of the landscape: (a) applied nitrogen, including N deposition; (b) applied phosphorus; (c) excess nitrogen; | 20 and (d) excess phosphorus. Source: West et al., 2014. Figure 3.1 | Nutrient availability in soils. Source: Fischer et al., 2008. | 36 | Global soil rooting conditions. Source: Fischer et al., 2008. | 36 Figure 3.2 Figure 3.3 | Soil Moisture storage capacity. Source: Van Engelen, 2012. | 38 -1 | Soil Organic Carbon pool (tonnes C ha ). | 39 Figure 3.4 | Soil erodibility as characterized by the k factor. Source: Nachtergaele and Petri, 2011. | 40 Figure 3.5 | Soil workability derived from HWSD. Source: Fischer et al., 2008. | 40 Figure 3.6 Figure 3.7 | Soil suitability for cropping at low input, based on the global agro-ecological zones study. Source: Fischer et al., 2008. | 41 Figure 3.8 | GLASOD results. Source: Oldeman, Hakkeling and Sombroek, 1991. | 44 Figure 3.9 | Example of the effect of land use on indicative factors for ecosystem goods and services | 45 | Soil compaction risk derived from intensity of tractor use in crop land and from livestock Figure 3.10 | 46 density in grasslands. Source: Nachtergaele et al., 2011 | Global Land Cover. Source: Latham et al., 2014. | 51 Figure 4.1 | Distribution of land cover in different regions. Source: Latham et al., 2014. | 51 Figure 4.2 Figure 4.3 | Historical land use change 1000 – 2005. Source: Klein Goldewijk et al., 2011. | 54 Figure 4.4 | Soil carbon and nitrogen under different land cover types. Source: Smith et al. (in press). | 57 Figure 4.5 | Maps of change in soil carbon due to land use change and land management from 1860 to 2010 from three vegetation models. Pink indicates loss of soil carbon, blue indicates carbon gain. The models were run with historical land use change. This was compared to a model run with only natural vegetation cover to diagnose the difference in soil carbon due to land cover change. Both model runs included historical climate and CO | 58 change. Source: Smith et al. (in press). 2 Figure 4.6 | Schematic diagram showing areas sealed (B) as a result of infrastructure development for a settlement (A). Source: European Union, 2012. | 66 Figure 4.7 | (A) Panoramic view of Las Medulas opencast gold mine (NW Spain). The Roman extractive technique – known as ‘ruina montis’ – involved the massive use of water that resulted in important geomorphological changes; (B) Weathered gossan of the Rio Tinto Cu mine, considered the birthplace of the Copper and Bronze Ages; (C) typical colour of Rio Tinto (‘red river’ in Spanish), one of the best known examples of formation of acid mine waters. These are inhabited by extremophile organisms. | 69 Status of the World’s Soil Resources | Main Report XXXV

36 Figure 4.8 | Eh-pH conditions of thionic/sulfidic soils and of hyperacid soils. Source: Otero et al., | 70 2008. Figure 4.9 | Use of different Technosols derived from wastes in the recovery of hyperacid soils and waters in the restored mine of Touro (Galicia, NW Spain). | 72 | Global distribution of (a) atmospheric S deposition, (b) soil sensitivity to acidification, (c) Figure 4.10 atmospheric N deposition, and (d) soil carbon to nitrogen ratio (soils most sensitive to eutrophication have a high C:N ratio; eutrophication is caused by N). Source: Vet et al., 2014; Batjes, 2012; FAO, | 75 2007. | Percentage of female landholders around the world. Source: FAO, 2010. | 92 Figure 5.1 Figure 5.2 | Major land deals occurring between countries in 2012. Source: Soil Atlas, 2015/Rulli et al., 2013. | 93 -1 -1 Figure 6.1 y | Spatial variation of soil erosion by water. High rates (>ca. 20 t ha ) mainly occur on cropland in tropical areas. The map gives an indication of current erosion rates and does not assess the degradation status of the soils. The map is derived from Van Oost et al., 2007 using a quantile classification. | 102 Figure 6.2 | Location of active and fixed aeolian deposits. Source: Thomas and Wiggs, 2008. | 103 Figure 6.3 | Soil relict in the Jadan basin, Ecuador. Photo by G. Govers | 103 In this area overgrazing led to excessive erosion and the soil has been completely stripped from most of the landscape in less than 200 years, exposing the highly weathered bedrock below. The person is standing on a small patch of the B-horizon of the original soil that has been preserved. Picture credit: Gerard Govers. | 103 | Dust storm near Meadow, Texas, USA Figure 6.4 | 106 Figure 6.5 | Distribution of carbon in biomass between ORNL-CDIAC Biomass and JRC Carbon | 113 Biomass Map | Prevalence of carbon in the topsoil or biomass | 114 Figure 6.6 Figure 6.7 | Proportion of carbon in broad vegetation classes for soil and biomass carbon pool | 115 Figure 6.8 | 124 | Estimated dominant topsoil pH. Source: FAO/IIASA/ISRIC/ISS-CAS/JRC, 2009. Figure 6.9 | Historical and predicted shift of the urban/rural population ratio. Source: UN, 2008. | 130 Figure 6.10 | Urbanisation of the best agricultural soils. | 131 Figure 6.11 | Major components of the soil nutrient balance. The red discontinuous line marks the soil volume over which the mass balance is calculated. Green | 133 arrows correspond to inputs and red arrows to losses. ΔS represents the change in nutrient stock. Figure 6.12 | The flows of water and energy through the soil-vegetation horizon | 140 Figure 6.13 | The soil-water characteristic curve linking matric potential, to the soil’s volumetric water content. Source: Tuller and Or, 2003. | 141 -1 Figure 6.14 | The soil’s hydraulic conductivity, K (cm day ) in relation to the matric potential, (MPa). As the matric potential becomes more negative the soil’s water content drops (see Figure 6.16) which 3 increases the tortuosity and slows the flow of water. Source: Hunter College. | 142 Status of the World’s Soil Resources | Main Report XXXVI

37 Figure 6.15 | Factors controlling soil water spatial variability and the scales at which they are | 143 important. Source: Crow et al., 2010) | (a) Global distribution of average soil moisture depth in the top 1 m of the soil. (b) Figure 6.16 Seasonal variability in soil moisture calculated as the standard deviation of monthly mean soil moisture over the year. (c-d) Global trends (1950-2008) in precipitation and 1 m soil moisture. (e-f ) As for (c-d) but for 1990-2008. Results for arid regions and permanent ice sheets are not shown. Source: Sheffield and Wood, 2007. | 145 Figure 7.1 | The 11 dimensions of society’s ‘social foundation’ and the nine dimensions of the ‘environmental ceiling’ of the planet. Source: Vince and Raworth, 2012. | 170 Figure 7.2 | Conceptual framework for comparing land use and trade-offs of ecosystem services. Source: Foley et al., 2005. | 171 2 Figure 7.3 across Great Britain. | Response curves of mean ecosystem service indicators per 1-km Source: Maskell et al., 2013. | 173 The curves are fitted using generalized additive models to ordination axes constrained by; (a) proportion of intensive land (arable and improved grassland habitats) within each 1-km square from CS field survey data; (b) mean long-term annual average rainfall (1978–2005); and (c) mean soil pH from five random sampling locations in each 1-km square. All X axes are scaled to the units of each constraining variable | 173 Figure 7.4 | The food wedge and the effect of soil change on the area of the wedge. Source: Keating et al., 2014. The relative sizes of the effects of soil change on the food wedge are not drawn to scale. | 174 Figure 7.5 | Direct impacts of soil threats on specific soil functions of relevance to plant production. | 176 Figure 7.6 | Some soil-related feedbacks to global climate change to illustrate the complexity and potential number of response pathways. Source: Heimann and Reichstein, 2008. | 183 | Definition of soil moisture regimes and corresponding evapotranspiration regimes. Figure 7.7 Source: Seneviratne et al., 2010. EF denotes the evaporative fraction, and EFmax its maximal value. | 186 Figure 7.8 | Estimation of evapotranspiration drivers (moisture and radiation) based on observation- driven land surface model simulation. Source: Seneviratne et al., 2010. The figure displays yearly correlations of evapotranspiration with global radiation Rg and precipitation P in simulations from the 2nd phase of the Global Soil Wetness Project (GSWP, Dirmeyer et al., 2006) using a two-dimensional color map, based on Teuling et al. 2009, redrawn for the whole globe. (Seneviratne et al., 2010) | 187 Figure 7.9 | A conceptual sketch of how vulnerability, exposure and external events (climate, weather, geophysical) contribute to the risk of a natural hazard. Source: IPCC, 2012. | 196 Figure 7.10 | Trends in landslide frequency and mortality on Asia. Source: FAO, 2011; EM-DAT, 2010. | 197 Figure 9.1 | Agro-ecological zones in Africa South of the Sahara. Source: Otte and Chilonda, 2002. | 245 Figure 9.2 | Extent of urban areas and Urbanization Indexes for the Sub-Saharan African countries. Source: Schneider, Friedl and Potere, 2010. | 253 Status of the World’s Soil Resources | Main Report XXXVII

38 | The fertility rate (the number of children a woman is expected to bear during her lifetime) Figure 9.3 | 255 for 1970 and 2005. Source: Fooddesert.org Figure 9.4 | Percentage of population living below the poverty line. Source: CIA World Factbook, | 255 2012. Table 9.3 | Estimated nutrient balance in some SSA countries in 1982-84 and forecasts for 2000. Surce: Stoorvogel and Smaling, 1990; Roy et al., 2003. | 262 Figure 9.5 | Major land use systems in Senegal. Source: FAO, 2010. | 264 Figure 9.6 Proportional extent of major land use systems in the Senegal. Source: Ndiaye and Dieng, 2013. | 264 Figure 9.7 | Extent of dominant degradation type in Senegal. Source: FAO, 2010. | 265 Figure 9.8 | Average rate of degradation in Senegal. Source: FAO, 2010. | 265 Figure 9.9 | Impact of degradation on ecosystem services in the local study areas in Senegal. Source: | 266 Ndiaye and Dieng, 2013. | Broad soil patterns of South Africa. Source: Land Type Survey Staff, 2003. Figure 9.10 | 268 | The national stratification used for land degradation assessment in South Africa, Figure 9.11 incorporating local municipality boundaries with 18 land use classes. Source: Pretorius, 2009. | 270 | 271 | Actual water erosion prediction map of South Africa. Source: Le Roux et al., 2012. Figure 9.12 | Topsoil pH derived from undisturbed (natural) soils. Source: Beukes, Stronkhorst and Figure 9.13 Jezile, 2008a. | 273 Figure 9.14 | Change in land-cover between 1994 and 2005 as part of the Five Class Land-cover of South Africa after logical corrections. Source: Schoeman et al., 2010. | 275 -1 | Length of the available growing period in Asia (in days yr Figure 10.1 | 289 ). Source: Fischer et al., 2012. Figure 10.2 | Threats to soils in the Asia region by country. | 291 Figure 10.3 | Nitrogen surplus or depletion, and nutrient use efficiency in crop production in Asia and the Middle East in 2010. | 304 Figure 10.4 | Degradation and wastelands map of India. Source: ICAR and NAAS, 2010. | 305 Figure 10.5 | Indonesian peatland map overlaid with land cover map as of 2011. Source: Wahyunto et al., 2014. | 310 Figure 10.6 | Distribution map of radioactive Cs concentration in soil in Fukushima prefecture (reference date of 5 November, 2011). Source: Takata et al., 2014. | 312 Figure 10.7 | Distribution map of the parameters of USLE and classification of estimated soil loss. -1 -1 -1 -1 -1 -1 Class I: less than 1 tonnes ha ; Class III: 5-10 tonnes ha ; Class II: 1-5 tonnes ha yr yr ; Class IV: 10-30 yr -1 -1 -1 -1 -1 -1 yr tonnes ha ; Class VI: more than 50 tonnes ha ; Class V: 30-50 tonnes ha yr yr . Source: Kohyama et al., 2012. | 313 Figure 10.8 | Estimate CH emission from rice paddy in Asia. Source: Yan et al., 2009. | 315 4 Figure 11.1 | Terrestrial eco-regions of the European region. Source: Olson et al., 2001. | 333 Figure 11.2 | Soil salinization on the territory of the European region. Source: Afonin et al., 2008; Toth et al., 2008; GDRS, 1987. | 343 | 353 | Some types and extent of soil degradation in Ukraine. Source: Medvedev, 2012. Figure 11.3 Status of the World’s Soil Resources | Main Report XXXVIII

39 Figure 11.4 | Soil map and soil degradation extent in Uzbekistan. Source: Arabov, 2010. | 355 | Biomes in Latin America and the Caribbean. Source: Olson et al., 2001. Figure 12.1 | 367 Figure 12.2 | Extent of the urban area and the urbanization index for Latin American and Caribbean countries. | 374 | shows soil organic carbon contents and stocks (taking into account soil bulk density) Figure 12.3 in different Mexican ecosystems. Carbon concentrations (left) and carbon stocks (right) in the main ecosystems of Mexico. In both cases the bars with the strongest tone indicate a primary forest, closed pasture or permanent agriculture. Bars with the softer tone indicate a secondary forest, open pasture or annual agriculture. Source: Cruz-Gaistardo, 2014. | 376 Figure 12.4 | Organic carbon stock (or density) in soils of Latin America and the Caribbean, expressed in Gigagrams per hectare. Source: Gardi et al., 2014. | 378 Figure 12.5 | Tree cover in the tonne 2000 and forest loss in the period 2000-2014. (A) Brazil, centered at 5.3°S, 50.2°W; (B) Mexico and Guatemala, centered at 16.3°N, 90.8°W and (C) Perú, centered at 8.7°S, 74.9°W; (D) Argentina, centered at 27.0°S, 62.3°W and (E) Chile, centered at 72.5°S, 37.4°W. Source: Hansen et al., 2013. | 379 Figure 12.6 | Expansion of the agricultural frontier under rainfed conditions in the north of Argentina. Source: Viglizzo & Jobbagy, 2010. | 383 Figure 12.7 | Percentage of areas affected by wind (a) and water erosion (b) in Argentina. Source: Prego et al., 1988. | 385 Figure 12.8 | Predominant types of land degradation in Cuba. Source: FAO, 2010. | 387 Figure 12.9 | Extent of land degradation in land use system units in Cuba. Source: FAO, 2010. | 387 | Intensity of land degradation in Cuba. Source: FAO, 2010. Figure 12.10 | 388 Figure 13.1 | Land use systems in the Near East and North Africa. Source: FAO, 2010. | 403 | Extent of the urban areas and Urbanization Indexes for the Near East and North African Figure 13.2 | 410 countries. Source: Schneider, Friedl and Potere, 2009. Figure 13.3 | Layout of the project site source (a) and conceptual design and layout of bioremediation | 421 system (b). Source: Balba et al., 1998. | Rate of water erosion in Iran. Source: Soil Conservation and Watershed Management Figure 13.4 Research Institute. | 424 Figure 13.5 | Shows days with dust storms in 2012, while Figure 13.6 shows the origin of dust storms in 2012. | 425 Figure 13.6 | Internal and external dust sources in recent years in Iran. Source: University of Tehran, 2013. | 426 Figure 13.7 | 427 | Assessment of Water (a) and Wind Erosion (b) in Tunisia Figure 13.8 | Soil Conservation in Tunisia | 428 Figure 13.9 | Type of ecosystem service most affected. | 429 Figure 14.1 | Level II Ecological regions of North America. Source: Commission for Environmental Cooperation, 1997. | 446 Figure 14.2 | Map of Superfund sites in the contiguous United States Yellow indicates final EPA National Priorities List sites and red indicates proposed sites. Source: EPA, 2014a. | 449 1 | 451 Figure 14.3 | Areas in United States threatened by salinization and sodification. Source: NRCS Status of the World’s Soil Resources | Main Report XXXIX

40 Figure 14.4 | Risk of soil salinization in Canada 2011. Source: Clearwater et al., 2015. | 452 | Risk of water erosion in Canada 2011. Source: Clearwater et al., 2015. Figure 14.5 | 461 Figure 14.6 | Risk of wind erosion in Canada 2011. Source: Clearwater et al., 2015. | 462 | Soil organic carbon change in Canada 201. Source: Clearwater et al., 2015. Figure 14.7 | 463 Figure 14.8 | Residual soil N in Canada 2011. Source: Clearwater et al., 2015. | 465 Figure 14.9 | Indicator of risk of water contamination by phosphorus (IROWC-P) in Canada in 2011. Source: Clearwater et al., 2015. | 466 Figure 15.1 | Nations in the Southwest Pacific region and the extent of Melanesia, Micronesia and Polynesian cultures. Figure based on base map imagery: exclusive economic zone boundaries (EEZ)v 8 2014, Natural Earth 11 3.2.0 | 478 Figure 15.2 | Change in the percentage area of all land prepared for crops and pastures under different tillage practices in Australia, 1996-2010 Source: SOE, 2011. | 486 Figure 15.3 | (a) Trends in winter rainfall in south-western Australia for the period 1900–2012. Source: 1 Australian Bureau of Meteorology . The 15-year running average is shown by the black line. (b) Annual mean temperature anomaly time series map for south-western Australia (1910–2012), using a baseline annual temperature (1961–1990) of 16.3 °C. The 15-year running average is shown by the black line. | 501 Figure 15.4 | Percentage of sites sampled (2005–12) with soil pH at 0–10 cm depth below the established target of pHCa 5.5 (left) and the critical pHCa 5.0 (right). Grey indicates native vegetation and reserves. Source: Gazey, Andrew and Griffin, 2013. | 502 | Agricultural lime sales 2005–12 in the south-west of Western Australia based on data for Figure 15.5 | 503 85–90 percent of the market. | MODIS image for 0000 23 September 2009 showing Red Dawn extending from south Figure 15.6 of Sydney to the Queensland/NSW border and the PM 10 concentrations measured using Tapered | 506 Element Oscillating Microbalances (TEOM) at the same time at ground stations. Figure A 1 | (a) A Histosol profile and (b) a peatbog in East-European tundra. | 529 Figure A 2 | (a) An Anthrosol (Plaggen) profile and (b) associated landscape in the Netherlands. | 531 Figure A 3 | 533 | (a) A Technosol profile and (b) artefacts found in Technosol. Figure A 4 | (a) A Cryosol profile and (b) associated landscape in West Siberia, Yamal Peninsula. | 535 Figure A 5 | (a) A Leptosol profile in the Northern Ural Mountains and (b) associated landscape. | 537 Figure A 6 | Vertisol gilgai patterns and associated soils: (a) linear gilgai pattern located on a moderately sloping hillside in western South Dakota. Distance between repeating gilgai cycle is about 4 m. (b) Normal gilgai pattern occurring on a nearly level clayey terrace near College Station, TX. After a rainfall event microlows have been partially filled with runoff water from microhighs - repeating gilgai cycle about 4 m in linear length. (c) Trench exposure of soils excavated across normal gilgai pattern - repeating gilgai cycle about 4 m in linear length. Dark-colored deep soil in microlow (leached A and Bss horizons) with light-colored shallow calcareous soils associated with diaper in microhigh (Bssk and Ck horizons). The diaper has been thrust along oblique slickenside planes towards soils surface. Vertical depth of soil trench in about 2 m. (d) Close up of dark-colored soil associated with microlow and light Status of the World’s Soil Resources | Main Report XL

41 colored diaper associated with microhigh of the trench in (c). | 539 | (a) A Solonetz profile and (b) the associated landscape in Hungary. Figure A 7 | 541 Figure A 8 | (a) A Solonchak profile and (b) a salt crust with halophytes. | 543 Figure A 9 | (a) A Podzol profile and (b) an associated landscape, West-Siberian Plain. | 545 | (a) A giant Podzol profile and (b) an associated landscape, Brazil. Figure A 10 | 546 Figure A 11 | (a) A Ferralsol profile and (b) an associated landscape, Brazil. | 548 Figure A 12 | (a) A Nitisol profile and (b) the associated landscape with termite mounds, Brazil. | 550 Figure A 13 | (a) A Plinthosol profile, (b) details of the plinthic horizon and (c) the associated landscape, South Africa. | 552 Figure A 14 | 554 | (a) A Planosol profile and (b) the associated landscape, Argentina. Figure A 15 | (a) A Gleysol profile and (b) associated landscape in the East European tundra. | 556 Figure A 16 | (a) A Stagnosol profile, (b) stagnic color patterns, (c) marble-like horizontal surface and (d) an associated landscape. | 558 Figure A 17 | (a) An Andosol profile and (b) the associated landscape in Japan. | 560 Figure A 18 | (a) A Chernozem profile (Photo by J. Deckers) and (b) the associated landscape in the Central Russian Uplands. | 562 Figure A 19 | (a) A Kastanozem profile and (b) the associated landscape in Mongolia. | 564 | (a) A Phaeozem profile and (b) the associated landscape, Argentinian Pampa. Figure A 20 | 566 Figure A 21 | (a) An Umbrisol profile, (b) associated vegetation and (c) an associated landscape. | 568 | (a) A Durisol profile and (b) the associated landscape, Ecuador. Figure A 22 | 570 Figure A 23 | (a) A Calcisol profile, (b) an associated landscape and (c and d) secondary carbonates in Calcisols. | 572 | (a) A Gypsisol profile and (b) an associated landscape. | 574 Figure A 24 Figure A 25 | (a) A Retisol profile, (b) the “retic” pattern in a Retisol and (c) the associated landscape, Belgium. | 576 Figure A 26 | (a) An Acrisol profile and (b) the associated landform in Kalimantan, Indonesia. | 578 Figure A 27 | (a) A Lixisol profile and (b) the associated landscape, Brazil. | 580 Figure A 28 | (a) An Alisol profile and (b) the associated landscape, Belgium. | 582 Figure A 29 | 584 | (a) A Luvisol profile and (b) the associated landscape, China. Figure A 30 | (a) A Cambisol profile and (b) the associated landscape, China. | 586 Figure A 31 | (a) A Regosol profile and (b) the associated landscape, China. | 588 Figure A 32 | (a) An Arenosol profile in South Korea and (b) an Arenosol profile in New Mexico. | 590 Figure A 33 | (a) A Fluvisol profile in Wisconsin and (b) a Fluvisol profile in Germany. | 592 Figure A 34 | (a) A Wassent profile and (b) the associated landscape, the Netherlands. | 594 Figure A 35 | Global Soil Map of the World based on HWSD and FAO Revised Legend (Nachtergaele | 595 and Petri, 2008) Status of the World’s Soil Resources | Main Report XLI

42 Status of the World’s Soil Resources | Main Report XLII

43 Preface The State of the World’s Soil Resources are: (a) to provide a global scientific The main objectives of assessment of current and projected soil conditions built on regional data analysis and expertise; (b) to explore the implications of these soil conditions for food security, climate change, water quality and quantity, biodiversity, and human health and wellbeing; and (c) to conclude with a series of recommendations for action by policymakers and other stakeholders. The book is divided into two parts. The first part deals with global soil issues (Chapters 1 to 8). This is followed by a more specific assessment of regional soil change, covering in turn Africa South of the Sahara, Asia, Europe, Latin America and the Caribbean, the Near East and North Africa, North America, the Southwest Pacific and Antarctica. (Chapters 9 to 16). The technical and executive summaries are published separately. In Chapter 1 the principles of the World Soil Charter are discussed, including guidelines for stakeholders to ensure that soils are managed sustainably and that degraded soils are rehabilitated or restored. For long, soil was considered almost exclusively in the context of food production. However, with the increasing impact of humans on the environment, the connections between soil and broader environmental concerns have been made and new and innovative ways of relating soils to people have begun to emerge in the past two decades. Societal issues such as food security, sustainability, climate change, carbon sequestration, greenhouse gas emissions, and degradation through erosion and loss of organic matter and nutrients are all closely related to the soil resource. These ecosystem services provided by the soil and the soil functions that support these services are central to the discussion in the report. In Chapter 2 synergies and trade-offs are reviewed, together with the role of soils in supporting ecosystem services, and their role in underpinning natural capital. The discussion then covers knowledge - and knowledge gaps - on the role of soils in the carbon, nitrogen and water cycles, and on the role of soils as a habitat for organisms and as a genetic pool. This is followed in Chapter 3 by an overview of the diversity of global soil resources and of the way they have been assessed in the past. Chapter 4 reviews the various anthropogenic and natural pressures - in particular, land use and soil management – which cause chemical, physical and biological variations in soils and the consequent changes in environmental services assured by those soils. Land use and soil management are in turn largely determined by socio-economic conditions. These conditions are the subject of Chapter 5, which discusses in particular the role of population dynamics, market access, education and cultural values as well as the wealth or poverty of the land users. Climate change and its anticipated effects on soils are also discussed in this chapter. Chapter 6 discusses the current global status and trends of the major soil processes threatening ecosystem services. These include soil erosion, soil organic carbon loss, soil contamination, soil acidification, soil salinization, soil biodiversity loss, soil surface effects, soil nutrient status, soil compaction and soil moisture conditions. Chapter 7 undertakes an assessment of the ways in which soil change is likely to impact on soil functions and the likely consequences for ecosystem service delivery. Each subsection in this chapter outlines key soil processes involved with the delivery of goods and services and how these are changing. The subsections then review how these changes affect soil function and the soil’s contribution to ecosystem service delivery. The discussion is organized according to the reporting categories of the Millennium Ecosystem Assessment, including provisioning, supporting, regulating and cultural services. Status of the World’s Soil Resources | Main Report Preface 1 1

44 Chapter 8 of the report explores policy, institutional and land use management options and responses to soil changes that are available to governments and land users. The regional assessments in Chapters 9 to 16 follow a standard outline: after a brief description of the main biophysical features of each region, the status and trends of each major soil threat are discussed. Each chapter ends with one or more national case studies of soil change and a table summarizing the results, including the status and trends of soil changes in the region and related uncertainties. Status of the World’s Soil Resources | Main Report Preface 2 2

45 Global soil resources Coordinating Lead Authors: Maria Gerasimova (Russia), Thomas Reinsch (United States), Pete Smith (United Kingdom) Contributing Authors: Lucia Anjos (Brazil), Susumu Asakawa ( Japan), Ochirbat Batkhishig (Mongolia), James Bockheim (United States), Robert Brinkman (Netherlands), Gabrielle Broll (Germany), Mercedes Bustamante (Brazil), Marta Camps Arbestain (ITPS/New Zealand), Przemyslaw Charzynski (Poland), Joanna Clark (United Kingdom), Francesca Cotrufo (United States), Maur’cio Rizzato Coelho (Brazil), Jane Elliott (Canada), Maria Gerasimova (Russia), Robert I. Griffiths (United Kingdom), Richard Harper (Australia), Jo House (United Kingdom), Peter Kuikman (Netherlands), Tapan Kumar Adhya (India), Richard McDowell (New Zealand), Freddy Nachtergaele (Belgium), Masami Nanzyo ( Japan), Christian Omutu (Kenya), Genxing Pan (China), Keith Paustian (United States), Dan Pennock (ITPS/Canada), Cornelia Rumpel (France), Jaroslava Sobocká (Slovakia), Mark Stolt (United States), Mabel Susna Pasos (Argentina), Charles Tarnocai (Canada), Tibor Toth (Hungary), Ronald Vargas (Bolivia), Paul West (United States), Larry P. Wilding (United States), Ganlin Zhang (ITPS/China), Juan JosŽ Ibánez (Spain), Felipe Macias (Spain). Reviewing Authors: Dominique Arrouays (ITPS/France), Richard Bardgett (United Kingdom), Marta Camps Arbestain (ITPS/New Zealand), Tandra Fraser (Canada), Ciro Gardi (Italy), Neil McKenzie (ITPS/Australia), Luca Montanarella (ITPS/EC), Dan Pennock (ITPS/Canada) and Diana Wall (United States). Status of the World’s Soil Resources | Main Report Global soil resources 3 3

46 1 | Introduction | The World Soil Charter 1.1 “Soils are fundamental to life on earth.” We know more about soil than ever before, yet perhaps a smaller percentage of people than at any point in human history would understand the truth of this statement. The proportion of human labour devoted to working the soil has steadily decreased through the past century, and hence the experience of direct contact with the soil has lessened in most regions. Soil is very different in this regard from food, energy, water and air, to which each of us requires constant and secure access. Yet human society as a whole depends more than ever before on products from the soil as well as on the more intangible services it provides for maintenance of the biosphere. Our goal in this report is to make clear these essential connections between human well-being and the soil, and to provide a benchmark against which our collective progress to conserve this essential resource can be measured. The statement that begins this section is drawn from the opening sentence of the preamble of the revised World Soil Charter (FAO, 2015): Soils are fundamental to life on Earth but human pressures on soil resources are reaching critical limits. Careful soil management is one essential element of sustainable agriculture and also provides a valuable lever for climate regulation and a pathway for safeguarding ecosystem services and biodiversity. The World Soil Charter presents a series of nine principles that summarize our current understanding of the soil, the multi-faceted role it plays, and the threats to its ability to continue to serve these roles. As such, the nine principles form a succinct and comprehensive introduction to this report. Principles from the World Soil Charter: Principle 1 : Soils are a key enabling resource, central to the creation of a host of goods and services integral to ecosystems and human well-being. The maintenance or enhancement of global soil resources is essential if humanity’s overarching need for food, water, and energy security is to be met in accordance with the sovereign rights of each state over their natural resources. In particular, the projected increases in food, fibre, and fuel production required to achieve food and energy security will place increased pressure on the soil. Principle 2 : Soils result from complex actions and interactions of processes in time and space and hence are themselves diverse in form and properties and the level of ecosystems services they provide. Good soil governance requires that these differing soil capabilities be understood and that land use that respects the range of capabilities be encouraged with a view to eradicating poverty and achieving food security. Principle 3 : Soil management is sustainable if the supporting, provisioning, regulating, and cultural services provided by soil are maintained or enhanced without significantly impairing either the soil functions that enable those services or biodiversity. Status of the World’s Soil Resources | Main Report Global soil resources 4 4

47 The balance between the supporting and provisioning services for plant production and the regulating services the soil provides for water quality and availability and for atmospheric greenhouse gas composition is a particular concern. Principle 4 : The implementation of soil management decisions is typically made locally and occurs within widely differing socio-economic contexts. The development of specific measures appropriate for adoption by local decision-makers often requires multi-level, interdisciplinary initiatives by many stakeholders. A strong commitment to including local and indigenous knowledge is critical. Principle 5 : The specific functions provided by a soil are governed, in large part, by the suite of chemical, biological, and physical properties present in that soil. Knowledge of the actual state of those properties, their role in soil functions, and the effect of change – both natural and human-induced – on them is essential to achieve sustainability. Principle 6 : Soils are a key reservoir of global biodiversity, which ranges from micro-organisms to flora and fauna. This biodiversity has a fundamental role in supporting soil functions and therefore ecosystem goods and services associated with soils. Therefore it is necessary to maintain soil biodiversity to safeguard these functions. : All soils – whether actively managed or not – provide ecosystem services relevant to global Principle 7 climate regulation and multi-scale water regulation. Land use conversion can reduce these global common- good services provided by soils. The impact of local or regional land-use conversions can be reliably evaluated only in the context of global evaluations of the contribution of soils to essential ecosystem services. Principle 8 : Soil degradation inherently reduces or eliminates soil functions and their ability to support ecosystem services essential for human well-being. Minimizing or eliminating significant soil degradation is essential to maintain the services provided by all soils and is substantially more cost-effective than rehabilitating soils after degradation has occurred. Principle 9 : Soils that have experienced degradation can, in some cases, have their core functions and their contributions to ecosystem services restored through the application of appropriate rehabilitation techniques. This increases the area available for the provision of services without necessitating land use conversion. These nine principles lead to guidelines for action by society (Box 1.1). The guidelines are introduced with ‘The overarching goal for all parties is to ensure that soils are managed a clear statement of our collective goal: This opening statement is followed by a series of sustainably and that degraded soils are rehabilitated or restored.’ specific guidelines for different segments of human society. Future updates of this report will document our success in implementation of these guidelines, and in achieving the goal set by the signatories of the World Soil Charter. Status of the World’s Soil Resources | Main Report Global soil resources 5 5

48 Security adopted by the Committee on World Box 1.1 | Guidelines for Action Food Security in May 2012. 3. Participate in the development of multi-level, (from the World Soil Charter) interdisciplinary educational and capacity- The overarching goal for all parties is to ensure building initiatives that promote the adoption that soils are managed sustainably and that of sustainable soil management by land users. degraded soils are rehabilitated or restored. 4. Support research programs that will provide Good soil governance requires that actions sound scientific backing for development at all levels – from states, and, to the extent and implementation of sustainable soil that they are able, other public authorities, management relevant to end users. international organizations, individuals, groups, and corporations – be informed by the principles Incorporate the principles and practices 5. of sustainable soil management and contribute of sustainable soil management into to the achievement of a land-degradation neutral policy guidance and legislation at all levels world in the context of sustainable development. of government, ideally leading to the All actors and, specifically, each of the following development of a national soil policy. stakeholder groups are encouraged to consider the 6. Explicitly consider the role of soil management following actions: practices in planning for adaptation to and Actions by Individuals and the Private Sector mitigation of climate change and maintaining biodiversity. All individuals using or managing soil must 1. Establish and implement regulations to limit 7. act as stewards of the soil to ensure that the accumulation of contaminants beyond this essential natural resource is managed established levels to safeguard human health sustainably to safeguard it for future and wellbeing and facilitate remediation of generations. contaminated soils that exceed these levels Undertake sustainable soil management in the 2. where they pose a threat to humans, plants, production of goods and services. and animals. Develop and maintain a national soil 8. Actions by Groups and the Science Community information system and contribute to the development of a global soil information Disseminate information and knowledge on 1. system. soils. 9. Develop a national institutional framework for Emphasize the importance of sustainable 2. monitoring implementation of sustainable soil soil management to avoid impairing key soil management and overall state of soil resources. functions. Actions by International Organizations Actions by Governments Facilitate the compilation and dissemination 10. 1. Promote sustainable soil management that is of authoritative reports on the state of the relevant to the range of soils present and the global soil resources and sustainable soil needs of the country. management protocols. 2. Strive to create socio-economic and Coordinate efforts to develop an accurate, 11. institutional conditions favourable to high-resolution global soil information system sustainable soil management by removal and ensure its integration with other global of obstacles. Ways and means should be earth observing systems. pursued to overcome obstacles to the Assist governments, on request, to establish 12. adoption of sustainable soil management appropriate legislation, institutions, associated with land tenure, the rights and processes to enable them to mount, of users, access to financial services and implement, and monitor appropriate educational programmes. Reference is made sustainable soil management practices. to the Voluntary Guidelines on the Responsible Governance of Tenure of Land, Forests and Fisheries in the Context of National Food Status of the World’s Soil Resources | Main Report Global soil resources 6 6

49 1.2 | Basic concepts Prior to the 20th century, soil was considered almost exclusively in the context of agriculture and food production. As the global impact of humanity on natural resources has increased over the past 150 years, the connections between soil and broader environmental concerns began to be made. The recognition of these connections has accelerated through time, and new and innovative ways of relating soils to people have begun to emerge in past the two decades. The rise in complexity of soil knowledge and application was synthesized by Bockheim et al. (2005) (Table 1.1) in their summary of milestones in pedology; concepts introduced since 2005 have been added by the authors of this chapter. We can see that the number and breadth of concepts have been expanding rapidly over the past two decades. Period Soil management Pedology Concept of soil as a medium for plant growth and as a -1 880 Pre weathered rock layer. Appearance of fundamental pedology concepts: soil as a natural 1880–1900 body; soil horizons/profiles; soil-forming factors; early ideas of soil geography. Global acceptance of concepts of soil as a natural body and soil- forming factors; development of first regional soil classification 1900–1940 Soil conservation systems; soil surveys initiated; identification of key soil-forming processes. Factors of soil formation and genesis of soils clarified; development of global soil taxonomic systems; intensified soil 1940– 1960 mapping. World Soil Charter Refinement of global soil taxonomic systems; identification (1981) Land capability/ of pedon concept; development of early soil models and soil suitability assessment 1960–1985 cover pattern concept; recognition of co-evolution of soils and Assessment of human- landforms. induced degradation (GLASOD) Increased understanding of soil processes; refinement of Sustainable soil global soil models; further refinement of global soil taxonomic management 1985– 2000 systems; development of statistical and computer-based soil Soil quality information systems. Soil health Earth System Science, pedosphere, digital soil mapping, Soil security 2000-2015 pedodiversity, ethnopedology, pedometrics, proximal sensing, Carbon sequestration soil systems. hydropedology, critical zone. Table 1.1. Chronology of introduction of major concepts in pedology and holistic soil management (after Bockheim et al., 2005). Status of the World’s Soil Resources | Main Report Global soil resources 7 7

50 The connections between soils and societal issues – such as food security, sustainability, climate change, carbon sequestration, greenhouse gas emissions, and degradation through erosion and loss of organic matter and nutrients – are central to the recently developed concept of soil security (McBratney, Field and Koch, 2014). Soil security has been defined as the maintenance or improvement of the world’s soil resources so that they can provide sufficient food, fibre, and fresh water, contribute to energy sustainability and climate stability, maintain biodiversity, and deliver overall environmental protection and ecosystem services (Bouma and McBratney, 2013). There have been major developments over the past three decades in our broader understanding of human impact on the earth and of frameworks to assess this impact. The structure and content of this report comprise a synthesis of themes and concepts from many major initiatives in environmental science and pedology. The most important of these themes and concepts are discussed in the following paragraphs. Sustainable soil management The concept of sustainable development is most closely associated with the 1987 report of the United Nations World Commission on Environment and Development, better known as the Brundtland Commission after its chairperson, Gro Harlem Brundtland of Norway (World Commission on Environment and Development, 1987). The report popularized a compelling definition of sustainability: development that meets the needs of the present without compromising the ability of future generations to meet their own needs. The concept of sustainability has since been widely applied to many aspects of human society, including wide application in soil science and land management generally. As defined in the World Soil Charter, sustainable soil management comprises activities that maintain or enhance the supporting, provisioning, regulating and cultural services provided by soils without significantly impairing either the soil functions that enable those services or biodiversity. The concept of sustainable soil management is central to pillar one of the Global 1 : “Promote sustainable management of soil resources for soil protection, conservation, and Soil Partnership sustainable production”. Soil degradation and threats to soil functions The concept of soil degradation and its assessment have been developed as part of more holistic assessments of human-induced degradation carried out by FAO, UNEP and other UN agencies. An early initiative was the Global Assessment of Soil Degradation (GLASOD) project undertaken in the late 1980s to inventory soil degradation. GLASOD evaluated 13 types of soil degradation: water erosion (topsoil loss and mass movement, including rill and gully formation), wind erosion (topsoil loss, terrain deformation – primarily dune activity), and overblowing (surface burial from aeolian deposition), loss of nutrients and/ or organic matter, salinization, acidification, pollution, compaction and physical degradation, waterlogging, and subsidence of organic soils. GLASOD has not been updated (see Chapter 3 for more details). The Soil Thematic Strategy of the European Union (CEC, 2006) formalized the concept of threats to soil and its many functions. Five specific threats are identified under Article 6 of the draft Soil Framework Directive proposed in the Strategy: (1) erosion by wind and water; (2) organic matter decline; (3) compaction; (4) salinization; and (5) landslides of soil and rock material. Elsewhere in the proposed Directive, soil sealing (‘the permanent covering of the soil with an impermeable surface’ p.15) and soil contamination (‘the intentional or unintentional introduction of dangerous substances on or in the soil’ p. 18) are also identified as threats. 8. For a full description of 1 The Global Soil Partnership was initiated by FAO and the EU in 2011. For a description of the five pillars, see Table 8.1 in Chapter see www.fao.org/globalsoilpartnership). the Partnership, Status of the World’s Soil Resources | Main Report Global soil resources 8 8

51 Soil functions and ecosystem services The assessments of threats to soil functions leads to a need to formally identify the functions that the soil performs. The proposed Soil Framework Directive (CEC, 2006) of the European Union recognizes seven soil functions that are vulnerable to soil threats: 1. biomass production, including agriculture and forestry storing, filtering and transforming nutrients, substances and water 2. 3. biodiversity pool, such as habitats, species and genes physical and cultural environment for humans and human activities 4. 5. source of raw materials 6. acting as a carbon pool 7. archive of geological and archaeological heritage. The EU Soil Thematic Strategy was developed at the same time as the Millennium Ecosystem Assessment (MA, 2005) initiated by the United Nations in 2000. The goal of the MA was to assess the consequences of ecosystem change for human well-being and to lay the scientific basis for actions that would promote conservation and sustainable use of ecosystems. The MA was built on the framework for ecosystem services developed by Daily, Matson and Vitousek (1997) and Costanza et al. (1997). The categories of ecosystem services were formalized by the Millennium Ecosystem Assessment into four broad classes: provisioning, regulating, supporting, and cultural services. The range of major ecosystem services provided by soil, and the specific soil functions that enable those services, are summarized in Table 1.2. Soils and natural capital The services provided by soils are primarily determined by the three core soil properties (texture, mineralogy, and organic matter), which together form the natural capital of soils (Palm et al. 2007). Soil texture and mineralogy are inherent properties of soil that are initially inherited from the parent materials and which change only very slowly over time. In a natural state, soil organic matter (SOM) reaches equilibrium with the environment in which the soil forms, but SOM responds quickly to human-induced changes. Management of SOM is central to sustainable soil management because of its rapid response to change and our ability to manipulate it. Planetary boundaries and safe operating space for humanity Specific soil processes are central to Earth-system processes that provide the safe operating space for humanity – the concept of ‘planetary boundaries’ that cannot be exceeded without causing potentially disastrous consequences for humanity (Röckstrom et al. 2009; Steffen et al. , 2015). Currently stresses in the nitrogen cycle, climate change, and biodiversity loss are suggested to be beyond safe operating boundaries. Human impact on the natural reservoir of soil biodiversity and on the rate of N and C cycling in soils is a significant aspect of this stress. Whereas GLASOD had highlighted nutrient depletion through crop production without the application of sufficient manure and fertilizer to replenish nutrient loss, the concept of planetary boundaries also focuses our attention on over-application of nutrients in some regions and its consequences for atmospheric and hydrological systems. Addressing the nutrient deficit in regions such as Sub-Saharan Africa while remaining within the safe operating space for humanity requires a significant reduction of nutrient additions in area of excess inputs (Steffen , 2015). et al. Status of the World’s Soil Resources | Main Report Global soil resources 9 9

52 Biodiversity Biodiversity cuts across most of the concepts presented above, and loss of biodiversity is identified by Röckstrom et al. (2009) as one of three components currently operating beyond safe planetary boundaries. Biodiversity is more than simply an ecosystem service, even though specific benefits can be identified from the biodiversity pool. This cross-cutting importance of biodiversity was formalized in the Convention on Biological Diversity signed in 1992 at the United Nations Conference on Environment and Development in Brazil. Soils are widely recognized as a major reservoir of global biodiversity, and preservation of this (largely unknown) pool of biodiversity is essential. Ecosystem service Soil functions Supporting services: Services that are necessary for the production of all other ecosystem services; their impacts on people are often indirect or occur over a very long time ∑ Weathering of primary minerals and release of nutrients ∑ Transformation and accumulation of organic matter ∑ Creation of structures (aggregates, Soil formation horizons) for gas and water flow and root growth ∑ Creation of charged surfaces for ion retention and exchange ∑ Medium for seed germination and root Primary production growth ∑ Supply of nutrients and water for plants Transformation of organic materials by soil ∑ organisms Nutrient cycling ∑ Retention and release of nutrients on charged surfaces Regulating services: benefits obtained from the regulation of ecosystem processes ∑ Filtering and buffering of substances in soil water Water quality regulation Transformation of contaminants ∑ Regulation of water infiltration into soil ∑ and water flow within the soil Water supply regulation ∑ Drainage of excess water out of soil and into groundwater and surface water Status of the World’s Soil Resources | Main Report Global soil resources 10 10

53 ∑ Regulation of CO , N O, and CH emissions Climate regulation 2 2 4 Erosion regulation ∑ Retention of soil on the land surface Provisioning Services: products (‘goods’) obtained from ecosystems of direct benefit to people ∑ Providing water, nutrients, and physical Food supply support for growth of plants for human and animal consumption ∑ Retention and purification of water Water supply ∑ Providing water, nutrients, and physical Fibre and fuel supply support for growth of plant growth for bioenergy and fibre ∑ Provision of topsoil, aggregates, peat etc. Raw earth material supply ∑ Supporting human habitations and related Surface stability infrastructure ∑ Providing habitat for soil animals, birds Refugia etc. Source of unique biological materials ∑ Genetic resources Cultural services: nonmaterial benefits which people obtain from ecosystems through spiritual enrichment, aesthetic experiences, heritage preservation and recreation ∑ Preservation of natural and cultural landscape diversity Aesthetic and spiritual Source of pigments and dyes ∑ Heritage ∑ Preservation of archaeological records Table 1.2: Ecosystem services provided by the soil and the soil functions that support these services. Status of the World’s Soil Resources | Main Report Global soil resources 11 11

54 The contribution of many of the concepts outlined above is apparent throughout the World Soil Charter. This synthesis of concepts is perhaps most evident in the definition of sustainable soil management used in the World Soil Charter: Soil management is sustainable if the supporting, provisioning, regulating and cultural services provided by soil are maintained or enhanced without significantly impairing either the soil functions that enable those services or biodiversity. The concepts of soil functions, the threats to functions, and the ecosystem services provided by soils are central both to the structure of this book and to the content of each chapter. References Bockheim, J.G., Gennadiyev, A.N., Hammer, R.D. & Tandarich, J.P. 2005. Historical development of key , 124: 23-36. Geoderma concepts in pedology. Bouma, J. & McBratney, A.B. 2013. Framing soils as an actor when dealing with wicked environmental -1 39. , 200: 130 problems. Geoderma Commission of the European Communities (CEC). 2006. Communication from the Commission to the Council, the European Parliament, the European Economic and Social Committee and the Committee of the Regions. Thematic Strategy for Soil Protection. COM 231 Final, Brussels. Costanza R., d’Arge R., de Groot R., Farber S., Grasso M., Hannon B., Limburg, K., Naeem, S., O’Neill, 1997. The value of the world’s ecosystem services Paruelo, J., Raskin, R.G., Sutton, P. & van den Belt, M. R .V. , and natural capital. Nature , 387: 253-260. -1 32. 1997. Ecosystem services supplied by soil. In G. Daily, ed. pp. 113 Daily, G.C., P.A. Matson & Vitousek P.M. Nature’s Services: Societal Dependence on Natural Ecosystems . Washington, DC, Island Press. 412 pp. http://www.fao.org/3/a-mn442e.pdf ) FAO . 2015. World Soil Charter (also available at Hole, F.D. & Campbell, J.B. 1985. Soil Landscape Analysis. London, Routledge & Kegan Paul. 196 pp. McBratney, A. B., Field, D. J., & Koch, A. 2014. The dimensions of soil security. Geoderma , 213: 203-213. Millennium Ecosystem Assessment. 2005. Ecosystems and Human Well-Being: Synthesis. Washington, DC, Island Press. 800 pp. rd NRC 1998. The Canadian System of Soil Classification. 3 ed. Canada, Ottawa. 187 pp. Palm, C., Sanchez, P., Ahamed, S. & Awiti, A. 2007. Soils: a contemporary perspective. Annu. Rev. Environ. -1 29. Resour. , 32: 99 Rockström, J., Steffen, W., Noone, K., Persson, Å., Chapin III, F.S., Lambin, E.F., Lenton, T.M., Scheffer, M., Folke, C., Schellnhuber, H.J., Nykvist, B., de Wit, C.A., Hughes, T., van der Leeuw, S., Rodhe, H., Sörlin, S., Snyder, P.K., Costanza, R., Svedin, U., Falkenmark, M., Karlberg, L., Corell, R.W., Fabry, V.J., Hansen, J., Walker, B., Liverman, D., Richardson, K., Crutzen, P. & Foley, J.A. 2009. A safe operating space for humanity. Nature , 461: 472-475. Steffen, W., Richardson, K., Rockström, J., Cornell, S.E., Fetzer, I., Bennett, E.M., Biggs, R. , Carpenter, S.R., de Vries, W., de Wit, C.A., Folke, C., Gerten, D., Heinke, J., Mace, G.M., Persson, L. M., Ramanathan, V., Reyers, B., & Sörlin, S. 2015. Planetary boundaries: Guiding human development on a changing planet. Science, 347 (6223): 1259855. 10 pp. 1987. Report of the World Commission on Environment World Commission on Environment and Development. UK, Oxford, Oxford University Press. 383 pp. and Development: Our Common Future. Status of the World’s Soil Resources | Main Report Global soil resources 12 12

55 2 | The role of soils in ecosystem processes Soils play a critical role in delivering ecosystem services. Management to change an ecosystem process in support of one regulating ecosystem service can either provide co-benefits to other services or require trade- offs (Robinson et al ., 2013; Dominati, Patterson, and Mackay, 2010). Recent reviews have provided examples of some of these synergies and trade-offs (Smith et al ., 2013) and illustrated the role of soils in supporting ecosystem services and underpinning natural capital (Robinson, Lebron and Vereecken, 2009, Robinson et al ., 2014, Dominati, Patterson and Mackay, 2010). In this chapter, we present current knowledge – and knowledge gaps – on the role of soils in the carbon, nitrogen and water cycles, and on their role as a habitat for organisms and as a genetic pool. | Soils and the carbon cycle 2.1 Carbon (C) storage is an important ecosystem function of soils that has gained increasing attention in recent years due to its interactions with the earth’s climate system. Soil is a major C reservoir that holds more carbon than is contained in the atmosphere and terrestrial vegetation combined. All three of these reservoirs are in constant exchange. In many soils, soil organic matter (SOM), which contains roughly 55–60 percent C by mass, comprises most or all of the C stock – referred to as soil organic carbon (SOC). In arid and semi- arid soils, significant inorganic C (IC) can be present as pedogenic carbonate minerals or ‘caliche’ (typically Ca/ ), formed from the reaction of biocarbonate (derived from CO in the soil) with free base cations, which MgCO 3 2 can then be precipitated in subsoil layers (Nordt, Wilding and Drees, 2000). Also soils derived from carbonate- containing parent material (e.g. limestone) can have significant amounts of inorganic carbon. However, in most cases changes in inorganic C stocks are slow and not amenable to traditional soil management practices. Hence inorganic carbon does not play a significant role in terms of management of ecosystem services. For this reason, the further discussion of soil C in this chapter will focus on soil organic carbon. A general overview of the ecosystem C cycle as it interacts with soils is given in Figure 2.1. The major input of by plants (the net result of photosynthesis and organic C to soils is provided by the uptake and fixation of CO 2 above- and below-ground plant respiration), and by the subsequent incorporation of plant residue C (both above- and below-ground) into soil. Some of the fixed plant C may be removed by harvest before entering the soil. Conversely, C additions from offsite sources (e.g. compost, manure) may occur. Organic matter on and in the soil is subject to comminution and mixing by soil fauna and to enzymatic breakdown and metabolism via microbial respiration (also referred to as organic carbon by microorganisms, resulting in release of CO 2 mineralization). Microbial transformations as well as interactions of organic matter with soil minerals greatly influence the stabilization of organic C and its rate of mineralization. In flooded soils, emissions of methane ) from microbial metabolism can represent a significant gaseous C efflux. Erosion can also directly (CH 4 Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 13 13

56 affect the soil C balance through the removal and/or deposition of the C contained in the transported soil. Leaching of dissolved organic (DOC) and dissolved inorganic carbon (DIC) through the soil profile and out into groundwater and surface water represents an additional loss pathway that can be significant in some soils. Maintaining and increasing SOC stocks through improved land use and management practices can help concentrations (Paustian et al. , 1998, Smith et al. , 2007; Whitmore, to counteract increasing atmospheric CO 2 Kirk and Rawlins, 2014). Increasing soil C content also improves other chemical and physical soil properties, such as nutrient storage, water holding capacity, aggregation and sorption of organic and/or inorganic pollutants (Kibblewhite, Ritz and Swift, 2008). Carbon sequestration in soils may therefore be a cost-effective and environmentally friendly way to store C. It can also enhance other ecosystem services derived from soil, such as agricultural production, clean water supply, and biodiversity by increasing SOM content and thereby improving soil quality (Lal, 2004). Plant photosynthesis CO 2 O site OM Plant additions respiration Harvest CO 2 Decomposition & microbial CO respiration 2 Litter fall Soil erosion Soil deposition SOM d turnover an stabilization Drawing by A. Swan and K. Paustian DOC & DIC Figure 2.1 Overview of ecosystem processes involved in determining the soil C balance. 2.1.1 | Quantitative amounts of organic C stored in soil Organic C stocks in the world’s soils have been estimated to comprise 1 500 Pg of C down to 1 m depth and 2 500 Pg down to 2 m (Batjes, 1996). Recent studies, based on newer estimates for the C stored in boreal soils under permafrost conditions, suggest that soil C storage may be even greater, accounting for as much as 2000 Pg to 1 m depth (Tarnocai et al ., 2009). Although the highest C concentrations are found in the top 30 cm of soil, the major proportion of total C stock in many soils is present below 30 cm depth (Batjes, 1996). In the northern circumpolar permafrost region, at least 61 percent of the total soil C is stored below 30 cm depth et al (Tarnocai ., 2009). Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 14 14

57 2.1.2 | Nature and formation of soil organic C Soil organic matter (SOM) is composed of plant litter compounds as well as of microbial decomposition products. SOM is thus a complex biogeochemical mixture derived from organic material in all stages of decomposition (von Lützow et al ., 2006; Paul, 2014). Due to microbial degradation and mineralization to (and CH in anaerobic environments), the majority of plant litter compounds added to soil remain for a CO 2 4 relatively short time (from a few days to a few years). This is particularly the case if the organic compounds are added on the soil surface. However, some organic matter compounds may persist in the soil for decades or , 2006). It is increasingly accepted that, despite et al ., 1997; von Lützow et al. centuries or even for millennia (Paul their recalcitrant nature, plant litter compounds (e.g. lignin) themselves do not substantially contribute to SOM persistence in soil (Thévenot, Dignac and Rumpel, 2010). Longer term stabilization is generally conferred through interactions with soil minerals (e.g. through surface binding or occlusion within microaggregates), which reduce SOM exposure to enzymatic degradation (Sollins, Homann and Caldwell, 1996; Six, Elliott and et al. Paustian, 2000; Schmidt , 2011). Thus, the location of SOM within the soil matrix has a much stronger influence on its turnover than its chemical composition (Chabbi, Kögel-Knabner and Rumpel, 2009; Dungait et al. , 2012) One consequence of the role of reactive mineral surfaces in SOC stabilization is that the surface area of the soil mineral fraction, which is finite and a function of soil texture (e.g. clay, silt or sand content) and of mineralogy, may set an upper limit for the amount of SOM that a particular soil can hold (Six, Elliott and et al. (2013), based on studies showing Paustian, 2002). A recent conceptual model (Figure 2.2) by Cotrufo that microbially-derived decomposition products make up most of the mineral-stabilized organic matter, postulates that relatively labile litter compounds with higher microbial growth yield efficiency contribute proportionally more to the stable mineral-associated SOM pool than do more recalcitrant plant compounds with low microbial growth yield efficiency. This concept is in agreement with the current understanding that microbial material is building up much of the stabilised SOM pool (Miltner et al. , 2012). Figure 2.2 Conceptual model of interactions between litter quality, microbial products and soil mineral interactions affecting the formation and stabilization of organic matter. 2013. Cotrufo et al., Source: Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 15 15

58 With this emphasis on the importance of SOM location within the soil, microbial accessibility of organic material at very small scales has become a focus of research in recent years (Lehmann, Kinyangi and Solomon, 2007). The development of powerful new tools like X-ray spectroscopy and secondary ion mass spectrometry now allows the visualisation of organo-mineral interactions at nanoscale. As a result, the location and distribution of organic matter within the soil mineral matrix may now be assessed in more detail (Lehmann et al. , 2008). However, before the results obtained with these tools yield information concerning soil C formation , 2013). at macroscale, upscaling and integration of spatial heterogeneity is necessary (Mueller et al. As well as exhibiting tremendous heterogeneity in terms of its composition, the distribution of SOC within the soil is also very heterogeneous, particularly with respect to depth within the soil profile. Whereas upper soil layers receive greater amounts of aboveground litter (‘shoot C’ from leaves and stems), subsoil C originates primarily from root-derived C as well as from plant- and microbial-derived dissolved organic carbon (DOC) transported down the soil profile. Root C has a greater likelihood of being preserved in soil compared to shoot C (Balesdant and Balabane, 1996) and studies suggest that root C therefore accounts for a larger proportion of SOM (Rasse, Rumpel and Dignac, 2005). In general, C cycling and C formation is most active in topsoil horizons, whereas stabilised C with longer turnover times makes up a greater proportion of the total SOC found in deep soil horizons (Scharpenseel and Becker-Heidmann, 1989; Trumbore, 2009). The accumulation of stabilised C with long residence times in deep soil horizons may be due to continuous transport, temporary immobilisation and microbial processing of DOC within the soil profile (Kalbitz and Kaiser, 2012) and/or efficient stabilisation of root-derived organic matter within the soil matrix (Rasse, Rumpel and Dignac, 2005). An additional long-term C pool in many soils is pyrogenic carbonaceous matter, formed from partially carbonised (e.g., pyrolysed) biomass during wildfires (Schmidt and Noack, 2000). A portion of this material has a highly condensed aromatic chemical structure (often referred to as pyrogenic carbon or black carbon) that resists microbial degradation and can persist in soils for long periods (Lehmann et al. , 2015). 2.1.3 | Soil C pools For modelling purposes, soil C is usually divided into a number of pools (typically from two to five) in order to represent the heterogeneity in residence time of the vast mixture of different organic compounds in soil et al. , 1997). A useful three pool split of soil C (excluding litter) – into a labile pool, an intermediate pool, (Smith and a refractory (stable) pool – is employed in several soil C models, including the Century model (Parton et al. , 1987). The labile pool represents easily degradable plant material, microbial biomass and labile metabolites, and may turn over within a few months or years. Conceptually, the intermediate pool comprises microbially- processed organic matter that is partially stabilized on mineral surfaces and/or protected within aggregates, refractory pool , including highly stabilized organic matter- with turnover times in the range of decades. The mineral complexes and pyrogenic C, may remain in soils for centuries or millennia. Individual model pools (as opposed to the total C stock) are typically not defined as measureable pools per se. The kinetics of the model conceptual pools are instead inferred from C dating and tracer studies, laboratory incubations and total SOC dynamics in long-term field experiments (McGill, 1996; Paustian, 1994). Many carbon cycle, ecosystem and crop growth models successfully employ this type of functional representation of SOM (Krull, Baldock and Skjemstad, 2003; Stockman et al. , 2013). Nonetheless, ways to reconcile ‘measurable’ and ‘modelable’ pools have been under discussion for a number of years (Elliott, Paustian and Frey, 1996; Smith et al. et al. , 2002; Dungait , 2012). This reconciliation remains a desirable goal for improving understanding of et al. SOC dynamics (Schmidt , 2011). Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 16 16

59 | Factors influencing soil C storage 2.1. 4 Fundamentally, the amount of SOC stored in a given soil is determined by the balance of C entering the ), driven soil, mainly via plant residues and exudates, and C leaving the soil through mineralization (as CO 2 by microbial processes, and to a lesser extent leaching out of the soil as DOC. Locally C can also be lost or gained through soil erosion or deposition (Figure 2.1), leading to a redistribution of soil C at local, landscape and regional scales. Consequently, a main control on SOC storage is the amount and type of residues that are produced by plants as the primary producers in the ecosystem. Plant productivity and subsequent senescence and death lead, through plant necromass breakdown, to the input of organic C to the soil system. Thus, broadly speaking for a given pedoclimatic condition, higher levels of plant residue inputs will tend to support higher SOC stocks, and vice versa. C levels of many soils are also influenced by fertiliser additions, which are indispensable for sustaining plant productivity in agricultural systems. In addition to productivity and plant C inputs, climatic factors, such as soil temperature and water content greatly influence soil C storage through their effect on microbial activity. In general, higher soil temperatures increase microbial decomposition of organic matter. Temperature is, therefore, taken as major control of SOM storage in soil C cycle models, although the temperature sensitivity of decomposition for different SOM et al. fractions remains an area of uncertainty (Conant , 2011). Water also influences soil C storage through several processes. Moist but well-aerated soils are optimal for microbial activity. Decomposition rates consequently decrease as soils become drier. However, flooded depletion due to limited soils have lower rates of organic matter decay due to restricted aeration (e.g. O 2 diffusion in water) and thus may often yield soils with very high amounts of soil C (e.g. peat and muck O 2 soils). High precipitation may also lead to C transport down the soil profile as dissolved and/or particulate organic matter. During extreme events, such as drought, SOM decomposition may initially decrease but may subsequently increase after rewetting (Borken and Matzner, 2008). Fire may decrease soil C storage at first, but over the longer term may increase C storage through positive effects on plant growth and through input of very stable pyrogenic C (Knicker, 2007). The quantity and composition of SOC in mineral soils is also strongly dependent on soil type, with clay content influencing not only the amount but also the composition of soil C. In clay rich soils, higher organic matter content and a higher concentration of O-alkyl C derived from polysaccharides may be expected, compared to sandy soils which are characterised by lower C contents and high concentrations of alkyl C (Rumpel and Kögel-Knabner, 2011). Aliphatic material may contribute to the hydrophobicity of soils, which could lead to reduced microbial accessibility and therefore increased C storage. Bioturbation (the reworking of soils by animals or plants) may further influence the amount as well as the chemical nature of soil C. It may greatly influence the heterogeneity of soils by creating hotspots. On biologically active sites, incorporation and transformation of organic compounds into soil is usually enhanced by bioturbation, leading to organo-mineral interactions and increase of C storage (Wilkinson, Richards and Humphreys, 2009). Microbial decomposition of SOM may be stimulated (or reduced) by labile organic matter input through the ‘priming effect’ ( Jenkinson, 1971; Kuzyakov, 2002). Positive priming refers to mineralisation of otherwise et al. , 2003). stable C through shifts in microbial community composition (Fontaine, Mariotti and Abbadie However, in some cases, the addition of organic matter to soil may also cause changes in the soil microbial communities with regard to the preferentially degraded substrate and therefore impede mineralisation of native SOM (Sparling, Cheschire and Mundie, 1982; Kuzyakov, 2002). Plant communities are main controlling factors of these processes because they influence organic matter input and microbial activity by their effects on soil water, labile C input, pH and nutrient cycling. Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 17 17

60 2.1.5 | Carbon cycle: knowledge gaps and research needs Substantial progress has been made in recent years towards a deeper understanding of the processes controlling soil C storage. There has been progress also in improving and deploying predictive models of soil C dynamics that can guide decision makers and inform policy. However, it is equally true that many new (and some old) gaps in our knowledge have been identified and the need for further research has been assessed. Recent research on soil C dynamics has been driven in part by increasing awareness of: (1) the importance et al. , 2014); (2) interactions between the C cycle and of small scale variability for microbial C turnover (Vogel et al. , 2011); and (3) the importance of soil C not only at the field scale other biogeochemical cycles (Gärdenäs but at regional to global scales (Todd-Brown et al. , 2013). The most cited knowledge gaps and research needs include: Basic understanding Controls on microbial efficiency of organic matter processing, including biodiversity • • The degree of association or separation of organic matter and microbial decomposer communities in the mineral soil matrix • Role of soil fauna in controlling carbon storage and cycling • Dynamics of dissolved organic carbon and its role in determining C storage and decomposition • Pyrogenic C stabilization and interactions of pyrogenic C with native soil C and mineral nutrients • Role of soil erosion in the global C cycle Predictive modelling and assessment Reconciliation of measured and modelled SOM fractions • • More explicit representation of microbial controls Improved modelling of C in subsurface soil layers • Distributed soil C observational and monitoring networks for model validation • More realistic and spatially-resolved representation of soil C in global-scale models • 2.1.6 | Concluding remarks Both biotic and abiotic factors control soil C content and dynamics through their effect on plant litter inputs and microbial decomposer communities. The understanding of the C cycle and the role of soils as a sink or source depends on our ability to integrate knowledge of physical, chemical and biological processes operating of CO 2 at small scales (nm, μm, soil profile) and of the spatial heterogeneity of SOM distribution and decomposition processes at increasing scales (field, region, globe). At the global scale, soils are a major component of the in the atmosphere. Thus, land planet’s C cycle and can have a strong influence on the concentration of CO 2 management needs to be based on an understanding of the controls on SOM distribution, stabilisation and turnover in order to safeguard and increase the organic matter content of our soils. This will be an important contribution to both food security and the mitigation of greenhouse gases. 2.2 | Soils and the nutrient cycle Soils support plant growth and so are vital to humanity. They provide nutrients such as nitrogen (N), phosphorous (P), potassium (K), Calcium (Ca), Magnesium (Mg), Sulphur (S) and many trace elements that support biomass production. Biomass is important for food supply, for energy and fibre production and as a (future) source for the chemical industry. Since the 1950s, higher biomass production and yield increases have been supported through mineral/synthetic fertilization (Figure 2.3). However, intensification of agricultural practices and of land use has in many regions resulted in a decline in the content of organic matter content in agricultural soils. In some areas, extensive use of mineral fertilizers has resulted in atmospheric pollution, et al. O), water eutrophication and human health risks (Galloway , and N greenhouse gas emissions (e.g. CO 2 2 2008). Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 18 18

61 In coming years, human population and demand for food, feed and energy will continue to rise. In order to sustain biomass production in the future and to mitigate negative environmental impacts, fertile soils need to be preserved. Where soil fertility has declined, it needs to be restored by maintaining sufficient amounts of organic matter in soils ( Janzen, 2006). This can be achieved by measures of sustainable management (see Chapter 8 of this volume), including by targeted additions of mineral and organic amendments to soils. The soil function ‘fertility’ refers to the ability of soil to support and sustain plant growth, including through making N, P and other nutrients available for plant uptake. This process is facilitated by: (i) nutrient storage in soil organic matter; (ii) nutrient recycling from organic to plant-available mineral forms; and (iii) physical and chemical processes that control nutrient sorption, availability, displacement and eventual losses to the atmosphere and water. Managed soils represent a highly dynamic system and it is this very dynamism that makes soils function and supply ecosystem services. Overall, the fertility and functioning of soils depend on interactions between the soil mineral matrix, plants and microbes. These are responsible for both building and decomposing SOM and therefore for the preservation and availability of nutrients in soils. To sustain soil functions, the balanced cycling of nutrients in soils must be maintained. After carbon (Section 2.1), N is the most abundant nutrient in all forms of life, since it is contained in proteins, nucleic acids and other compounds. Humans and animals ultimately acquire their N from plants, which in + and NO - ) in soils. The parent material of terrestrial ecosystems occurs mostly in mineral form (e.g. NH 3 4 soils does not contain significant amounts of N (as opposed to P and other nutrients). New N enters the soil by a specialized group of soil biota. However, the largest flux of N in through the fixation of atmospheric N 2 Figure 2.3 Global (a) nitrogen (N) and (b) phosphorus (P) fertilizer use between 1961 and 2012 split for the different continents in Mt P per year. Source: FAO, 2015. soils is generated through the continuous recycling of N internal to the plant-soil system: soil mineral N is taken up by the plant, it is fixed into biomass, and eventually N returns in the form of plant debris to the soil. Here soil biota decompose it, mineralizing part of the N and making it newly available for plant growth, while transforming the other part into SOM, which ultimately is the largest stock of stable N in soil. Nitrogen is lost , N ). O and N from the soil to the water system by leaching and to the atmosphere by gas efflux (NH 3 2 2 In most natural ecosystems, N availability is a limiting factor to productivity and N cycles tightly in the fixing crops, the production and application of system with minimal losses. Through the cultivation of N 2 synthetic N fertilizer, and the deposition of atmospheric N, humans have applied twice as much reactive N to soils as the N introduced by natural processes, thereby significantly increasing biomass production on land (Vitousek and Matson, 1993). However, since mineral fertilizer use efficiency is generally low and far more Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 19 19

62 fertilizer is often used than plants actually need, a high percentage of N fertilizer is lost from the soil. This is et al. , generating a myriad of deleterious cascade effects on the environment and on human health (Galloway 2008). This phenomenon is spread over most of the globe. However, in some regions of the world, in particular Sub-Saharan Africa, which are characterized by eroded soils and where economic constraints limit the use of fertilizers, productivity is still strongly constrained by low levels of soil-available N and other nutrients, notably P (Figure 2.2). Phosphorus is an essential element for all living organisms. It cycles internally in the plant-soil system, moving from the parent material through weathering to biochemical molecules (e.g. nucleic acid, phospholipids) and PO ). In natural soils P is among the most limiting nutrients, back to mineral forms after decomposition (e.g. H 4 3 since it is present in small amounts and only available in its soluble forms, which promptly react with calcium, iron and aluminum cations to precipitate as highly insoluble compounds. Adsorbed on those compounds, P can be lost from soils, entering the aquatic system through erosion and surface runoff. To correct this lack of available P, ‘primary’ P is mined and added to soils in the form of mineral fertilizer. This external input has led to positive agronomic P balances (McDonald et al. , 2011). There are, however, large variations in the world, with large surpluses in the United States, Europe and Asia, and deficits in Russia, Africa and South-America (Figure 2.4). Additionally, since plant P uptake is a relatively inefficient process with roughly 60 percent of the total P input to soils not taken up, it has been estimated that the amount of P exported from terrestrial to aquatic systems has tripled, with significant impacts on the environment (Bennett, Carpenter and Caraco, 2001). Figure 2.4 Applied and excess nitrogen and phosphorus in croplands. Nitrogen and phosphorus inputs and excess were calculated using a simple mass balance model, extended to include 175 crops. To account for both the rate and spatial extent of croplands, the data are presented as kg per ha of the landscape: (a) applied nitrogen, including N deposition; (b) applied phosphorus; (c) excess et al. nitrogen; and (d) excess phosphorus. Source: West , 2014. Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 20 20

63 Management practices need to be implemented that sustain, restore or increase soil fertility and biomass production while limiting associated negative impacts. This can be achieved by promoting the accrual of soil organic matter and nutrient recycling, applying balanced C amendments and fertilization of N, P and other nutrients to meet plant and soil requirements, while limiting overuse of fertilizer. Carbon, N and P cycling in soils is coupled by tight stoichiometric relationships (e.g. relatively fixed C:N:P in plants and microorganisms). This means that an enduring increase or decrease of carbon in soils cannot be achieved without a proportional change in nitrogen and phosphorous (and several other nutrients). This is a fundamental consideration in any programs for carbon sequestration and land restoration because of the significant costs. Therefore, their management needs to be planned in concert. Nutrient management has been extensively studied, with the aim of identifying and proposing management practices (e.g. precision agriculture) that improve nutrient use efficiency and productivity while reducing potentially harmful losses to the environment (van Groenigen et al. , 2010; Venterea, Maharjan and Dolan, 2011). However, our ability to predict the ecosystem response to balanced fertilization is still limited and the relationship requires continued monitoring. Further benefits are anticipated from improved plant varieties with root morphologies that have better capacity to extract P from soils or use it more efficiently. More generally, further research is needed into organic matter responses to agricultural C inputs and into the potential for restoring and increasing soil organic matter to promote long term soil fertility (e.g. Lugato, Berti and Giardini, 2006). Hence, we stress the importance of an integrated approach to nutrient management which supports plant productivity while preserving or enhancing soil organic matter stocks and reducing nutrient losses to the atmosphere or aquatic systems. Prediction and optimization of performance would benefit from continued data acquisition across the whole range of climate and environmental and agro-ecological conditions. 2.2.1 | The nutrient cycle: knowledge gaps and research needs In the second half of the 20th century, higher biomass yields were supported by higher use of fertilizer (N, P) inputs. This is now considered unsustainable in many situations. Alternatives are required that make better use of inherent soil fertility, improve resource use efficiency, and prevent losses of N and P. Examples in agriculture include sustainable intensification and new crop varieties that have root systems with improved extraction capability or which have higher internal P use efficiency. At the food system level, more effective nutrient management would benefit from a focus on a ‘5R strategy’: (1) realign P and N inputs; (2) reduce P and N losses to water, thereby minimizing eutrophication impacts; (3) recycle the P and N in bio-resources; (4) recover P and N from wastes to use as fertilizer; and (5) redefine use and use-efficiency of P in the food chain (Withers et al. , 2015). In addition, a better understanding of biogeochemical processes at the molecular level is needed. This should include: (i) research into the role of plant symbionts on the weathering of minerals and support of nutrient uptake, and (ii) development of target-specific ‘smart’ agrochemical agents that enhance nutrient uptake. 2.3 | Soils and the water cycle Soils provide important ecosystem services through their function within the water cycle. These services include provisioning services of food and water security, regulating services associated with moderation and purification of water flows, and cultural services such as landscapes and water bodies that meet recreation and aesthetic values (Dymond, 2014). Water stored in soil is used for the evapotranspiration and plant growth that supply food and fibre. Soil water also stabilizes the land surface to prevent erosion and regulates nutrient and contaminant flow. At a catchment and basin scale, the capacity of the soil to infiltrate water attenuates stream and river flows and can prevent flooding, while water that percolates through soil can replenish groundwater and related streamflow and surface water ecosystems. Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 21 21

64 The soil functions of accepting, storing, transmitting and cleaning of water shown in Table 2.1 are inter- related. Soil water storage depends on the rate of infiltration into the soil and on soil hydraulic conductivity that redistributes water within and through the soil profile. Similarly, infiltration and hydraulic conductivity are dependent on the water stored in the soil. The initially high rate of infiltration into dry soil declines as the soil water content increases and water replaces air in the pore space. Conversely, hydraulic conductivity increases with soil moisture content as a greater proportion of the pores are transmitting water. Water content and transmission times are also important to the filtering function of soil because contact with soil surfaces and residence time in soil are controls on contaminant supply and removal. Optimum growth of most plants occurs when roots can access both oxygen and water in the soil. The soil must therefore infiltrate water, drain quickly when saturated to allow air to reach plant roots, and retain and redistribute water for plant use. The ideal soil for plant production depends on climatic conditions and on the soil requirements of the crop. For instance, in dry regions it can be an advantage to have soils with a high clay content to retain water, while sandier soils that drain quickly are better suited to wetter regions. Soil structural stability and porosity are also important for the infiltration of water into soil. Organic matter improves soil aggregate stability. While plant growth and surface mulches can help protect the soil surface, a stable, well-aggregated soil structure that resists surface sealing and continues to infiltrate water during intense rainfall events will decrease the potential for downstream flooding. Porosity determines the capacity of the soil to retain water and controls transmission of water through the soil. In addition to total porosity, the continuity and structure of the pore network are important to these functions and also to the further function of filtering out contaminants in flow. Ecosystem service Mechanism Consequence Soil Function Water held in soil pores Food Stores Biomass production supports plant and Aesthetics (Storage) Surface protection microbial communities Erosion control Incident water Accepts Erosion control infiltrates into soil with Storm runoff reduction (Sorptivity) Flood protection excess lost as runoff Water entering the soil Groundwater recharge Transmits is redistributed and Percolation to Stream flow (Hydraulic conductivity) excess is transmitted as groundwater maintenance deep percolation Water passing through Contaminants Cleans the soil matrix interacts removed by biological Water quality (Filtering) with soil particles and degradation/retention biota on sorption sites Table 2. Soil functions related to the water cycle and ecosystem services Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 22 22

65 Another important role of soil water is its support of biota that can degrade compounds into beneficial forms that may also retain nutrients. Soil organic matter is important to this role - together with mineral soil (especially the clay fraction), SOM provides sorption sites, but sorption capacity is finite. Flow through macropores that bypass the soil matrix where biota and sorption sites are generally located can quickly transmit water and contaminants through the soil to groundwater or artificial drains. However, for filtering purposes a longer, slower route through the soil matrix is more effective. Soil management alters the ecosystem services provided by water (Table 2.2). Soil conservation practices and sustainable management help to retain regulating ecosystem services such as soil organic matter and structural stability. Similarly, the promotion of soil as a C-sink to offset greenhouse gas emissions helps to maintain or improve soil functions. On the other hand, deforestation, overgrazing and excessive tillage of fragile lands lead to deterioration of the soil structure and to loss of soil function and surface water quality (Steinfield et al. , 2006). Anthropogenic modifications to the water cycle can aid soil function. In dry regimes, inadequate soil moisture can be mitigated through supplementary irrigation, and where excessive precipitation causes problems, waterlogging can be relieved by land drainage. However, irrigation and drainage can have consequences for water regulation services. Irrigation that enables a shift to intensive land use can increase the contaminant load of runoff and drainage water (McDowell , 2014). Furthermore, drainage of wetland et al. soils has been shown to reduce water and contaminant storage capacity in the landscape and can increase the potential for downstream flooding. The abstraction of surface or groundwater for irrigation disrupts the natural water cycle and may stress downstream ecosystems and communities. Irrigation of agricultural lands accounts for about 70 percent of ground and surface water withdrawals, and in some regions competition for water resources is forcing irrigators to tap unsustainable sources. Irrigation with wastewater may conserve et al. fresh water resources but brings the risk of water-borne contaminants in soil and crops (Sato , 2013) and the accumulation of salts in some environments. Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 23 23

66 Management Provisioning Cultural Regulating (global trend) Increased impervious Decreased biomass, surface, decreased Land use change decreased availability of Decreased natural infiltration, storage, (agricultural to urban) water for agricultural environment soil-mediated water use regulation Increased C Land use change Land use change sequestration, greater (increase in change (increase in change requirement for water, of arable to intensive of arable to intensive stress on ecosystem grassland) grassland) health of downstream waterways Increased biomass over Increased C dryland agriculture, sequestration, but Infrastructure alters Irrigation (increase) decreased availability of decreased filtration landscape water for urban use potential Decreased soil Decreased C Decreased recreational Drainage (increase in saturation, increased sequestration, potential (e.g. marginal land) biomass, reduction in denitrification and flood ecotourism) wetlands attenuation Table 2.2 Examples of global trends in soil management (Steinfield et al., 2006; Setälä et al., 2014) and their effects on the ecosystem services mediated by water. The soil management practices to maintain the ecosystem services of food and water security and flow regulation within the soil and water cycle are reasonably well established. However, their application is not universal and poor management leads to a loss of function. Under climate change scenarios of increased climatic variability with more extremes of precipitation, soil functions will be stressed and better soil management will be required (Walthall , 2012). et al. | Soil as a habitat for organisms and a genetic pool 2.4 Soils represent a physically and chemically complex and heterogeneous habitat supporting a high diversity of microbial and faunal taxa. For example, 10 g of soil contains about 1010 bacterial cells of more than 106 , 2005), and an estimated 360 000 species of animals are dwellers in soil (Decaëns species (Gans et al. et al. , 2006). These complex communities of organisms play critical roles in sustaining soil and wider ecosystem functioning, thus conferring a multitude of benefits to global cycles and human sustainability. Specifically, soil biodiversity is critical to food and fibre production. It is also an important regulator of other vital soil services including nutrient cycling, moderation of greenhouse gas emissions, and water purification (Wall et , 2012). It is also recognized that the stocks of soil biodiversity represent an important biological and genetic al. resource for biotechnological exploitation (Brevik and Sauer, 2015). Previous methodological challenges in characterizing soil biodiversity are now being overcome through the use of molecular technologies. As a result significant progress is currently being made in opening the ‘black box’ of soil biodiversity (Allison and Martiny, 2008), particularly in assessing the normal operating ranges of soil biodiversity under different soil, climatic and land use scenarios. Addressing these knowledge gaps is of fundamental importance, both as an entry point to understanding wider soil processes and as a way to gauge the likely consequences of land use or climatic change on both biodiversity and soil ecosystem services. Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 24 24

67 The development of molecular technologies has aided morphological characterisations and allowed quantification of stocks and changes in soil biodiversity. This has led to a surge in studies characterizing soil biodiversity at different scales – from large landscape-scale surveys to locally focused studies. The large- scale surveys yield the broader picture, and conclusions are emerging identifying the importance of soil parameters in shaping the biodiversity of soil communities (Fierer and Jackson, 2006). In essence, the same geological, climatic and biotic parameters that ultimately dictate pedogenesis are also involved in shaping the communities of soil biota and thus in regulating the spatial structure of soil communities observed over large areas (Griffiths et al. , 2011). Locally focused experimentation then typically reveals more specific changes in broad taxonomic features with respect, for example, to local changes in land use or climate. Many studies have focused on assessing one component of soil diversity, but even greater advances utilizing next-generation high throughput sequencing now allow the analysis of ‘whole soil foodwebs’. This permits a thorough interrogation of trophic and co-occurrence interaction networks. The challenge is to consolidate both approaches at different scales to understand the differing susceptibility of global soil biomes to change. Alongside these new developments in assessing biodiversity, it is essential to link the biodiversity characteristics measured to specific soil functions. This helps understanding the pivotal roles of soil organisms in , 2000) et al. mediating soil services. The development of stable isotope tracer methodologies (e.g. Radajewski to link substrate utilization to the identified active members in situ serves to clarify the physiological activity of these soil organisms. Additionally, improved sequencing techniques are now becoming an increasingly cost- effective for assessing the biodiversity of functional genes in soils for both eukaryotes and prokaryotes (Fierer et al. , 2013). This potentially allows a more trait-based approach to understanding soil biodiversity, akin to recent approaches applied to larger and more readily functionally understood organisms above-ground. It is becoming increasingly apparent that often, as is typical in natural ecosystems, functionality and biodiversity co-vary with other environmental parameters. Further manipulative experimentation is required to determine the fundamental roles of soil biodiversity versus other co-varying factors in driving soil functionality. Clearly, we are learning more and more about how global change affects soil biodiversity and functioning. Global-scale syntheses on soil biodiversity are still lacking, but projects such as the Global Soil Biodiversity Atlas (European Commission, 2015) are combining information from across the globe and making it publicly available. However, much remains to be done. More than 20 years ago, many of these issues were raised (for example, in Furusaka, 1993), and to date many of the factors involved have yet to be unravelled. A key barrier to achieving syntheses is the lack of concerted soil surveys that address multiple functions using standardized methodologies. New technologies for soil biodiversity assessment generate large sequence datasets that are typically archived in publicly accessible databases. However, morphological datasets remain largely unpublished. The best approach to addressing the gaps would be to adopt agreed standard operating procedures for soil function measurements (e.g. as developed in the recent EU-funded EcoFINDERS project) and to ensure that results are widely accessible. Ultimately the new methods are revealing the high sensitivity of changes in soil biological and genetic resources to threats such as poor management. We now need to recognize the distinct types of organisms found in different soils globally, and to understand their functional roles in order to predict vulnerability of these resources to future change. Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes 25 25

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73 3 | Global Soil Resources 3.1 | The evolution of soil definitions The definition of soil has changed over time. Early definitions (Kraut, 1853; Ramann, 1919) emphasized the geological or substrate aspect of soil as the upper weathering mantle of the earth’s crust. At the end of the 19th century, Vasiliy Dokuchaiev formulated the paradigm of soil as a natural body formed by the combined effect of five soil-forming factors (climate, organisms, parent material, time and relief ). This formulation effectively made Dokuchaiev the founder of a new science – pedology. His ideas were translated into English and promulgated by Coffey (1912) and Marbut (1921). Jenny (1941) published the equation of soil forming factors as independent variables; S = f(cl, o, r, p, t...). Dudal, Nachtergaele and Purnell (2002) added a human factor of soil formation, implying that soil is not exclusively a natural body. For digital soil mapping, the soil forming factors were modified by McBratney, Mendonça-Santos and Minasny (2003) as Sc = f(s, c, o, r, p, a, n...) or Sa = f(s, c, o, r, p, a, n...) where Sc is soil classes, Sa is soil attributes, s is the soil or property at a point, and n is the spatial position. Grunwald, Thompson and Boettinger (2011) further expanded the factor model to the STEP-AWBH Model by including space and time to infer soil properties and their evolution in which the factors of human action, atmosphere, and water are added. Defined in the simplest terms, soil is the upper layer of the Earth’s crust transformed by weathering and physical/chemical and biological processes. It is composed of mineral particles, organic matter, water, air and living organisms organized in genetic soil horizons (ISO, 2013). Status of the World’s Soil Resources | Main Report Global Soil Resources 31 31

74 3.2 | Soil definitions in different soil classification systems The World Reference Base for Soil Resources (FAO, 2014) classifies as soil any material within 2 m of the Earth’s surface that is in contact with the atmosphere, but excluding living organisms, areas with continuous ice not covered by other material, and water bodies deeper than 2 m. In the United States Soil Taxonomy (Soil Survey Staff, 1999) soil is considered to be a natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface, occupies space, and is characterized by one or both of the following: (i) horizons or layers that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter; and (ii) the ability to support rooted plants in a natural environment. In the Russian Classification System (Shishov et al. , 2004), soil is defined as a solid-phase natural-historical body with a system of inter-related horizons composing a genetic profile and which derives from the transformation of the uppermost layer of the lithosphere by the integrity of soil-forming agents. French pedologists put emphasis on the spatial aspects of soil as an ‘objet naturel, continu et tridimensionnel’ (a natural, continuous and three dimensional object) (AFES, 2008). A related variant considers that “soil in nature is a three-dimensional continuum, temporally dynamic and spatially anisotropic, both vertically and laterally” (Sposito and Reginato, 1992). Urban soils including those ‘sealed’ by concrete or asphalt, strata of composts or other fertile materials applied to construct lawns and gardens, superficial layers, mine spoil or garbage heaps are also considered in some soil classification systems (Rossiter, 2007). The concept of soils as natural bodies also includes very thin films in caves or fine earth patches within desquamation cracks of hard rocks as found in Antarctic endolithic soils (Goryachkin et al. , 2012) and in underwater soils (Demas, 1993). Thus, the concept of soil becomes very broad. Soil scientists have even proposed to extrapolate it to other planets (Targulian et al. , 2010). 3.3 | Soils, landscapes and pedodiversity The relationships between soils and landscapes were at the core of the ‘zonality’ concept developed by Dokuchaev and tested during his excursion to the Caucasus in 1898. He expressed the concept at the global scale in the form of many-coloured soil bands around the Earth. This zonal concept was also used in the United States 1938 classification of zonal, azonal, and intrazonal soils (Baldwin, Kellogg and Thorp, 1938). Along with zonal ideas, concepts of regularities in local soil patterns emerged. The earliest among these was the concept of soil series developed in the United States in 1903 (Simonson, 1952). The work of Neustuev (1931) on soil geography further developed the concept of regularities. Another set of spatial soil patterns related to topography was recognized by Milne (1935) and Bushnell (1945) who proposed the term ‘catena’ (chain) and applied it to soil sequences on the slopes of mountains. Different soil catenas in landscapes all over the world were subsequently described and attempts were made to inventory them systematically (Sommer and Schlichting, 1997). Fridland (1976) gave a new impulse to the theory of the ‘soil/landscape’ relationship by defining the types of soil systems related to landforms at different scales (‘soil associations’). The relationships between soils – their ingredients, taxonomic distances, geometric shape and kinds of boundaries - were described and for some of them mathematic formulas were proposed. Status of the World’s Soil Resources | Main Report Global Soil Resources 32 32

75 Fridland’s was the first attempt to analyse and quantify the pedological diversity of a territory. The concept et al. , 1995; of soil diversity, or pedodiversity (Ibáñez, Jiménez-Ballesta and García-Álvarez, 1990; Ibáñez McBratney, 1992), opened a new conceptual window in soil science (Ibañez and Bockheim, 2013; Toomanian and Esfandiarpoor, 2010). Approaches comprised the description and measurement of either the spatial distribution of soils, or their evolutionary stages by indicating rates of soil development. Soil development makes a contribution to the spatial heterogeneity of the soil because, together with other agents, soils with different evolutionary pathways participate in forming the soil cover and so contribute to the creation of specific soilscapes. The term ‘pedodiversity’ and many tools for studying pedodiversity were adapted from biology. Pedodiversity, for example, can be measured just as biodiversity is measured - by means of special indices showing the abundance of species and the taxonomic distances between them. A set of mathematical methods, both parametric and non-parametrical, can be applied to quantify soil spatial heterogeneity. The pedodiversity concept is an updated, quantification-oriented branch of soil geography. Its advantage is its compatibility with GIS and remote sensing technologies and its solid base in mathematics and statistics, which leads to a broad applicability in environmental sciences and biology. 3.4 | Properties of the soil Because soils have physical, chemical, mineralogical, and biological characteristics, knowledge of the basic sciences of geology, chemistry, physics and biology contributes to understanding basic soil properties. The solid inorganic fraction defines the soil’s texture, the amount of sand, silt, and clay. Solid particles are arranged into aggregates to form diverse structures by biological, chemical and physical processes. Structure describes the size, organization, and shape of the soil aggregates. Consistence and strength are how the soil deforms under pressure. Texture and structure influence porosity and bulk density. Gases or solutions occupy the soil pores. Soil reaction (pH), redox status, carbon, nutrients, and cation exchange capacity are key chemical properties. Secondary clay minerals e.g. smectite, vermiculite, illite, influence the soil physical and chemical properties and are the primary source of ionic exchange. The abiotic, inorganic properties create a platform for the biotic soil component. Properties that are seen or felt are part of the soil morphology. Soil morphology is the object of study both in nature and in laboratories – micro morphology – with the help of microscopy and computer tomography. Soil colour is influenced by the content and type of organic matter and specific minerals including oxides (e.g. Fe oxi-hydroxides), and redox conditions. Horizon and total soil thickness describe internal organization and root and moisture availability. 3.5 | Global soil maps Local soil investigations started at the end of the 19th century in Russia (see 3.3. above), but only after World War II were efforts geared towards more systematic national soil inventories. The first regional maps were produced in the early 1960s for Europe (FAO/UNESCO, 1962) and for Africa (D’Hoore, 1964). The development of a global soil map was initiated by the International Soil Science Society in 1960 and implemented by FAO and UNESCO between 1971 and 1980, resulting in the FAO-UNESCO Soil Map of the 1 World. 1 A digital version of this map is downloadable at: http://www.fao.org/geonetwork/srv/en/resources.get?id=14116&fname=DSMW.zip&access=private Status of the World’s Soil Resources | Main Report Global Soil Resources 33 33

76 This Soil Map of the World was, from 1995 onwards, systematically updated under the Soil and Terrain Database (SOTER) program carried out by FAO, ISRIC and UNEP together with national soil survey services. This resulted in several regional updates, including for Latin America and the Caribbean, large parts of Africa, and Eastern and Central Europe. In parallel, other organizations, notably the Joint Research Centre ( JRC) of the European Commision (EC) and the USDA, undertook regional soil updates, while several countries completed national soil inventories and maps (China, Brazil, Botswana and Kenya etc.). This updated information was harmonized with the digitalized Soil Map of the World and published by a consortium of FAO, IIASA, JRC, ISRIC and CAS in 2006 as the Harmonized World Soil Database (HWSD). Although not fully harmonized and consistent, the HWSD contains the most up-to-date and comprehensive soil information that is currently available. The latest version of this database, giving geo-referenced estimates of twenty soil characteristics, 2 is available online. In 2006, work began on the design and planning for a soil grid of the world at fine resolution (100 m) and this became known as GlobalSoilMap. The intent was to integrate the best available data from local and national sources and deliver the information online. The format and resolution was to be compatible with other fundamental data sets on terrestrial systems (e.g. vegetation, land cover, terrain, remote sensing). The initial focus was Africa (Sanchez et al. , 2009) and this led to the establishment of the African Soil Information 3 The technical and logistical complexity of the project has been substantial but good progress System (AfSIS). has been made during the initial research phase of the project and continental coverages are starting to be 4 (2014). et al. A full summary is provided by Arrouays published. 5 Another, more recent initiative that arose from the GlobalSoilMap effort is Soil Grid 1km which is a collection of updatable soil property and class maps of the world at a relatively coarse resolution of 1 km. These maps are being produced using state-of-the-art model-based statistical methods: 3D regression with splines for continuous soil properties and multinomial logistic regression for soil classes. SoilGrids 1km are outputs of a system for automated global soil mapping developed within the Global Soil Information Facilities framework. This system is intended to facilitate global soil data initiatives and to serve as a bridge between et al. , 2014). global and local soil mapping (Hengl Information on the availability of global, regional and national soil maps has been summarized by Omuto, Nachtergaele and Vargas (2012). The plan for developing the global soil information system was endorsed by 6 the Plenary Assembly of the Global Soil Partnership in July 2014 and it is now being implemented. A simplified global soil map with the major soil groups is given in Figure A 35 (Annex). 3.6 | Soil qualities essential for the provision of ecosystem services Soil functions depend on a number of physical, chemical and biological soil properties that in combination determine essential soil qualities. These qualities in turn guarantee that the soil can fulfil its ecological and productive services. Soils differ considerably in terms of properties, qualities, limitations and potential. Significant changes may occur over very short distances, making environmental and soil monitoring difficult (Brammer and Nachtergaele, 2015). 2 http://www.fao.org/soils-portal/soil-survey/soil-maps-and-databases/harmonized-world-soil-database-v12/it/ 3 http://www.africasoils.net 4 http://www.clw.csiro.au/aclep/soilandlandscapegrid/ 5 http://www.isric.org/content/soilgrids 6 http://www.fao.org/fileadmin/user_upload/GSP/docs/plenary_assembly_II/pillar4.pdf Status of the World’s Soil Resources | Main Report Global Soil Resources 34 34

77 Soil management has a considerable effect on how the soil may fulfil its ecosystem services. Mineral and organic fertilizer may compensate for poor inherent nutrient conditions in a soil; drainage may remedy excessive wetness in soils, or leach salts when these are present; amendments (lime or gypsum) may correct very acid or highly sodic soils. However, these interventions always have a cost in terms of labour and inputs, and they may also have negative side effects, such as groundwater contamination. In this section a number of soil qualities essential for the provision of ecosystem services are discussed and 35. related to the major soil groups summarized and illustrated in Annex A 3.6.1 | Inherent soil fertility The capability of a soil to provide sufficient nutrients to crops, grasses and trees is a major quality of soils that supports all provisioning services of the ecosystem. Sixteen nutrients are essential for plant growth and living organisms in the soil. These fall into two different categories: macronutrients and micronutrients. Macronutrients are the most important nutrients for plant development and relatively high quantities are required. Macronutrients include: carbon (C), oxygen (O), hydrogen (H), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulphur (S). Micronutrients, on the other hand, are needed in smaller amounts, but are still crucial for plant development and growth. Micronutrients include iron (Fe), zinc (Zn), manganese (Mn), boron (B), copper (Cu), molybdenum (Mo) and chlorine (Cl). Nearly all plant nutrients are taken up in ionic forms from the soil solution as cations or as anions. Soil properties directly related to the amount and availability of nutrients in the soil are: (i) soil texture (clayey soils contain more nutrients than sandy ones); (ii) the type of clay minerals present (smectitic clays absorb more ions than kaolinitic ones); (iii) the soil organic carbon content (more SOC corresponds with a larger amount of nutrients); and (iv) the cation exchange capacity that corresponds to the total of Ca, Mg, K, Na (basic ions) and Al and H (acidic ions) exchangeable with the soil solution. A large amount of available nutrients is present in Vertisols, Chernozems (Borolls), Kastanozems (Ustolls) and Phaeozems (Udolls). Also volcanic soils (Andosols) and alluvial soils (Fluvisols/Fluvents) generally have a large nutrient content. On the other hand, sandy soils (Arenosols/Psamments) and highly leached soils (Ferralsols/Oxisols and Acrisols/ Ultisols) generally have a small nutrient content. The amount of nutrients that a soil can provide to plants within the growing season represents a limit to nutrient mining. Nutrient mining occurs when crops take out a high proportion of the nutrients available in the soil, leaving a nutrient imbalance that threatens the sustained provision of food and ecosystem services. These challenges are discussed in Section 6.8. Figure 3.1 illustrates an estimation of the nutrient availability in soils globally based on information contained in HWSD. Soil depth to a hard or an impermeable layer is a vital factor that determines the capability of roots to take hold and determines the total volume of nutrients and water available to crops and vegetation. Soils tend to be deeper when strong weathering conditions prevail over a long period and wherever the parent material is readily weathered. Typical soils include Ferralsols and Nitisols). Shallow soils often occur in mountainous areas (Leptosols) and in dry areas characterized by indurated layers of silica, calcium carbonate or gypsum (Durisols/ Durids, Calcisols/Calcids and Gypsisols/Gypsids). Each plant type has its own ideal rooting conditions. Tubers are the most sensitive to soil depth and volume limitations (Fischer et al. , 2008; Grossnickle, 2005; Unger et al. and Kaspar, 1994; McSweeney and Jansen, 1984; Myers , 2007). Figure 3.2 illustrates global soil rooting conditions Status of the World’s Soil Resources | Main Report Global Soil Resources 35 35

78 No o ts strain r slight con re con Very seve nstraints re co Seve Wate dies straints r bo erate con strains Mod rea st a Permafro Mainly non-soil Figure 3.1 Nutrient availability in soils. Source: Fischer et al., 2008. is a measure of its hydrogen ion concentration and indicates the acidity or alkalinity of the The soil pH soil. Optimum availability of nutrients occurs around pH=6.5. Toxic concentrations of H and Al occur when the pH drops below 5.5. Values of pH above 7.2 indicate an alkaline reaction and may be symptomatic for the immobilization of nutrients. Very high pH values over 8.5 result in the dispersion of the soil particles and a collapse of structure. High rainfall results in more acid soils (Ferralsols/Oxisols, Alisols, Plinthisols, Acrisols/ Ultisols, Podzols/Spodosols), while drier conditions often lead to the accumulation of Gypsum (Gypsisols/ Gyspsids) or other less soluble salts (Silicon and Calcium Carbonate) in Durisols/Durids and Calcisols/Calcids. The soil pH is also important to the characterization of soil threats to ecosystem services such as acidification (section 6.4) and sodification (Section 6.5). A global map of soil pH is given in Section 6.4. afro st are a Moderate constraints No or slight constra ints Perm Mainly non-s oils Very severe constra ints Severe constra ints Water bodies Figure 3.2 Global soil rooting conditions. Source: Fischer et al., 2008. Status of the World’s Soil Resources | Main Report Global Soil Resources 36 36

79 Accumulation of water soluble salts : soils in relatively dry areas are often characterized by the accumulation ). These salts may , etc.) and of less water-soluble salts (CaCO , CaSO SO of water-soluble salts (NaCl, Na 4 2 3 4 form indurated layers that limit the soil depth available for roots. This accumulation is often a natural process resulting in soils such as Solonchaks/Salids, Calcisols/Calcids, Gypsisols/Gypsids, Durisols/Durids. In irrigation schemes, which are most commonly developed in dry areas, the problem may be human-induced and made worse by the use of saline irrigation water, by insufficient leaching/drainage, or by the conversion to irrigation of soils formed from marine sediments. Most salt-affected soils have moderate to severe limitations for crop production. Section 6.5 deals specifically with salinization and sodification problems. Toxic elements and other soil fertility problems : some toxic elements such as aluminium occur naturally in acid soils. The parent material may also be a natural source of undesirable elements (for instance cadmium) that may be a problem for human and animal health. Some soils have a high phosphorus adsorption ratio (Andosols and Nitisols/Kandi subgroups) that make P fertilization cumbersome. Atmospheric deposition of toxic elements may also contaminate soils as discussed in section 4.4. 3.6.2 | Soil moisture qualities and limitations The moisture stored in or flowing through the soil affects soil formation , its structure and stability , and erosion run-off. Soil moisture is of primary concern with respect to plant growth. The depth of the groundwater table and the availability of in the soil also affect soil ecosystem functions. The physical properties of oxygen soils (texture, structure, porosity, drainage class, permeability) are of prime importance in this respect. The capacity to store water and moisture in a soil is largely determined by its texture, structure, organic carbon content and depth. Soil moisture provides a buffer for crops during dry periods and is a built- in safeguard against run-off and erosion. Ecological functions of this parameter are discussed in Chapter 7. High soil moisture capacities are typical for deep clayey soils, rich in organic matter and containing modest (Chernozems, Cambisols). The lowest soil moisture capacities are encountered in sandy amounts of CaCO 3 soils (Arenosols) or very shallow soils (Leptosols). Very high soil moisture storage occurs in volcanic soils (Andosols) and in many peat soils (Histosols). Figure 3.3 illustrates the distribution of different soil moisture storage classes globally. Oxygen availability is a critical factor for plant growth. Inadequate oxygen supply to the roots leads to the formation of an underdeveloped root system which is not able to provide sufficient nutrients and water to the plant. Oxygen availability is basically defined by drainage characteristics of soils related to soil type, soil texture, soil phases and terrain slope, all of which play an important role in determining the proportion of gases and water into the soil. Soil phases define specific soil and terrain characteristics. Gleysols/Aquic suborders, Stagnosols and Plinthosols often suffer from temporary saturation with groundwater or rain water, resulting in poor oxygen availability for part of the year. Oxygen availability can be improved by farming practices (e.g. adapted tillage) and by farming inputs such as artificial drainage (Crawford, 1992; Erikson, 1982; Fischer et al. , 2008). 3.6.3 | Soils properties and climate change Soils are both affected by and contribute to climate change. The carbon that is fixed by plants is transferred to the soil via dead plant matter including dead roots and leaves. This dead organic matter creates a substrate which soil micro-organisms respire back to the atmosphere as carbon dioxide or methane depending on the availability of oxygen in the soil. Some of the carbon compounds are easily digested and respired by the microbes, resulting in a relatively short residence time. Others become chemically and/or physically stabilised in soils and have longer residence times (as described in Chapter 2). Soil organic carbon can also be thermally decomposed during fire events and returned to the atmosphere as carbon dioxide. Remaining charred material can persist in soils for long periods (Lehmann , 2015). et al. Status of the World’s Soil Resources | Main Report Global Soil Resources 37 37

80 Average water capacity class (mm/m) < 50 50 - 100 100 - 150 > 150 Figure 3.3 Soil Moisture storage capacity. Source: Van Engelen, 2012. Soil organic carbon improves the physical and chemical properties of the soil by increasing the cation exchange capacity and the water-holding capacity. It also contributes to the structural stability of soils by helping to bind particles into aggregates. Soil organic matter (SOM), of which carbon is a major part, holds a great proportion of nutrients, including trace elements, which are of importance to plant growth. SOM mitigates nutrient leaching and contributes to soil pH-buffering capacity. It is widely accepted that the organic matter content of the soil is a major factor contributing to soil functions, including that of organic C storage, which has important feedbacks with the Earth’s climate system (Chapter 2). A large organic carbon content is found in peat soils (Histosols/Histisols), in volcanic soils (Andosols/ Andisols) and in steppe soils (Chernozem/Borolls, Kastanozems/Ustolls and Phaeozems/Udolls). Large organic carbon contents are not always indicative of fertile soils because carbon may also accumulate under wet and cold conditions as in Podzols/Spodosols and Cryosols/Gelisols, and in some hydromorphic soils such as Gleysols. Changes in SOC represent one of the major soil threats – see the discussion in section 6.2. The global distribution of soil organic carbon is given in Figure 3.4. Crysols/Gelisols are soils which are frozen for a large part of the year. In taiga areas they often occur together with Histosols. Global warming in these areas will have a significant effect by allowing agriculture to move more northwards. However, mineralization of organic carbon may be accelerated, with negative consequences for GHG release. 3.6.4 | Soil erodibility and water erosion The susceptibility of a soil to water erosion is primarily determined by the erosive potential of the rainfall, the slope of the land surface and position of the soil in the catchment, and the vegetative cover on the soil surface. Soil erodibility refers to the susceptibility of soil to erosion by water and is an important secondary control on the intensity of water erosion. Most clay-rich soils (e.g. Vertisols with the exception of erodible self-mulching forms) have a high resilience because they are resistant to detachment. Coarse textured, sandy soils (e.g. Arenosols/Psamments) are also resilient because of low runoff even though these soils are easily detached. Medium textured soils, such as silt loam soils are only moderately resistant to erosion because they are moderately susceptible to detachment and they produce moderate runoff. Soils having a high silt content are the most erodible of all soils. They are easily detached, tend to crust and produce high rates of runoff. Organic matter reduces erodibility because it reduces the susceptibility of the soil to detachment, Status of the World’s Soil Resources | Main Report Global Soil Resources 38 38

81 and increases infiltration, which reduces runoff and thus erosion. Soil structure affects both susceptibility to detachment and infiltration. Permeability of the soil profile affects erodibility because it affects runoff. Past management or misuse of a soil (e.g. by intensive cropping) can increase a soil’s erodibility, for example if the subsoil is exposed or if the organic matter has been depleted, or where the soil’s structure has been destroyed or soil compaction has reduced permeability. Section 6.1 discusses soil erosion by water in more detail. Soil erodibility worldwide, as characterized by the k factor in the RUSLE equation, is represented in Figure 3.5. Prepared by R. Hiederer -1 Figure 3.4 Soil Organic Carbon pool (tonnes C ha ). | Soil workability 3.6.5 Soil workability refers to the ease of tillage, which depends on the soil’s interrelated characteristics of texture, structure, organic matter content, etc., on the soil’s gravel content, and on the presence of continuous hard rock at shallow depth. Depending on the soil characteristics, soil workability also varies with the soil moisture content. Some soils are easy to work regardless of the moisture content, but other soils – such as Vertisols - can be worked only at a specific moisture status. This is true especially for farming systems employing manual cultivation methods or using only light machinery. Soil workability is also related to the type of soil management adopted. While low and intermediate input farming systems mainly face constraints related to soil texture and soil structure, high-level input mechanized farming systems mainly face constraints related to irregular soil depth and stony and rocky soil conditions. Indeed, the use of heavy field equipment is not possible on stony soils or on soils characterized by irregular soil depth. This factor can prevent soil degradation, for , 2008; Müller et al. , 2011; Rounsevell, 1993). Figure 3.6 shows example by compaction (Earl, 1997; Fischer et al. the distribution of the constraints to soil management and food production due to soil workability worldwide. Status of the World’s Soil Resources | Main Report Global Soil Resources 39 39

82 < 0.06 - 0.12 Undefined 0.06 0.18 - 0.24 0.12 - 0.18 < 0.54 0.3 - 0.36 0.24 - 0.3 0.36 - 0.42 0.48 - 0.54 0.42 - 0.48 Figure 3.5 Soil erodibility as characterized by the k factor. Source: Nachtergaele and Petri, 2011. 3.6.6 | Soils and ecosystem goods and services Figure 3.7 illustrates the suitability of soils for supporting crops. The evaluation is based on soil health but excludes climatic considerations (except for low temperatures). In Table 3.1, the contribution of the main soil types to major ecosystem services (food security, climate regulation, water regulation and socio-cultural provisions) is estimated at a scale from zero to five. The ratings are based on soil characteristics and quality as measured by: suitability for growing crops; organic carbon content; water holding capacity; and capacity to support infrastructure and store archaeological remains. Severe constraints Moderate constraints No or slight constraints Permafrost areas Water bodies Very severe constraints Mainly non-soils Figure 3.6 Soil workability derived from HWSD. Source: Fischer et al., 2008. Status of the World’s Soil Resources | Main Report Global Soil Resources 40 40

83 Figure 3.7 Soil suitability for cropping at low input, based on the global agro-ecological zones study. Source: Fischer et al., 2008. Status of the World’s Soil Resources | Main Report Global Soil Resources 41 41

84 Ecosystem Services Reference Climate Cultural SUM Major Service Food Water Soil Groups 5 5 3 Histosols Climate Change 2 15 5 5 5 4 19 Food Security Anthrosols 1 3 2 4 10 Infrastructure Technosols 0 2 3 10 Climate Change 5 Cryosols 1 1 2 1 5 Water runoff Leptosols 4 2 3 1 10 Food Security Vertisols 1 1 4 1 1 Solonetz Very few Solonchaks 1 1 1 4 Very few 1 1 1 1 Podzols 6 Biomass 3 Ferralsols 4 3 1 10 Biomass 2 Nitisols 4 3 4 1 12 Food Security Plinthosols 1 2 1 6 Biomass 2 Planosols 1 1 1 1 4 Very few Gleysols 2 1 3 1 7 Food Security Water storage Stagnosols 2 1 3 1 7 1 13 Food Security Andosols 4 3 5 Chernozems 5 4 1 14 Food Security 4 3 2 1 10 Food Security Kastanozems 4 4 4 3 Phaeozems 12 Food Security 1 Umbrisols 3 3 3 1 10 Water runoff Durisols 1 1 1 1 4 Very few Calcisols 1 2 1 5 Very few 1 Gypsisols 1 1 1 1 4 Very few Retisols 2 1 2 1 6 Biomass 1 Acrisols 2 2 Food Security 1 6 Lixisols 2 1 6 Food Security 1 2 1 1 2 1 5 Biomass Alisols 3 2 2 1 8 Food Security Luvisols 3 3 2 Food Security 1 9 Cambisols Regosols 1 1 1 5 Biomass 2 Arenosols 1 1 1 1 4 Biomass Fluvisols 4 2 4 2 12 Food security Very few Wassents 0 2 2 1 5 Prepared by R. Hiederer, JRC 7 Table 3.1: Generalized ecosystem service rating of specific soil groups (WRB) Annex, except for Taxonomy 7 Soil Taxonomy equivalents given in the Wassents that are a suborder in Soil Status of the World’s Soil Resources | Main Report Global Soil Resources 42 42

85 3.7 | Global assessments of soil change - a history Global assessments of soil and land degradation started more than 40 years ago, but have until now not achieved a clear answer on where soil degradation takes place, what impact it has on the population, and what the cost to governments and land users would be if the decline in soil, water and vegetation resources continued unabated. Although institutional, socio-economic and biophysical causes of soil degradation have been identified locally in many case studies, these have seldom been inventoried systematically at national or regional level. Much of the investment in land reclamation and rehabilitation during recent years has been driven by donor interest to fund action, rather than research to understand the scope of the problem. Even knowledge about what works and what does not work in combating soil degradation is scanty, and there has been little systematic investigation. In recent years, however, the World Overview of Conservation Approaches and Technologies (WOCAT) consortium has begun to make a substantial contribution through its systematic collection of information on sustainable soil and water conservation practices and their impacts. The first comprehensive assessment of global soil degradation was based on expert opinion only. This was the - GLASOD, published by UNEP/ISRIC (Oldeman, GLobal Assessment of human-induced SOil Degradation Hakkeling and Sombroek, 1991). The Land Degradation Assessment in Drylands project (LADA) was launched by GEF, implemented by UNEP and executed by FAO between 2006 and 2011 in support of the UNCCD. LADA developed an approach based on remotely-sensed NDVI data (the Global Land Degradation Assessment – GLADA). The project also used an ecosystems approach that brought together and interpreted information from pre- existing and newly developed global databases to inform decision makers on all aspects of land degradation Global LAnd Degradation Information System ). at a global scale (GLADIS: the During this period other important and broader environmental assessments took place, notably the Millennium Ecosystem Assessment (MA, 2005) and the periodical review of the by UNEP State of the Environment State of Land and Water (SOLAW) in 2011. The Economics of with the GEO- reports (UNEP, 2012). FAO published a Land Degradation (ELD) initiative (ELD, 2015) provided in 2015 a first estimate of the cost of land degradation at global scale based on rather scattered and uncertain information. The annual economic losses due to deforestation and land degradation were estimated at EUR 1.5–3.4 trillion in 2008, equaling 3.3–7.5 percent of the global GDP in 2008. All of these studies used the results of one of the three global inventories: GLASOD, GLADA or GLADIS which are discussed in more detail below. 3 .7.1 | GLASOD: expert opinion An expert consultation on soil degradation convened by FAO and UNEP in Rome in 1974 recommended that a global assessment be made of actual and potential soil degradation. This assessment, which was conducted in collaboration with UNESCO, WMO and ISSS, was based on the compilation of existing data and the interpretation of environmental factors influencing the extent and intensity of soil degradation. The assessment considered such environmental factors as climate, vegetation, soil characteristics, soil management, topography and type of land utilization. The results of this assessment were compiled as a world map of soil degradation. During the next four years FAO, UNESCO and UNEP developed a provisional methodology for soil degradation assessment and prepared a first approximation study identifying areas of potential degradation hazard for soil erosion by wind and water, salinization and sodification. Maps at a scale of 1:5 M covering Africa north of the equator and the Middle East were prepared (FAO/UNEP/ UNESCO, 1979). These first efforts were then scaled up into the Global Assessment of Human Induced Soil Degradation Project or GLASOD. The project was initiated by UNEP. It had a duration of 28 months and was executed by ISRIC. In order to cover the whole world, 21 regions and individual countries were defined and experts on these regions were asked to prepare detailed maps of soil degradation. More than 250 soil scientists and environmentalists cooperated in this project (Oldeman, Hakkeling and Sombroek, 1991). 8 The global results of the GLASOD project are available online. 8 http://www.isric.org/UK/About+ISRIC/Projects/Track+Record/GLASOD.htm Status of the World’s Soil Resources | Main Report Global Soil Resources 43 43

86 A regional follow-up in Southeast Asia resulted in a more detailed database for that region: ASSOD (Van Lynden and Oldeman, 1997). Since its publication, some expert opinion has faulted GLASOD, questioning the objectivity and reproducibility of an assessment based on expert opinion as an assessment approach (Sonneveld and Dent, 2007). However, at the time GLASOD was developed there were few alternatives available, especially given the overall lack of remotely sensed data at the time. Even today the criticism seems unwarranted as remotely sensed techniques and most modelling approaches have so far failed to come up with more useful assessments. GLASOD results are presented in Figure 3.8. Figure 3.8 GLASOD results. Source: Oldeman, Hakkeling and Sombroek, 1991. Status of the World’s Soil Resources | Main Report Global Soil Resources 44 44

87 3.7.2 | LADA-GLADIS: the ecosystem approach Global Land The first approaches of LADA (see 3.7 above) used remotely-sensed NDVI data to prepare the , 2008). However, this was soon superseded by a complementary – GLADA (Bai Degradation Assessment et al. approach that focused on the actual status and trends of land resources in terms of six factors: biomass, 9 , above-ground biodiversity, and economic and social provisions that contribute water resources, soil health to ecosystem goods and services (Figure 3.9). The evaluation was based on interpretation of global databases available in the public domain, using documented algorithms to achieve a rating for each of the six factors in terms of status and trends. In order to map the various aspects, a special ‘global land use system’ was developed (Nachtergaele and Petri, 2011) which allowed cause and effect to be linked. Results were presented in radar diagrams (Figure 3.10) that showed the variability of ecosystem services provided as a function of land use and the need for trade-offs between different factors related to ecosystem goods and services. The GLADIS system is accessible on-line at: http://www.fao.org/nr/lada/index.php?option=com_content&view=article&id=161&Itemid=113&lang=en An example of an output for global soil compaction is shown in Figure 3.10. Criticism of the GLADIS system focused on the unreliability of some of the global databases used and on questions about the downscaling relationships that were developed at local scale (such as the RUSLE). For the specific factor - soil health - the absence of an assessment of wind erosion is certainly a limitation, while the fact that no difference is made between ‘natural’ and ‘human induced’ soil erosion is also confusing. These weaknesses have been recognized and should be corrected where possible during the further development of the GLADIS information system which is pending. Urban Forest Biomass (Acc) Biomass (Acc) Soc./Cult. Benet Soc./Cult. Benet Biomass (Ann) Biomass (Ann) Soil health Economic benet Soil health Economic benet Water Q/Q Water Q/Q Biodiv. Biodiv. Agriculture Biomass (Acc) Biomass (Ann) Soc./Cult. Benet Economic benet Soil health Water Q/Q Biodiv. Figure 3.9: Example of the eect of land use on indicative factors for ecosystem goods and services Figure 3.9 Example of the effect of land use on indicative factors for ecosystem goods and services 9 The soil health status was obtained by comparing the soil suitability for the actual land use. The soil health trend was based on a combination of ratings for the the soil compaction risk, a nutrient balance, and the soil contamination and soil salinization risks. risk of erosion by water, Status of the World’s Soil Resources | Main Report Global Soil Resources 45 45

88 Inland water Ocean / Seas (0) Figure 3.10 Soil compaction risk derived from intensity of tractor use in crop land and from livestock density in grasslands. Source: Nachtergaele et al., 2011 3 .7. 3 | Status of the World’s Soil Resources The present book – The Status of the World’s Soil Resources - takes a different approach from the ones described above by focusing on well documented and peer reviewed research data on soil degradation processes, status and trends in scientific literature at all levels. It also draws attention to the uncertainty of estimates made. The quantity and quality of information on soil degradation is shown to be very variable in different regions. Some regional statements - Africa, Eurasia, Near East, Latin America - still rely on GLASOD or ASSOD. For other regions, such as North America, no regional harmonized approach has been undertaken. Only the EU and the South West Pacific have made progress in establishing new regional updated approaches. The report also shows the great differences that exist in data and data availability on soil resources and soil change information at national level. Systematic sampling/surveying and monitoring does take place for selected major land uses (forests, arable lands) in most EU countries, the United States and Canada, China, Australia and New Zealand. However, results are not always made available in the public domain. The progress in digital soil mapping may help more countries to produce harmonized data and to make the information public. The data presented in this book constitute a baseline inventorying the documented knowledge at a point in time: 2015. Future progress can thus be measured against this baseline. Status of the World’s Soil Resources | Main Report Global Soil Resources 46 46

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92 4 | Soils and Humans 4.1 | Current land cover and land use The new Global Land Cover Share database (Latham et al. , 2014) includes eleven global land cover layers, each representing the major land cover classes defined by the FAO and SEEA legend (Weber, 2010). Analysis of the database indicates that of the global land mass, artificial surfaces occupy 0.6 percent, croplands 12.6 percent, grasslands 13.0 percent, tree-covered areas 27.7 percent, shrub-covered areas 9.5 percent, herbaceous vegetation 1.3 percent, mangroves 0.1 percent, sparse vegetation 7.7 percent, bare soils 15.2 percent, snow and glaciers 9.7 percent and inland water bodies 2.6 percent. The intensity of each land-cover type varies substantially across the globe according to numerous factors, including soils, altitude, climatic conditions and anthropogenic influences. For example, while cultivated land is less than 10 percent in most African regions, it accounts for more than 25 percent of the land in the Asia region. A land cover map is given in Figure 4.1. Summary statistics by region, derived from the respective GIS layers are given in Figure 4.2. In the following discussion, attention is focused on three main land cover classes: cropland, grasslands/grazing lands and forests. The management of these three classes has large impacts on soils and ecosystem services. The presence of artificial surfaces is treated in more detail in Section 6.7. More than 25 percent of the land mass carries almost no vegetation because of climatic factors (glaciers, deserts) or topographic or soil conditions. Status of the World’s Soil Resources | Main Report Soils and Humans 50 50

93 50-75% forest 50-75% grass/shrub >75% forest >75% grass/shrub > 50% non vegetated 50-75% crops >75% crops Water >50% artificial Mixed , 2014. Figure 4.1 Global Land Cover. Source: Latham et al. 2014. Latham et al., Figure 4.2 Distribution of land cover in different regions. Source: Status of the World’s Soil Resources | Main Report Soils and Humans 51 51

94 Cropland SOLAW (FAO, 2011) established that the cultivated land area in terms of per capita use in 2000 was highest in Australia (more than 2.2 ha per person), followed by North America and Eastern Europe and Russia (about 0.7 ha per person). In contrast, current cultivated land used per capita is only 0.2 ha in Western Europe and in most less developed countries. By dividing the current cultivated land by the projected populations, the anticipated cultivated land area per capita in 2050 can be estimated. In the more developed countries, the cultivated area per capita would change little. In less developed countries, the cultivated area per capita is expected to halve to 0.1 ha by 2050, unless there is further expansion of the cultivated area. Further characterization of cropland and land use at a global scale by remote sensing is difficult because: 1. The spatial extent of croplands is highly variable between and within nations. Cropland characteristics such as field size can be highly variable, even for the same crop type. Spatial extent of cropland depends on a host of factors, including the historical, political, social and technological context of agricultural development as well as natural factors such as landscape patterns. 2. Patterns of agricultural intensification – for example, the use of fertilizer – vary greatly, especially between developed and developing nations. 3. Each crop type has a specific growth phenology and structure, with significant seasonal variation between and even within individual crop types. Cropland can be confused with natural vegetation cover types – for example, surveys may confuse 4. et al. , 2010). Better cropland information – in terms of cereal grains with tall-grass prairie (Pittman both its extent and the purpose and intensity of its use – is vital to understanding soil change and to formulating adequate responses. Special attention should be paid to irrigated agriculture in developing countries, which covers about one-fifth of all arable land, and accounts for 47 percent of all crop production and almost 60 percent of cereal production (Nachtergaele et al. , 2011). Grazing lands Grazing lands, including sown pasture and rangeland with various coverage (grasslands, bush/shrublands), are among the largest ecosystems in the world and contribute to the livelihoods of more than 800 million people. They are a source of goods and services such as food and forage, energy and wildlife habitat, and also provide carbon and water storage and watershed protection for many major river systems. Grasslands are also important for in situ conservation of genetic resources. Of a total of 10 000 species, only 100 to 150 forage species have been cultivated, but many more hold potential for sustainable agriculture. Estimates of the proportion of the Earth's land area covered by grasslands vary between 20 and 40 percent, depending on the definition. Those differences are due to a lack of harmonization in the definition of grasslands. There has been a significant reduction of pasture in Eastern Africa, partially because large grassland areas have been destroyed or converted to agricultural land. In South America, pastures have been lost because of conversion to soybean cultivation. In Europe there has been a gain in grazing lands because European policies such as the ‘set-aside’ measures oblige farmers to leave a portion of their agricultural land in fallow as a condition for benefiting from direct payments (Suttie, Reynolds and Batello, 2005). Forests In 2010, forests covered about 28 percent of the world’s total land area. Deforestation affected an estimated 13 million ha per year between 2000 and 2010. Net forest loss was, however, considerably less – 5.2 million ha per year – as losses were compensated by afforestation and some natural expansion (FAO, 2014a). Most deforestation takes place in tropical countries, whereas most developed countries with temperate and boreal forest ecosystems – and more recently, countries in the Near East and Asia – are experiencing stable Status of the World’s Soil Resources | Main Report Soils and Humans 52 52

95 or increasing forest areas. Between 1990 and 2010, the amount of forest land designated primarily for the conservation of biological diversity increased by 35 percent, indicating a political commitment to conserve forests. These forests now account for 12 percent of the world’s forests. Approximately 13.2 million people worldwide are formally employed in the forestry sector. Many more depend directly on forests and forest products for their living. In developing countries, wood-based fuels are the dominant source of energy for more than two billion mostly poor people. In Africa, over 90 percent of harvested wood is used for energy. Wood accounts for 27 percent of total primary energy supply in Africa, 13 percent in Latin America and the Caribbean and five percent in Asia and Oceania. However, it is also increasingly used in developed countries with the aim of reducing dependence on fossil fuels. For example, about 90 million people in Europe and North America now use wood energy as the main source of domestic heating (FAO, 2014a). Conclusion Land cover and land use are essential factors to understand soil change. In particular, better cropland information, in terms of extent, purpose and intensity of use, is vital to understanding soil change and to formulating adequate responses. 4.2 | Historical land cover and land use change Since the early days of agriculture, human activity has altered vegetation cover and soil properties. ‘Land use change’ or ‘land cover change’ typically refers to changing from one type of vegetation cover to another (e.g forest to pasture, natural grassland to cropland). Although the terms land use change and land cover change are often used interchangeably, ‘land use’ is more typically used to refer to management within a land cover type. Land use is thus “characterised by the arrangements, activities and inputs people undertake in a certain land cover type to produce, change or maintain it" (FAO/UNEP, 1999). Land use change has been accelerated by migration and population increase as food, shelter, and materials are sought and acquired. It 2 , or >50 percent of Earth’s ice-free land is estimated that humans have directly modified at least 70 million km area (Hooke, Martín-Duque and Pedraza, 2012). For a long period of human activity, until about a thousand years ago, cropland and pasture occupied less than one to two percent each of the global ice-free land area (based on a range of data sources in Klein Goldewijk et al. , 2011 and depicted in Figure 4.3; also see Ramankutty, Foley and Olejniczak, 2002). Subsequently, as the population centres of Europe, South Central Asia and Eastern Asia expanded, more land was converted from natural vegegation to cultivated lands. Cover of croplands and pastures was about two to four percent each by 1700 (Klein Goldewijk et al. , 2011). By 1900, agriculture had further expanded in these areas, and spread to North America. Since 1900 rapid expansion has continued, including the arable areas of South America, Africa and Australia. As a result, today nearly all soils and climates suitable for cultivation in industralized countries are in use for crop production. In some of these countries, cropland expansion has been reversed in recent years, as with the EU set-aside programme. South America and Africa continue to convert land use to crop production. By 2000, global cropland cover had reached 11 percent and pasture cover 24 percent, according to Klein Goldewijk (2011) based on FAO statistics. et al. Status of the World’s Soil Resources | Main Report Soils and Humans 53 53

96 Prepared by P. Reich Figure 4.3 Historical land use change 1000 – 2005. Source: Klein Goldewijk et al., 2011. 2 ), tropical The net loss of natural land has been dominated by loss of tropical forests (3.3 million km 2 2 ) and temperate grasslands (5.5 million km ). Quantification from satellite imagery grasslands (6.8 million km of global forest change over the period 2000-2012 shows that tropical deforestation remains the predominant et al. , 2013). However, there has been a reduced rate of deforestation in some regions source of losses (Hansen over the last decade, most notably in Brazil. This is coupled with a rising rate of afforestation in some areas in recent decades, notably in Europe and the United States, and more recently in China, Vietnam and India (FAO, 2013). 4.3 | Interactions between soils, land use and management Many soils are subject to some degree of direct or indirect human disturbance. However, distinguishing natural from direct and indirect human influence is not always straightforward (Smith, 2005). Nonetheless, some human activities have clear direct impacts. These include land use change, land management, land degradation, soil sealing, and mining. The intensity of land use also has a great impact on soils. Soils are also subject to indirect impacts arising from human activity, such as acid deposition (for example, sulphur and nitrogen) and heavy metal pollution. In this section, we report the state-of-the-art understanding and the knowledge gaps concerning these impacts on soils. 4.3.1 | Land use change and soil degradation Land cover change (Section 4.2), for example from forest or natural grassland to pasture or cropland, removes biomass and disturbs soils. This in turn leads to loss of soil carbon and other nutrients and to changes in soil properties and in soil biodiversity. Some land cover conversions – for example, afforestation after abandonment of cropland – can result in increases of soil carbon and nutrients. Land use that does not result in a change of cover, such as forest harvest and regrowth, or increasing grazing intensity, can nonetheless result in degradation of soil properties. Status of the World’s Soil Resources | Main Report Soils and Humans 54 54

97 2 Degrading land covers approximately 24 percent of the global land area (35 million km ). 23 percent of et al. , degrading land is broadleaved forest, 19 percent needle-leaved forests, 20–25 percent rangeland (Bai 2008). The scale and nature of the changes are highly variable with type of land cover change, climate, and method of vegetation removal (e.g. land clearing fires, mechanical harvest). This section focuses on meta- analyses of field data and global model results. The effects of land use changes within agricultural lands are dealt with in Section 4.3.2. Impacts of land cover change i et al. (2014) collated observations from 119 publications of 453 paired or chrono-sequential sites in 36 We countries where tropical, temperate, and boreal forests were converted to agricultural land. The SOC stocks were corrected for changes in soil bulk density after land-use change and only SOC in the upper 0–30 cm was considered. The SOC stocks decreased at 98 percent of the sites by an average of 52 percent in temperate regions 41 percent in tropical regions and 31 percent in boreal regions. The decrease in SOC stocks and the turnover rate constants both varied significantly according to forest type, cultivation stage, climate and soil factors. A meta-analysis (Guo and Gifford, 2002) of 74 publications across tropical and temperate zones showed a decline in soil C stocks after conversion from pasture to plantation (−10 percent), native forest to plantation (−13 percent), native forest to crop (−42 percent), and pasture to crop (−59 percent). Soil C stocks increased after conversions from native forest to pasture (+8 percent), crop to pasture (+19 percent), crop to plantation (+18 percent), and crop to secondary forest (+53 percent). Broadleaf tree plantations placed onto prior native forest or pastures did not affect soil C stocks whereas pine plantations reduced soil C stocks by – 12 to – 15 percent. In this study, soil depth varied from less than 30 cm to more than 100 cm and was not adjusted to account for changes in bulk density with land use change. In a meta-analysis of 385 studies on land use changes in the tropics (Don, Schumacher and Freibauer, 2011), SOC decreased when primary forest was converted to cropland (-25 percent), perennial crops (-30 percent) -1 2 percent). SOC increased when cropland was afforested (+29 percent) or under cropland and grassland ( fallow (+32 percent) or converted to grassland (+26 percent). Secondary forests stored 9 percent less SOC than primary forests. Relative changes were equally high in the subsoil as in the surface soil (Don, Schumacher and Freibauer, 2011). In this study, SOC stocks were corrected to an equivalent soil mass and sampling depth was on average 32 cm. The response of soil organic carbon (SOC) to afforestation in deep soil layers is still poorly understood. Shi et al. (2013) compiled information on changes in deep SOC (defined as at least 10 cm deeper than the 0–10 cm layer) after afforestation of croplands and grasslands (total 63 sites from 56 literature). The responses of SOC to afforestation were slightly negative for grassland, and significantly positive for cropland. The SOC in soil depth layers (up to 80 cm) was reduced after afforestation of grassland but not significantly. By contrast, conversion of cropland to forests (trees or shrubs) increased SOC significantly for each soil layer up to 60 cm depth. et al. (2011) compiled 95 studies conducted on conversion in temperate climates. One finding Poeplau was that topsoil (0-30 cm) SOC decreases quickly (~20 years) when cropland is established on grassland (-32 percent) or forest (-36 percent). By contrast, long lasting (> 120 years) sinks are created through conversion of cropland to forest (+16 percent) or grassland (+28 percent). Afforestation of grassland did not result in significant long term SOC stock trends in mineral soils, but did cause a net carbon accumulation in the labile -1 over 100 years). However, this carbon accumulation cannot be considered as an forest floor (e.g. 38 Mg ha intermediate or long-term C storage since it may be lost easily after disruptions such as fire, windthrow or clear cut (Poeplau et al. , 2011). Peatlands (organic soils) store a large amount of carbon which is rapidly lost when these peatlands are , 2010). A rapid increase in decomposition drained for agriculture and commercial forestry (Hooijer et al. , and N O, and vulnerability to further impacts through fire. rates leads to increased emissions of CO 2 2 Status of the World’s Soil Resources | Main Report Soils and Humans 55 55

98 2 The FAO emissions database estimates globally there are 250 000 km of drained organic soils under cropland -1 in 2010. The largest contributions are from Asia and grassland, with total GHG emissions of 0.9 Gt CO2eq yr -1 -1 ) and Europe (0.18 Gt CO2eq yr ; FAO, 2013). Joosten (2010) estimated that there are (0.44 Gt CO2eq yr 2 of drained peatlands in the world including under forests, with CO emissions having increased >500 000 km 2 -1 -1 yr yr in 2008. This is despite a decreasing trend in Annex I countries, in 1990 to 1.30 Gt CO from 1.06 Gt CO 2 2 -1 yr , primarily due to natural and artificial rewetting of peatlands. In Southeast Asia, from 0.65 to 0.49 Gt CO 2 -1 yr (Hooijer et al. , 2010). emissions from drained peatlands in 2006 were 0.61 ± 0.25 Gt CO CO 2 2 Soil drainage also affects mineral soils. Meersmans et al. (2009) showed that initially poorly drained -2 for the valley soils in Belgium have lost significant amount of topsoil SOC (e.g. between – 2 and – 4 kg C m 1960-2006 period). The cause is most probably intensified soil drainage in these environment for cultivation purposes. A serious consequence of deforestation is extensive loss of carbon from the soil, a process regulated by (2014) assessed the effects of deforestation on soil microbial communities et al. microbial diversity. Crowther across multiple biomes, drawing on data from eleven regions ranging from Hawaii to Northern Alaska. The magnitude of the vegetation effect varied between sites. Deforestation dramatically altered the microbial communities in sandy soils, while the effects were minimal in clay-rich soils, even after extensive tree removal. Fine soil particles have a larger surface area to bind nutrients and water. This capacity might buffer soil microbes in clay-rich soils against the disturbance of deforestation. Sandy soils, by contrast, have larger particles with less surface area and so retain fewer nutrients and less organic matter. Microbial community changes were associated with distinct changes in the microbial catabolic profile. Dynamic Global Vegetation Models (DGVMs) can be used to look at the combined effects of land use , and in some cases N deposition, on vegetation and soil properties over time. In Table change, climate, CO 2 et 4.1, Figure 4.4 and Figure 4.5 we show results from three vegetation models: ISAM ( Jain et al. , 2013; El-Masri et al. , 2015) and al. , 2013; Barman et al. , 2014 a, b), LPJ-GUESS (Smith et al. , 2001; Pugh , et al. LPJmL (Bondeau et al. , 2013). The ISAM model includes a nitrogen cycle, N deposition and changes in soil N. 2007; Schaphoff The ISAM and LPJ-GUESS models were run with the HYDE historical land use change data set ( History Database , 2011). The LPJmL group combined three land use change data of the Global Environment , Klein Goldewijk et al. sets (Klein Goldewijk and Drecht, 2006; Ramankutty , 2008; Portmann, Siebert and Döll, 2010) with the et al. global geographic distribution of agricultural lands in the year 2000 (Fader et al. , 2010). The models were also (and N deposition in the case of ISAM). Figure 4.4 shows the mineral soil C run with historical climate and CO 2 and N concentration of different land cover types in different geographic ranges while Table 4.1 and Figure 4.5 show the loss of carbon due to historical land use change from 1860 to 2010. Differences between the models are large for some systems and regions due to different landuse change data, different land cover definitions, different processes included in the models, etc. For example, soil carbon losses are higher in the LPJmL model in part due to greater land cover change in their land cover reconstructions. The highest carbon losses are associated with the conversion of forests to croplands (Figures 4.4 and 4.5). While Table 4.1 shows the global mean soil carbon loss, the effects are not the same everywhere (Figure 4.5). This may be the case, for example, when forests are converted to pastures in regions where pastures strongly favour soil C accumulation. Status of the World’s Soil Resources | Main Report Soils and Humans 56 56

99 70 (A) soil carbon 60 50 40 ISAM 30 LPJml 20 LPJ_GUESS 10 Soil Carbon (kg/m2) 0 crop crop crop forest forest forest pasture pasture pasture grassland grassland grassland shrubland shrubland shrubland All "natural" All "natural" All "natural" Boreal Tropics Temperate 70 (A) soil carbon 60 50 40 ISAM 30 LPJml 20 LPJ_GUESS 10 Soil Carbon (kg/m2) 0 crop crop crop forest forest forest pasture pasture pasture grassland grassland grassland shrubland shrubland shrubland All "natural" All "natural" All "natural" Boreal Tropics Temperate Figure 4.4 Soil carbon and nitrogen under different land cover types. Source: Smith et al. (in press). Panel (a) shows mean soil carbon stocks; Panel (b) shows mean soil nitrogen stocks. Based on three vegetation models ISAM ( Jain et al. , 2013; El-Masri et al. , 2013; Barman, Jain and Liang, 2014 a, b), LPJ-GUESS (Smith , 2013). The soil carbon et al. , 2007; Schaphoff et al. , 2001; Pugh et al. , 2014); and LPJmL (Bondeau et al. and soil nitrogen are the average over the period 2001 to 2010 (2003 for LPJmL) in model simulations with for the ISAM model). All ‘natural’ land is the mean of all (and N historical land-use change, climate, and CO 2 2 lands without pasture or crop land cover. It includes ‘un-managed’ forest, grassland and shrubland categories and may include other land cover types depending on the models e.g. bare soil. Status of the World’s Soil Resources | Main Report Soils and Humans 57 57

100 Figure 4.5 Maps of change in soil carbon due to land use change and land management from 1860 to 2010 from three vegetation models. Pink indicates loss of soil carbon, blue indicates carbon gain. The models were run with historical land use change. This was compared to a model run with only natural vegetation cover to diagnose the difference in soil carbon due to land cover change. Both model runs included change. Source: Smith historical climate and CO 2 et al. (in press). Panel (a) of Figure 4.5 shows cropland and pasture coverage in 2003. The model was run with historical land use change. This was compared to a model run with only natural vegetation cover to diagnose the difference in soil carbon due to land cover change up to year 2003 as shown in Panel (b). Both model runs included change. Pink indicates loss of carbon due to land use, blue indicates areas of carbon historical climate and CO 2 gain. Tropical Temperate Boreal Global Model LPJ-GUESS 12.63 15.01 0.37 29.85 LPJmL 34.86 25.99 0.05 61.86 ISAM 1 7. 24 5.28 60.35 37.83 Mean 26.27666667 1.9 50.68666667 21.57666667 Table 4.1 Soil carbon lost globally due to land use change over the period 1860 to 2010 (PgC) Data are from three vegetation models ISAM ( Jain et al. , 2013; El-Masri et al. , 2013; Barman, Jain and Liang, , 2007; Schaphoff 2014 a, b); LPJ-GUESS (Smith et al. , 2001; Pugh et al. , 2015); and LPJmL (Bondeau et al. et al. , 2013). Each model is run with and without historical land use change data and the difference between the ‘with land use change’ and ‘no land use change’ runs gives the loss due to land use change. The runs also included and cover the period from 1900 to 2010. historical climate and CO 2 Impacts of land management and degradation Logging and fire are the major causes of forest degradation in the tropics (Bryan et al. , 2013). Logging removes nutrients. Logging operations also cause soil disturbance affecting soil physical properties and nutrient levels (soil and litter) in tropical (e.g. Olander et al. , 2005; Villela et al. , 2006; Alexander, 2012) and temperate forests (Perez , 2009). Many physical, chemical, mineralogical, and biological soil properties can be affected by et al. forest fires depending on fire regime (Certini, 2005). Increased frequency of fires contributes to degradation and reduces the resilience of the biomes to natural disturbances Status of the World’s Soil Resources | Main Report Soils and Humans 58 58

101 A meta-analysis of 57 publications (Nave et al. , 2011) showed that fire had significant overall effects on soil C (-26 percent) and soil N (-22 percent). Fires reduced forest floor storage (pool sizes only) by an average of 59 percent (C) and 50 percent (N), but the concentrations of these two elements did not change. Prescribed fires caused smaller reductions in C and N storage (-46 percent and – 35 percent) than wildfires (-67 percent and – 69 percent). Burned forest floors recovered their C and N pools in an average of 128 and 103 years, respectively. Among mineral soil layers, there were no significant changes in C or N storage, but C and N concentrations -1 1 percent and – 12 percent, respectively). Mineral soil C and N concentrations were declined significantly ( significantly reduced in response to wildfires but not after prescribed burning. A large field study in the Amazon (225 forest plots) examined the effects of anthropogenic forest disturbance (selective logging, fire, and fragmentation) on soil carbon pools. Results showed that the first 30 cm of the soil pool did not differ between disturbed primary forests and undisturbed areas of forest, suggesting a resistance et al. , 2014). However, impacts of human to impacts from selective logging and understory fires (Berenguer disturbances on the soil carbon are of particular concern in tropical forests growing on organic soils. Forest fires produce pyrogenic carbonaceous matter (PCM), which can contain significant amounts of fused aromatic pyrogenic C (often also called black C), some of which can be preserved in soils over centuries and even millennia. This was found to be the reason for similar soil organic C contents modelled for scenarios with and without burning in Australia: the loss in litter C input by fire was compensated by the greater persistence of the pyrogenic C (Lehmann et al. , 2008). Dissolved pyrogenic carbon (DPyC) from burning of the Brazilian Atlantic forest continued to be mobilized from the watershed each year in the rainy season, despite the fact et al. that widespread forest burning ceased in 1973 (Dittmar , 2012). Fire events are a source of carbonaceous aerosol emissions, and these are considered a major source of global warming (Kaufman, Tanre and Boucher, 2002) Shifting cultivation practices of clearing land through fire have been used for thousands of years but in recent years increasing demographic pressure has often reduced the duration of the fallow period and so affected system sustainability. A review by Ribeiro Filho, Adams and Sereni Murrieta (2013) reported negative impact on SOC associated with the conversion stage, although impacts depended on the characteristics of the burning. Chop-and-mulch of enriched fallows appears to be a promising alternative to slash-and-burn. A study in the Amazon (Comtea et al. , 2012) found that this technique conserves soil bulk density and significantly increases nutrient concentrations and organic matter content compared to burnt cropland and to a control forest. Climate change and land use dynamics are the major drivers of dryland degradation with important feedbacks through changes in plant community composition – for example shrub encroachment or decrease in vegetation cover (D’Odorico et al. , 2013). A review conducted by Ravi et al. (2010) indicated soil erosion as the most widespread form of land degradation in drylands, with wind and water erosion of dryland soils accounting for 87 percent of the land degradation. Grazing pressure, loss of vegetation cover, and the lack of adequate soil conservation practices increase the susceptibility of these soils to erosion. An analysis of 224 dryland sites highlighted a negative effect of aridity on the concentration of soil organic C and total N, et al. , 2013). Because aridity is but a positive effect on the concentration of inorganic P (Delgado-Baquerizo negatively related to plant cover, the authors argue that these effects might be related to the dominance in arid areas of physical processes such as rock weathering, a major source of P to ecosystems, over biological processes that provide more C and N, such as litter decomposition. Grasslands, including rangelands, shrublands, pastureland, and cropland sown with pasture and fodder crops, covered approximately 3.5 billion ha in 2000. This represented 26 percent of the global ice-free land area and 70 percent of the agricultural area, and contained about 20 percent of the world’s soil organic carbon (C) stocks. Portions of the grasslands on every continent have been degraded due to human activities – about Status of the World’s Soil Resources | Main Report Soils and Humans 59 59

102 7.5 percent of grassland worldwide has been degraded because of overgrazing (Conant, 2012). Grassland management and grazing intensity can affect the stock of SOC. A multifactorial meta-analysis of grazer effects on SOC density (17 studies that include grazed and ungrazed plots) found a significant interaction between grazing intensity and grass type. Specifically, higher grazing intensity was associated with increased grasses (increase of SOC by 6–7 percent), but with lower SOC in grasslands SOC in grasslands dominated by C 4 grasses (decrease of SOC by an average 18 percent). Impacts of grazing were also influenced dominated by C 3 by precipitation. An increase in mean annual precipitation of 600 mm resulted in a 24 percent decrease in grazer effect size on finer textured soils, while on sandy soils the same increase in precipitation produced a 22 percent increase in grazer effect on SOC (McSherry and Ritchie, 2013). 4.3.2 | Land use intensity change Land use intensity has increased in recent decades, largely driven by the need to feed a growing population, by shifts in dietary patterns towards more meat consumption, and by the growing production of biofuels. At the same time, fast urbanization has occupied more of the land, reducing the stock available for agricultural production. Intensification has been widely advocated because of the many negative environmental consequences of clearing natural ecosystems to expand agricultural areas. However, intensifying management practices, such as fertilization, irrigation, tillage and increased livestock density, can have negative environmental impacts (Tilman et al. , 2002). Intensifying land use can potentially reduce soil fertility. Intensification can also reduce soil resilience to extreme weather under climate change, to pests and biological invasion, to environmental pollutants and to other disasters. This section provides an overview of the benefits and consequences of intensifying use of agricultural lands. The section also highlights examples of how negative consequences can be minimized. Several factors influence the increase in land use intensity during the recent decades. On the demand side, three main factors are at play: (i) the need to meet the food, fibre, and fuel demands of a growing population; (ii) an increase in meat consumption as developing nations become wealthier and tastes change; and (iii) rising demand for crops for biofuels. On the supply side, settlements are occupying more land and so reducing the land available for agriculture. -1 00 percent To meet the increased demand, it is estimated that food production will need to increase by 70 et al. , 2014). Of the two pathways of by 2050 (World Bank, 2008; Royal Society of London, 2009; Keating increasing production—intensification and expansion—intensification is widely promoted as the more sustainable option because of the negative environmental consequences of land expansion through deforestation and conversion of wetlands to cultivation (Foley et al. , 2011; MA, 2005). However, the current increase in land use intensity is generally not sustainable. In order to give a clear picture of the effects of increased land use intensity, this section is organized according to the primary management practices that characterize intensification of agricultural lands (see Table 4.2 for summary). Nutrient management Nutrient inputs, from both natural and synthetic sources, are needed to sustain soil fertility and to supply the nutrient needs of higher yielding crop production. Intensification in recent years has led to the annual global flows of nitrogen and phosphorus now being more than double the natural levels (Matson et al. , 1997; Smil, 2000; Tilman, 2002). The trend is still increasing – in China, for example, N input in agriculture in the 2000s was more than double the levels of the 1980s (State Bureau of Statistics-China, 2005). Nutrient management is particularly intensive in greenhouse production systems. In some parts of Asia, for example, up to six tons of chemical nutrient and hundreds tons of organic fertilizers are applied per hectare each year et al. in order to achieve high yielding multiple cropping of vegetables (Liu , 2008). Between 50-60 percent of Status of the World’s Soil Resources | Main Report Soils and Humans 60 60

103 the nutrient inputs remain in the croplands after harvest (West , 2014). When these nutrients are later et al. mobilized, they become a major source of pollution to local, regional and coastal waters (Carpenter et al. , 1998). Intensive nutrient input in agriculture has been shown to be a major cause of eutrophication and algae blooming in lakes and inshore waters. In addition, over-use of nitrogen chemical fertilizers has been found in many locations globally to be a cause of acidification and accelerated decomposition of soil organic matter, leading to further soil degradation in over-fertilized soils ( Ju et al. , 2009; Tian et al. , 2012). Nutrient inputs also affect the earth’s climate. Globally, approximately one percent of nitrogen additions O), a gas which has 300 times the warming power of are released to the atmosphere as nitrous oxide (N 2 carbon dioxide (Klein Goldewijk and van Drecht, 2006). China, India, and the United States account for ~56 , 2014). et al. O emissions from croplands, with 28 percent originating from China alone (West percent of all N 2 One remedy is to increase the efficiency of nutrient use. Nutrient efficiency can be significantly increased – O emissions can be reduced – through changes in the rate, timing, placement, and type of application and N 2 et al. , 2011). In addition, if best of nutrients, and by improving the balance amongst nutrients applied (Venterea management practices are used, agricultural soils have the potential to be carbon storage areas (Paustian et al. , 2004; Smith, 2004). Technological improvements are being made to the production of biochar which converts a fraction of the C present in the original material into a more persistent form through carbonisation. Biochar can then be used as a soil amendment to provide agronomic and environmental benefits (Lehmann O emissions, especially and Joseph, 2015). In many cases, the presence of biochar has caused a reduction in N 2 when these originate from denitrification. However, the mechanics of the process are not yet fully understood (Cayuela et al. , 2013; 2014). The effect of pesticides on soil biodiversity The large-scale use of pesticides may have direct or indirect effects on soil biodiversity. With the intensification of agriculture, the use of pesticides has increased worldwide to approximately two million tonnes per year (herbicides 47.5 percent, insecticides 29.5 percent, fungicides 17.5 percent, other 5.5 percent et al. (2014)). Studies of the effect that pesticides have on soil biodiversity have shown contradictory by De results. Effects are dependent on a variety of factors including the chemical composition, the rate applied, the buffering capacity of the soil, the soil organisms in question, and the time-scale. For example, Boldt and Jacobsen (1998) tested the effects of sulfonylurea herbicides on strains of fluorescent pseudomonads cultured from agricultural field soils. They found that the herbicide Metsulfuron methyl was toxic to the majority of fluorescent pseaudomonads (77 strains) in low concentrations, while Chlorsulfuron was only toxic at high concentrations, and Thifensulfuron methyl was toxic only to a few strains, even at high concentrations. In a review by Bünemann, Schwenke and Van Zwieten (2006) of the effects of pesticide application on soil organisms, there were no data available for 325 of 380 active constituent pesticides registered for use in Australia. The review thus effectively highlighted the huge gap in knowledge. A synthesis of the impact of herbicides on non-target organisms concluded that herbicides did not have a major effect on soil organisms (Bünemann, Schwenke and Van Zwieten, 2006) with the exception of butachlor, which was toxic to earthworms when applied at typical agricultural rates (Panda and Sahu, 2004). In addition, the application of bromoxynil herbicides caused a shift in the communities of four out of five targeted bacterial taxa even after degradation of the herbicide (Baxter and Cummings, 2008). Avoidance behaviour to phendimedipham has also been observed for collembola (Heupel, 2002) and earthworms (Amorim, Rombke and Soares, 2005). Insecticide application, however, has a much greater effect on soil biota, including changes in microbial community composition (Pandey and Singh, 2004), lower collembolan abundance (Endlweber, Schadler and Scheu, 2005) and earthworm reproduction. Because some species of earthworm such as Eisenia Fetida can be easily bred and because they ingest large quantities of organic matter in the soil, earthworms have often been used as bioindicators of chemical toxicity in soils (Yasmin and D’Souza, 2010). A variety of studies have reported changes in earthworm reproductive rates, growth rates and weight loss when the pesticides Malathion Status of the World’s Soil Resources | Main Report Soils and Humans 61 61

104 (Espinoza-Navarro and Bustos-Obregon, 2005), Chlorpyrifos (Zhou , 2007; De Silva et al. , 2010), Benomyl et al. (Römbke, Garcia and Scheffczyk, 2007), Carbofuran (De Silva et al. , 2010) were applied to soil in laboratory experiments. Non-target effects of insecticide applications may be highly dependent on the organism since field application of Chlorpyrifos did not affect the abundance of soil predatory mites (Navarro-Campos et al. , 2012). Fungicides have also demonstrated significant negative effects on earthworms (Eijsackers et al. , 2005). In particular, copper-based fungicides that are resistant to degradation have caused long-term reductions in earthworm populations (Van Zwieten et al. , 2004). Although an assessment of soil food webs across Europe did not specifically focus on pesticide application, the study demonstrated that land-use intensification was related to decreased diversity of soil fauna and resulted in less diversity among functional groups. Larger soil animals showed the most sensitivity (Tsiafouli et al. , 2015). However, there have been no such comprehensive studies to quantify the effects of pesticides on soil organisms at multiple trophic levels across regions. Such studies need to consider also the indirect effect of pesticides, including interactions between pesticides and biotic factors. Since below-ground biodiversity is intimately linked to above-ground vegetation patterns (De Deyn and van der Putten, 2005) and vice versa (Bardgett and van der Putten, 2014), changes in plant diversity resulting from herbicide may cause indirect effects of herbicide application. Water management The area of irrigated croplands has doubled in the last 50 years and irrigation now accounts for 70 percent of all water diversions on the planet (Gleick, 2003). Irrigated areas account for 34 percent of crop production, yet only cover 24 percent of all cropland area (Siebert and Doll, 2010). With the increased frequency of drought under climate change, demand for agricultural water is rising in many locations. Not surprisingly, irrigation is most commonly used in more arid areas. Where a high proportion of available water is used for agriculture, this can cause water stress for both people and nature. Water efficiency can be improved through infrastructure and through better management practices. Irrigation can potentially increase soil salinity in dry regions (Ghassemi, Jakeman and Nix, 1995). Where salinization occurs, additional irrigation is needed to ‘flush’ the salts beyond the root zone of the crops. This additional water requirement can further exacerbate water stress. Harvest frequency Land use intensity can also be increased by harvesting a parcel of farmland more frequently (double cropping, triple cropping). Approximately 9 percent of crop production increases from 1961-2007 came from increases in the harvest frequency (Alexandratos and Bruinsma, 2012). As more land was double cropped, the global harvested area increased four times faster than total cropland between 2000 and 2011 (Ray and Foley, 2013). In addition, with global warming, the areas suited for double or even triple cropping are extending into subtropical and warm temperate regions (Liu et al. , 2013a). The factors involved in this fast rate of increase include: fewer crop failures; fewer fallow years; and an increase in multi-cropping. Greenhouse production has allowed multiple cropping around the world. For fruit and vegetable crops, world greenhouse cultivated area reached a total area of 408 890 ha in 2013, which includes as many as five harvests in a single year. This increasing harvest frequency has reduced soil quality through soil compaction and has increased the risk of pathogen diseases. The intensive use of pesticides and herbicides in greenhouses not only affects soil quality but creates risks to human health. In some greenhouse systems, long term multiple cropping has led to soil acidification, salinization and biological deterioration, especially where large amounts of fertilizer and pesticide/herbicide have been used. In these situations, there is a need to improve management practices, using organic matter, balancing nutrient additions and adopting intermittent fallow. Status of the World’s Soil Resources | Main Report Soils and Humans 62 62

105 Livestock density Livestock production is projected to increase to meet the growing demand for livestock products from a rising population and from an increase in per capita consumption. The greatest increases in per capita demand are projected to be in developing and transition countries (Bouwman et al. , 2006). Since the 1970s, most increases in livestock production have resulted from intensification, with a shift to a greater fraction of livestock raised in industrial conditions (Bouwmann et al. , 2006). For example, 76-79 percent of pork and poultry production is now industrialized (Herrero et al. , 2013). Industrial livestock production systems can be highly polluting. The manure from animals, the inputs for growing animal feed, and the soil loss from intensively managed areas can all be major sources of water pollution to local and downstream freshwater ecosystems. Where natural ecosystems are cleared and converted to pasture, particularly in arid and semi-arid regions, the lands are typically low potential and have , 1999; Seré and Steinfeld, 1996). et al. a high risk of soil erosion and soil carbon/nutrient depletion (Delgado The soils capacity for water storage and their biodiversity are also at risk. Moreover, intensified livestock production requires an increased use of veterinary medicines, sulfa-antibiotics and hormones, all of which carry risks of pollution to soil, water and the livestock products themselves, with risks to biological and human health. Forestry harvest and wetland draining Forests and wetlands and their soils are massive reservoirs of carbon. In fact, forest soils store approximately the same amount of carbon as the living biomass of the forest itself (FAO, 2010). Wetlands are important not only for the huge carbon pool they contain but also for their role in the hydrological cycle. However, wetlands along big river banks, lakes and estuaries have been increasingly developed for croplands/bioenergy production in recent decades, particularly in Asia. The majority of soil carbon is concentrated in peatlands within the boreal forest as well as tropical forests in Southeast Asia. Around the world, deforestation causes ~25 percent of the total loss of soil carbon (Guo and Gifford, 2002; Murty et al. , 2002). This loss largely stems from oxidation of the organic matter and from soil erosion. In China over the last four decades, almost 1.3 million ha of wetlands have been converted to crop production, causing the loss of about 1.5 Pg C of soil carbon , 2009). Deforestation continues through conversion to agriculture and through extraction of (Zhang et al. forest products. Between 2000 and 2012, there was a new loss of 1.5 million square kilometres of forests, with 2013). Soil erosion and organic matter oxidation can et al. the most pronounced trend in the tropics (Hansen be reduced through selective tree harvesting rather than clear felling, and by avoiding deforestation on steep slopes. Draining and cultivating wetlands can also affect local and regional water storage. Status of the World’s Soil Resources | Main Report Soils and Humans 63 63

106 Research needs It will be evident from the discussion in this section that much remains to be learned. Amongst the priority research questions are the following: Sustainable intensification – How can we get the benefits from intensification while minimizing the 1. associated environmental and social costs? Trade-offs between soils and efficiency – How can we manage for resilient soil and related ecosystem 2. services while continuing to maximize efficiency? To what extent can we have both? – What is the extent of degraded soils? There are currently no sound 3. Soil degradation and intensification estimates. What portion of degraded soils can be attributed to un-sustainable intensification? 4. Options and trade-offs for improved soil management – What can we learn from management practices used in intensification areas to help restore degraded soils? Are there any options that can integrate best management practice for sustainable intensification? What are the short – and long-term trade- offs of resource use and sustainability? What are the environmental and social costs and economic benefits of land use intensification? 5. Farming practices and soil health – How do changes in harvest frequency and crop rotation affect soil resilience? How much change is needed to restore degraded soils? Land Major Distribution Sector Knowledge gap intensification environmental consequence Soil quality and Cropping Ecosystem service Harvest Globally frequency resilience intensification Developing Continuing Soil health, Biological resilience monoculture and transition pesticide residue countries Rate reducing versus Developing Nutrient Over fertilization Soil acidification, balancing? intensification water pollution, countries O emission N 2 and nitrate accumulation Irrigation Submerged Rice Developing Water scarcity, Trade-offs C and water, countries, Asia methane emission Dry crops Arid/semi-arid Secondary Competition for water regions salinization, water scarcity Over grazing Soil degradation, Livestock Developing Forage versus feed crops? intensification countries water storage, C loss Industrial Industrialized Waste, water Safe waste treatment pollution, residue countries breeding and recycling of veterinary medicine and antibiotics Forest clearance, Developing Deforestation. Biodiversity, Agro-benefit versus wetlands and transition wetland shrink natural wealth, natural value drainage countries C loss Table 4.2 Threats to soil resource quality and functioning under agricultural intensification Status of the World’s Soil Resources | Main Report Soils and Humans 64 64

107 4.3.3 | Land use change resulting in irreversible soil change In this section we deal with soil sealing and mining, which have been identified as two important soil degradation processes occurring around the world. The current extent and rate of growth of soil sealing and mining are significant, and create considerable risks to essential ecosystem services. These changes in land use nearly always require a trade-off between various social, economic and environmental needs. Sealing and land take The ongoing urbanization and conversion of the landscape with settlements, infrastructure and services is occurring in many regions. Europe and Asia, in particular, are experiencing high rates of urban expansion and urban sprawl, and there are often insufficient incentives to re-use brownfield sites. These factors are causing an increase in land take and soil sealing. The drivers are essentially economic and demographic growth. In Europe, America and Oceania, at least 70 to 80 percent of the population currently lives in urban areas. The rate of urbanization is expected to continue to increase, particularly in Asia and Africa. land take covers all forms of conversion for the purpose of settlement, including: the The concept of development of scattered settlements in rural areas; the expansion of urban areas around an urban nucleus; the conversion of land within an urban area (densification); and the expansion of transport infrastructure such as roads, highways and railways. Broadly, this discussion considers as land take any conversion of agricultural, natural or semi-natural land cover to an ‘artificial’ (e.g. human-made) area. Artificial land cover classes are categorized in the Corine Land Cover system – see Table 4.3. A greater or smaller part of land take will result in soil sealing. Soil sealing means the permanent covering of an area of land and its soil by impermeable artificial material such as asphalt or concrete, for example through buildings and roads. As shown in Figure 4.6, the sealed area is only part of a settlement area. Gardens, urban parks, leisure areas and other green spaces within the boundaries of settlements are not covered by an impervious surface or are only partially covered. They thus form part of a land take but do not contribute to soil sealing (Prokop, Jobstmann and Schöbauer, 2011.) The ratio between sealed area and total area for a given land use class is measured by the soil sealing index. An example of this index, calculated for the Italian region of Emilia-Romagna, is shown in Table 4.4. Table 4.3 Artificial areas in Corine Land Cover Legend Status of the World’s Soil Resources | Main Report Soils and Humans 65 65

108 Typical structure of settlement A) B) Sealed areas about 70 percent (black color) Figure 4.6 Schematic diagram showing areas sealed (B) as a result of infrastructure development for a settlement (A). Source: European Union, 2012. Table 4.4 Artificial areas in Emilia Romagna according to the Corine Land Cover Legend and sealing index. Status of the World’s Soil Resources | Main Report Soils and Humans 66 66

109 Impact of land take Land take, by its definition, is the subtraction of an area from a previous agricultural, natural or semi-natural land use. According to this definition, the most obvious impact on the ecosystem services that can be provided by soil is on the production of biomass, and in particular of food. To clarify the concept, we may imagine that a city expands its urbanized area by a new allotment of 100 ha created at the expense of agricultural land. This area will be covered by buildings, private and public gardens, commercial centres, roads, etc. The entire area will clearly lose most of its capacity to produce food, with the possible minor exception of family horticulture in unsealed areas such as gardens or allotments. Had the entire area been previously cultivated with, say, -1 , the total loss in terms of food production potential will be winter wheat with an average yield of 5 tonnes ha equal to 500 tonnes of winter wheat per year. Other ecosystem services are at risk also. Water infiltration and purification and carbon storage are mainly reduced by the effective sealed area, and not by the entire land taken. Support to biodiversity is clearly affected, although the degree depends on the different groups of organisms and also on the design of the urbanized area. In this context, a positive mitigation role can be played by ‘Urban Green Infrastructure’ – the incorporation of a network of high-quality green spaces and other environmental features. Green Infrastructure can include natural areas as well as human-made rural and urban elements such as urban green spaces, reforestation zones, green bridges, green roofs, eco-ducts to allow crossing of linear barriers, corridors, parks, restored floodplains, biodiverse farmland. Regulation of land take and mitigation of its impacts Where policy aims to minimize land take, measures can be implemented to encourage re-use of existing urban areas such as derelict areas, brownfields and upgrading of degraded neighborhoods. Measures promoting densification of existing urban areas can also contribute to the reduction of land take. Fiscal measures can prevent speculative urban sprawl. A number of municipalities, and regional governments, especially in Europe, have already adopted policies designed to achieve zero net urban expansion. However, zero expansion becomes more problematic when there is significant demographic pressure and a high rate of rural to urban migration. Rational and efficient urban planning and intelligent building and infrastructure design can also help reduce land take. In the past, urban planners, architects and civil engineers too often considered soil as a raw material, abundantly available and of limited value. Examples of efficient consideration of the value of soil in urban development include: the construction of parking lots in the basement of buildings; and ‘green’ covering of areas that are only occasionally used, such as parking lots for exhibitions and fairs etc. Where expansion of urban and built-up areas is a policy and planning imperative, intelligent urban planning needs to take account of the soil dimension to mitigate the impact of land take. An education process is needed to make urban planners aware of the value of soil quality and land capability and of the options for mitigating negative impacts of land take. Impacts of soil sealing Sealing by its nature has a major effect on soil, diminishing many of its benefits. Normal construction practice is to remove the upper layer of topsoil, which delivers most of the soil-related ecosystem services, in order to be able to develop strong foundations in the subsoil or underlying rock to support the building or infrastructure. Where strong foundations are not required, only a thin layer of topsoil is generally excavated and the surfaces are simply covered by a layer of impervious material, such as asphalt or concrete. Both techniques impair or eliminate the soil’s capacity to deliver ecosystem services. Status of the World’s Soil Resources | Main Report Soils and Humans 67 67

110 The main impacts include the following. Water infiltration and purification are lost, and regulation of the water cycle is completely altered. The 1. concentration time of water flow is shortened, promoting flood events. 2. Soil biodiversity is impaired, as sealing prevents the production, release and recycling of organic material, et al. , 2008). In addition, the alteration of soil so affecting the soil biological communities (Marfenina water regimes, soil structure and redox potential have a strong impact on soil biodiversity. 3. Soil carbon storage potential is fundamentally altered ( Jones et al. , 2005), particularly where topsoil, which normally contains about half of the organic carbon in mineral soils, is stripped off. 4. The urban microclimate is altered. The reduction of evapotranspiration in urban areas due to the loss of vegetation and through alteration of albedo strengthens the ‘urban heat island’ effect (Früh , 2011). et al. Prevention of soil sealing and mitigation of its impacts Appropriate mitigation measures can be taken in order to maintain some of the ecosystem functions of soils and to reduce negative effects on the environment and human well-being. Key options available to urban planners and managers include: (i) minimizing conversion of green areas; (ii) re-use of already built-up areas, such as brownfield sites; (iii) using permeable cover materials instead of concrete or asphalt; (iv) supporting Green Infrastructure (see above); and (v) providing incentives to developers to minimize soil sealing. In practice, planners need to be able to evaluate the tradeoffs and ensure that policy instruments are used to ensure optimal outcomes which consider both human needs for urbanization and the preservation of the integrity of the soil and its services: 1. Existing policies for development of settlements and infrastructure should be reviewed and adapted to take account of the value of soils, particularly where subsidies or other incentives are driving unplanned land take and soil sealing (Prokop, Jobstmann and Schöbauer, 2011). 2. An integrated approach to urban planning should be followed. Existing best practice has demonstrated that soil sealing can be limited, mitigated and compensated. This requires that spatial planning follow an integrated approach and involve the full commitment of all relevant public authorities and governance entities responsible for land management, such as municipalities, counties and regions (Siebielec et al. , 2010). Specific regional and local approaches can be developed. These could, for example, take into account 3. unused resources at the local level such as a particularly large number of empty buildings or brownfield sites. Mining Ancient mining valuable minerals , and other geological materials of economic Mining is the extraction from the Earth of rocks, interest. It is one of the most ancient activities in human history (Mighall et al. , 2002; Shotyk et al. , 1998). Mining for specific materials such as quartz, silex and clays began as far back as the Palaeolithic – the Old Stone Age – when the first stone tools were developed. In the Neolithic era – the New Stone Age – flint mines existed in Belgium, Britain and elsewhere. Landscape records and evidence from bogs show that mining activities became more intense with the development of metal tools in the Bronze Age, and subsequently , 1998). Examples of the environmental impact , 2002; Shotyk et al. in the Iron Age (Martínez-Cortizas et al. et al. of ancient mining are numerous (Figure 4.7) (López – Merino , 2010; Grattan, Huxley and Pyatt, 2003; Fernández Caliani, 2008). Status of the World’s Soil Resources | Main Report Soils and Humans 68 68

111 Photo by F. Macias Photo by J.C. Fernández Caliani Prepared by P. Reich Photo by F. Macias Figure 4.7 (A) Panoramic view of Las Medulas opencast gold mine (NW Spain). The Roman extractive technique – known as ‘ruina montis’ – involved the massive use of water that resulted in important geomorphological changes; (B) Weathered gossan of the Rio Tinto Cu mine, considered the birthplace of the Copper and Bronze Ages; (C) typical colour of Rio Tinto (‘red river’ in Spanish), one of the best known examples of formation of acid mine waters. These are inhabited by extremophile organisms. Impact of mining The impact of mining on the environment differs greatly depending on the type of extraction, the ore or material exploited, and the method used to process the material extracted (Moore and Luoma, 1990). Traditional underground mining, which follows profitable veins beneath the earth’s surface, has less impact than open cast mining activities – also referred to as strip mining − which grew very rapidly in the last hundred years (Salomons, 1995). In some instances, entire mountains have been literally blasted apart to reach thin ore vein seams within, leaving permanent scars on the landscape. Nonetheless, mining operations themselves affect relatively small areas. By contrast, significant environmental problems are caused by tailing and waste rock deposits and by subsequent smelting operations. Pollutants can be transferred to surrounding areas by acid mine drainage or by atmospheric deposition of wind-blown dust. The incidence of these problems depends on local climatic and hydrologic conditions (Aslibekian and Moles 2003; Batista, Abreu and Serrano, 2007; López, Gónzalez and Romero, 2008). Other environmental effects, in addition to those caused by pollutants, include deforestation, erosion and formation of sinkholes (Meuser, 2010; Hester and Harrison, 2001). Only a small fraction of the material extracted is valuable ore. The ore needs to be separated by milling and flotation from the large volume of other material discarded as tailings. When the remaining concentrate is refined by processes such as smelting, flue dust and slag are produced (Hutchinson, 1979). Atmospheric contamination has commonly occurred throughout the world during smelting operations, leading to contaminated soils and risks to livestock (Down and Stocks, 1977; Munshower, 1977). Mining for coal, gold, uranium, wolfram, tin, platinoids and, in particular, poly-metallic sulphides has created large environmental impacts on soil, water and biota. Sulphide minerals include iron sulphides such as pyrite and pyrrhothite, and other poly-metallic sulphides, such as those containing Cu, Pb, Zn, Hg, Cd, Tl, Sb, Bi etc. These sulphides can also in some instances combine with arsenides or selenides to form sulfoarsenides or sulfoselenides (Evangelou, 1995; Abreu , 2010). et al. Sulphide minerals oxidise when brought to surface conditions (Nordstrom and Southam, 1997; Nordstrom and Alpers, 1999). The sulphide oxidation can cause extreme changes in Eh and pH (Figure 4.8) – negative pH values (as low as -3.6) have been measured in the acid mine waters of the Richmond mine in California (Nordstrom and Alpers, 1999). Depending on the local geochemical and hydrological conditions, sulphide oxidation can also affect the electrical conductivity of the system and may lead to elevated concentrations of many toxic elements in soils and waters nearby. Waters downstream of these mine systems (Figure 4.7C) are frequently hyperacid, hyperoxidant and hyperconductive. These waters may exhibit high activities of: (i) +3 0 +2 +2 +2 +2 ); (ii) heavy metal species, for example Cu , Zn , Al-SO , Hg , Cd y Hg ; various metal species such as Al 4 and (iii) metalloids, including arseniates, arsenites and seleniates (Sengupta, 1993; Macías, 1996; Monterroso, et al. , 1998, 1999; Azcue, 1999). Smelting operations of sulphide minerals Alvarez and Macías, 1994; Monterroso , which, if not recovered, is released into the atmosphere and thus contributes to acid also generate SO 2 deposition (described in Section 4.4). Status of the World’s Soil Resources | Main Report Soils and Humans 69 69

112 The mining of gold deserves special attention given its contribution to Hg emissions (Drude de Lacerda, 2003). Mercury is used to concentrate the fine gold particles through amalgamation and then the gold is separated from the amalgam by applying heat. When this process is carried out under uncontrolled conditions – as in small-scale gold mining (Drude de Lacerda, 2003) – Hg volatilises to the atmosphere. Tailings from Hg amalgamation are then leached with cyanide, and waste contaminated with metals and cyanide is released into the environment (Veiga et al. , 2009). Arsenic exposure has also been recorded in many gold and base metal producing countries (Williams, 2001). However, arsenate and arsenite mobilisation can be controlled with soil colloidal compounds such as reactive Fe and Al (Goldberg, 2002). As materials from mining are exposed to the environmental conditions of the Earth’s surface, these minesoils develop through weathering (Sencindiver and Ammons, 2000). However, their properties differ considerably from the original soil. They contain a high percentage of rock fragments, a low nutrient content, and elevated levels of potentially harmful trace elements. They also usually lack a distinct horizonation. These soils are in fact very young soils characterised by properties that limit their functions and their capability to support vegetation (Macias, 1996; Vega et al. , 2004; Abreu and Magalhães, 2009). When the overburden contains sulphidic material such as pyritic mine waste, the major weathering process is the oxidative dissolution of pyrite. Here the rate of soil formation is mainly controlled by the sulphide content and its particle-size distribution, causing strongly acidic conditions, as described above (Neel et al. , 2003; Haering, Daniels and Galbraith, 2004). Quite often, restoration of mine soils requires the addition of exogenous material to correct the extreme pH, Eh and/or EC values and the anomalous concentrations of toxic elements common in these systems which are generally bioavailable and susceptible to mobilisation. 1.2 20 O P 2 =1 O2 Hyperacid soils Circum-neutral soils Calcareous soils 0.6 10 Acid Alkaline soils soils Eh pe (volts) 0 0 Hydric soils Thionic soils P =1 h2 -10 -0.6 H 2 12 0 2 4 6 8 14 10 pH Figure 4.8 Eh-pH conditions of thionic/sulfidic soils and of hyperacid soils. Source: Otero et al., 2008. Status of the World’s Soil Resources | Main Report Soils and Humans 70 70

113 The formation of sulfidic material requires strongly reducing conditions and slight acidity. Once these are oxidised, and in the absence of minerals with high acid buffering capacity, extremely acid and oxidising conditions are generated. The dashed envelope in Figure 4.8 is the approximate extent of redox-pH conditions of mineral soils (with the exception of hyper-acid soils). Preventing impacts from mining The rehabilitation of abandoned mines is a difficult and costly task. In fact, in many instances, the landscape cannot be repaired. Some mining methods may have significant environmental and public health effects. The Aznalcollar pyritic sludge spill (SW Spain) (López-Pamo et al. , 1999; Grimalt, Ferrer and McPherson, 1999; Aguilar et al. , 2004; Calvo de Anta and Macias, 2009) is such an example. It occurred in 1998 in the surroundings of Doñana Park − the largest reserve of bird species in Europe − as a result of the failure of a tailings dam which contained several million tons of pyrite stockpile, flotation tailings and acid waters. The 2 of riverbanks and adjacent farmlands, extending 45 km downstream, with toxic spill contaminated ca. 26 km an estimated quantity of 16 000 tonnes of Zn and Pb, 10 000 tonnes of As, 4 000 tonnes of Cu, 1 000 tonnes of Sb, 120 tonnes of Co, 100 tonnes of Tl and Bi, 50 tonnes of Cd and Ag, 30 tonnes of Hg, and 20 tonnes of Se. Mining operations have a responsibility to protect the environment: air, water, soils, ecosystems and landscape. Many countries require reclamation plans for mining sites to follow environmental and rehabilitation codes. Nonetheless, mine restoration is still problematic, mainly because the environmental impacts were only recently understood or appreciated (Azcue, 1999; Sengupta, 1993). In addition, the technology available has not always been adequate to prevent or control environmental damage. Restoration of such systems requires a thorough understanding of material properties and their geochemistry. Only through such an understanding can the current and future behaviour of such systems be predicted and appropriate decisions taken to ensure their restoration (Gil , 1990; Macías-García, Camps Arbestain and Macías, 2009; Macías- et al. et al. , 2009). García Development of tailor-made Technosols to restore mine soils Technosols are defined by the FAO (2014b) as those soils with recent human activities in industrial and urban environments which have resulted in the presence of artificial and human-made objects. Technosols often result from the abandonment of urban, mining or industrial waste. These soils tend to have a large content of artefacts – that is objects that are either human-made, strongly transformed by human activity, or excavated (e.g. mine spoils, rubbles, cinders) (FAO, 2014b). Throughout history, humans have formed soils – ‘anthropogenic soils’ - and in certain cases these soils have proved more fertile that natural soils nearby (Sombroek, Nachtergaele and Hebel, 1993). Thus, it is feasible to produce specific Technosols which can fulfil the environmental and productive functions of natural soils – essentially, tailor-made Technosols. This may require the formulation and mixing of artefacts and other waste materials such as manure and biosolids. The production of these Technosols could be a feasible technique through which waste products are reused and the elements they contain are returned to their biogeochemical cycles, while restoring degraded areas and contributing to the sequestration of C in soils and biomass (Macias and Camps Arbestain, 2010). Environmental problems associated with this use of Technosols may be prevented if: (i) the characteristics of the materials used provide the soil with adequate buffering properties against contaminants, pH and/or redox changes; and (ii) there is a good understanding of how the constituent mixtures will evolve over time under the pedoclimatic conditions of the area to be restored. Figure 4.9 illustrates the benefits of the use of tailor-made Technosols in the restoration of an abandoned Cu mine rich in pyrite (Macías-García, Camps , 2009; Macías and Camps Arbestain, 2010). et al. Arbestain and Macías, 2009; Macías-García Status of the World’s Soil Resources | Main Report Soils and Humans 71 71

114 Prepared by P. Reich Figure 4.9 Use of different Technosols derived from wastes in the recovery of hyperacid soils and waters in the restored mine of Touro (Galicia, NW Spain). | Atmospheric deposition 4.4 4.4.1 | Atmospheric deposition The impacts of the deposition of atmospheric pollutants on soils vary with respect to soil sensitivity to a specific pollutant and to the total pollutant load. Anthropogenic emissions of sulphur, nitrogen and trace elements to the atmosphere mainly derive from fossil fuel and waste combustion in, for example, power generation, incineration, industry and transport. Emissions may also derive from non-combustion processes such as agricultural fertilizers or waste amendments. Mining activities may also contribute, for example Hg mining. Once in the atmosphere, these pollutants can be transported off-site and even cross national borders before being deposited either as dry or wet deposition. Deposition is more accentuated in forests, especially in coniferous forests (because of reduced wind speeds) and in areas of high elevation because of high precipitation rates. Once in the soil, pollutants can be mobilised by being: (i) released back to the atmosphere; (ii) made available to biota; (iii) leached out to surface waters; or (iv) transported to other areas by soil erosion. Pollutants disrupt natural biogeochemical cycles by altering soil functions. This disruption may come about through direct changes to the nutrient status, acidity, and bioavailability of toxic substances, or through indirect changes to soil biodiversity, plant uptake and litter inputs. Soil sensitivity to atmospheric pollution varies with respect to: (i) key properties influenced by geology and associated pedogenesis such as cation exchange capacity, soil base saturation, aluminium, or rate of base cation supply by mineral weathering); (ii) organic matter content and carbon to nitrogen ratio (C:N); and (iii) position of the water table. When atmospheric pollution is associated with sulphate deposition, the capacity of soils to adsorb sulphate (e.g. soils with a dominance of short-range ordered constituents) plays a key role in buffering the acidification process (Camps Arbestain, Barreal and Macías, 1999; Rodríguez-Lado, Montanarella and Macías, 2007). Harmful effects on soil function and structure occur where deposition exceeds the ‘critical load’ - the specific amount of one or more pollutants that a particular soil can buffer (Nilsson and Grennfelt, 1988). Estimates and mapping of critical loads of acidity Status of the World’s Soil Resources | Main Report Soils and Humans 72 72

115 are however strongly dependent on the neutralisation mechanisms considered in the analysis, for example, the inclusion or exclusion of sulphate adsorption (Rodríguez-Lado, Montanarella and Macías, 2007). Spatial differences in soil sensitivity − commonly defined by the ‘critical load’ − and in pollutant deposition result in an uneven global distribution of impacted soils (Figure 4.10). For instance, global emissions of sulphur and et al. , 2001), yet critical loads nitrogen have increased 3–10 fold since the pre-industrial period (van Aardenne for acidification are only exceeded in 7–17 percent of the global natural terrestrial ecosystems area (Bouwman et al. , 2002). 4.4.2 | Main atmospheric pollutants: Synopsis of current state of knowledge Since the 1980s, emissions of pollutants, notably sulphur, across Europe and North America have declined. The decline is due to the establishment of protocols under the 1979 Convention on Long-range Transboundary et al. , 2012; Reis et Air Pollution (LRTAP) and the 1990 United States Clean Air Act Amendments (CAAA) (Greaver al. , 2012; EEA, 2014). Conversely, emissions in South and East Asia, sub-Saharan Africa and South America are likely to increase in response to industrial and agricultural development (Kuylenstierna et al. , 2001; Dentener et al. , 2006). Further emission increases are also occurring in remote areas due to mining activity, such as oil sands extraction in Canada (Kelly , 2010; Whitfield et al. , 2010). et al. Sulphur deposition Sulphur emissions primarily result from combustion of coal and oil and are typically associated with power -1 -1 yr were detected in regions generation and heavy industry. In 2001, deposition exceedances of 20 kg S ha of China and Republic of Korea, Western Europe and eastern North America (Vet et al. , 2014; Figure 4.10.(a)). -1 -1 yr (Figure 4.10a). The deployment of sulphur emission Deposition in unaffected ecosystems is <1 kg S ha protocols led to the reduction of approximately 80 percent in the deposition levels of sulphur across Europe between 1990 and 2010 (Reis , 2012). This reduction led to an increase in the use of sulphur fertilizer to et al. combat crop sulphur deficiencies in agricultural soils in Europe (Bender and Weigel, 2011). Sulphur emissions et al. , 2013). in China also declined between 2005 and 2010 (Fang Soil acidification is a natural process that is altered and accelerated by anthropogenic sulphur and nitrogen ) gases react with water vapour in the atmosphere to form deposition (Greaver et al. , 2012). Sulphur oxide (SO x SO ). Once in the soil, excess inputs of acidity (H+) displace base cations (e.g. calcium (Ca +) sulphuric acid (H 2 4 2 +)) from soil surfaces to the soil solution, and the base cations are subsequently lost from and magnesium (Mg 2 the soil profile by leaching (Reuss and Johnson, 1986). In mineral soils, these base cation losses can be balanced by rock weathering or atmospheric dust deposition. Thus, the global distribution of acid sensitive soils is mainly associated with conditions that favour development of soils with low cation exchange capacity and base saturation (Bouwman et al. , 2002; Figure 4.10b). The exception is where soils are dominated by variable- charge constituents, as in the case of Acrisols, Ferrasols, Nitosols and Andosols. On these soils, sulphate adsorption may become the most important acid-buffering mechanism (Rodríguez-Lado, Montanarella and Macías, 2007). Wetlands can also buffer inputs of acidity through biological sulphate reduction, although et al. acidity can be mobilised again following drought and drainage (Tipping , 2003; Laudon , 2004; et al. Daniels et al. , 2008). Organic acids can also buffer acid deposition in naturally acidic organic soils (Krug and Frink, 1983; Monteith et al. , 2007). Acidification decreases soil fertility due to loss of nutrients and increases the mobilisation of toxic metals, particularly Al and heavy metals. The negative effect of Al species on crop yield is particularly strong in soils with a dominance of 2:1 clay minerals with high CEC and low organic matter content. The atmospheric deposition of acid compounds had a huge impact on Scandinavian ecosystems over the 1960s-80s, including declines in freshwater fish populations and damage to forests (EEA, 2014). Sulphur inputs can also stimulate microbial processes that increase Hg bioavailability, leading to bioaccumulation of Hg in the food chain (Greaver et al. , 2012). Status of the World’s Soil Resources | Main Report Soils and Humans 73 73

116 The increase in soil pH following the reduction of sulphur emissions shows that the acidification process is reversible, although the recovery time is highly variable and dependent on soil properties. Some areas , 2012; et al. with organic soils where deposition has declined are showing either slow or no recovery (Greaver , 2012; RoTAP, 2012). On agricultural soils, lime can be applied to increase soil pH. However, et al. Lawrence 50-80 percent of sulphur deposition on land is on natural land (Dentener et al. , 2006). Application of lime to naturally acidic forest soils can cause further acidification of deep soil layers by increasing the decomposition in surface litter (Lundström et al. , 2003). In acid waters, the addition of liming material may favour the formation OH +12), which are highly toxic to aquatic species (Monterroso, Alvarez and of polymeric Al hydroxides (e.g. Al 27 13 Macías, 1994). Wider effects of acidification are starting to be understood through long-term monitoring. Decreased organic matter decomposition due to acidification has increased soil carbon storage in tropical forests (Lu ) emissions have also been suppressed. This is because sulphate- et al. , 2014). In wetland soils, methane (CH 4 and acetate) than methanogenic microbes (Gauci reducing bacteria have a higher affinity for substrate (H 2 , 2004). Conversely, declining sulphur deposition has been associated with increased dissolved organic et al. et al. , 2007) and decreased soil carbon stocks in temperate forest carbon fluxes from organic soils (Monteith et al. , 2011; Lawrence et al. , 2012). soils (Oulehle Nitrogen deposition Nitrogen deposition covers a wider geographical area than sulphur deposition. This is because the sources are more varied, including extensive agriculture fertilizer and animal waste application, biomass burning, and -1 -1 yr in 2001 include fossil fuel combustion (Figure 4.10c). Regions with deposition in excess of 20 kg N ha Western Europe, South Asia (Pakistan, India, Bangladesh) and eastern China (Vet et al. , 2014). In addition, -1 -1 or more were found across North, Central and South America yr extensive areas with deposits of 4 kg N ha and parts of Europe and Sub-Saharan Africa. By contrast, ‘natural’ deposition in un-impacted areas is as little -1 -1 yr (Dentener et al. , 2006). While both nitrogen and sulphur emissions related to fossil fuel as 0.5 kg N ha combustion have declined across Europe, agricultural sources of nitrogen in the region are likely to stay constant in the near future (EEA, 2014). At the same time, overall global emissions are likely to increase et al. , 2008). Nitrogen deposition in China in the 2000s was similar to peaks in Europe during the (Galloway et al. , 2013b). 1980s before Europe embarked on mitigation measures (Liu Deposition of nitrogen induces a ‘cascade’ of environmental effects, including acidification and eutrophication that can have both positive and negative effects on ecosystem services (Galloway et al. , 2003). Soils with low nitrogen content are most sensitive to eutrophication - typically Histosols, Cryosols and Podzols located in cold areas in northern countries such as northern Canada, Scandinavia and northern Russia (Bouwman et al. , 2002; Rodríguez-Lado, Montanarella and Macías, 2007; Figure 4.10d). Excluding agricultural areas where nitrogen deposition is beneficial, 11 percent of the world’s natural land experiences nitrogen -1 -1 yr (Dentener et al. , 2006). In Europe, eutrophication has and will continue to exceedances above 10 kg N ha impact a larger area than acidification (Rodríguez-Lado and Macias, 2005; EEA, 2014). Nitrogen fertilisation can increase tree growth (Magnani et al. , 2007) and cause changes in plant species and diversity (Bobbink et al. , 2010). This can in turn alter the amount and quality of litter inputs to soils, notably the C:N ratio and soil-root interactions (RoTAP, 2012). However, increased global terrestrial carbon sink can be (Liu and Greaver, 2009). Long- O and CH largely offset by increased emissions of the greenhouse gases N 2 4 term changes caused by nitrogen deposition are uncertain as transport times vary between environmental , 2008). et al. systems. The only way to remove excess nitrogen is to convert it to an unreactive gas (Galloway Status of the World’s Soil Resources | Main Report Soils and Humans 74 74

117 Figure 4.10 Global distribution of (a) atmospheric S deposition, (b) soil sensitivity to acidification, (c) atmospheric N deposition, and (d) soil carbon to nitrogen ratio (soils most sensitive to eutrophication have a high C:N ratio; eutrophication is caused by N). Source: Vet et al., 2014; Batjes, 2012; FAO, 2007. Atmospheric deposition data in (a) and (c) were provided by the World Data Centre for Precipitation Chemistry ( http://wdcpc.org , 2014) and are also available in Vet et al. (2014). Data show the ensemble-mean values from the 21 global chemical transport models used by the Task Force on Hemispheric Transport of Air Pollution (HTAP) (Dentener et al. , 2006). Total wet and dry deposition values are presented for sulphur, oxidized and reduced nitrogen. Soil data in (b) and (d) were produced using the ISRIC-WISE derived soil properties (ver 1.2) (Batjes, 2012) and the FAO Digital Soil Map of the World. Trace element deposition Global trace element emissions and deposition are poorly understood in comparison to our understanding of emissions of sulphur and nitrogen. Emissions of trace elements are associated with combustion of fossil fuel (V, Ni, Hg, Se, Sn), traffic (Pb), insecticides (As), steel manufacture (Mn, Cr), and mining and smelting (As, Cu, Zn, Hg) (Mohammed, Kapri and Goel, 2011). In the United Kingdom, trace element deposition is responsible for et al. , 2003). In Europe, the area at risk from Cd, 25-85 percent of total trace element inputs to soils (Nicholson Hg and Pb deposition in 2000 was 0.34 percent, 77 percent and 42 percent respectively, although emissions are declining (Hettelingh et al. , 2006). In China, 43-85 percent of total As, Cr, Hg, Ni and Pb inputs to agricultural soils originate from atmospheric deposition (Luo et al. , 2009). In bioavailable form these elements have a toxic effect on soil organisms and plants, influencing the quality and quantity of plant inputs to soils and the rate of decomposition. Significantly, they can also bioaccumulate in the food chain. Activity of trace elements in soils will depend on the specific mobility of the element and this will be influenced by pH, Eh and the concentration of dissolved organic matter with complexing properties (Blaser et al. , 2000). Some trace elements will persist for centuries as they are strongly bound to soil particles. However, they can become bioavailable, as observed , 2003; Rothwell et al. in peatlands following drought-induced acidification, drainage and soil erosion (Tipping et al. , 2005). Status of the World’s Soil Resources | Main Report Soils and Humans 75 75

118 4.4.3 | Knowledge gaps and research needs Atmospheric pollution is a global phenomenon impacting large areas of the land surface. Regional and global scale assessment relies on the use of simple models to: (i) upscale site-specific soil data, in some instances using soil databases collected as long ago as the 1970s; and (ii) estimate where soil sensitivity – the ‘critical load’ − of a single pollutant is exceeded. There are few locations with long-term soil monitoring data, particularly in comparison to the data available on air, rain and surface water quality. Therefore, the actual global extent and magnitude of polluted soils are unclear. Essentially, we lack data at adequate scales to check the model outputs. A long-term global soil monitoring network is needed. While the direct impacts of sulphur, nitrogen and trace elements on inorganic soil chemical processes are generally well understood, many uncertainties still exist about pollutant impacts on biogeochemical cycling, particularly interactions between organic matter, plants and organisms in natural and semi-natural systems (Greaver et al. , 2012). Process understanding is dominated by research in Europe and North America (e.g. Bobbink et al. , 2010). Research is needed in other regions where soil properties and environmental conditions differ from the empirically studied areas in Europe and North America. Models need to be developed to examine the combined effects of air pollutants and their interactions with climate change and feedbacks on et al. , 2008; RoTAP, 2012). Air quality, biodiversity and greenhouse gas balances and carbon storage (Spranger climate change polices all impact on soils. A more holistic approach to protecting the environment is needed, particularly as some climate change policies (e.g. biomass burning, carbon capture and storage) have potential to impact air quality and, therefore, soil functions (Reis et al. , 2012; RoTAP, 2012; Aherne and Posch, 2013). References Abreu, M.M. & Magalhães, M.C.F. 2009. Phytostabilization of Soils in Mining Areas. Case studies from Portugal. In L. Aachen, P. Eichmann, eds., Soil Remediation . pp 297-344. New York, Nova Science Publishers, Inc. 2010. Acid Mine Drainage in the Portuguese Abreu, M.M., Batista, M. J., Magalhães, M.C.F. & Matos, J,X. Iberian Pyrite Belt. In B.C. Robinson, ed. pp 71-118. New York, Nova Science Mine drainage and Related problems. Publishers, Inc. 275 pp. 2004. Soil Aguilar, J., Dorronsoro, C., Fernández, E., Fernández, J., García, I., Martín, F. & Simón, M. pollution by a pyrite mine spill in Spain: evolution in time. Environmental Pollution , 132: 395-401. Aherne, J. & Posch, M. 2013. Impacts of nitrogen and sulphur deposition on forest ecosystem services in Canada. Current Opinion in Environmental Sustainability, 5: 108–115. Alexander, A.B . 2012. Soil compaction on skid trails after selective logging in moist evergreen forest of 3(6): 262-264 Ghana. Agriculture and Biology Journal of North America, Alexandratos, J. & Bruinsma, J. 2030/2050: the 2012 revision. Rome, FAO. World agriculture towards 2012. Amorim, M.J.B., Rombke, J. & Soares, A.M.V.M . 2005. Avoidance behavior of Enchytraeus albidus : Effects Chemosphere of Benomyl, Carbendazim, Phenmedipham and different soil types. 59: 501-510. Aslibekian, O. & Moles, R. 2003. Environmental risk assessment of metals contaminated soils at Silvermines Environmental Geochemistry and Health, 25: 247-266. abandoned mine site, Ireland. 1999. Environmental impacts of Mining Activities. Emphasis on Mitigation and Remedial Azcue, J.M. Measures. Berlin, Springer. 300 pp. 2008. Global assessment of land degradation Bai, Z.G., Dent, D.L., Olsson, L. & Schaepman, M.E. and improvement. 1. Identification by remote sensing. Report 2008/01, ISRIC – World Soil Information, Wageningen. Status of the World’s Soil Resources | Main Report Soils and Humans 76 76

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130 Global Soil Change Drivers, Status and Trends Coordinating Lead Authors: André Bationo (Burkina Faso), Srimathie Indraratne (Sri Lanka) Contributing Authors: Sayed Alavi (ITPS/Iran), Abdullah Alshankiti (ITPS/Saudi Arabia), Dominique Arrouays (ITPS/France), Charles Bielders (United States), Keith Bristow (Australia), Marta Camps Arbestain (ITPS/New Zealand), Lucrezia Caon (Italy), Brent Clothier (New Zealand), Tandra Fraser (United States), Ciro Gardi (Italy), Gerard Govers (Belgium), Roland Hiederer (Germany), Jeroen Husing (TSBF-CIAT), Joyce Jefwa (TSBF-CIAT), Shawntine Lai (United States/Taiwan, Province of China), Rattan Lal (United States), John P. Lamers (Germany), Dar-Yuan Lee (Taiwan, Province of China), Fredah Maina (Kenya), Luca Montanarella (ITPS/EC), Joseph Mung'atu (TSBF- CIAT), Freddy Nachtergaele (Belgium), Peter F. Okoth (TSBF-CIAT), Asad Qureshi (ICBA), Shabbir Shahid (ICBA), Manuela Ravina da Silva (Sweden), Justin Sheffield (United Kingdom), Tran Tien (Vietnam), Kristof Van Oost (Belgium), Boris Vrscaj (Slovenia), Diana Wall (United States), Boaz Waswa (Kenya), Jeewika Weerahewa (Sri Lanka), Kazuyuki Yagi (ITPS/Japan), Ted Zobeck (United States). Reviewing Authors: Dominique Arrouays (ITPS/France), Richard Bardgett (United Kingdom), Marta Camps Arbestain (ITPS/New Zealand), Tandra Fraser (Canada), Ciro Gardi (Italy), Neil McKenzie (ITPS/Australia), Luca Montanarella (ITPS/ EC), Dan Pennock (ITPS/Canada) and Diana Wall (United States). Status of the World’s Soil Resources | Main Report Soils and Humans 88 88

131 5 | Drivers of global soil change Drivers in general comprise the factors that bring about socio-economic and environmental changes. They operate at various spatial and temporal levels in society. They differ from one region to another, and within and between nations. Drivers are diverse in nature and they include: demographics; economic factors; scientific and technological innovation; markets and trade; wealth distribution; institutional and socio-political frameworks; value systems; and climate and climate change (UNEP, 2007; IAASTD, 2009). Drivers have an impact on natural resources including soil services and functions, with impacts on biodiversity, environmental health and ultimately human well-being. Globalization has particularly affected these drivers, leading to an increase in human mobility with social, economic and environmental implications. Patterns of settlement and consumption result in pressures on ecosystem services, including those provided by soils. Rural-urban migration and associated livelihood changes contribute to changing patterns of energy use and shifts in diet – for example, towards meat – which can intensify pressures on land and soils in producing areas (UNEP, 2012). In addition, climate change may have significant impacts on soil resources through changes in water availability and soil moisture, as well as through sea level rise (IPCC, 2014b). 5.1 | Population growth and urbanization 5.1.1 | Population dynamics Changing global population trends The world population of 7.2 billion in mid-2013 is projected to increase by almost one billion by 2025. By 2050 it is expected to reach 9.6 billion, and to rise to 10.9 billion by 2100 (UN, 2014). The principal factor in this continual rise is the rapid increase in the population of developing countries, in particular in Africa, where the population is projected to increase from the current 1.1 billion to reach 2.4 billion by 2050 (Table 5.1.). Many countries of Sub-Saharan Africa are still experiencing fast population growth with high fertility rates. Other countries with similar trends include India, Indonesia, Pakistan, the Philippines and the United States. By 2030 Status of the World’s Soil Resources | Main Report Drivers of global soil change 89 89

132 India’s population is expected to surpass China’s, to become the most populous country in the world. Nigeria’s population is expected to surpass the United States population in 2045 to become the world’s third most populous country. Nigeria’s population is likely to rival that of China by the end of the century (Table 5.2). Over the period 2013–2100, eight countries are expected to account for over half of the world’s projected population increase: Nigeria, India, the United Republic of Tanzania, the Democratic Republic of Congo, Niger, Uganda, Ethiopia and the United States of America. On the other hand, Europe’s population is projected to decline, since fertility rates are far below the level for replacement of population in the long run. As fertility decreases and life expectancy rises, population ageing is a challenge for Europe (UN, 2014). Other developing countries with young populations but lower fertility (e.g. China, Brazil and India) are also likely to face challenges of an , 2014). ageing society by the end of this century (Gerland et al. Percent % of world % Change 2050 2013 Density Area Region pop. population. (millions of 2013-2050 (p/km²) of world Population (projected) km²) (millions) population Asia 3 1.9 4 298 60.0 135 5 164 54.1 20 Africa 1 110 115 2 393 15.5 36 31.0 25.1 Europe -4 709 32 10.4 742 23.0 7. 4 LAC 8.6 30 782 8.2 27 20.5 617 North 355 21.8 5.0 16 446 4.7 26 America Oceania 0.6 48 8.6 38 0.5 4 57 100 52 33 7 162 9 551 136.8 World 100.0 Table 5.1 World population by region Country Country Proj. Popul. Population Country Country Population Projected 2100 Population in 2013 in 1950 in 2050 China 544 China 1 386 India 1 620 India 1 547 1 086 China 1 385 China 1 252 India 376 India United United 158 914 Nigeria 440 Nigeria 320 States States Russian United United 401 103 Indonesia 250 462 States States Federation Brazil 200 Indonesia 321 Indonesia Japan 82 315 276 Tanzania 271 Pakistan 182 Pakistan 73 Indonesia Germany 70 Nigeria 174 Brazil 231 Pakistan 263 Dem. Rep of 262 Bangladesh 157 Bangladesh 202 54 Brazil Congo United Russian Ethiopia Ethiopia 51 143 188 243 Federation Kingdom Italy 46 Japan 127 Philippines 157 Uganda 205 Table 5.2 The ten most populous countries 1950, 2013, 2050 and 2100 (population in millions). Source: United Nations, 2014. Status of the World’s Soil Resources | Main Report Drivers of global soil change 90 90

133 5.1.2 | Urbanization In tandem with the rate of population increase is the rising rate of urbanization. According to the United Nations, by 2014 more people were living in urban areas (54 percent) than in rural areas. The urbanization trend is expected to continue in all regions, and by 2050, 66 percent of the world’s population is projected to be urban. Today some of the most urbanized regions are Northern America (82 percent), Latin America and the Caribbean (80 percent) and Europe (73 percent). However, Africa and Asia are now the fastest urbanizing regions, with the share of the population urbanized expected to rise from today’s 40 and 48 percent respectively to 56 and 64 percent by 2050. Three countries together are expected to account for 37 percent of the growth of the world’s urban population between 2014 and 2050: India (adding 404 million), China (adding 292 million) and Nigeria (adding 212 million). Whereas in the past mega-cities were located in more developed regions, today’s large cities are principally found in lower income countries. Since 1990 the number of these mega-cities has nearly tripled globally; and by 2030, the world is projected to have 41 global agglomerations, housing more than 10 million inhabitants each. In developing countries, the competition between demand for agricultural land and the needs of growing cities is a mounting challenge ( Jones et al. , 2013). The rural population globally is now close to 3.4 billion but is expected to decline to 3.2 billion by 2050. Africa and Asia are home to nearly 90 percent of the world’s rural population. India has the world’s largest rural population (857 million), followed by China (635 million). Rural/urban migration continues to feed urban growth, causing environmental changes including effects on land use and soils. Policy and poverty also drive the threats to land and soils. Many rural poor live under regimes of weak land policy and insecure tenure systems. They often farm marginal lands of low agricultural productivity, typically employing traditional farming methods. This may aggravate soil degradation and biodiversity decline, with resulting yield losses and food insecurity ( Jones et al. , 2013; Barbier, 2013). In addition, land grabs may lead to eviction of farming families, for whom rural to urban migration may be the only option, so accelerating the pace of urbanization (Holdinghausen, 2015). 5.2 | Education, cultural values and social equity Education influences decisions regarding land use and land management. Farmers’ decisions result from many factors, including incentives, access to capital and risk management, but also from knowledge and level of education, all of which may affect land use and management practices (MA, 2005). Land use and management is dependent on the sum total of all decisions taken by individual farmers of different education and gender groups in a community (IAASTD, 2009). Women play a key role in agriculture. They represent 43 percent of the agricultural labour force world-wide, ranging from around 20 percent in Latin America to 50 percent in parts of Africa and Asia (FAO, 2011b). Women are responsible for half of the world’s food production, providing between 60 and 80 percent of the food in most developing countries (World Bank/FAO/IFAD, 2009). However, evidence shows that women still own less land and have smaller landholdings with generally poor soil quality. Improving women’s access to land and secure tenure can have direct impacts on farm productivity and in the long run improve household welfare (FAO, 2013). FAO’s Gender and Land Rights Database (2010) suggests that less than one quarter of agricultural land holdings in developing countries are operated by women. Latin America and the Caribbean have the largest mean share of female agricultural land holders, exceeding 25 percent in Chile, Ecuador and Panama. In North Africa and West Asia, female landholders represent fewer than five percent of the owners. In sub- Saharan Africa the average rate is 15 percent, although there are wide variations within the region, from less than five percent in Mali to over 30 percent in Botswana, Cape Verde and Malawi (Figure 5.1). Status of the World’s Soil Resources | Main Report Drivers of global soil change 91 91

134 Percentage of female landholders No data 9 - 15.7 > 29 22.3 - 29 15.7 - 22.3 < 9 Figure 5.1 Percentage of female landholders around the world. Source: FAO, 2010. 5.3 | Marketing land Today land is used more intensively than ever. The expansion of markets, rising population, and economic development and higher incomes have pushed up demand for land for both agriculture and for settlements and so driven unprecedented land use change (Section 4.1, this volume). The most dramatic changes have been in reduction in forest cover, in expansion and intensification of cropland, and in urbanization (UNEP, 2007). In agriculture, production of crops and livestock products for markets is fundamental to the economies of many countries. One new segment of market-driven production is biofuels, where incentives have strengthened as a result of higher and volatile oil prices and because a number of countries have introduced renewable energy , 2013). North America is leading global biofuel production, with 48 percent promotion policies (Rulli et al. of the global market. The second largest producer of biofuels is Brazil, producing 24 percent of the world’s biofuels (OECD/FAO, 2011). The growth of biofuels production is driving an increase in deforestation and other land use changes. It is widely accepted by economists that when land markets function in an efficient manner, the resulting land use patterns provide the highest possible benefits to the society. However, empirical research findings reveal that the functioning of land markets in many developing countries is inefficient and the resulting land use patterns are sub-optimal (Pinstrup-Anderson and Watson II, 2011). Amongst the causes of inefficiencies the following have been cited: lack of well-defined property rights (Allen, 1991; Alston, Libecap and Schneider, 1995; Besley, 1995); higher bargaining power exercised by different groups of buyers (Sengupta, 1997; Ghebru and Holden, 2012); non-existence or under-functioning of insurance markets to absorb risk and uncertainties in the natural environment (such as climate change) (Dayton-Johnson, 2006; Auffret, 2003); and environmental externalities like soil erosion. Land grabbing - large scale land acquisitions - started initially in response to the 2007-2008 increase in food prices. Since then the phenomenon has intensified (IMF, 2008). Foreign states and companies and national investors, often with the support of the national government, see land as an attractive asset in order to meet the demands of food supply and energy. Experience in Africa, Eastern Europe, South America and South and Southeast Asia has shown that in an unregulated environment this ‘land grab’ can lead to the displacement et al. of local farmers (Rulli , 2013). Since fertile land is a limited resource, competition for it may lead to a rise in poverty, violence and social unrest in countries with weak regulatory systems or power imbalances (Nolte and Ostermeier, 2015). Status of the World’s Soil Resources | Main Report Drivers of global soil change 92 92

135 Large areas of arable land have been bought or leased in recent years, mainly in developing countries (Figure 5.2). According to the Land Matrix Global Observatory database, since the year 2000 over 1 000 land deals involving foreign investors have been struck, covering 39 million ha, while another 200 deals cover 16 million ha. The main driver of large land-scale acquisitions continues to be agricultural production, with 40 percent of deals for food crop production and livestock farming, followed by agrofuels as the second most important driver with 190 deals, and forestry projects which have increased by 50 percent (Land Matrix Newsletter, 2014). Other acquisitions have been for urban expansion, mining, infrastructure projects and tourism (Nolte and Ostermeier, 2015). Figure 5.2 Major land deals occurring between countries in 2012. Source: Soil Atlas, 2015/Rulli et al., 2013. In addition to these commercial land transactions, policy responses for climate change adaptation and mitigation have led to market-based approaches which attach a value to ecosystem services. In this context, there is the allocation of land for environmental ends, for example, offsetting emissions in the industrialized North by protecting forests in the South. These approaches in practice have sometimes required curtailment of customary or community access rights to forest and water. In other cases, these approaches have encouraged the shift of smallholder labour from subsistence farming and cash crop production to carbon sequestration (UNEP, 2012). A number of projects focusing on soil health and carbon sequestration in Africa have aimed to benefit individual farmers and at the same time to mitigate climate change. These pioneering projects have faced implementation challenges, including high unit costs, small land sizes, and weak land tenure rights. In addition, the incentive framework has been weakened by the small size of the cash payments the projects can offer for carbon sequestration, due to the low value of carbon credits and periodic market volatility in international voluntary carbon markets. Nevertheless, the non-carbon benefits gained from the projects, such as improved agricultural productivity through sustainable land management and soil health and strengthening of community solidarity, are important results to be prioritized in future projects (Shames, 2013). Status of the World’s Soil Resources | Main Report Drivers of global soil change 93 93

136 5.4 | Economic growth Economic growth and urbanization generate immense benefits to humankind but also contribute to unsustainable consumption patterns. They may lead to increased levels of emissions from mining, manufacturing, sewage, energy and transport and to the consequent release of persistent pollutants to land, air and water (UNEP, 2012). By 2050 the population around the globe is expected to be generally wealthier and more urbanized, resulting in an increase and shift in consumption and food demand and consequently in a rise in pollution risk. In developing economies, livestock production is already increasing at a rapid rate as a result of structural change in diets and consumption. FAO predicts that the total demand for animal products will increase at more than double the rate of increase in demand for food of vegetable origin, such as cereals (FAO, 2011a). This will lead to the expansion of land dedicated to livestock, both pasture and feed production. The largest expansion is predicted in the tropics, particularly in South America and Africa where vast areas of tropical forests, semi-arid lands, savannah, grassland and wetland ecosystems could be exploited for livestock - with potentially devastating environmental results (Laurance, Sayer and Cassman, 2014). In developing countries, difficult decisions on the trade-offs between preserving natural ecosystems and economic development will be required. In any case, it is likely that agricultural expansion and biofuel production will continue to trigger deforestation, and consequently soil degradation, pollution of land and water and increase in greenhouse gas emissions (FAO, 2003; Alexandratos and Bruinsma, 2012). Despite improvements in income growth in many countries, poverty and access to food remain problematic. According to FAO (2014), an estimated 842 million people around the world are currently undernourished. The 2007-2008, 2010 and 2012 price hikes in commodity markets evidenced how price shocks can trigger prolonged crises leading to food insecurity amongst the most vulnerable (FAO, 2011b). Global agendas such as those stated in the Sustainable Development Goals and the Post-2015 Agenda argue that environmental stewardship and sustainable management of natural resources provide opportunities to decrease inequality while increasing production of goods and services. However, this is a complicated agenda, as links between human well-being and natural resources, including soils, are influenced by a host of factors, including economic wealth, trade, technology, gender, education etc. Turning these lofty themes into real policies and programs to reduce poverty equitably and sustainably remains the key development challenge for the coming decades (UNEP, 2007). 5.5 | War and civil strife In the course of history, many conflicts over fertile land have occurred. Until the twentieth century, most of these conflicts were local and had relatively little impact on the soils themselves. However, modern warfare makes use of non-degradable weapons of destruction and of chemicals that may remain in the affected soils for centuries after the conflict. The impacts of war and civil strife on the environment in general, and on soils in particular, are both direct physical impacts and indirect socio-economic impacts. Direct physical impacts of war on the soil resource include weapons and bombs remaining in the soil, the destruction of structures with consequent terrain deformation, heavy military transport that results in compaction, and chemical spraying that leads to contamination of both soils and groundwater. Socioeconomic impacts of war include local desertification and displacement of large populations of refugees towards safe regions, resulting in pressure on the environment and soils in the receiving sites (Owona, 2008). Extensive areas in the world are still affected by remnants of past and present war events. Especially affected are zones where land mines have been buried (Box 5.1), making these soils unsuitable for any exploitation and provisioning of services. There are approximately 110 million mines and other unexploded ordnance (UXO) scattered in sixty-four countries on all continents, remnants of wars from the early twentieth century to the present (Kobayashi, A., 2013). Africa alone has 37 million landmines in at least 19 countries. Angola is by far the Status of the World’s Soil Resources | Main Report Drivers of global soil change 94 94

137 most affected zone with 15 million landmines and an amputee population of 70 000, the highest rate in the world. The problem persists despite campaigns to raise awareness, including the International Campaign to Ban Landmines (ICBL), which was awarded the 1997 Nobel Peace Prize. Removal of mines is proceeding, but at a glacial pace due to the danger, the cost (US$300 to US$1 000 per mine removed), and lack of international agreement on priorities. Minefields Box 5.1 | Minefields are one of the main constraints to the development of rural areas in Bosnia and Herzegovina 2 (BIH), where large tracts (ca. 4 000 km ) of agricultural land and forest areas cannot be used because they remain mined after the war that ended two decades ago (ICBL, 2002). BIH is the most mine-affected country in Europe with an estimated one million mines (mostly antipersonnel) remaining in the soil, and only 60 percent of which are located (Bolton 2003; Mitchell, 2004). This affects about 1.3 million people, roughly one third of the population. At current rates of de-mining, it will take several generations before rural areas are again safe. The displacement of people as a result of wars and conflicts has also created severe environmental and soil problems (Box 5.2). Box 5.2 | Migration/Refugee Camps -1 Acholiland in northern Uganda has suffered from persistent insecurity since the mid 980s. The massive disruption, dislocation and displacement and suffering of the people in the region are well-known. As a way of protecting the local people, the government placed most inhabitants of those districts in camps popularly referred to as Internally Displaced Peoples (IDP) camps. As a result, land has been abandoned and farming and other socio-economic activities are only possible near the protected camps in a restricted radius not exceeding seven kilometres. War creates refugees, leaves government and environmental agencies impaired or destroyed, and substitutes short-term survival for longer-term environmental considerations. This means that ecosystems continue to suffer even after the fighting has stopped (Owona, 2008). The Uganda analysis shows that the creation of 157 IDP camps has significantly affected 2 the environment in terms of deforestation (140 km ), soil erosion, habitat destruction and pollution (Owona, 2008). Often war results in a combination of negative effects on soils. These may include soil compaction, soil contamination, soil sealing and enhanced wind erosion and dust fall out (Box 5.3). Box 5.3 | Combined effects of war and strife on soils. During the 1991 Gulf War in Iraq and Kuwait, there were massive impacts on the environment, resulting from heavy vehicle movements, hundreds of oil well fires, numerous oil lakes and spill-outs (Stephens and Matson, 1993; El-Baz and Makharita, 1994; El-Gamily, 2007). The desert ecosystem was severely damaged by the war: the rate of sand dune movement increased while in addition, new sand sheets and sand dunes were formed in several areas where there had been no sheets or dunes previously (Misak et al. , 2002; Misak, Al-Ajmi and Al-Enezi, 2009). The building of many fortifications exposed huge amounts of fine particles to wind erosion Off-site impacts included an increase in the rates of sand transport and dust fallout (Misak, Al-Ajmi and Al-Enezi, 2009). The damage remains years afterwards below the surface. Status of the World’s Soil Resources | Main Report Drivers of global soil change 95 95

138 5.6 | Climate change The IPCC Fifth Assessment Report reveals that the globally-averaged combined land and ocean surface temperature data show a linear trend of global warming due to increases in anthropogenic emissions of greenhouse gases of 0.85°C (90 percent uncertainty intervals of 0.65 to 1.06°C). Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems (IPCC, 2014a). Climate change will have significant impacts on soil resources and food production in both irrigated and rainfed agriculture across the globe. Changes in water availability due to changes in the quantity and pattern of precipitation will be a critical factor (Turral, Burke and Faurès, 2011). Also, higher temperatures, particularly in arid conditions, entail a higher evaporative demand. Where there is sufficient soil moisture, for example in irrigated areas, this could lead to soil salinization if land or farm water management, or irrigation scheduling or drainage are inadequate. The amount of water stored in the soil is fundamentally important to agriculture and is an influence on the rate of actual evaporation, groundwater recharge, and generation of runoff. Soil moisture contents directly simulated by global climate models give an indication of possible directions of climate model, Gregory, Mitchell and Brady (1997) show change (IPCC, 2014b). For example, using the HadCM 2 that a rise in greenhouse gas concentrations is associated with reduced soil moisture in Northern Hemisphere mid-latitude summers. This results from higher winter and spring evaporation caused by higher temperatures and reduced snow cover, and from lower rainfall inputs during summer. The local effects of climate change on soil moisture, however, will vary not only with the degree of climate change but also with soil characteristics (IPCC, 2014b). The water-holding capacity of soil will affect possible changes in soil moisture deficits; the lower the capacity, the greater the sensitivity to climate change. Climate change also may affect soil characteristics, perhaps through changes in waterlogging or cracking, which in turn may affect soil moisture storage properties. Infiltration capacity and water-holding capacity of many soils are influenced by the frequency and intensity of freezing. Boix-Fayos et al. (1998), for example, show that infiltration and water-holding capacity of soils on limestone are greater with increased frost activity. From this, they infer that increased temperatures could lead to increased surface or shallow runoff. Komescu, Erkan and Oz (1998) assess the implications of climate change for soil moisture availability in southeast Turkey, finding substantial reductions in availability during summer. The probable effects on soil characteristics of a gradual eustatic rise in sea-level will vary from place to place depending on a number of local and external factors, and interactions between them (Brammer and Brinkman, 1990). In principle, a rising sea level would tend to erode and move back existing coastlines. In coastal lowlands which are insufficiently defended by sediment supply or embankments, tidal flooding by saline water will tend to penetrate further inland than at present, extending the area of perennially or seasonally saline soils. Climate change such as uncharacteristic droughts or rainfall and flooding have detrimental influences on soil microorganisms, changing the natural growing conditions for a region (Gschwendtner, 2014). Soil formation is strongly dependent on environmental conditions of both the atmosphere and the lithosphere. Soil temperature is an important factor in this physical, chemical and biological process. Soil temperature is also an important parameter for plant growth. For example, excessive high temperature is harmful to roots and causes lesions of stems, while extreme low temperatures impede intake of nutrients. Extreme low and high soil temperatures also influence the soil microbial population and the rate of organic matter decomposition. Recent studies have shown that soil temperature is one of the main climate factors emission. High soil temperatures accelerate soil respiration and thus increase CO emission that influence CO 2 2 Status of the World’s Soil Resources | Main Report Drivers of global soil change 96 96

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140 FAO . 2011b. . ESA Working Paper No. 11- 02, Agricultural Economics Division, The Role of women in Agriculture Food and Agricultural Organization of the United Nations. Rome, FAO. 48 pp FAO. Policy on Gender Equality: Attaining Food Security Goals in Agriculture and Rural Development. 2013. FAO Rome, FAO Gerland, P., Raftery, A.E. (co-first authors); Ševčíková, H., Li, N., Gu, D., Spoorenberg, T., Alkema, L., 2014. World Population Fosdick, B.K., Chunn, J.L., Lalic, N., Bay, G., Buettner, T., Heilig, G.K. & Wilmoth, J. Science, 346: 234-237 Stabilization Unlikely This Century. Ghebru, H.H. & Holden, S.T . 2012. Reverse share-tenancy and marshallian inefficiency: bargaining power of landowners and the sharecropper’s productivity . International Association of Agricultural Economists (IAAE) Triennial Conference, Foz do Iguaçu, Brazil Gregory, J.M., Mitchell, J.F.B. & Brady A.J. 1997. Summer drought in northern midlatitudes in a time- climate experiment. Journal of Climate, 10: 662–686 dependent CO 2 Gschwendtner, S., Tejedor, J., Bimueller, C., Dannenmann, M., Knabner, I.K. & Schloter M. 2014. Climate change induces shifts in abundance and activity pattern of bacteria and archaea catalysing major transformation steps in nitrogen turnover in a soil from a mid-European beech forest. PLoS ONE, 9(12): e 114278. Holdinghausen, H. 2015. Big Business: Fighting back against foreign acquisitions. In Heinrich Böll Foundation, ed. Soil Atlas 2015- Facts and Figures about earth, land and fields . pp. 42-43. Institute for Advanced Sustainability Studies (IASS). IAASTD. 2009. Agriculture at as crossroad. International assessment of agricultural knowledge, science and Global Report. Washington, DC, Island Press. technology for development. Bosnia Herzegovina Landmine Monitor Report 2002. International Campaign to Ban Landmines. ICBL. 2002. IMF. Food and Fuel Prices, Recent Developments, Macroeconomic Impact and Policy responses. Washington, 2008. DC, International Monetary Fund. IPCC . 2014a. Climate Change 2014: Synthesis Report . Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Switzerland, Geneva, IPCC. 151 pp IPCC . 2014b. Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. UK, Cambridge, Cambridge University Press & USA, New York. 1132 pp. Jones, A., Breuning-Madsen, H., Brossard, M., Dampha, A., Deckers, J., Dewitte, O., Gallali, T., Hallett, S., Jones, R., Kilasara, M., Le Roux, P., Micheli, E., Montanarella, L., Spaargaren, O., Thiombiano, L., Van Ranst, E., Yemefack, M. & Zougmore, R . 2013. Soil Atlas of Africa. Luxembourg, European Commission, Publications Office of the European Union. 176 pp Kobayashi, A . (ed.) 2013. Geographies of Peace and Armed Conflict. Routledge. 248 pp Komescu, A.U., Erkan, A. & Oz, S . 1998. Possible impacts of climate change on soil moisture availability in the Southeast Anatolia Development Project Region (GAP): an analysis from an agricultural drought perspective. Climatic Change, 40: 519–545 Land Matrix Newsletter . Land Matrix Newsletter. October 2014. (Also available at https://www.landmatrix. org ) Laurance, W.F., Sayer, J. & Cassman, K . 2013. Agricultural expansion and its impacts on tropical nature. Trends in Ecology & Evolution , S 0169-5347(13): 00292-9. Laurance, W.F., Sayer, J. & Cassman, K.G . 2014. Agricultural expansion and its impact on tropical nature. Trends in Ecol. Evol ., 29: 107-116 1992. Simulation of soil temperature in crops. Agricultural and Forest Luo, Y., Loomis, R.S. & Hsiao, T.C. 61(1): 23-38 Meteorology, Status of the World’s Soil Resources | Main Report Drivers of global soil change 98 98

141 MA. 2005. . A report of the Millennium Ecosystem Assessment. Ecosystems and Human Well-being: Synthesis Washington, DC, Island Press Misak, R., Al-Ajmi, D. & Al-Enezi, A. 2009. War-Induced Soil Degradation, Depletion, and Destruction (The Case of Ground Fortifications in the Terrestrial Environment of Kuwait). In T.A., Kassim, & D., Barceló, eds. Environmental Consequences of War and Aftermath pp. 125-139. Springer Berlin Heidelberg . 2002. Soil degradation in Kabd area, southwestern Misak, R.F., Al-Awadhi, J.M., Omar, S.A. & Shahid, S.A Kuwait City. 13(5): 403-415 Land degradation & development, Mitchell, S.K. 2004. Death, disability, displaced persons and development. The case of landmines in Bosnia and Herzegovina. World Development, 32(12): 2105-2120 Nolte, K. & Ostermeier, M. 2015. Land Investments: A new type of territorial expansion. In Heinrich Böll Foundation, ed. Soil Atlas 2015- pp. 38-39. Institute for Advanced Facts and Figures about earth, land and fields. Sustainability Studies (IASS). OECD/FAO. 2011. OECD-FAO Agricultural Outlook 2011-2020. OECD Publishing & FAO. Owona, J.C. 2008. Land degradation and internally displaced person’s camps in Pader District—Northern Uganda. Pader Pader District Local Government. (Also available at http://www.unulrt.is/static/fellows/document/joel.pdf Pinstrup-Andersen, P. & Watson II, D.D. 2011. Food Policy for Developing Countries: The Role of Government in Global, National, and Local Food Systems . Cornell University Press. Rulli, M.C., Saviori, A. & D’Odorico, P. 2013. Global land and water grabbing, Proc. Natl. Acad. Sci., 110(3): 892-897 Sengupta, K . 1997. Limited liability, moral hazard and share tenancy. Journal of Development Economics, 52: 393-407 Shames, S . 2013. How can small-scale farmers benefit from carbon markets? CCAFS Policy Brief no. 8. Copenhagen, Denmark, CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS). . 2015. Soil Atlas: Facts and Figures about earth, land and fields. Berlin, Institute for Advanced Soil Atlas Sustainability Studies,Heinrich-Böll-Stiftung Stephens, G. & Matson, M. 1993. Monitoring the Persian Gulf War with NOAA AVHRR data. International Journal of Remote Sensing, 14 (7): 1423-2 Turral, H., Burke, J. & Faurès, J.-M. Climate change, water and food security. FAO Water Report 36, Rome, 2011. FAO UNEP. 2007. Global Environmental Outlook, GEO 4. Nairobi & New York, UNEP. UNEP . 2012. Global Environmental Outlook: Fifth Edition. Nairobi & New York, UNEP. United Nations. 2014. World Urbanization Prospects: The 2014 Revision, Highlights. Department of Economic and Social Affairs, Population Division, ST/ESA/SER.A.352 World Bank/FAO/IFAD Gender in Agriculture Sourcebook. . 2009. Washington, DC, World Bank. Status of the World’s Soil Resources | Main Report Drivers of global soil change 99 99

142 6 | Global soil status, processes and trends 6.1 | Global status, processes and trends in soil erosion 6.1.1 | Processes Soil erosion is broadly defined as the accelerated removal of topsoil from the land surface through water, wind or tillage. Water erosion on agricultural land occurs mainly when overland flow entrains soil particles detached by drop impact or runoff, often leading to clearly defined channels such as rills or gullies. Wind erosion occurs when dry, loose, bare soil is subjected to strong winds. Wind erosion is common in semi-arid areas where strong winds can easily mobilize soil particles, especially during dry spells. This dynamic physical aeolian process includes the detachment of particles from the soil, transport for varying distances depending on site, particle and wind characteristics, and subsequent deposition in a new location, causing onsite and offsite effects. During wind erosion events, larger particles creep along the ground or saltate (bounce) across et al. , 2007). Finer particles (< the surface until they are deposited relatively close to field boundaries (Hagen 80 μm) can travel great distances, with the finest particles entering global circulation (Shao, 2000). Tillage erosion is the direct down-slope movement of soil by tillage implements where particles only redistribute within a field. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 100 100

143 6.1.2 | Status of Soil Erosion Over the last decade, the figures published for water erosion range over an order of magnitude of ca. 20 Gt -1 -1 to over 200 Gt yr . While this huge variation may at first seem to suggest that our estimates of (gigaton) yr -1 are global soil erosion are very uncertain, a more detailed analysis shows that estimates exceeding ca. 50 Gt yr not realistic. In most cases, excessively high estimates can be traced back to conceptually flawed approaches and/or inappropriate model applications. Considering only those estimates that are not manifestly affected -1 , while tillage erosion by such problems, the most likely range of global soil erosion by water is 20–30 Gt yr -1 . may amount to ca. 5 Gt yr Total erosion rates for wind erosion are highly uncertain. Estimates of the total amount of dust that is yearly mobilized on land place an upper limit on dust mobilization by wind erosion on arable land at ca. 2 -1 . However, wind not only mobilizes dust but also coarser soil particles (sand), implying much higher Gt yr total wind erosion rates. A large number of studies have made global estimates of wind erosion and dust transport. Approximately 430 million ha of drylands, which comprise 40 percent of the Earth’s surface (Ravi et al. , 2011), are susceptible to wind erosion (Middleton and Thomas, 1997). In a survey of global estimates of present-climate dust emissions, Shao et al. (2011) described 13 studies that estimated global dust emissions in -1 . Ginoux et al. (2012). The studies used global-scale high-resolution satellite a range from 500 to ~ 3320 Tg yr imagery to study dust sources. They found that natural dust sources do account for about 75 percent of dust emissions and the remaining 25 percent of emissions were attributed to anthropogenic sources. The fraction of dust sources was highly variable. For example, although North Africa accounted for about 55 percent of the global dust emissions, only 8 percent originated from anthropogenic sources. In contrast, anthropogenic dust et al. , 2012). sources contributed 75 percent of the dust emissions in Australia (Ginoux Translating these global estimates into accurate local soil erosion rates is not straightforward as soil erosion is highly variable, both in time and in space. However, typical soil erosion rates by water can be defined for representative agro-ecological conditions. Hilly croplands under conventional agriculture and orchards -1 without additional soil cover in temperate climate zones are subject to erosion rates up to 10-20 tonnes ha -1 -1 -1 , while average rates are often < 10 tonnes ha yr . Values during high-intensity rainfall events may reach yr -1 and lead to muddy flooding in downstream areas. Erosion rates on hilly croplands in tropical 100 tonnes ha -1 -1 -1 00 tonnes ha yr . Average rates, however, are lower and and subtropical areas may reach values up to 50 -1 -1 yr . These high rates are due to the combination of an erosive climate (high intensity often 10-20 tonnes ha rainfall) and slope gradients which are generally steeper than those on cultivated land in the temperate zones. The incidence of erosion on steep slopes is due not only to specific topographic conditions, but also to the combination of a high population pressure with low-intensity agriculture, leading to the cultivation of marginal steeplands. Rangelands and pasturelands in hilly tropical and sub-tropical areas may suffer erosion rates similar to those of tropical croplands. Due to the lack of field boundaries, which often act as barriers for sediment and runoff and promote infiltration, these rangelands may also be particularly vulnerable to gully formation. This may not affect topsoil so much but may make land inaccessible and hence unusable. Rangelands and pasturelands in temperate areas are characterized by erosion rates which are generally much lower and -1 -1 yr . These rangelands are less intensively used and better managed than are most often below 1 tonnes ha (sub-) tropical rangelands. It is possible to identify the areas in the world where soil erosion by water is problematic based on a relatively simple modelling approach combining information on soil type, land use, topography and climate , 2007). Soil erosion by water is problematic in much of the et al. (Doetterl, Van Oost and Six, 2012; Van Oost hilly areas that are used as croplands on all continents, even where there have been significant conservation efforts as in the Mid-West of United States. Cropland in Europe is characterized by somewhat lower, yet still very significant soil erosion rates (Figure 6.1). Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 101 101

144 Prepared by K. Van Oost -1 -1 y ) mainly occur on cropland in tropical areas. Figure 6.1 Spatial variation of soil erosion by water. High rates (>ca. 20 t ha The map gives an indication of current erosion rates and does not assess the degradation status of the soils. Van Oost et al., 2007 using a quantile classification. The map is derived from The redistribution of soil within fields due to tillage erosion rates may lead to (very) high erosion rates -1 -1 yr ; and to deposition rates in hollows and at down slope on convexities (knolls) exceeding 30 tonnes ha -1 -1 . These rates are not directly comparable to wind or water erosion yr field borders exceeding 100 tonnes ha rates, as soil eroded by tillage will not leave the field. However, tillage erosion may significantly reduce crop productivity on convexities and near upslope field or terrace borders. Evidence of past erosion is extensive. This is demonstrated by wind-blown sands of sandstone bedrock, extensive loess accumulations of silt-sized aeolian sediments, and other formerly aeolian-affected landscapes. Large areas of sand seas, dune fields and other aeolian features and observations of activity provide further evidence of past wind erosion (Figure 6.2). -1 -1 yr on average over all cropland of the United USDA estimates place wind erosion rates at ca. 2.5 tonnes ha -1 -1 . There are very few quantitative yr States while the average erosion rate for pastureland is ca. 0.1 tonnes ha assessments of wind erosion rates on arable land outside of the United States. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 102 102

145 Figure 6.2 Location of active and fixed aeolian deposits. Source: Thomas and Wiggs, 2008. 6.1.3 | Soil erosion versus soil formation The accelerated loss of topsoil through erosion from agricultural land was recognized as an important threat to the world’s soil resource many decades ago. Furthermore, it was feared that soil was, in many areas, eroding much faster than that it could be replaced through soil formation processes. More recent studies have confirmed that these early observations were not just perceptions. Estimated rates of soil erosion of arable or -1 000 times higher than natural background erosion rates. intensively grazed lands have been found to be 100 These erosion rates are also much higher than known soil formation rates which are typically well below 1 -1 -1 -1 -1 yr with median values of ca. 0.15 tonnes ha yr . The large difference between erosion rates under tonnes ha conventional agriculture and soil formation rates implies that we are essentially mining the soil and that we should consider the resource as non-renewable. The imbalance between erosion rates under conventional agriculture and the rate of soil formation implies that conventional agriculture on hilly land is not sustainable because the soil resource is mined and will ultimately become depleted. This has most likely already happened in many areas around the Mediterranean Sea and in tropical mountain regions. So-called soil loss tolerance levels may help to set objectives for short- term action. However, long-term sustainability requires that soil erosion rates on agricultural land are reduced to near-zero levels. Figure 6.3 Soil relict in the Jadan basin, Ecuador. Photo by G. Govers In this area overgrazing led to excessive erosion and the soil has been completely stripped from most of the landscape in less than 200 years, exposing the highly weathered bedrock below. The person is standing on a small patch of the B-horizon of the original soil that has been preserved. Picture credit: Gerard Govers. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 103 103

146 6.1. 4 | Soil erodibility Soil erodibility refers to the degree or intensity of a soil’s state or susceptibility to being eroded (SSSA, 2008). A critical review of research into the factors controlling susceptibility of soils to wind erosion (‘soil wind erodibility’) has been provided by Webb and Strong (2011). Factors controlling soil wind erodibility include physical, chemical and biological characteristics of the soil, including texture, aggregation, stability, crusting, the amount of loose erodible sediment available, soil water content, roughness due to surface features (including tillage marks and vegetation) etc. The factors controlling soil wind erodibility differ somewhat among land uses and management approaches. For example, the factors controlling erodibility on rangeland differ from the factors controlling erodibility on farmland. In cropped soils at the field scale, disturbance due to tillage modifies the soil surface roughness, the amount and distribution of surface cover, soil water content aggregation and other properties, all of which affect soil erodibility for short periods of time (Zobeck, 1991; Zobeck and Van Pelt, 2011). In arid and semiarid rangeland ecosystems, wind erosion depends on vegetative cover and patchiness (Okin et al. , 2009) and on surface soil texture and crusting, characteristics that change more slowly unless disturbed. Not only do the factors controlling erosion by wind differ among land uses, but differences occur in their spatial and temporal variability. Natural and anthropogenic disturbances such as grazing, fire and other activities alter the surface and vegetation on rangeland while crop management practices often control erodibility of farmland. Webb and Strong (2011) described the dynamics of soil erodibility as a continuum that responds to changes in climate variability and disturbance. Factors such as rain and crusting on some soils may initially produce low erodibility that will subsequently increase with disturbance and drying. The exact timing and variability of changes in erodibility will vary with inherent soil physical properties such as soil texture. | Soil erosion and agriculture 6.1.5 Soil erosion has direct, negative effects for global agriculture. Soil erosion by water induces annual fluxes of 23-42 Mt (megaton) N and 14.6-26.4 Mt P off agricultural land. These fluxes may be compared to annual fertilizer application rates, which are ca. 112 Tg for N and ca. 18 Tg of P. These nutrient losses need to be replaced through fertilization at a significant economic cost. Using a United States farm price of ca. US$ 1.45 per kg of N -1 40 billion for and ca. US$ 5.26 per kg of P implies an annual economic cost of US$ 33-60 billion for N and US$ 77 1 . It is therefore clear that compensation for erosion-induced nutrient losses requires a massive investment in P fertilizer use. In poor regions such as sub-Saharan Africa, the economic resources to achieve compensations for nutrient losses do not exist. As a consequence, the removal of nutrients by erosion from agricultural fields is much higher than the amount of fertilizer applied. The detrimental removal of soil and nutrients from upland fields may be partly offset through the deposition of the eroded soil and nutrients in depositional areas. While this is true, such gains should not be exaggerated: the deposition of sediments and nutrients in large floodplains is not directly coupled to actual agricultural soil erosion, as in most cases sediments are provided by other sources (natural erosion, landslides) and the residence time of such sediments in large river systems is several thousands of years. In other words: the sediments that are currently being deposited in the Nile valley are not coming from the soils that are currently being eroded in Ethiopia. On a smaller scale, the deposition of eroded sediment may indeed locally increase local crop productivity, but such effects may be overshadowed by other factors, such as water availability. Soil erosion does not induce an important carbon loss from the soil to the atmosphere: erosion mostly induces a transfer of carbon from eroding locations to depositional locations. Net losses are limited as the carbon lost at eroding locations is partially replaced through dynamic replacement whereas the soil carbon that is deposited in colluvial and alluvial settings may be stored there for several centuries. 1 www.ers.usda.gov/data-products/fertilizer-use-and-price.aspx#26727 Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 104 104

147 High soil erosion rates will also have significant negative effects over longer time spans: the loss of topsoil will result in a reduction in the soil’s capacity to provide rooting space and, more importantly, in the capacity to store water that can be released to plants. This may reduce soil productivity. However, these changes occur relatively slowly: the reduction in soil water holding capacity and and/or root space accommodation results in yield declines of ca. 4 percent per 0.1m of soil lost. Except for areas where erosion rates are very high (e.g. -1 -1 -1 yr ) this means that effects of erosion on crop productivity will or ca. 4 mm yr exceeding 50 tonnes ha be relatively small on the decennial or centennial time scale, provided that nutrient losses due to erosion are compensated. Over longer time spans, however, the effect of these losses becomes very significant. On the positive side, transported dust affects distant ecosystems, increasing plant productivity by providing nutrients not provided by the parent soil, as seen in Hawaii (Chadwick et al. , 1999) and the Amazon (Mahowald et al. , 2008). Transported dust can also provide chemical constituents that affect soil development, as seen in , 2010, 2012). et al. the development of terra rossa soils in Bermuda and Spain (Muhs 6.1.6 | Soil erosion and the environment The direct negative effects of soil erosion are not limited to agriculture. The sediment produced by erosion also pollutes water streams with sediment and nutrients, thereby reducing water quality. In addition, sediment contributes to siltation in reservoirs and lakes. However, not all sediments trapped in reservoirs originate from agricultural land. Other processes such as bank erosion, landslides and natural surface erosion which contribute to reservoir sedimentation are also very important and are often dominant at large scales. Wind erosion and dust transport have been studied for many years. For example, in 1646, Wendelin first described purple rain in Brussels that we now recognize as coloured dust transported to Europe from Africa (Wendelin, 1646 as cited in Stout, Warren and Gill, 2009). Charles Darwin studied dust that fell on the HMS Beagle in the 1830s and 1840s (Darwin, 1845, 1846) and the dust collected was found to contain viable microbes et al. even today (Gorbushina , 2007). Wind erosion can originate from natural landscapes and from landscapes affected by anthropogenic (human-related) activities (Figure 6.4). Aeolian processes impact soil development, mineralogy, soil physical and biogeochemical properties, and redistribution of soil nutrients, organic materials, and sequestered contaminants. Wind erosion also affects landscape evolution, plant productivity, human and animal health (Ravi et al. , 2011), atmospheric properties including effects on solar radiation and cloud attributes (Shao et al. , , 2011). The effects of wind erosion occur at the et al. , 2010; Ravi 2011), air quality, and other factors (Field et al. field, landscape, regional, and global scales. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 105 105

148 Photo by T.M. Zobeck Figure 6.4 Dust storm near Meadow, Texas, USA At the field and landscape scales, wind erosion winnows the finer and more chemically active portion of the soil which carries biogeochemicals, including plant nutrients, soil carbon and microbial products. In some cases, wind erosion processes modify the surface properties by causing increases in sand content while reducing the soil water holding capacity and plant productivity (Zobeck and Van Pelt, 2011). Although some of this eroded sediment is deposited relatively close to field boundaries, often much of it enters into suspended mode and may be transported high in the atmosphere to travel great distances. This long-range transport of dust produces effects at the global and regional scales Atmospheric dust produced by wind erosion profoundly influences the energy balance of the Earth system by carrying organic material, iron, phosphorus and other exchange (Shao nutrients to the oceans, affecting ocean productivity and subsequent ocean-atmosphere CO 2 et al. , 2011). 6.1.7 | Effects of hydrology and water Wind erodibility and subsequent erosion and dust emissions are affected by hydrology and water in several ways. Remote sensing studies of dust sources by Prospero et al. (2002) showed that many major dust sources originate from deep alluvial deposits formed by intermittent flooding during the Quaternary and Holocene. These sources, now in drylands, originated when water was more plentiful and produced an ample supply of wind-erodible sediment (Ginoux et al. , 2012). In many areas, particularly in areas with more limited erodible sediment supply, dust emissions increase after new inundations of ephemeral water supplies provide additional erodible sediment. However, many fluvial-related dust sources have also developed from the exposure, due to anthropogenic factors, of the bottoms of former lakes such as at Owens Lake in the United States (Reheis, , 2003). In these cases, usually water has been extracted 1997) and the Aral Sea Basin in Uzbekistan (Singer et al. from the lake for irrigation or human consumptive needs. This issue will be accentuated as increasing demand for water in dryland regions is met from reservoirs. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 106 106

149 Near-surface soil water content has long been recognized to have a significant effect on the threshold wind velocity needed for wind erosion (Akiba, 1933; Chepil, 1956). Soil water acts to bind particles together to resist the shearing force of wind on the particles. In addition, soil water affects vegetative growth, which also affects wind erosion. Research has shown a time-dependent change in the controlling factors for sediment emission and transport from soil water to wind speed (Wiggs, Baird and Atherton, 2004). The change of controlling factors was found to be very sensitive to the prevailing water conditions and, for the sandy soil tested, took place in a very short period of time. They found the soil water content where wind erosion commenced was between 4 and 6 percent (Wiggs, Baird and Atherton, 2004). However, the effect of soil water on wind erosion et al. of dry soils is also sensitive to changes in air relative humidity (Ravi , 2006). Recent work on atmospheric dust concentrations have confirmed this sensitivity, finding that dust concentration increased with relative humidity, reaching a maximum around 25 percent and thereafter decreased with relative humidity (Csavina et al. , 2014). Climate-induced changes in hydrology and water may produce profound changes in wind erosion and dust emissions as the soil erodibility is altered. 6.1.8 | Vegetation effects The effect of vegetation on wind erosion is complex. In native conditions, the wind influences patterns of vegetation and soils and these patterns, in turn, affect wind erosion at patch to landscape scales (Okin, Gillette and Herrick, 2006; Okin et al. , 2009; Munson, Belnap and Okin, 2011). In agricultural systems, the vegetation is manipulated by managers and its effects vary spatially and temporally from non-managed systems. The protective effects of vegetation are well known. A wide variety of methods and models has been devised to describe the protective effects of vegetation. In general, as vegetation height and cover increase, wind erosion of erodible land decreases. Vegetation affects wind erodibility by: (1) acting to extract momentum from the wind and thereby reducing the wind energy applied to the soil surface; (2) directly sheltering the soil surface from the wind by covering part of the surface and reducing the leeside wind velocity; and (3) trapping windborne particles, so reducing the horizontal and vertical flux of sediment (Okin, Gillette and Herrick, 2006). Trapping of sediment leads to redistribution of nutrients and modifies surface soil properties such as water infiltration rate and soil bulk density. Vegetation cover affects nutrient removal, which in turn affects plant productivity. A study of the effects of grass cover on wind erosion in a desert ecosystem found increased wind erosion removed 25 percent of the total soil organic carbon and nitrogen from the top 5 cm of soil after only three windy seasons (Li et al. , 2007). Studies of agricultural crops on severely eroded cropland found 40 percent reductions in cotton and kenaf yields and 58 percent reduction in grain yield in sorghum (Zobeck and Bilbro, 2001). The eroded areas in this study had statistically significantly less phosphorus than the adjacent non-eroded areas. Climatic changes that reduce the cover of vegetation in drylands will increase wind erosion and dust emissions, and likely result in increased soil degradation and reduced plant productivity. 6.1.9 | Alteration of nutrient and dust cycling Recognition of a dust cycle, along with other important cycles such as the energy, carbon and water cycles, has become an emerging core theme in Earth system science (Shao et al. , 2011). Dust cycles are dependent upon the soil and climate systems within which they operate. The dust cycle is a product, in part, of the soil system. As dust is transported globally, it interacts with other cycles by participating in a range of physical and biogeochemical processes. The dust carries important nutrients to otherwise sterile soils and so may improve productivity (Chadwick , 2008). Dust may also transport soil parent et al. et al. , 1999; Mahowald , 2012) and material (Reynolds et al. , 2006), trace metals (Van Pelt and Zobeck, 2007), soil biota (Gardner et al. toxic anthropogenics (Larney et al. , 1999) among ecosystems. Although the fact is not widely recognized, the global dust cycle is intimately tied to the global carbon cycle (Chappell , 2013). Wind and water erosion et al. both redistribute soil organic carbon within terrestrial, atmospheric and aquatic ecosystems. This carbon is selectively removed from the soil. This was recently demonstrated in an Australian study where the soil organic , 2012). Changing climate will et al. carbon in dust was from 1.7 to over seven times that of the source soil (Webb alter these cycles, producing complex and uncertain environmental effects. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 107 107

150 | Trends in soil erosion 6.1.10 While rates of soil erosion are still very high on extensive areas of cropland and rangeland, erosion rates have been significantly reduced in several areas of the world in recent decades. The best documented example is the reduction of erosion rates on cropland in the United States. Average water erosion rates on cropland were -1 -1 yr between 1982 and 2007, while wind erosion rates reduced from 8.9 to reduced from 10.8 to 7.4 tonnes ha -1 -1 over the same time span. Another example is the reduction of soil erosion in Brazil through yr 6.2 tonnes ha the application of no-tillage from ca. 1980 onwards. This is estimated to have led to a reduction of erosion rates by 70-90 percent over large parts of Brazilian cropland. Studies have shown that erosion rates can be greatly reduced in nearly every situation through the application of appropriate management techniques and structural measures such as terrace and waterway construction (see, for example, Pansak et al. , 2008). However, in many areas of the world, adoption of soil conservation measures is slow. While the reasons for this are diverse, a key point is that the adoption of soil conservation measures is generally not directly beneficial to farmers. This is as true in intensive mechanized systems in the West as it is for smallholder farming in the developing world. This is not surprising: the implementation of conservation measures does not, as such, directly increase yields or efficiencies while the detrimental effects of erosion on the soil capital only become visible over time scales that range from decades to centuries. Hence, farmers do not have a direct incentive to adopt soil conservation measures. In some cases, this problem may be overcome through financial incentives or by regulation. It is clear, however, that this is not always possible. We need, therefore, to rethink our vision on soil conservation. Essentially, further adoption of soil conservation measures will not in the first place depend on refinement or optimization of technologies. Technology already exists to reduce erosion to acceptable levels under most circumstances. What is critically important is to work out how to incorporate soil conservation in an agricultural system that, as a whole, increases the net returns of farmers. In developing approaches that build in incentives to soil conservation, it is vital to account for local conditions, including the extent to which local markets can provide incentives to sustainable agriculture. The potential for agricultural intensification is key here. In many areas around the world, crop yields are low and more land is cultivated than is strictly necessary. As a result, large tracts of steep, marginal land are at present used for agriculture without the implementation of proper soil conservation technology, with the result that these areas are subject to high erosion rates. Intensification of production on higher potential land is an option. This not only reduces extension into marginal, highly erodible areas but may also benefit biodiversity and overall carbon storage at the landscape scale. Erosion can also be checked by forestation. In many areas there is now a net gain of forest area. This reforestation, which is largely of marginal land, is related to four main factors: agricultural intensification; diminishing need for firewood; an increase in exchange and trade making it possible to grow products in the most suitable areas; and an increased public awareness of the problems caused by deforestation. Development of conservation policies should consider these tendencies and stimulate them wherever possible. 6.1.11 | Conclusions Soil erosion has been recognized as a main problem threatening the sustainability of agriculture for a long time and the magnitude of the problem can now be correctly quantified. The technology to reduce erosion now exists and, over the last decades, significant efforts have been to reduce erosion rates. These efforts have been partially successful. However, erosion rates are still high on much of the agricultural land of the globe, and this is related to the lack of economic incentives for today’s farmers to conserve the soil resource for future generations. Tackling this problem requires the soil erosion problem to be reframed. Solutions need to be embedded in policies and programs that support the development of more sustainable agricultural systems. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 108 108

151 6.2 | Global soil organic carbon status and trends 6.2.1 | Introduction An evaluation of the various functions of carbon (C) stored in the soil and its role in the global C-cycle require knowledge of the amount and geographic distribution of C stored in the soil. The functions of soil C are determined by the chemical and physical properties of the components that contain C. Chemical properties of soil C determine properties such as soil pH, nutrient storage and availability and regulating functions affecting the water cycle. Soil physical properties related to functions of C are: soil structure, particle agglomeration, and stability. These properties in turn influence water infiltration rates and resistance to water and wind erosion. Soil C is separated into: (i) inorganic chemical substances (soil inorganic carbon: SIC), mainly carbonates; and (ii) C as part of organic compounds (soil organic carbon: SOC). The amount of SIC in the first one meter of soil was estimated at 695 - 748 Pg carbonate C (Batjes, 1996). The C stored as SOC is about twice the C stored as SIC (1 502 Pg C; Jobbágy and Jackson, 2000). Carbonates are less susceptible to react to anthropogenic changes to the environment than are organic compounds. In addition, the amount and type of organic C compounds are interdependent with environmental conditions, such as land use and management practices. These two characteristics have led to the definition of the persistence of SOC as an ecosystem property (Schmidt et al. , 2011). Thus, assessments of soil C stocks and their spatial distribution often concentrate on SOC alone. Although SOC mainly originates from plant material there is no simple correlation between the amount of C stored in the above-ground plant material and the SOC stocks (Amundson, 2001; Smith, 2012). In fact, the processes involved in decomposing organic material and their mineralization are complex and details are not yet fully understood (Schmidt et al. , 2011). However, the effects on SOC of anthropogenic activities of land use change and management practices are known. Given the large amount of C stored in soils and the possibility of influencing this amount through land management to act as a source or sink for atmospheric C, strategies for maintaining SOC have been devised. These strategies follow two main approaches: (i) seeking to enhance existing SOC by increasing the amount of biomass of the terrestrial biosphere; (ii) seeking to decrease the loss of SOC by reducing the respiration rate (Smith et al. , 2008). To provide a quantitative appraisal of the possible gains or losses in SOC from measures taken either to increase the input of organic material or decrease losses of soil organic matter (SOM), an assessment of the current situation is needed. Studies on historic developments in SOC stocks concentrate on the effect of changes in land use. These changes mainly concern the transformation of land from a natural state to an agricultural ecosystem, which in fact now covers more than one third of the global terrestrial area. For the conversion of forest to cropland, losses in SOC stocks of 25-30 percent were observed for temperate regions, with higher losses recorded for the tropics. Estimates of future trends in SOC stocks concentrate on the effect of changing climatic conditions on rates of organic matter accumulation and decomposition. As options for changes in land use are relatively limited, approaches to mitigation of climate change effects have focussed largely on management practices. 6.2.2 | Estimates of global soil organic carbon stocks It is important to know past, current and likely future SOC stocks because of their importance to climate change and food security. When assessing the amount of C stored in the soil, studies often concentrate on C contained in dead and decomposed organic material or in organic matter located within the soil profile to a given depth and for a specific area. The mass of C stored in the SOM is also termed SOC stocks. SOC stocks are computed as a function of organic C-content, bulk density, depth and the amount of soil remaining after removing the volume taken up by coarse fragments in a unit of volume. Any of these factors can introduce uncertainties to the estimates. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 109 109

152 Global estimates of SOC stocks have been published for many decades. One of the earliest estimates was published in 1951 (Rubey, 1951), indicating a global SOC stock of 710 Pg C. This estimate remained current for 25 years until the FAO-UNESCO soil map became available. Analysis of the map data led to a much higher estimate of 3 000 Pg C in the soil (Bohn, 1976). Several studies of global SOC stock followed with varying estimates (Bohn, 1982: 2 200 Pg organic C; Post et al. , 1982: 1 395 Pg organic C) An estimate of 1 576 Pg of SOC to 1 m depth was put forward by Eswaran, Van Den Berg and Reich, 1993. Global SOC stocks to 1 m depth of 1 462 – 1 548 Pg of SOC were estimated by Batjes, 1996. An estimate of 1 502 Pg organic C for the first 1 m of soil is often used ( Jobbágy and Jackson, 2000; Batjes, 2002). The estimate of 1 500 Pg of SOC for the top 1 m of soil was adopted by the IPCC (IPCC, 2000). Current global estimates, derived from the Harmonized World Soil Database (HWSD; FAO/IIASA/ISRIC/ISS-CAS/JRC, 2009), suggest that approximately 1 417 Pg of SOC are stored in the first meter of soil and about 716 Pg organic C in the top 30 cm (Hiederer and Köchy, 2011). Fewer estimates of global SOC stock estimates are available for a depth below 1 m. Global SOC stocks to a depth of 3 m are estimated at 2 344 Pg of SOC ( Jobbágy and Jackson, 2000) or 3 000 Pg of SOC ( Jansson , et al. 2010). Recent estimates of SOC in Cryosols may further increase the estimates of global SOC stocks (Tarnocai et al. , 2009). In a comparison of 27 studies on global SOC stock published between 1951 and 2011, the estimates published were found to range from 504 to 3 000 Pg of SOC (Scharlemann et al. , 2014). The median of all published estimates is 1 460 Pg of SOC to 1 m depth. Spatially explicit estimates were found to span over 1 965 Pg of SOC. Large uncertainties over SOC stocks concern Histosols since soil data are often limited to a depth of 1 m , 2009) et al. (Eswaran, Van Den Berg and Reich, 1993). Particularly affected are the soils of the Arctic (Tarnocai and peatlands in South Asia (Couwenberg, Dommain and Joosten, 2010). The range in the estimates of global SOC stocks correspond to or exceed the amount of C held in the atmosphere, which was estimated at 720 Pg , 2013). C (Falkowski et al. , 2000) and at 820 Pg C for present conditions (Mackey et al. With respect to the uncertainty in the estimates of global SOC stocks, various approximations are observed. For an estimated SOC stock of 1 395 Pg of SOC Post et al. (1982) assume a standard deviation of ± 200 Pg organic C, provided that the SOC density data are the only source of uncertainty. For the estimate of 1 502 Pg organic C to 1 m depth, Jobbágy and Jackson (2000) suggested an error of the mean of ± 320 Pg C at 1 standard deviation, provided that the SOC content data are the only source of uncertainty. The different assumptions on the causes of uncertainty between the studies (SOC density or content) are quite significant. Based on the HWSD, Todd-Brown et al. (2013) provide an interval of estimated global SOC stock of 890 to 1 660 Pg of SOC to a depth of 1 m with a 95 percent confidence level. This range corresponds to approximately 385 Pg SOC at 2 standard deviations from the mean. With a small number of large-scale data sets available, the variations in SOC stock estimates may be attributed to the analysis method applied as much as to the data used. It also implies that various global SOC stock estimates are not independent and that the variability in the estimates could not necessarily be reduced by an increase in the number in such estimates. One problem common to all large databases is that the properties were assessed decades ago and stretched over long periods. For example, the DSMW or the ESDB, of which components are included in the HWSD, originated from data collected during the 1950s and 1960s. With the dependence of SOC on climatic conditions and anthropogenic activities, SOC stocks established decades apart are likely to represent significantly different levels, notably in areas where changes in land use or management occurred, such as conversion of natural grassland and forest to agricultural land or urban areas. In extreme cases draining peatlands can lead to a loss of organic material to the degree that the soil no longer qualifies as peat because the organic C content decreases below 12 percent content and the thickness of the remaining organic layer is less than 40 cm (FAO/ ISRIC/ISSS, 1998). An example of this change is given by the agricultural areas in north-eastern Netherlands, Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 110 110

153 where the drainage in the 1960’s of areas previously classified as peatland caused the SOC content to fall to 7.5 et al. , 2013). Without further adjustments of SOC stock estimates to take account of local percent (Panagos changes in the factors that influence SOC, no clear timestamp can be attached to the global estimates. This lack of a clear timestamp of SOC stocks is of consequence when estimating temporal changes in SOC stocks. Estimates of changes in SOC stock therefore concentrate on modelling variations in SOC from changes in land use and cover. 6.2.3 | Spatial distribution of SOC Different methods of combining point data from soil profiles with soil spatial layers and ancillary ecological data can be applied to derive spatial estimates of SOC stocks (Kern, 1994). SOC density and stock estimates et al. from soil profile data were combined with spatial data of major ecosystems by Post (1982). The total SOC stocks for all life zones to a depth of 1 m was 1 395 Pg of SOC. A combination of soil profile data with ancillary information on climate, vegetation and land use was used by Jobbágy and Jackson (2000) to estimate SOC stocks in 11 biomes. The estimates for the biomes were further divided into increments of 1 m soil depth and of 20 cm for the first meter. The distribution of SOC stocks by ecological regions has also been presented, for et al. (2010) used the SOC stock example by Amundson (2001), who used life zones as the study unit. Eglin estimates to a depth of 3 m from Jobbágy and Jackson (2000) and modified SOC stocks in permafrost areas (Tarnocai , 2009). These SOC stock estimates were combined with estimates provided by the IPCC (IPCC, et al. 2000) of C in vegetation to derive estimates of C in soil and biomass for 10 biomes, with an explicit class for peatlands. A step towards adding a temporal dimension to spatial SOC stock estimates, assessing historical and future trends, was made possible by the availability of SOC models. Combining the models with historic land use and climate data has allowed estimation of SOC stocks with a timestamp and with regional variations et al. , 2010; Schmidt , 2011). (Eglin et al. et al. Carré (2010) produced estimates of SOC stocks and density using climate data, IPCC methodology and the Harmonized World Soil Database. The results by IPCC Climate Region are presented in Table 6.1. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 111 111

154 IPCC Climate Region HWSDa IPCC Tier 1 Topsoil Subsoil Soil Density 0-≤30 cm 30-≤100 cm 0-≤100 cm 0-≤30 cm 0-30 cm -1 Pg C Pg C Pg C* Mg C ha Pg C Tropical Wet 52.4 62.6 65.4 128.0 66.5 Tropical Moist 94.5 78.6 72.3 150.9 45.0 Tropical Dry 6 7. 3 69.0 136.2 22.0 9 9.9 Tropical Montane 49.8 29.6 26.5 5 6.1 40.3 Warm Temperate Moist 41.7 33.3 29.7 63.0 60.2 30.8 78.5 Warm Temperate Dry 42 .9 38.9 39.6 88.2 210.3 106.2 104.1 110.6 Cool Temperate Moist 42.7 5 6.9 52.2 50.0 102.2 Cool Temperate Dry 137.3 Boreal Moist 162.0 194.7 356.7 1 1 7. 6 68.1 84.0 Boreal Dry 30.3 32.0 3 7. 0 52.4 26.8 Polar Moist 40.4 21.7 30.6 8.0 Polar Dry 7. 2 4.3 12.3 40.5 52.1 699.3 1415.7 716.4 Total 750.3** Table 6.1 Distribution of Soil Organic Carbon Stocks and Density by IPCC Climate Region * Differences in topsoil and subsoil sum are due to data rounding ** Total includes 1.4 Pg C in undefined climate regions The table shows that according to the processed data from HWSD, most SOC (356.7 Pg C) is stored in the ‘Boreal Moist’ climatic region. The second largest stock is found in the ‘Cool Temperate Moist’ region (210.3 Pg -1 -1 , these climate regions also have the highest SOC densities. These and 88.2 Mg C ha C). With 117.6 Mg C ha et al. figures compare poorly with those presented by Post (1982). A major source for the deviation is the difference in the definition of the life zones as compared to the climatic regions, which lead to the delineation of different areas. Using the IPCC Tier 1 default values for organic C in mineral soils and retaining the stocks for organic soil gives global organic C stock in the upper 30 cm of soil of 750.3 Pg C. This estimate is 51 Pg C (7.3 percent) higher than the estimates derived from the HWSDa topsoil layer. When comparing the two spatial SOC stock estimates by IPCC climate region, the stocks within each region are broadly similar. A notable difference is for soils in the ‘Tropical Dry’ climate region. The IPCC Tier 1 SOC map gives 99.9 Pg C for this zone, compared to 67.3 Pg C found in the HWSDa. In the interpretation of the figure for SOC stocks of the IPCC Tier 1 Soil Organic Carbon layer, it should be considered that organic soils were only added to the mineral soil layer in places where this soil type is not found in association with mineral soils. Using all organic soil data is likely to increase the global SOC stocks. However, the Tier 1 default values are calculated over a constant depth of 30cm, although some soils are shallower, which in turn would reduce the stocks. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 112 112

155 6.2.4 | Spatial distribution of carbon in biomass A global map of C stored in biomass following the IPCC Tier 1 approach was produced by the European Commission Joint Research Centre (Carré at al., 2010; EU, 2004; Hiederer et al. , 2010). The C stocks are determined for above- and below-ground biomass and include dead organic matter for the relevant vegetation types. The default factors largely follow the IPCC specification, with specific attention given to agricultural areas. The underlying vegetation data are based on the GlobCover V 2.2 (ESA, 2011). Because the GlobCover data limits cropland to areas below 57º N in Europe the data were merged with the M 3-Cropland (Ramankutty et al. , 2008) and Crops (Monfreda, Ramankutty and Foley, 2008). In a comparison of the geographic distribution of IPCC vegetation classes between the GlobCover and the M 3 Cropland and Pasture data, some notable differences were identified (Hiederer et al. , 2010). Some of the differences were attributed to the dissimilar definition of the vegetation classes in the data sets, although others, such as the separation of shrub land from open forest or confusion between cropland and pastures, seem to be the result of the classification algorithm used or of sensor characteristics. The global biomass map thus generated by the Joint Research Centre ( JRC) estimates the storage of C in the above-ground and below-ground vegetation and dead organic matter to be 456 Pg C. The JRC estimates -1 Global Biomass Carbon Map for the are thus 44 Pg C (8.8 percent) lower than those of the ‘New IPCC Tier Year 2000’ (Ruesch and Gibbs, 2008). The difference is not evenly distributed between geographic regions. A comparison of carbon in C by climatic region is given in Figure 6.5. Figure 6.5 Distribution of carbon in biomass between ORNL-CDIAC Biomass and JRC Carbon Biomass Map The graph shows that the ORNL-CDIAC Biomass and the JRC Carbon Biomass map are mostly comparable, but the JRC map places relatively more C in the biomass in ‘Cool Temperate Moist’ (11.4 percent of the total C stock in biomass; 51.8 Pg C) and ‘Warm Temperate Moist’ (8.7 percent of the total C stock in biomass; 39.9 Pg C) climate regions at the expense of other regions. By contrast, the ORNL-CDIAC Biomass map locates only 5.7 percent of the total C stock in biomass (28.4 Pg C) in the ‘Cool Temperate Moist’ and 5.7 percent of the total C stock in biomass (28.7 Pg C) in the ‘Warm Temperate Moist’ climate region. For the total terrestrial pool of organic C, biomass is the more important pool only in the climate regions ‘Tropical Wet’ and ‘Tropical Moist’. For all other climatic regions, the soil stores more organic C than the biomass et al. (Scharleman , 2014). Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 113 113

156 6.2.5 | Distribution of terrestrial carbon pool by vegetation class Areas where SOC or biomass C dominate could be identified by computing the difference between the two layers. The resulting layer is presented in Figure 6.6. Figure 6.6 Prevalence of carbon in the topsoil or biomass The figure shows that, as a general propensity, soil dominates the terrestrial C pool in cooler climates while vegetation forms the dominant pool of terrestrial C in tropical regions. In an attempt to provide C stock estimates for broad land use activities, global GLC 2000 data layers were used. The GLC 2000 categories were re-classified according to the assignments for these classes given by Ruesch and Gibbs (2008). A difference in the assignment was applied to GLC 2000 classes 16 (Cultivated and Managed Areas) and 23 (Irrigated Agriculture). In the broad classification these areas were grouped with other areas mainly associated with an absence of soil or biomass (bare areas, glaciers, etc.). For the analysis Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 114 114

157 Terrestrial Soil Biomass Subsoil Topsoil Vegetation Classes C Stock Pg C Pg C percent Pg C percent Pg C percent Pg C 124.7 112.4 237.1 16.8 272.2 54.4 509.4 26.6 Broadleaf Forest 266.4 126.8 139.7 9.3 18.8 46.4 Evergreen Forest 312.9 16.3 Mixed Forest 4 7. 8 88.3 6.2 21.8 4.4 110.1 5.7 40.5 Burnt Forest and Natural Forest 3 .9 27.4 36.2 63.6 4.5 10.9 2.2 74.5 Mosaic Forest/Cropland 74.6 5.6 23.2 23.4 46.6 3.3 28.0 3 .9 Mosaic Forest 1081.5 56.4 75.9 342.6 359.5 702.0 49.6 379.3 Shrub Cover 102.4 191.6 13.5 51.8 10.4 243.4 12.7 89.2 Grasslands 60.5 52.1 112.6 8.0 18.0 3.6 130.5 6.8 Sparse Grassland 134.5 and Grassland 7. 7 69.0 65.5 12.7 9.5 2.5 147.2 Mosaic 218.7 220.0 438.7 31.0 82.5 16.5 5 21.1 27.2 Grassland Agriculture and 80.8 79.4 160.2 11.3 26.7 5.3 186.9 9.8 managed areas 2.3 6.6 126.2 Other Classes 5 7. 3 57.4 114.7 8 .1 11.4 Figure 6.7 Proportion of carbon in broad vegetation classes for soil and biomass carbon pool Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 115 115

158 of the distribution of organic C, a separate class of ‘Agriculture and Managed Areas’ was created by merging 2000 classes 16 and 23. For each of the broad vegetation classes the organic C stock was extracted by the GLC pool. The results are presented in Table 6.2. The single largest stock for terrestrial C is attributed to areas with broadleaf forest (509.4 Pg C). This forest type contains approximately one quarter of all terrestrial organic C in either the soil or the biomass. The proportions of the C stored in the soil and biomass stocks by broad vegetation class is graphically presented in Figure 6.7. For the biomass C stock alone, broad forests account for over 50 percent of the C in that pool, but only 16.8 percent of the organic C is stored in the soils under this vegetation type. With the exception of the ‘Forest/ Cropland Mosaic’, in all other vegetation classes the soil stores more C than the biomass. 6.2.6 | Historic trends in soil carbon stocks The SOC stocks are more susceptible to anthropogenic activities and natural factors than are SIC stocks. Conversion of natural to agro-ecosystems in the past has led to decline in the SOC stock of the surface layers and also in SOC in the total profile for most soils. The magnitude of the historic loss, however, differs among soils and climates. The magnitude and rate of loss are higher for soils within the tropics than for those of temperate climates. Losses are also higher for coarse-textured than for heavy-textured soils, higher for soils containing higher SOC stocks, and higher for soils under subsistence or ‘extractive’ farming than for those farmed with more science-based agricultural practices. Depletion is also exacerbated by drainage of wetlands, by ploughing, and by biomass burning or removal. Some soils in the tropics can lose 50 percent of their previous pool within five years following deforestation and conversion to agricultural land use. The rate and magnitude of SOC loss are exacerbated in soils vulnerable to accelerated erosion, salinization, nutrient depletion or imbalance, structural decline and compaction, acidification, elemental toxicity, pollution and contamination. Estimates of the magnitude of historic SOC loss vary widely. The historic loss has been estimated at 40 Pg by Houghton (1995), 55 Pg by IPCC (1995) and Schimel (1995), 150 Pg by Bohr (1978), 500 Pg by Wallace (1994) and -1 . Lal (1999) estimated the magnitude 537 Pg by Buringh (1984). The average of these estimates is 223 Pg C year of SOC loss since 1850 at 47 to 104 Pg for different biomes (Table 6.3); 66 to 90 Pg for major soils (Table 6.4); Historic SOC Loss Change in Area Biome 6 ha Pg C 10 Forests 1300 23 - 53 Woodlands 180 3 - 7 Shrublands 140 1 - 4 Grasslands 20 - 40 660 47 - 104 Total Table 6.3 Estimate of the historic SOC depletion from principal biomes. Source: Lal, 1999. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 116 116

159 Present SOC Historic SOC Loss Historic Area Soil Order 6 ha Pool Pg C Pg C 10 1330 91 15 - 18 Alfisols 110 30 5 - 7 Andisols Aridsols 1560 54 0.2 - 0.3 Entisols 2170 232 0.8 - 1.3 Histosols 312 ? 160 Inceptisols 950 324 8 - 13 Mollisols 920 120 7 - 11 Oxisols 1010 99 22 - 27 1 - 3 Spososols 350 67 98 1170 6 - 7 Ultisols Vertisols 1 - 2 18 320 1120 238 0 Gelisols 1870 Others 0.2 - 3 17 Total 13050 1700 66 - 90 Table 6.4 Estimates of historic SOC depletion from major soil orders. Source: Lal, 1999; Hillel and Rosenzweig, 2009. Area Historic SOC Loss Erosion Wind Water Pg 6 6 ha ha 10 10 343 269 2 - 3 Light 254 Moderate 527 10 - 16 Strong 224 26 7 - 12 Total 19 - 31 Table 6.5 Estimates of historic SOC loss from accelerated erosion by water and wind. Source: Lal, 1999. and 19 to 31 Pg by erosional processes (Table 6.5). While the historic loss from Gelisols or permafrost soils is zero, these soils, which contain a vast amount of SOC reserves, are vulnerable to projected warming and the attendant positive feedback. Estimates of the historic C loss are useful as a reference point for assessing the technical potential of C re- sequestration in soil. While the loss of SOC can be rapid, especially in soils of the tropical ecosystems, the rate of re-carbonization is extremely slow. The slow rate of re-sequestration is a major challenge to identifying appropriate land use and to promoting adoption of soil/water/animal/plant management systems that could create a positive soil/ecosystem C budget. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 117 117

160 6.2.7 | Future loss of SOC under climate change Projected changes in climate (temperature and precipitation) are likely to affect the SOC stock both directly and indirectly. Directly, the rate of decomposition by microbial processes is affected by both soil temperature and moisture regimes. Indirectly, changes in climate affect plant growth, net primary productivity, above and below-ground biomass, and the type and amount of residues with differential amounts of materials recalcitrance. Further, the rate and susceptibility to accelerated erosion, salinization and other degradation processes may be exacerbated by an increase in frequency of extreme events. Indeed, climate change can impact several soil forming factors, including rainfall, temperature, micro-organisms/biota and vegetation, thus affecting the rate of SOC accumulation ( Jenny, 1930). Climate change may also alter species composition, and the rate of litter fall. However, disagreement exists regarding the effect of warming on SOC stock. The annual rate of litter return, on which the rate of SOC accretion depends, varies among biomes (White, -1 -1 ) is estimated at 0.1 to 0.4 for alpine and arctic regions, yr 1987; Grunwald, 1999). The rate of litterfall (Mg ha 2 - 4 for temperate grassland, 1.5 - 3 for coniferous forest, 1.5 - 4 for deciduous forest, 5 - 10 for tropical rainforest, and 1 to 2 for arable land (White, 1987). Increase in soil temperature may exponentially increase the rate of soil respiration (Tóth et al. , 2007; Lenton and Huntingford, 2003). However, because of increase in the number and activity of soil fungi in the warmer soil, there may also be increase in the relative amount of lignin and other , 2007). The SOM decomposition is also more temperature-sensitive at recalcitrant compounds (Simpson et al. low than at high temperature (Kirschbaum, 1995, 2000, 2006). Thus, knowledge about the temperature–sensitivity of diverse SOC fractions, and their change in the soil -1 1 under climate change, is important. Change in temperature by 1º Celsius may decrease the turnover times of 4 -1 6 percent for the intermediate and stabilized fractions, respectively (Hakkenberg et al. , 2008). percent and 8 The decomposition rate is also influenced by the presence of physicochemical protection mechanisms (Conant et al. , 2011), especially occlusion within aggregates and by association with mineral surfaces (Freedman, emissions from soil response to climate warming are over-estimated, because the 2014). It is argued that CO 2 decomposition of old SOM is tolerant to temperature (Liski et al. , 1999). Thus, the effects of warming on SOM decomposition are governed by complex and interactive factors, and are difficult to predict. Despite much research, no consensus has yet emerged on the temperature sensitivity of SOM decomposition (Davidson and Janssens, 2006). 6.2.8 | Conclusions Global SOC stocks have been estimated at about 1 500 Pg C for the topmost 1 m. However, a large uncertainty attaches to this estimate, which cannot easily be assigned to a specific period in time. Local variations may also be high, for example for SOC stocks in arctic regions and peatlands. Estimates of SOC stocks below 1 m depth are still evolving, with a tendency for more recent estimates to be higher than previous values. Estimates of the historic loss of SOC pools are also highly variable, ranging from 40 to 537 Pg. The global loss of SOC pool since 1850 is estimated at about 66 ±12 Pg. The projected response of SOC stock to climate change is a debatable issue. While an increase in temperature may increase the rate of respiration at low soil temperature, it may also shift microbial populations to fungi, increase relative proportions of lignin and other recalcitrant fractions, and increase protective mechanisms such as aggregation and reaction with mineral surfaces. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 118 118

161 | Soil contamination status and trends 6.3 6.3.1 | Introduction Soil contamination as a result of anthropogenic activities has been a widespread problem globally (Bundschuh , 2009; SSR, 2010). Soil contamination can be local or diffuse. Local et al. , 2012; DEA, 2001; EEA, 2014; Luo et al. soil contamination occurs where intensive industrial activities, inadequate waste disposal, mining, military activities or accidents introduce excessive amounts of contaminants. Diffuse soil contamination is the presence of a substance or agent in the soil as a result of human activity and emitted from dispersed sources. Diffuse contamination occurs where emission, transformation and dilution of contaminants in other media have occurred prior to their transfer to soil. The three major pathways responsible for the introduction of diffuse contaminants into soil are atmospheric deposition, agriculture, and flood events. These pathways can also cause local contamination in some instances. Causes of diffuse contamination tend to be dominated by excessive nutrient and pesticide applications, heavy metals, persistent organic pollutants and other inorganic contaminants. As a result, the relationship between the contaminant source and the level and spatial extent of soil contamination is indistinct. While some soil degradation processes are directly observable in the field (erosion, landslides, sealing or even decline of organic matter), soil contamination as well as soil compaction or decline in soil biodiversity cannot be directly assessed, which makes them an insidious hazard. Moreover, diffuse contamination is linked to many uncertainties. The diversity of contaminants (particularly of the persistent organic pollutants, which are in constant evolution due to agrochemical developments) and the transformation of organic compounds in soils by biological activity into diverse metabolites make soil surveys to identify contaminants difficult and expensive. The effects of soil contamination also depend on soil properties, as these have an impact on the mobility, bioavailability, residence time and levels of contaminants. Direct effects of pollutants may not be immediately revealed because of the capacity of soils to store, immobilize and degrade them. Effects can, however, suddenly emerge after changes such as changes in land use that may alter environmental , 1991 - see also Chapter 7 on processes impacting service provision). Contaminants conditions (Stigliani et al. include inorganic compounds such as metallic trace-elements and radionuclides, and organic compounds like xenobiotic molecules. The application of some organic wastes to soils – for example, untreated biosolids – also increases the risk of spread of infectious diseases. A new challenge is that the so-called ‘chemicals of emerging concern’ (CECs) – for example, veterinary and human therapeutic agents such as antibiotics and hormones – are present in amendments added to soils, such as manures. These CECs can have an adverse effect on ecosystems and on human health ( Jjemba, 2002; Osman, Rice and Codling, 2008; Jones and Graves, 2010). 6.3.2 | Global status of soil contamination In most developed countries, waste disposal and treatment, industrial and commercial activities, storage, transport spills on land, military operations, and nuclear operations are the key sources of local soil contamination. Management of local soil contamination requires surveys to seek out sites that are likely to be contaminated, site investigations where the actual extent of contamination and its environmental impacts are defined, and implementation of remedial and after-care measures. By contrast, diffuse soil contamination is much harder to manage: in many instances it is not directly apparent but it may cover very large areas and represent a substantial threat. Despite the fact that most developed countries have implemented long-term soil surveys, even these countries still lack a harmonized soil monitoring system, and the real extent of diffuse soil contamination is not known. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 119 119

162 According to the most recent data provided by the European Environmental Agency (EEA, 2014), total potentially contaminated sites in Europe are estimated to be more than 2.5 million, of which 340 000 are thought to be actually contaminated. Approximately one third of the high risk sites have been positively identified as contaminated, and of these only 15 percent have so far been successfully remediated (EEA, 2014). While trends vary across Europe, it is clear that the remediation of contaminated sites is still a significant undertaking. Waste disposal and industrial activities are the most important sources of soil contamination overall in Europe. The most frequent contaminants are heavy metals and mineral oils (EEA, 2014). In the United States, sites contaminated with complex hazardous substances that impact soil, groundwater or surface water are placed on the Superfund National Priorities List (NPL). As of September 29, 2014, there were 1 322 final sites on the NPL. On 1 163 of these sites, measures to address the contamination threat have been completed. An additional 49 sites have been proposed. In addition, the Office of Solid Waste and Emergency Response (OSWER) has cleaned up over 540 000 sites and 9.3 million ha of contaminated land, all of which can be put back into use. In Canada, a total of 12 723 soil contaminated sites has been identified, with 1 699 sites related to surface soil contamination (Treasury Board of Canada Secretariat, 2014). The key soil contaminants include metals, petroleum hydrocarbons (PHCs), and polycyclic aromatic hydrocarbons (PAHs). The pattern of contamination in Australia is similar to that of other developed countries. Industry, including the petroleum industry, mineral mining, chemical manufacture and processing facilities, and agricultural activities with their use of P fertilizer and pesticides, have caused soil contamination with heavy metals, hydrocarbons, mineral salts, particulates, etc. The total number of contaminated sites is estimated at 80 000 across Australia (DECA, 2010), with approximately 1 000 actual or potentially contaminated sites in South Australia (SKM, 2013). Developing countries are undergoing significant industrialization. If appropriate legal and regulatory frameworks and enforcement capability are not developed, this may lead to soil contamination and pose risks to the environment and human health. In large conurbations, there is also a need for adequate provision of sanitation and drainage so that household wastes are collected and managed safely. Asian countries experience considerable contamination of agricultural soil and crops by trace elements, and this contamination is becoming a threat to human health and the long-term sustainability of food production in the contaminated areas. In China, it is estimated that nearly 20 million ha of farmland (approximately one fifth of China’s total farmland) is contaminated by heavy metals (Wei and Chen, 2001). This may result in a reduction of more than 10 million tons of food supplies each year in China (Wei and Chen, 2001). Atmospheric deposition (mainly from mining, smelting and fly ash) and livestock manures are the main sources of trace elements contaminating arable soil (Luo et al. , 2009). Among the different trace elements contaminating Chinese agricultural soils, Cd is the biggest concern. Due to its high mobility in the soil (except in poorly drained soil where sulphides are present), it can be easily transferred to the food chain and so poses risks to human health. Arsenic is also naturally present in groundwater in many regions of Southeast Asia. This represents a threat to agriculture, particularly in rice paddy fields where anaerobic conditions prevail (Smedley, 2003; Hugh and Ravenscroft, 2009). Asia is also the largest contributor to the atmosphere of anthropogenic Hg, which originates from the chemical industry, from Hg mining and from gold mining (Li et al. , 2009). All across Asia, areas under rapid economic development are experiencing moderate to severe contamination by heavy metals (Ng, 2010). In many parts of Latin America, the results of anthropogenic activities, such as tailings and smelting operations in mining areas, have resulted in arsenic contamination in the soil. These operations enhance the mobilization of arsenic and cause adverse environmental impacts (see Section 4.3). Also in Latin America, the problem of arsenic contamination in water has been identified in 14 of the continent’s 20 countries: Argentina, Bolivia, Brazil, Chile, Colombia, Cuba, Ecuador, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Peru Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 120 120

163 and Uruguay. The number of exposed people in these countries is estimated to be about 14 million (Bundschuh , 2012; Castro de Esparza, 2006). It is also estimated that during the late 1980s and early 1990s, 3 000 to et al. 4 000 t of Hg were deposited in the Amazon basin as a result of artisanal gold-mining activities, mainly in Brazil, Bolivia, Venezuela and Ecuador (de Lacerda, 2003). In addition, intensive use of fertilizers and pesticides in many parts of Latin America contributes to soil contamination and causes a range of environmental pollution and human health problems (UNEP, 2010). In Africa, soil contamination has resulted from mining, spills, and improper handling of waste (Gzik et al. , 2003; SSR, 2010; EA, 2010). The Nigerian federal government reported more than 7 000 spills between 1970 and 2000. In Botswana and Mali, over 10 000 tonnes of pesticides, including DDT, aldrin, dieldrin, chlordane and heptachlor, have leaked from damaged containers and contaminated the soil (SSR, 2010). Soil contamination in the Near East and North Africa is linked to oil production and heavy mining. In arable land, a common source of soil pollution is the use of contaminated groundwater or wastewater for irrigation. 6.3.3 | Trends and legislation In developed countries, legislation on contaminated land and the related regulatory mechanisms are well established. As a result, the extent of contaminated land is thoroughly reported. The European countries have created a common framework in the Thematic Strategy on Soil Protection (COM (2006) 231), which aims at sustainable use of soil, preservation of soil as a resource, and remediation of contaminated soil. The EC has also created networks such as CLARINET, NICOLE and SNOWMAN (Vicent, 2013). Investigations of suspected contaminated sites continue in Europe and as a result the total of contaminated sites listed is expected to increase by 50 percent by 2025 (EEA, 2007, 2012; EC, 2013). The number of remediated sites is expected to grow as well. In addition, regulation now requires industrial plants to control their wastes and prevent accidents, limiting the introduction of contaminants into the environment. As noted above, the United States has introduced a regulatory regime and has made significant progress on site clean-up. In Asia, early legislation on contaminated land management (CLM) focused on contamination of agricultural land caused by industrialization and urbanization. Thus Japan, Taiwan, Province of China and South Korea have developed comprehensive CLM frameworks of laws, regulations and guidelines. Other Asian countries, however, are still at early stages of developing a CLM framework (Ng, 2010). et al. , 2007) and air quality Atmospheric deposition (Section 4.4.1) is an important input of pollutants (Lofts regulation to decrease the load of contaminants on soils is therefore important. In most developed countries, relevant legislation is well established. In the case of long-range atmospheric pollution, international agreements are needed. In this regard, the Convention on Long-Range Transboundary Air Pollution (LRTAP) was signed in 1979. Conceived in response to the detrimental impact of acid rain in Europe, the Convention entered into force in 1983. Over the past 30 years, the Convention has been extended by eight further protocols that target pollutants such as S, NOx, persistent organic pollutants, volatile organic compounds, ammonia and heavy metals. More recently, a global treaty to protect human health and the environment from the adverse effects of mercury - the 2013 Minamata Convention on Mercury - has been established. CECs require due attention and they can include, but are not limited to, nanoparticles, pharmaceuticals, personal care products, estrogen-like compounds, flame retardants, detergents, and some industrial chemicals (including those in products and packaging) with potential significant impact on human health and aquatic life ( Jones and Graves, 2010). Electronic waste (also referred to as ‘e-waste’) is of great concern given the increasing volumes generated each year, the hazardous nature of some of the components, and the exportation of this waste from industrialized countries to recycling centres in China, India and Pakistan (UNEP DEWA/GRID-Europe, 2005). This chain risks violating the Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal, which was adopted in 1989 and came into force in 1992. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 121 121

164 Recently some countries have implemented policies and programmes to encourage waste minimization. These programmes of ‘Extended Producer Responsibility’ make producers responsible for the costs of managing their products at the end of their life. This approach is expected to encourage the manufacture of more environmentally-friendly electronic products (UNEP DEWA/GRID-Europe, 2005). 6.4 | Soil acidification status and trends 6. 4.1 | Processes and causes of acidification Soil acidity increases with the build-up of hydrogen (H+) and aluminium (Al +) cations in the soil or when 3 +) and sodium (Na+) are leached and +), magnesium (Mg base cations such as potassium (K+), calcium (Ca 2 2 replaced by hydrogen or aluminium (Bolan, Hedley and White, 1991; Helyar and Porter, 1989; von Uexküll and Mutert, 1995). The main causes of soil acidification are: (1) long term rainfall that results in on-site leaching of base cations; (2) draining of potentially acid sulphate soils; (3) acid deposition when urbanization, industrialization, mining, construction or dredging release acid substances into the air or water, causing off- site acidification; (4) excessive application of ammonium-based fertilizers (e.g. ammonium sulphate) as part of intensive agriculture cropping practices; and (5) deforestation and other land use practices that remove all harvested materials, often resulting in a drop of the pH in the topsoil. Only the first of these five causes is a natural phenomenon; all others are human-induced. In natural ecosystems, soils become more acid with time. Consequently old soils, particularly in humid climates or those developed from acidic rocks, are more weathered and acidic than younger soils or soils of dry climates or those developed from more basic rocks (Helyar and Porter, 1989; von Uexküll and Mutert, 1995). Soil acidification is of the greatest concern in soils that have a low capacity to buffer the decrease in pH and in soils that already have a low pH, such as acid soils in highly weathered tropical areas (Harter, 2007; Johnson, Turner and Kelly, 1982). Soil texture and soil organic matter content play an important role in the buffering capacity of a soil and hence in determining how prone a soil is to acidification (Helyar and Porter, 1989; Steiner et al. , 2007). Light sandy soils poor in organic matter are the least buffered against acidification. Acid sulphate soils contain metal sulphides which, when exposed to oxidation, produce sulphuric acid. Inland, acid sulphate soils form naturally in aquatic ecosystems and also as a consequence of human-induced changes to land use and hydrology. Structures regulating water flow such as dams, weirs and locks prevent flushing of metals, salts and organic matter, and promote the build-up of acid sulphate soils. Acid sulphate soils also form in coastal areas and are common in mangrove forests, saltmarsh, floodplains, and salt- and freshwater wetlands (Lin and Melville, 1994; Pons, van Breemen and Driessen, 1982; Pannier, 1979). Due to the abundance of metal sulphides in rocks, mining activities also foster the formation of acid sulphate soils (Dent, 1986). ), nitrogen oxides (NOx) and ammonia (NH ) leads to The atmospheric deposition of sulphur dioxide (SO 2 3 acid deposition. This can affect not only areas near to the urban, industrial and mining sites where the oxides , 2004; Menz et al. are produced and released into the environment, but also sites located far away (Fanning and Seip, 2004; Mylona, 1996; Orndorff and Daniels, 2004). The term ‘acid deposition’ includes both wet and dry (gaseous) precipitation, usually in the form of acid rain or fog. Besides affecting the chemistry of soil and water resources, acid deposition directly harms plants and fish. Acid deposition is currently a major concern in fast-developing countries such as China (Chen, 2007). Land use and soil management play a crucial role in determining the chemical characteristics of the soil. Intensive farming practices that employ large inputs of nitrogen fertilizers and remove large quantities of Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 122 122

165 , 1997; Bolan, Hedley and White, 1991). Indeed, the conversion of et al. products increase soil acidity (Barak ammonium to nitrate releases hydrogen ions (H+) into the soil solution that can potentially lower the soil pH. This is a problem in soils with low ability to buffer the increase in H+ such as those poor in lime and negatively charged organic matter and clay. Harvesting has the potential to increase soil acidity by removing base cations from the soil. This is an issue in both agricultural and forested areas wherever large amounts of biomass are removed by crop harvesting and deforestation (Cavelier et al. , 1999; von Uexküll and Mutert, 1995). 6.4.2 | Impact of soil acidification On acid soils (pH < 5.5), crops and pastures suffer from the resulting increased phytotoxicity (Al, Fe, Mn, etc.), from the reduced availability of nutrients, and from decreased microbiological activity (Cronan and Grigal, 1995; Robson and Abbott, 1989; Slattery and Hollier, 2002; Sverdrup and Warfvinge, 1993; Whitfield et al. , 2010). Onsite soil acidification reduces net primary productivity and carbon sequestration by accelerating leaching of nutrients such as manganese, calcium, magnesium and potassium, resulting in nutrient deficiencies for plants (Haynes and Swift, 1986). On-site soil acidification is also responsible for the development of subsoil acidity (Tang, 2004), for the breakdown and subsequent loss of clay materials from the soil (Chen, 2007), and for the erosion which results from decreased groundcover (Slattery and Hollier, 2002). Soil acidification also leads to off-site effects such as surface water acidification through sediment losses, and groundwater enrichment of soluble metals. In turn, these processes mobilize heavy metals into water resources and the et al. , 1980; Slattery and Hollier, 2002; food chain (Driscoll et al. , 2003; Reuss and Johnson, 1986; Schindler Voegelin, Barmettler and Kretzschmar, 2003). 6.4.3 | Responses to soil acidification Soil acidification is an insidious process. It develops slowly and, if not corrected by lime applications for example, can continue until the soil is irreparably damaged (Edmeades and Ridley, 2003; Liu and Hue, 2001; Slattery and Hollier, 2002). Biological recovery can potentially be improved by an increase in pH and acid-neutralising capacity (ANC) (Marschner and Noble, 2000). Of main concern is subsoil acidity, which is particularly difficult to correct with conventional methods (Farina, Channon and Thibaud, 2000; Liu and Hue, 2001; Hue and Licudine, 1999). Actions to mitigate global warming can reduce the emission of pollutants such ) which contribute to soil acidification (NADP, 2014; Smith, Pitcher and Wigley, 2001; as sulphur dioxide (SO 2 Vestreng et al. , 2007). However, soil response to decreases in acid deposition is slow and acid-affected sites may require many decades to recover (Zhao et al. , 2009). 6.4.4 | Global status and trends of soil acidification Soil acidity is a serious constraint to food production worldwide. Traditionally it has been counteracted by applying lime to the topsoil but little could be done to increase the pH of the subsoil. Programmes to improve soil pH have been undertaken largely in developed countries, which are able to implement soil management plans to preserve soil properties and to bear the cost of lime to buffer soil acidity. However, even in developed counties, for example Australia, there have been cases where subsoil acidity increased due to failures in correcting topsoil acidity. In developing countries the situation is more stark as the use of lime is constrained by poverty. As a result, the farmed area affected by acidification is on the rise (Sumner and Noble, 2003). Soil acidification affects not only agricultural areas but also forests and grasslands. According to Sumner and Noble (2003), topsoil acidity (pH <5.5) affects around 30 percent of the total ice- free land area of the world, and subsoil acidity affects as much as 75 percent. Figure 6.8 illustrates the pH status worldwide. The most acidic topsoils (pH <3.5) in the world are located in South America in areas where deforestation and intensive agriculture are practiced, and also in river deltas populated by mangroves, for , 2006; Moormann, 1963). Elsewhere, the regions et al. example the Amazon and Orinoco Deltas (Marchand with the highest presence of acid soils are: northern and eastern regions of North America; South-East Asia; Central and South Africa; and northern regions of Europe and Eurasia. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 123 123

166 Estimated dominant topsoil pH Water < 4.5 4.5 - 5.5 5.5 - 7.2 7.2 - 8.5 > 8.5 Rocks outcrops, glaciers, salt at Figure 6.8 Estimated dominant topsoil pH. Source: FAO/IIASA/ISRIC/ISS-CAS/JRC, 2009. The main causes of soil acidification vary by region: Regions where soil acidification occurs because of soil texture – parts of North America, Southeast, • et al. et al. 2008; Shamshuddin East and South Asia (Aherne and Posch, 2013; Eswaran et , 1996; Hicks , 2006) et al. , 2014; Ouimet al. • Regions where proximity to deltas and coastal plains is a primary cause – parts of West Africa (Bullock et al. , 1996), • Regions where weather conditions are a main cause – parts of Africa and Asia (Breuning-Madsen and , 2006; Wilke, Duke and , 1996; Kottek Awadzi, 2005; Drees, Manu and Wilding, 1993; Eswaran et al. et al. Jimoh, 1984), Regions where acid deposition is an important factor – parts of East Asia and North America (Aherne • and Posch, 2013; Quinn, 1989; Wolt, 1981) • Regions where the massive application of ammonium-based fertilizers plays an important role – parts , 2010; Wang, Zhang and Zhang, 2010). of East and South Asia (Guo et al. In Europe, soil acidification is an issue only in some highly urbanised and industrialized hotspots (EEA, , 2004; Menz and Seip, 2004; Moser and Hohensinn, 1983). In the Southwest Pacific, soil et al. 2010; Kopáček acidification is of concern only in intensively farmed areas (Brennan, Bolland and Bowden, 2004; Hartemink, et al. , 2003; NLWRA, 2001). Thus soil acidification affects all regions to some 1998; Xu et al. , 2002; Lockwood extent, but it is of main concern in poor and developing countries which are growing rapidly but are unable to buffer the decrease in soil pH through conventional means. | Global status of soil salinization and sodification 6.5 6.5.1 | Status and extent Salt-affected soils occur in more than 100 countries and their worldwide extent is estimated at about 1 billion ha. Salt-affected soils include those affected by salinity, where the electrical conductivity of the soil exceeds 4dSm–1; and those affected by sodicity, where the exchangeable sodium percentage (ESP) exceeds 6 (Ghassemi, Jakeman and Nix, 1995). Saline soils contain excessive soluble salts, mainly sodium chloride (NaCl) ) or other neutral salts. These salts increase osmotic pressure, diminish water SO and sodium sulphate (Na 4 2 Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 124 124

167 availability and inhibit plant growth. Sodic soils generally have a low salt content but a high ESP, which causes dispersion of clay particles and results in deterioration of the soil structure. These soils generally have low air and water permeability and a pH above 8.2. Salinity problems are encountered in all climates and are a consequence of both natural (primary) and human-induced (secondary) processes. Soil salinity and sodicity problems are more common where rainfall is insufficient to leach salts and excess sodium ions out of the rhizosphere. Salt-affected soils often occur on irrigated lands, especially in arid and semiarid regions, where annual rainfall is insufficient to meet the evapotranspiration needs of plants and to provide for leaching of salt. In humid areas, soluble salts are carried down through the soil profile by percolating rainwater and ultimately are transported to sea. Although salt-affected soils are widespread and an increasingly severe problem, no accurate recent statistics are available on their global extent. The best available estimates suggest that about 412 million ha are affected by salinity and 618 million ha by sodicity (UNEP, 1992), but this figure does not distinguish areas where salinity and sodicity occur together. The Soil Map of the World (FAO/UNESCO, 1980) depicted a similar extent Saline soils Sodic soils Total Continent (million ha) (million ha) (million ha) Africa 122.9 86.7 209.6 South Asia 82.3 1.8 84.1 211.7 North and Central Asia 91.5 120.2 Southeast Asia 20.0 20.0 - 69.5 59.8 129.3 South America 6.2 North America 9.6 15.8 2.0 Mexico/Central America 2.0 - 340.0 357.6 Australasia 1 7. 6 World total 618.0 1030 412.0 Table 6.6 Distribution of salt-affected soils in drylands different continents of the world. Source: UNEP, 1992. of 953 Mha affected by salinity (352 million ha) and sodicity (580 million ha). Table 6.6 shows the distribution of dryland salinity in different continents. Human-induced salinity, mainly caused by irrigation without adequate drainage, affects a much smaller area than natural salinity. According to GLASOD, the extent of human-induced salinity is about 76 million ha (Oldeman, Hakkeling and Sombroek, 1991) of which 52.7 million ha occurs in Asia. In Europe, significant parts of Spain and areas in Italy, Hungary, Greece, Portugal, France and Slovakia are also affected by human-induced salinization. In 2006 the global area equipped for irrigation stood at 301 million ha. At present in developing countries, irrigated agriculture covers about one fifth of all arable land, but accounts for nearly half of all crop production and 60 percent of cereal production. About 70 percent of the world area equipped for irrigation is in Asia where it accounts for 39 percent of the cultivated area. India and China each have 62 million ha equipped for irrigation (FAO, 2011). An estimated 60 million ha (or 20 percent of the total irrigated area) are affected by soil salinity, of which 35 million ha are located in four countries e.g. Pakistan (3.2 million ha), India (20 million ha), China (7 million ha) and the United States (5.2 million ha). Other countries with large amounts of salt-affected lands in irrigation districts include Afghanistan, Egypt, Iraq, Kazakhstan, Turkmenistan, Mexico, Syria and Turkey (Squires and Glenn, 2011). Australia has the largest extent of naturally sodic soils of any continent (Table 6.5). Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 125 125

168 6.5.2 | Causes of soil salinity The distribution of salt-affected soils varies geographically with climate, landscape type, agricultural activities, irrigation methods and policies related to land management. Natural causes of salinity and sources of salt 1. Rock weathering : Significant quantities of sodium, and to a lesser extent chloride, occur widely in the parent rocks from which soils form. Over time, rock weathering can lead to appreciable salt accumulation in soils if leaching is restricted. Rock weathering is the primary source of salt in seawater. 2. Sea water and accession of salt in marine sediments : Saline soils can form from sediments and parent materials that were once under the sea. Likewise, the salts can be due to tidal inundation. Typical examples include the pseudo-delta of Senegal and the Gambia and in the Philippines where coastal tideland reclamation has created about 0.4 million ha of agricultural salt-affected soils. In the United Arab Emirates, areas -1 ). In the along the coastal sabkha (salt marshes or lagoonal deposits) are highly salinized (28.8 dS m -1 (Abdelfattah and Shahid, 2007) coastal region of the Abu Dhabi Emirate, salinity is more than 200 dS m 3. Atmospheric deposition : Salt derived from the sea, either deposited via rain or dry fallout, is the primary source of salt across large areas: for example, many millions of hectares in southern Australia. In arid areas, salt can also be derived from dry lake beds and then blown considerable distances by wind (e.g. Eurasia and parts of Australia). Human-induced causes 1. The management of land and water resources is responsible for the development of human-induced saline and sodic soils. The main causes are: Poor drainage facilities which induce a rise of the groundwater table. This is a major cause of soil 2. salinization in India, Pakistan, China, Kenya and the Central Asian countries. 3. The use of brackish groundwater for irrigation. This is a major cause of secondary salinization in parts of Asia, Europe and Africa. The intrusion of seawater in coastal areas, for example in Bangladesh. 4. Poor on-farm water management and cultural practices in irrigated agriculture. 5. Continuous irrigation over very long periods, particularly in the Middle East. 6. 7. Replacement of deep rooted perennial vegetation with shallower rooted annual crops and pastures that use less water leading to the rise of saline groundwater, for example southern Australia. 6.5.4 | Trends and impacts Soil salinity is becoming a significant problem worldwide. From the very scattered information on the extent and characteristics of salt-affected soils, salinity and sodicity are rapidly increasing in many regions, both in irrigated and non-irrigated areas. Increasing soil salinity problems are taking an estimated 0.3 to 1.5 million ha of farmland out of production each year and decreasing the production potential of another 20 to 46 million ha. The annual cost of salt-induced land degradation was estimated in 1990 at US$ 264 ha−1. By , 2013, the inflation-adjusted cost of salt-induced land degradation was reported as US$ 441 ha–1 (Qadir et al. 2014). | Responses 6.5.5 There are many available responses to contain the salinity threat. These include: (1) direct leaching of salts; (2) planting salt tolerant varieties; (3) domestication of native wild halophytes for use in agro-pastoral systems; (4) phytoremediation (bioremediation); (5) chemical amelioration; and (6) the use of organic amendments. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 126 126

169 In several Asian countries, a blend of engineering, reclamation and biological approaches has been adopted to address salinity and waterlogging problems. In Pakistan, engineering solutions included large-scale Salinity Control and Reclamation Projects (SCARPs), which covered 8 million ha at an estimated cost of US$2 billion (Qureshi et al. , 2008). Two big drainage water disposal projects were also undertaken. Measures to address the saline soil problem included leaching of salts by excess irrigation, use of chemicals (such as gypsum and acids), the addition of organic matter, and biological measures such as salt-tolerant plants, grasses, and shrubs. Improvements in on-farm water and crop management have also been practiced. In North America, changes in land use and management practices have reduced the risk of salinization and helped to improve soil health and agri-environmental sustainability. In Iraq and Egypt, surface and subsurface drainage systems have been installed to control rising water tables and arrest soil salinity. In Iran, Syria and other Gulf countries, crop-based management, and fertilizers are used to combat salinization (Qadir, Qureshi and Cheraghi, 2007). In Iran, Haloxylon aphyllum, Haloxylon persicum, Petropyrum euphratica and Tamarix aphylla are potential species for saline environments (Djavanshir, Dasmalchi and Emararty, 1996). Also in Iran, Atriplex has been shown to be a potential fodder -1 (Koocheki, 2000; Nejad and shrub in the arid lands which could bring annual income as high as US$ 200 ha Koocheki, 2000). Breeding of salt tolerant crop varieties (e.g. wheat, barley, alfalfa, sorghum etc.) is also a recognized management response for saline environments. However, most results have been obtained in controlled environments, with few real field results so far. The use of organic amendments in Egypt showed that the mixed application of farmyard manure and gypsum (1:1) significantly reduces soil salinity and sodicity (Abd Elrahman , 2012). Recently, phytoremediation or et al. plant based reclamation has been introduced in the Near East region. In Sudan good responses for control of sodicity have been obtained through phytoremediation. The production of H+ proton in the rhizosphere during N-fixation from legumes such as the hyacinth bean (Dolichos lablab L.) removed as much Na+ as gypsum application. This indicates the importance of this technology in calcite dissolution of calcareous salt affected soils (Mubarak and Nortcliff, 2010). 6.6 | Soil biodiversity status and trends | Introduction 6.6.1 Over the last few decades the importance of soil biota for terrestrial functioning and ecosystem services has emerged as an important focus for soil science research. Current evidence shows that soil biota constitute an important living community in the soil system, providing a wide range of essential services for the sustainable functioning of global terrestrial ecosystems and thereby impacting human wellbeing, directly and indirectly (van der Putten et al. , 2004). Soil organisms (e.g. bacteria, fungi, protozoa, insects, worms, other invertebrates and mammals) shape the metabolic capacity of terrestrial ecosystems and many soil functions. Below-ground biodiversity represents one of the largest reservoirs of biodiversity on earth (Bardgett and van der Putten, 2014). Essential services provided by soil biota include: regulating nutrient cycles; controlling the dynamics of soil organic matter; supporting soil carbon sequestration; regulating greenhouse gas emissions; modifying soil physical structure and soil water regimes; enhancing the amount and efficiency of nutrient acquisition by vegetation through symbiotic associations and nitrogen fixation by bacteria; and influencing plant and animal health through the interaction of pathogens and pests with their natural predators and parasites. Fungi and bacteria are important decomposers in the soil. They are remarkably efficient. The smaller the pieces to be decomposed, the faster these microorganisms are able to do their job. Organic waste such as Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 127 127

170 leaf matter and the droppings of herbivores first feed a host of small animals including insects, earthworms and other small invertebrates which live in the plant litter. The combined fauna break up the organic matter, digesting part of it, and thus facilitating the task of the microorganisms and invertebrates that complete the process of decomposition. In turn, soil macro-fauna affect soil organic matter dynamics through organic matter incorporation, decomposition and the formation of stable aggregates that protect organic matter against rapid decomposition. Successive decomposition of dead material and modified organic matter results in the formation of a more complex organic matter called humus, which affects soil properties by increasing soil aggregation and aggregate stability, increasing the cation-exchange capacity (the ability to attract and retain nutrients), and increasing the availability of N, P and other nutrients. Many scientists have reported the role of macro-fauna in the accumulation of soil organic matter. For example the work by Snyder, Baas and Hendrix (2009), showed that millipedes and earthworms, both by themselves and taken together, reduce particulate organic matter. In addition, earthworms create significant shifts in soil aggregates from the 2000–250 and 250–53 μm fractions to the > 2000 μm size class. Earthworm- induced soil aggregation was lessened in the 0-2 cm layer in the presence of millipedes. Further, Hoeksema, there was a higher density of Lussenhop and Teeri (2000) found that in high-N soil with twice-ambient CO 2 . predator/omnivores, lower diversity, and a larger value of Bonger’s Maturity Index compared to ambient CO 2 . This indicates In this experiment, fine root biomass and turnover were significantly greater under elevated CO 2 higher vigour in plant root development and growth and hence increased carbon sequestration conditioned by enhanced soil biota activity. Studies also show the role of soil biota (including fungi, bacteria and plant parasitic nematodes) as pathogens and parasites or herbivores in decreasing root and plant productivity or reducing fruit quality. Recent research has focussed on the use of nematode and fungal resistant plant species or of other soil organisms as suppressive agents to modify the pathogens. 6.6.2 | Soil biota and land use Losses in soil biodiversity have been demonstrated to affect multiple ecosystem functions including plant diversity, decomposition, nutrient retention and nutrient cycling (Wagg , 2014). Links between above- et al. ground and below-ground communities (Wardle , 2004; De Deyn and van der Putten, 2005; Bardgett et al. and van der Putten, 2014) suggest that factors affecting above-ground extinction may also be affecting soil organisms. Agricultural intensification, in particular, may reduce soil biodiversity, leading to decreased food-web et al. , 2015). Other driving forces that influence biodiversity complexity and fewer functional groups (Tsiafouli in agricultural soils include the influence of crops/plants, fertilizers and pH, tillage practices, crop residue retention, pesticides, herbicides and pollution (Breure et al. , 2004; Bardgett and van der Putten, 2014). Soil biological and physical properties (e.g. temperature, pH, and water-holding characteristics) and microhabitat are altered when natural habitat is converted to agricultural production (Crossley et al. , 1992; Bardgett and van der Putten, 2014). Changes in these soil properties may be reflected in the distribution and diversity of soil meso fauna. Organisms adapted to high levels of physical disturbance become dominant within agricultural communities, thereby reducing richness and diversity of soil fauna (Paoletti et al. , 1993). The management practices used in many agro-ecosystems (e.g. monocultures, extensive use of tillage, chemical inputs) degrade the fragile web of community interactions between pests and their natural enemies. The intensification of agricultural management may result in increased incidence of pests and diseases, with numerous studies reporting declines in the biodiversity of soil fauna (Decaens and Jimenez, 2002; , 2002). In addition, the contribution of soil fauna globally to organic matter decomposition Eggleton et al. et al. rates may be highly dependent on the temperature and moisture of an ecosystem (Wall , 2008). This Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 128 128

171 underlines the need for global-scale assessments. In a global study of soil fungi using 365 soil samples from natural ecosystems, Tedersoo (2014) found that distance from the equator and annual precipitation had et al. considerable effect on fungal species richness. They also identified various other controls on soil fungi and this is starting to provide a benchmark for assessing the impacts of human activities on an important component of soil biodiversity. Soil management strongly influences soil biodiversity, resulting in changes in abundance of individual species. Using a soil biodiversity pressure index calculation from the European Soil Data Centre, Gardi, Jeffery and Saltelli (2013) estimated that 56 percent of soils within the European Union have some degree of threat to soil biodiversity. Based on a questionnaire completed by 20 experts, the study found that the main anthropogenic pressures on soil biodiversity are (in order of importance): (1) intensive human exploitation; (2) reduced soil organic matter; (3) habitat disturbance; (4) soil sealing; (5) soil pollution; (6) land-use change; (7) soil compaction; (8) soil erosion; (9) habitat fragmentation; (10) climate change; (11) invasive species; and (12) GMO pollution (Gardi, Jeffery and Saltelli, 2013). There is some experimental evidence that there may be threshold levels of soil biodiversity below which functions decline (e.g. Van der Heijden et al. , 1998; Liiri et al. , 2002; Setälä and McLean, 2004). However, in many instances this is at experimentally prescribed levels of diversity that rarely prevail in nature. Although some studies demonstrate some functional redundancy in soil communities (e.g. Setälä, Berg and Jones, 2005), high biodiversity within trophic groups may be advantageous since the group is likely to function more efficiently under a variety of environmental circumstances, due to an inherently wider potential. In a synthesis et al. , (2011) concluded of diversity-function relationships of soil biodiversity focusing on carbon cycling, Nielsen that although there is considerable functional redundancy in soil communities for general processes, change may readily have an impact on specialized processes. However, data to support this conclusion are still limited. More diverse systems may be more resilient to perturbation since, if a proportion of components are removed or compromised in some way, others that prevail will be able to compensate (Kibblewhite, Ritz and Swift, 2008). 6.6.3 | Conclusions A comprehensive global-assessment on below-ground biodiversity has yet to be carried out. Although there is a Global Soil Biodiversity Atlas (EU/JRC, in press), no benchmark values exist on a global scale. This makes it difficult to quantify changes or future losses that may result from natural or anthropogenic-induced changes. Although progress is being made, few monitoring programs exist that quantify soil biodiversity across regions and at multiple trophic levels, especially outside of Europe. Regarding the threats to soil biodiversity and the effects on ecosystem functioning, more comparative and coordinated studies (from local to global scales) are needed across all ecosystems. These studies should quantify threats and determine the consequences of soil biodiversity loss to ecosystem functions, as well as the effects of interactions between threats. In addition, there is a need for standardization of methods in soil biodiversity studies so that multiple datasets can be synthesized and benchmark values for global soil biodiversity may be established. The use of DNA-based approaches is accelerating the speed at which data is being collected for all organisms. However, although sequencing data must be deposited into a public database (e.g. Genbank) before publication, the majority of morphological data still remains inaccessible and hence largely unavailable for meta-analysis. International 2 , ECOFINDERS, and the EU-sponsored Global Soil initiatives such as the Global Soil Biodiversity Initiative Biodiversity Atlas are steps in the right direction but a common database of soil biodiversity data for both morphological and molecular data is still needed (Orgiazzi et al. , 2015). 2 www.globalsoilbiodiversity.org Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 129 129

172 Figure 6.9 Historical and predicted shift of the urban/rural population ratio. Source: UN, 2008. | Soil sealing: status and trends 6.7 For millennia, the vast majority of people lived a rural life, largely dependent on agriculture and other rural occupations. Only over the last two centuries has the ratio between the urban and non-urban population started to change rapidly. In 1800, only 3 percent of the world’s population lived in cities; in 1900 14 percent, 47 percent in 2000, 50 percent in 2007, and 54 percent in 2014. The proportion of the urban population is expected to rise to 66 percent by 2050 (Figure 6.9). The world’s urban population is growing and cities are expanding in order to accommodate the increasing population and economic activity. It is not known with any certainty what share of the Earth’s land surface (ca. 2 ) is now occupied by cities or how much land will be required to accommodate the expected urban 144 million km expansion (Potere , 2009). One of the most accurate estimates of the extent of urban areas at global scale, et al. 2 based on the use of MODIS satellite data at a resolution of 500 m, indicates for the year 2000 an area of 657 000 km et al. , 2009), equivalent to 0.45 percent of the Earth’s land surface. Urbanization is an important contributor (Potere to regional and global environmental change (Foley et al. , 2005, Ellis and Ramankutty, 2008). The growth of cities has , 2014). a vast impact on the landscape and significant impact on soil resources (Chen, 2007; Gardi et al. Global soil status, processes and trends Status of the World’s Soil Resources | Main Report 130 130

173 Figure 6.10 Urbanisation of the best agricultural soils. 2 Between 1990 and 2000, the total extent of urban areas worldwide increased by 58 000 km . During this period, 2.8 percent of Europe’s total land was affected by land use change, including a significant increase in urban land. Of the total land take in the EU between 1990 and 2000, 71 percent was for agriculture. Between 2000 and 2006, the equivalent figure was only 53 percent. Had the land taken for urban expansion been devoted to agriculture instead, the land would have produced more than 6 Mt of wheat. More generally, the best quality soil in alluvial plains is often sealed by expanding cities and the rate of conversion is expected to increase rapidly, especially in developing countries. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 131 131

174 The term ‘soil sealing’ is defined as the permanent covering of the soil surface with an impermeable material. Urbanisation affects the inner urban ecosystem as well as the neighbouring ecosystems. Besides the economic and social effects, negative environmental effects are predominantly linked to land consumption, the loss of high quality agricultural soil (Figure 6.10), the destruction of habitat, fragmentation of existing ecosystems, increased fuel consumption, air, water and soil pollution, and the alteration of microclimate. Soil sealing is in practice equivalent to total soil loss – virtually all services and functions are lost except the carrying capacity as a platform for supporting infrastructure. The main negative impacts on ecosystem services include: virtually total loss of food and fibre production; a significant decrease or total loss of the soil’s water retention, neutralization and purification capacities; the loss of the carbon sequestration capacity; and a significant decrease in the ability to provide (micro) climate regulation. The results include the loss of habitat for soil organisms, loss of soil biodiversity and nutrient cycling, and often a diminished landscape and natural heritage. Urban expansion is, of course, both beneficial and essential. Historically, the beginning of the most important civilizations was associated with both the development of agriculture and the creation of urban settlements. As early as 3000 BC, cities had arisen in the Fertile Crescent, on the banks of Nile, in the Indus River valley and along major rivers in China. However, the very rapid urban expansion of recent times is creating the need for trade-offs, including decisions regarding soil health and the rate of soil sealing. 6.8 | Soil nutrient balance changes: status and trends 6.8.1 | Introduction Though changes in soil nutrient balances may possibly affect all types of terrestrial ecosystems, rapid changes are more likely to occur in managed ecosystems as a result of the export of biomass or the addition of nutrients to sustain productivity. These managed ecosystems include cropland, intensively or extensively grazed rangelands or meadows, and forests. Monitoring changes in soil nutrient content is of particular relevance in managed ecosystems because it provides a means to evaluate future changes in the ability of soils to maintain their ecosystemic functions. On the one hand, negative balances (‘nutrient mining’) ultimately translate into crop nutrient deficiencies (, food production deficits and human nutritional imbalances. On the other hand, positive balances may lead to negative environmental and health externalities. Eutrophication, increased frequency and severity of algal blooms, hypoxia and fish kills and loss of habitat and biodiversity have been related to excessive inputs of N and P into fresh and coastal waters. Excess application of N has . Gaseous emissions of ammonia and nitrous also lead to widespread contamination of groundwater by NO 3 oxide may also degrade air quality and contribute to acidification, eutrophication, ground-level ozone and climate change (Oenema, 2004; Chadwick et al. , 2011). In addition, strongly positive balances may reflect poor economic management of managed ecosystems. Nutrient balances can thus be viewed as indicators of sustainability of human-induced land use changes and land use practices. Soil nutrients include the macronutrients nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S). In addition, the soil supplies micronutrients (boron, copper, iron, manganese, chloride, molybdenum, zinc), whose concentrations in plants are typically one or two orders of magnitude less than those of macronutrients. In most cases, N, P and K taken individually or in combination are the most limiting nutrients for plant growth. This section will therefore focus on these three elements. In soils, these nutrients may be present in different pools. Because the amount of nutrients in certain pools may vary strongly and erratically over short time intervals, stocks and mass balances are generally calculated on , 2003). et al. the basis of total nutrient content, without distinction among different forms (Roy Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 132 132

175 Figure 6.11 Major components of the soil nutrient balance. The red discontinuous line marks the soil volume over which the mass balance is calculated. Green arrows correspond to inputs and red arrows to losses. ΔS represents the change in nutrient stock. 6.8.2 | Principles and components of soil nutrient balance calculations Because the magnitude of the nutrient fluxes is often small compared to the total stock of nutrients in the soil profile, changes in soil nutrient stocks can be rather slow and difficult to detect over short time scales (< decades). Hence calculating nutrient balances from nutrient flows rather than from changes in nutrient stocks has been preferred in many studies (Figure 6.11). Table 6.6 lists the main inputs and outputs used for calculating the mass balances of N, P and K. Inorganic amendments are mostly composed of mineral fertilizers, but also comprise urine or minerals contained in irrigation water. Organic amendments include liquid, semi-solid or solid manures, compost, mulching material not produced on-site, and household refuse. It also includes faeces dropped by animals. In systems such as urban gardening, the re-use of waste water may also input organic compounds. Biological fixation by bacteria is restricted to N. Wet deposition refers to nutrients supplied with rainwater, whereas dry deposition refers to nutrients deposited as dust and aerosols. Dry deposition is a particularly important phenomenon in the case of K in areas downwind of major dust producing areas (e.g. West Africa;). Sedimentation refers to the deposition of sediment eroded upstream or to sediment deposited during river flooding. Additional fluxes from groundwater (). may exist in specific situations (e.g. nutrients in subsurface lateral flows ; supply of NO 3 Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 133 133

176 N P K Nutrient inputs Inorganic amendments Ye s Ye s Ye s Organic amendments Ye s Ye s Ye s Biological fixation Ye s No No Dry or wet deposition Ye s Ye s Ye s Sedimentation and run-on Ye s Ye s Ye s Nutrient outputs Harvested products Ye s Ye s Ye s Grazed products Ye s Ye s Ye s Leaching Ye s Generally negligible Low Gaseous emissions No No Ye s Erosion and runoff Ye s Ye s Ye s Table 6.7 Major components of soil nutrient mass balances for N, P and K The main losses are related to nutrients contained in exported harvested products (crops or fodder), and nutrients contained in food ingested by primary grazers (Table 6.7). Nutrients may also be lost by gaseous O), through erosion and in surface runoff, or by leaching. The latter applies mostly to , N , N emissions (NH 3 2 2 -N and K, and to a very limited extent to PO -P except in coarse textured soils -N, to a lesser extent to NH NO 4 4 3 saturated with P. 6.8.3 | Nutrient budgets: a matter of spatial scale The larger the spatial scale, the more certain nutrient flows are internalized. For instance, in a self- sufficient, well-managed farm, the net balance may be nil or close to nil. However, different parts of the farm may well have very different balances. Likewise, in extensively-managed agropastoral systems, nutrient flows mediated through livestock occur between rangelands and croplands. At a regional scale, the balances may thus be nil or only slightly negative, whereas large imbalances exist within the region (see Box 6.1). At the global scale, fertilizer use and the growing of leguminous crops have resulted in a doubling of the rate at which N enters the terrestrial ecosystems as compared to pre-industrial levels. Likewise, the use of P fertilizers, animal feed supplements and detergents has led to a doubling of P inputs in the environment as compared to background P release from weathering. This is indicative of a net positive balance but hides large regional disparities. Bouwman, Beusen and Billen (2009) calculated global soil N and P balances for the year 2000. Outputs were restricted to harvested and grazed crops and grasses, whereas inputs included manure, -1 and fertilizers, N deposition and N fixation. These authors estimated the inputs to soils at 249 Tg N and 31 Tg P yr -1 . Assuming no build-up of N in the soil, their model losses through harvest and grazing at 93 Tg N and 16 Tg P yr -1 ) of the inputs may be lost by erosion and leaching, thereby contributing predicted that 16 percent (41 Tg yr to a loss in environmental quality. In the case of P, their calculations predicted a net accumulation of P at a -1 -1 and losses of P through leaching and erosion of 2 Tg yr . On a continental scale, considering rate of 12 Tg yr both natural and agro-ecosystems, balances were always positive and comprised between 8.5 (North Asia) -1 -1 -1 -1 yr , and between 0.22 (Africa) and 5.5 (Europe) kg P ha yr . Focusing specifically on and 35 (Europe) kg N ha P and cropland, but restricting the balance calculations to fertilizer and manure inputs and harvest outputs, highlighted large P deficits in South America, northern United States and eastern Europe. Large P surpluses were found in the coastal United States, western and southern Europe, East Asia and southern Brazil. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 134 134

177 Within the same continent, large variations in nutrient balances may occur. For 13 African countries, estimated balanced or negative nutrient budgets for N, P and K. At the national level, estimated soil nutrient -1 -1 -1 -1 -1 1 kg P ha yr , from 0 to , and from -2 to -61 yr balances for the year 2000 ranged from -2 to -60 kg N ha -1 -1 yr . A later study at 1 km² resolution confirmed the overall negative balances but highlighted larger kg K ha variability over short distances. The rate of nutrient mining by crops was generally low or moderate, because of low land productivity (low yields), but accumulated over many decennia nutrient depletion may become severe and may be strongly aggravated by soil erosion. Based on a review of 57 nutrient budget studies related to the African continent, confirmed that N budgets at field and farm scale were largely negative whereas for phosphorus negative balances were reported in only 56 percent of the studies. Going from the continental scale to the plot scale, there was a tendency for the variability in nutrient budgets to increase. This is to be expected, as land uses and management practices in smallholder agriculture in Africa are highly diversified between farms, within farms and even within plots. The study did not find a clear trend in the magnitude of the nutrient budgets from plot to continental scales. This is in contrast to other studies which did report increasingly negative balances as the scale increased. Box 6.1 | Livestock-related budgets within village territories in Western Niger (Schlecht et al., 2004) -1 -1 -1 and between 0.06 and 0.7 kg P ha In the Sahelian zone of West Africa, between 1.5 and 9 kg N ha yr -1 are taken in by grazing livestock. The quantity varies by location and land use type (rangeland, yr cropland, fallow). However, up to 95 percent of the nutrients consumed by livestock are recycled through faeces. About 40-50 percent of these faeces end up being spatially concentrated at corralling spots or in farmyards, which represent only a few percent of the total village lands. Though nutrient in- and out- flows related to livestock account for only a small fraction of the nutrient flows in Sahelian crop-livestock systems, livestock thus plays a major role in the spatial redistribution of nutrients. Negative balances occur on rangelands and variable (positive or negative) balances are found in croplands depending on the intensity of application of organic amendments. At even smaller scales, differences in soil fertility may arise from differential nutrient budgets. Strong gradients in soil fertility have been reported around villages, compounds, trees and shrubs as a result of higher levels of inputs (litter, household refuse, human excreta, manure and urine from resting animals, sedimentation, etc.) near these features. These are referred to as ‘fertility rings’ or ‘fertility islands’. 6.8.4 | Nutrient budgets: a matter of land use system, land use type, managementand household equity Nutrient balances vary greatly across land use (LU) systems. Intensive growing of industrial crops in Europe is generally characterized by excess inputs of N, despite a recent tendency towards reduced fertilization driven by EU regulations and the economics of fertilizer use. As a result of the decoupling of livestock and land and because livestock are increasingly fed with imported feed, pastures are commonly exposed to excessive applications of manure (e.g. in Normandy in France, and in Denmark and Holland). Regarding P, after decades of excess application of P, there is nowadays a tendency for farmers to reduce their P application rates, or even to stop applying P altogether and to rely only on accumulated soil reserves and P released from soil mineral weathering. At the other extreme, subsistence farming in developing countries is commonly characterized by negative , 2003). examined nutrient balances for different land uses in et al. balances, reflecting nutrient mining (Roy Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 135 135

178 -1 -1 -1 00 kg ha yr were found for maize, sugar cane, and pyrethrum. P a Kenyan district. N deficits in excess of -1 -1 -1 0 kg ha yr were found for sugar cane, pyrethrum, and beans, but P excesses occurred deficits in excess of -1 -1 yr in tea and maize-bean plots. Except for coffee, tea and seasonal fallow, K deficits in excess of -50 kg ha occurred in all systems. These observed differences reflect differences in the use of (in-)organic amendments, but also nutrient transfers across LU types. In the case of coffee for instance, mulching is recommended, which is done by using residues from other crops (e.g. bananas) or grasses from fallow land. In Asia, both strongly positive and strongly negative balances have been reported. K deficits have been -1 -1 . also reported yr reported for rice-based systems across several Asian countries ranging from -25 to -70 kg ha K deficits in 71 paddy farms in south China, but found N and P surpluses. Based on negative nutrient balances for Bangladesh, Vietnam, Indonesia, Myanmar, the Philippines, and Thailand, and positive balances for Japan, Malaysia and Korea, it has been argued that lower-income countries with large and growing population were more likely to present negative balances whereas higher income countries with stable populations tended to have positive balances. In sub-Saharan Africa, the larger the population density, the more negative the N and P balances. For similar systems, differences in nutrient balances may also arise from variable access of farmers to external inputs. In the Sudanian zone of west Africa, cultivated plots near hamlets tended to have less negative or more positive balances than plots near larger villages because farmers in hamlets cared better for their crops, earned more income from sales and therefore could invest more in fertilizers. Generally, cultivated plots near hamlets and villages benefit from greater additions of household refuse and human and animal faeces. However, social inequality in access to resources has been found to have an equally large or even larger effect on nutrient balances than distance from the village. For instance, positive N, P and K balances were observed for Fulani cropland because their large herds supply them with abundant manure. Likewise, nutrient budgets ranging from strongly negative to strongly positive were reported for banana-based systems in Tanzania depending on access to cattle and cattle management (Roy et al. , 2003). Especially in small-holder agriculture, site-specific management may also induce large fertility gradients over short distances. (Peri-)urban agriculture is characterized by large excesses in nutrients, especially N. This is commonly driven by the market-oriented nature of this production system, which allows farmers to invest in external inputs. In addition, these systems often rely heavily on the re-use of urban solid waste and waste water. Hence, (peri-) urban production systems exemplify another form of large scale fertility transfer, from rural areas to urban areas. Food produced by nutrient mining in rural areas is consumed in cities, leading to strong soil enrichment of urban soils, especially at urban vegetable production sites (see Box 6.2). 6.8.5 | What does the future hold? Soil nutrient budgets depend on the local socio-economic conditions but also on market prices of inputs and on policies. In Western Europe for instance, rising prices of fertilizers and the strengthening of environmental policies has led to reductions in N and P inputs into farmland, and this trend is expected to continue. Dwindling P resources and climate change may further affect soil nutrient balances, in managed but also in natural ecosystems. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 136 136

179 Nutrient balances in urban vegetable production in West African cities Box 6.2 | Based on a two year study of urban gardening sites in Niamey (Niger), it was found that N, P and K -1 balances were all positive, with values for high and low input gardens respectively of 1133 and 290 kg ha -1 -1 for N; 223 and 125 kg ha for P; and 312 and 351 kg ha for K. Similar N and P balances were reported for urban vegetable gardens in Kano (Nigeria), Bobo Dioulasso (Burkina Faso) and Sikasso (Mali). However, at these latter sites, K balances tended to be negative. Overall, urban vegetable production sites appear to be major nutrient sinks from which large environmental externalities can be expected. Bouwman, Beusen and Billen (2009) evaluated the impact of four future development scenarios on nutrient balances for the year 2050. The scenarios, describing contrasting future development in agriculture nutrient use under changing climate, are based on the Millennium Ecosystem Assessment. In the most pessimistic case, the global N balance may increase by 50 percent in the coming decades. In case of proactive -1 . policies aiming at closing the nutrient balance, the N balance is expected to remain constant at 150 Tg yr Regarding P, all scenarios predict a future increase in global soil P balance. These global balances hide large variations across regions and even across land uses. Unfertilized rangelands are likely to maintain negative P balances. Scenarios with a reactive approach to environmental problems portray significant increases in N and P balances in Asia, Central and South America and Africa, which can be strongly reduced by a proactive approach. For North America, Europe and Oceania, a shift from reactive to proactive environmental policies could allow limiting the increase in N and P balances, or even a decrease in the overall nutrient balance. Whereas large positive nutrient balances sustained for extended periods of time in industrialized countries have resulted in negative environmental externalities, positive nutrient balances should not be viewed as necessarily environmentally harmful. Indeed, in many developing regions (e.g. sub-Saharan Africa), positive P balances are needed to restore soil fertility potential depleted by long lasting nutrient mining and to boost the often very low crop yields. Inputs of N in organic form may also be beneficial as part of a strategy to restore the soils’ organic carbon stocks. Possible negative environmental externalities should be weighed against the benefits of food security, economic welfare and social well-being. To minimize the negative externalities, the best nutrient management approaches should be promoted through judicious policies. 6.9 | Soil compaction status and trends Soil compaction is an important problem affecting productivity of soils across the globe. A hidden problem of soils occurring on or below the surface, compaction impairs the function of the subsoil by impeding ). Soil compaction reduces soil McGarry and Sharp, 2003 root penetration and water and gaseous exchanges ( macroporosity e.g. from an optimum of 6 to 17 percent, and hence reduces pasture and crop yield (Drewry, Cameron and Buchan, 2008). Soil compaction in most circumstances is a function of soil type (texture, mineralogy, organic matter), soil-water content and land management (e.g. tillage practices, traffic, grazing intensity). The problem is not limited to crop land but is also prevalent in rangelands and grazing fields, and even in natural non-disturbed systems. Soil compaction occurs when compressible soils are subjected to traction e.g. in forest harvesting, amenity land use, pipeline installation, land restoration, wildlife trampling (Batey, 2009) or winter grazing (Tracy and Zhang, 2008). et al. Trampling mechanically disrupts soil aggregates and reduces aggregate stability (Warren , 1986) and its effect increases with stocking intensity (Willatt and Pullar, 1983). The degree of damage associated with Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 137 137

180 trampling at a particular site depends on soil type (Van Haveren, 1983), soil water content, seasonal climatic , 1986), and vegetation type (Wood and Blackburn, 1984). Climate is therefore an et al. conditions (Warren important determinant of the effects of compaction. Where soil moisture deficits are large, a restriction in root depth may have severe effects but the same level of compaction may have a neglible effect where soil moisture deficits are small (Batey, 2009). Soil compaction effects are long lasting or even permanent (Håkansson and Lipiec, 2000). Especially in cultivated land, soil compaction is exacerbated by low soil organic matter content. Intensive use of farm machinery including tillage implements such as the mould board, disc ploughs and disc harrows contributes to soil compaction, depending on the pattern of load and stress applied and the number of passes. The initial condition of the soil also plays a role, including soil moisture, organic matter content, bulk density, particle Materechera, 2008 ; Horn et al. , 2005; size distribution (including high silt content), and aggregate stability ( Imhoff, Da Saliva and Fallow, 2004). Alfisols, a major soil used for crop production in the tropics and covering approximately 4 percent of the African land mass, are particularly vulnerable. They are strongly weathered and inherently of low organic matter and nutrient status, have a weak structure, and are highly susceptible to crusting, compaction and accelerated erosion (Lal, 1987). Soil compaction decreases soil physical fertility by impairing storage and supply of water and nutrients, and by increasing erosion hazards and the transport of phosphorus and other nutrients out of the farming system. Soil compaction can reduce crop yields by as much as 60 percent (Sidhu and Duiker, 2006). The range of yield effects is variable, and depends partly on the crop. Cotton was found to be more sensitive to soil compaction than were soybeans, corn or Brachiaria brizantha (Busscher, Frederick and Bauer, 2000). Yields of sugarcane (Saccharum officinarum L.) were reduced by 40 percent with sub-surface compaction of a clay soil ( Jouve and Oussible, 1979), while in a clay loam soil wheat yields were reduced by 12 to 23 percent (Oussible, Crookstone and Larson, 1992). The compaction effects on yield are greatest when the crop is under stress, such as from drought or an excessively wet growing season (Sidhu and Duiker, 2006). Krmenec (2000) observed stand count reductions of 20 to 30 percent, plant height decreases of up to 50 percent and yield reductions of about 19 percent in compacted compared to non-compacted plots. The study of Voorhees, Nelson and Randall (1986) illustrates that a one-time compaction event can lead to reduced crop yields up to 12 years later. In another study, soil compaction reduced grass yield by up to 20 percent due to N-related stresses (Smith, McTaggart and Tsuruta, 1997; Douglas, Campbell and Crawford, 1998). In addition, the creation of waterlogged zones or of dry zones caused by shallow rooting can deny plants access to deeper reserves of water (Batey and McKenzie, 2006). Additional consequences include chemical changes, such as the amount of greenhouse gases (nitrous oxide and methane) emitted from or taken up in a soil (Hansen, Maehlum and Bakken, 1993; Ruser et al. , 1998), and reduced root growth and consequently lower crop yields. A study by Gray and Pope (1986) showed also that the incidence of Phytophthora root rot in soybeans (Glycine max. L.) was greater with soil compaction. Soil compaction increases the abundance of anaerobic microsites and decreases the proportion of coarse and N O (Ball, Scott and Parker, 1999a). Only rarely has soil pores, which may favour emissions of both CH 2 4 compaction been associated with positive impacts, such as increasing the plant-available water capacity of sandy soils (Rasmussen, 1985) or reducing nitrate leaching (Badalıkova and Hruby, 1998) or benefiting soybean grown in areas prone to iron deficiency chlorosis in wet years (DeJong-Hughes et al. , 2001). 6.9.1 | Effect of tillage systems on compaction While all tillage methods tend to reduce soil bulk density and penetration resistance to the depth of tillage , 1992), equipment used in modern agriculture causes soil compaction of topsoil and subsoil. (Erbach et al. Working the soil to avoid compaction requires timing of tillage in relation to soil water moisture content and soil texture (Håkansson and Lipiec, 2000). No-tillage (NT) agriculture is gaining wide acceptance and Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 138 138

181 is among the top options in the portfolio of technologies to reduce tillage costs, conserve soil and water, emissions, which contribute to global warming increase soil organic carbon (SOC) pools, and reduce net CO 2 (Lal , 2004). Despite the numerous benefits of NT, there is no consensus yet on its role in alleviating et al. et al. , soil compaction: some researchers report increased compaction associated with the practice (Bueno 2006) and others a decrease in compaction (Gregory, Shea and Bakko, 2005). Increasing soil organic matter, as practiced in conservation agriculture, reduces soil compactibility (Thomas, Haszler and Blevins, 1996), but residue availability remains a key challenge, especially in Africa. 6.9.2 | What is the extent of deep soil compaction? Soil compaction affects mainly topsoils (Balbuena et al. , 2000; Flowers and Lal, 1998) but can also affect subsoils at depths >30 cm. Most subsoil compaction occurs when the soil is wet and field equipment weights exceed 10 tons per axle. The average weight and power of vehicles used on farms has approximately tripled since 1966 and maximum wheel loads have risen by a factor of six (Chamen, 2006). While remediation of shallow compaction is possible, for example by ripping and subsoiling, correcting soil compaction at depths below 45 cm is challenging (Batey, 2009; Berli et al. , 2004). Both topsoil and subsoil compaction have been acknowledged by the European Union as a serious form of soil degradation, estimated to be responsible for degradation of up to 33 million ha in Europe (Akker and Canarache, 2001). Similar compaction problems have been reported elsewhere, including in Australia, Azerbaijan, Japan, Russia, China, Ethiopia and New Zealand (Hamza and Anderson, 2005). The total amount of compacted soil worldwide has been estimated at approximately 68 million ha or around 4 percent of the total land area (Oldeman, 1992; Soane and Van Ouwerkerk, 1994). Nearly 33 million ha is located in Europe, where the use of heavy machinery is the main cause. Cattle trampling and insufficient cover of the top soil by natural vegetation or crops account for ). Flowers and Lal, 1998 Hamza and Anderson, 2003 ; compaction of 18 million ha in Africa, and 10 million ha in Asia ( Agricultural mismanagement (80 percent) and overgrazing (16 percent) are the two major causative factors of human induced soil compaction (Oldeman, 1992). 6.9.3 | Solutions to soil compaction problems Soil compaction, like soil chemical characteristics, should be monitored routinely and corrected as part of soil management (Batey, 2009). Although soil compaction effects on soil biodiversity and related functions and processes depend on several site and soil properties, a threshold of effective bulk density of 1.7 g cm–3 is the maximum above which only negative effects are observed (Beylich et al. , 2010). Managing soil compaction can be achieved through appropriate application of some or all of the following techniques: (a) addition and maintenance of adequate amount of soil organic matter to improve and stabilize soil structure (Heuscher, Brandt and Jardine, 2005); (b) guiding, confining and minimizing vehicular traffic to the absolutely essential by reducing the number and frequency of operations, and performing farm operations only when the soil moisture content is below the optimal range for the maximum proctor density (Kroulik et al. , 2009); (c) mechanical loosening such as deep ripping (Hamza and Anderson, 2005); and (d) selecting a rotation which includes crops and pasture plants with strong tap roots able to penetrate and break down compacted soils (Hamza and Anderson, 2005). Promoting macrofauna activity can accelerate creation of channels for water infiltration and root growth. Arbuscular mycorrhiza can to some extent alleviate the stress of soil compaction. This effect has been observed on wheat growth following increased root/shoot ratio of wheat under et al. compaction (Miransari , 2008). In the long-term, soil compaction can be reduced by natural processes that cause the soil to shrink and swell such as wetting and drying (Shiel, Adey and Lodder, 1988), and freezing and thawing (Miller, 1980). Soil moisture lower than the plastic limit is desirable for cultivation. Traffic should be avoided or restricted when condition are otherwise. For farmers, a simple test to avoid soil compaction involves squeezing a small lump of soil into a ball and rolling it into a rod about 3 mm in diameter. If a rod can be made easily, the soil is too wet and will compact if it is worked or has animals or machinery on it. If the rod is crumbly the water content should allow traffic and cultivation without compaction. If a rod will not form at all, the soil could be too dry for tillage in a sandy or loamy soil. This test should be run at several points over the full depth of any proposed cultivation. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 139 139

182 | Global soil-water quantity and quality: status, processes and trends 6.10 The world relies on its freshwater for ecosystem health and human well-being and prosperity. Yet only 2.5 percent of the world’s water is fresh, and of that, 68.7 percent is in the form of ice. Groundwater comprises 30.1 percent of the freshwater, and just 0.4 percent of the world’s freshwater is in lakes, rivers and the soil. 6.10.1 | Processes Soil water comprises only 0.05 percent of the world’s store of freshwater. However, the upward and downward fluxes of water and energy through the soil are massive, and they are strongly linked. The flows are upward in the form of water vapour, long-wave radiation and reflected short-wave radiation, and downward in the form of liquid water and short-wave radiation (Figure 6.12). The soil-vegetation system is the first receiver of the rain and energy that fall on our lands. The soil-vegetation system, which encompasses the upper reaches of the groundwater or basement rock to just above the soil-vegetative layer, is the critical zone for controlling terrestrial water quantity and quality. -1 3 yr et al. (2015) estimate the total annual precipitation onto continents to be 116 500±5 100 km Rodell – equivalent to approximately five-times the water stored in the Great Lakes of North America. Sixty percent -1 3 ) returns to the atmosphere through evapotranspiration. The remaining 40 yr of this (70 600±5 000 km -1 3 yr ) leaves the continents as runoff, with the greatest proportion either running percent (45 900±4 400 km off the surface of the soil or returning to streams via the groundwater flow system after passing through the soil. Thus small changes due to human intervention and climate change that alter these fluxes can have very large impacts on the store of soil water. The quantity, quality and flow of water over and through soil affect the spatial and temporal availability and usage of water. The quantity of soil water in a particular layer of soil can be determined by the soil-water retention curve, the so-called ‘soil-water characteristic’ (Figure 6.13). This curve describes the relationship between the amount of water a particular soil can hold and the energy, or matric potential, required to overcome adhesive and cohesive forces to extract water from the soil. Soils of different textures have very differing characteristic curves (Figure 6.13) and this affects the movement and storage of water in the landscape. © European Space Agency Figure 6.12 The flows of water and energy through the soil-vegetation horizon Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 140 140

183 The quality of the soil’s water is determined by the impurities and pollutants present in the soil water, which may, or may not be adsorbed to and/or exchanged in some part with the soil’s reactive matrix materials. The flow of soil water is determined by the gradient in the matric potential, and the soil’s hydraulic -1 ) (Figure 6.14), which describes the ease with which water flows through the soil conductivity, K (cm day pore space. The hydraulic conductivity curve is highly non-linear and strongly dependent on the soil’s water θ , and hence matric potential (Figure 6.14). Soil water flow can vary from very slow in soil with small content, pores, to very fast in soil with large interconnected pores. Figure 6.13 The soil-water characteristic curve linking matric potential, to the soil’s volumetric water content. Source: Tuller and Or, 2003. The soil-water characteristic (Figure 6.14) is an important factor affecting soil microbiology and rhizosphere ecology. It controls the stability of the spatial and temporal geometry of the soil pore space, which in turn defines the allocation of resources to soil biota, the transport of liquids, gases and solutes to and from roots, and the diversity of microbial habitats (Hinsinger , 2009). The soil micro-organisms are largely aquatic in et al. nature and do not inhabit the air-filled pores. They live instead in the liquid phase of the pores, the thickness of which is controlled by the matric potential, which also controls the size and distribution of water-filled pores that provide the hydraulic connectivity through soils. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 141 141

184 -1 Figure 6.14: The soil’s hydraulic conductivity, K (cm day ) in relation to the matric potential, ψ (MPa). As the matric potential becomes more negative the soil’s water content drops (see Figure 6.16) which increases the tortuosity and slows the flow of water. Source: 3 Hunter College. The interactions between the structure and physical, chemical and biological components of the soil control the myriad soil functions and processes that are essential for healthy soils, ecosystems and human well-being. The soil acts as buffer and filter. Indeed, our soil is the world’s largest water filter. And through this buffering and filtering, soil controls the quantity and quality of the world’s liquid freshwater. 6.10.2 | Quantifying soil moisture Soil water varies on multiple time and space scales, driven by climate, weather variability, land cover, topography and soil type and structure (Figure 6.15). Measuring variations in soil water is challenging especially at large scales where the cost of direct measurement would be very high. Long-term measurement networks et al. , 2000). However, with the recognition have historically been limited to a few locations globally (Robock of soil water as an essential climate variable and the realization that in-situ measurements are necessary for the calibration and validation of remote sensing, the number of operational monitoring networks is increasing (Dorigo , 2011). There are also short-term experimental campaigns with multi-scale soil water sampling et al. , 2012). For example, the Soil Climate Analysis Network (SCAN) in the United States provides soil et al. (Crow water measurements for 174 sites across the United States, with some measurements dating back to 1992. New technologies such as the COsmic-ray Soil Moisture Observing System (COSMOS) cosmic-ray neutron probes (Zreda et al. , 2012) have enabled more efficient and larger measurement footprints of the order of several hundreds of square meters. 3 http://www.geo.hunter.cuny.edu/tbw/soils.veg/lecture.outlines/soils.chap.5/soils_chapter.5.htm Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 142 142

185 At continental scales, the only practical means of estimating soil water is from satellite sensors or simulation models. Satellite-based measurements of soil water are generally based on measuring microwave emissions that vary because of the sensitivity of the soil dielectric constant to its wetness. These approaches use radiative transfer models to simulate the transfer of radiation emitted from the soil through the vegetation canopy and atmosphere to the satellite sensor. However, measurements have generally been restricted to the top centimetre of the soil column because of the penetration depth of microwave signals for current sensors (> 6 GHz). They are also restricted to sparsely vegetated regions. The recently launched Soil Moisture Ocean , 2010) satellite et al. Salinity (SMOS) (Kerr et al. , 2001) and Soil Moisture Active Passive (SMAP) (Entekhabi missions improve on this by using L-band (1-2 Ghz) sensors that have penetration depths of the order 5 cm and are less restricted by dense vegetation. Estimates from land surface models have also contributed to understanding the variation of soil water at large scales (Sheffield and Wood, 2008). These simulation models are driven by observations of precipitation, temperature and other meteorology and simulate the surface hydrological cycle with soil water as a prognostic state variable. Recent efforts have developed long-term simulations of soil water at regional to global scales (Sheffield and Wood, 2007, 2008; Haddeland , 2011), et al. although uncertainties exist because of missing process representation in the models and because of errors in model structure, parameters and the meteorological forcings. 6.10.3 | Status and trends Understanding variations in soil water is critical for a range of applications including drought risk management, agricultural decision making, and understanding and attributing climate change impacts. Currently, long-term (multi-decadal) time series of soil water which have been developed from models and satellite retrievals are being used to understand variability and long-term changes in soil water Figure 6.15 Factors controlling soil water spatial variability and the scales at which they are important. Source: Crow et al., 2010) Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 143 143

186 (Sheffield and Wood, 2008; Dorigo , 2012). Figure 6.16(a) shows the spatial variability of soil water globally et al. from model simulations, ranging from high values in the wet tropics and northern boreal forests, to the desert regions, such as North Africa, the Middle East, central Asia and Australia. Seasonally, soil water varies with changes in precipitation (Figure 6.16 b) with the largest variations in the monsoonal regions of south and southeast Asia, west and central Africa and the Amazon. From year-to-year, the El Niño Southern Oscillation (ENSO) is the main driver of soil water variability globally (Sheffield and Wood, 2011), often leading to drought conditions in the Amazon, south Asia, eastern Australia and southern Africa during El Niño years, and to drought in the United States southwest and the Horn of Africa in La Niña years. Longer-term changes in soil water are mostly driven by changes in precipitation (Figure 6.16 c and d). Global warming may be playing a role in drying soil water in some regions, although this is a subject of debate. Over the past 60 years, soil water has been generally wetting over the western hemisphere and drying over the eastern hemisphere, mostly in Africa, East Asia and Europe. Trends over the past 20 years (Figure 6.16 e and f ) indicate intensification of drying in northern China and southeast Australia, and switches from wetting to drying across much of North America, and southern South America, in part because of several large-scale and lengthy drought events. 6.10.4 | Hotspots of pressures on soil moisture Hotspots of pressures on soil water quantity and quality have emerged around the globe. These result from changes in soil water driven by climate change and variability, coupled with human pressures on soil water through, for example, agricultural intensification and extensification. We describe three hotspots: the North China Plain, the Horn of Africa, and the southwestern United States. The North China Plain has seen rapid expansion of agriculture driven by population growth and increasing -1 of precipitation and so irrigation from demand for food. This area is relatively dry with around 500 mm yr groundwater has become an important feature of agricultural intensification. However, groundwater has been used at unsustainable rates, with the result that groundwater levels are dropping by over 1 m per year in , 2003). Furthermore, precipitation has decreased over the past few decades (Figure some parts (Kendy et al. 6.16 f ). Coupled with intensive irrigation and fertilizer application, this has led to declines in soil water quality et al. through salinization and nitrogen leaching (Kendy , 2003). Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 144 144

187 Figure 6.16 (a) Global distribution of average soil moisture depth in the top 1 m of the soil. (b) Seasonal variability in soil moisture calculated as the standard deviation of monthly mean soil moisture over the year. (c-d) Global trends (1950-2008) in precipitation and 1 m soil moisture. (e-f ) As for (c-d) but for 1990-2008. Results for arid regions and permanent ice sheets are not shown. Source: Sheffield and Wood, 2007. Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 145 145

188 Drought has plagued many parts of Africa because of high climate variability from year to year. Severe droughts in the 1970s and 1980s led to the deaths of hundreds of thousands of people across the Sahel (Sheffield and Wood, 2011). Recent droughts in the Horn of Africa have continued to affect millions of people (Ledwith, 2011; UN, 2011), driven by an overall decline in rainfall that is expected to continue and may be linked to anthropogenic warming of the Indian Ocean (Funk et al. et al. , 2011). Monitoring soil water , 2008; Williams and its impacts on food security in the Horn of Africa is particularly difficult because of the lack of ground measurements. Nonetheless, the use of satellite and modelling technologies has the potential to provide drought and famine early warning (Anderson et al. , 2012; McNally et al. , 2013; Sheffield et al. , 2014). Soil water in the southwestern United States has been affected over the past two decades by frequent severe drought events (2000-2002, 2007, 2009), culminating in a three year drought in California (2011- 2014) with state-wide impacts on agriculture (Howitt et al. , 2014). A shortfall in irrigation water owing to a depleted mountain snowpack was partly offset by increasing groundwater pumping. Recent analysis using Gravity Recover and Climate Experiment (GRACE) satellites has confirmed the resulting massive losses of groundwater since the 1980s from the aquifers underlying California’s agriculturally important Central Valley (Famiglietti and Rodell, 2013). McNutt (2014) concludes that “... it is this underground drought we can’t see that is enduring, worrisome, and in need of attention”. 6.10.5 | Conclusions Soil water is vital for the health of terrestrial ecosystems and human well-being. Although only a small fraction of the world’s water is stored in the soil, the fluxes of water through the soil are massive. On the time-scale of years, the El Niño Southern Oscillation is the prime control on the global variability in soil water. At longer time-scales, the global pattern of precipitation is the dominant driver in controlling changes in soil water. This pattern may be influenced by climate change. Global analysis of the changing patterns of soil water has revealed the emergence of three global hotspots in terms of quantity and quality. These are the North China Plan, the Horn of Africa and the southwestern United States. There will be great challenges to address in these hotspot regions and in other pockets where declining soil water quantity and quality is threatening ecosystem health and human well-being. References 2012. Effect of different Abd Elrahman, S.H., Mostafa, M.A.M., Taha, T.A., Elsharawy, M.A.O. & Eid, M.A. amendments on soil chemical characteristics, grain yield and elemental content of wheat plants grown on salt-affected soil irrigated with low quality water. Annals Agric. Sci ., 57: 175-182. Abdelfattah, M.A. & Shahid, S.A . 2007. A comparative characterization and classification of soils in Abu Dhabi coastal area in relation to Arid and Semi-Arid conditions using USDA and FAO soil classification System. , 21: 245-271. Arid Land Research & Management Abdulkadir, A., Sangaré, S.K., Amadou, H. & Agbenin, J.O. 2014. Nutrient balances and economic performance in urban and peri-urban vegetable production systems of three west African cities. Experimental Agriculture , 51: 126–150 Aherne, J. & Posch, M. 2013. Impacts of nitrogen and sulphur deposition on forest ecosystem services in , 5: 108–115 Canada. Current Opinion in Environmental Sustainability Journal of Agricultural . 1933. The threshold wind speed of sand grains on a wetted sand surface. Akiba, M Status of the World’s Soil Resources | Main Report Global soil status, processes and trends 146 146

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210 Soil change: impacts and responses Coordinating Lead Authors: Chencho Norbu (Bhutan), David Robinson (United Kingdom), Miguel Taboada (Argentina) Contributing Authors: Marta Alfaro (Chile), Richard Bardgett (United Kingdom), Sally Bunning (United Kingdom), Jana Compton (United States), William Critchley (United Kingdom), Warren Dick (United States), Scott Fendorft (United States), Gustavo Ferreira (Uruguay), Tsuyushi Miyazaki ( Japan), Carl Obst (Australia), Dani Or (Switzerland), Dan Pennock (ITPS/Canada), Matthew Polizzotto (United States), Dan Richter (United States), Marta Rivera- Ferre (Spain), Sonia Seneviratne (Switzerland), Pete Smith (United Kingdom), Garrison Sposito (United States), Susan Trumbore (United States) and Kazuhiko Watanabe ( Japan). Reviewing Authors: Dominique Arrouays (ITPS/France), Richard Bardgett (United Kingdom), Marta Camps Arbestain (ITPS/New Zealand), Tandra Fraser (Canada), Ciro Gardi (Italy), Neil McKenzie (ITPS/Australia), Luca Montanarella (ITPS/ EC), Dan Pennock (ITPS/Canada) and Diana Wall (United States). Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 168 168

211 7 | The impact of soil change on ecosystem services 7.1 | Introduction Soils are now recognized to be in the ‘front line’ of global environmental change and we need to be able to predict how they will respond to changing climate, vegetation, erosion and pollution. This requires a better understanding of the role of soils in the Earth system to ensure that they continue to provide for humanity et al. , 2011). Although only a thin layer of material at the Earth’s surface, soils and the natural world (Schmidt like many interfaces play a pivotal role in regulating the flow and transfer of mass and energy between the atmosphere, biosphere, hydrosphere and lithosphere. Moreover, the structure and organization of soils leaves an important imprint on the Earth’s surface in terms of how land is used and how ecosystems develop. Soils help regulate the Earth’s physical processes such as water and energy balances, and act as the biogeochemical engine at the heart of many of the Earth system cycles and processes on which life depends. Some soil processes contribute directly to the delivery of ecosystem goods and services, while other soil processes influence the delivery of goods and services. This section examines how soil processes affect soil and ecosystem function and the production of goods and services of benefit to humanity. Humanity has had an indelible impact on the Earth’s surface, so much so that it has been proposed that the planet has entered a new geological epoch, the Anthropocene (Crutzen, 2002). A population of ca. 7 billion people that will likely grow to 9.6 billion by 2050 is stressing Earth’s resources. Maintaining the planet in an equitable state for human life is perhaps our greatest challenge. Currently, humans have adapted 38 percent of the earth’s ice-free land surface to agriculture, crops and pasture (Foley et al. , 2011). Agricultural production, driven by the need to produce food for a growing population, has had a tremendous impact on our ecosystems and resources, especially through the abstraction of water and the leaving of residues. Rockström et al. (2009) proposed that we need a ‘safe operating space for humanity with respect to the Earth system’. They argue that that there exist biophysical planetary boundaries (or thresholds) which it is inadvisable to cross if we are to maintain the needed balance. Vince and Raworth (2012) adapted these concepts to include social goals (1). This presentation underlines the fact that we live in a coupled human earth system. The ecosystem services analytic approach has been developed in order to bridge the science/policy divide. The approach aims to make the concepts clear for all and to set out what needs to be considered in order for humanity to live within sustainable boundaries. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 169 169

212 Soils and soil security are at the heart of this effort. Soil security is defined in McBratney, Field and Koch (2014) as “maintaining and improving the world’s soil resources to produce food, fibre and freshwater, to contribute to energy and climate sustainability, and to maintain the biodiversity and the overall protection of the ecosystem”. Soils perform important ecosystem services (e.g. functions for humanity) including: biomass production; storing, filtering and transforming nutrients and water; maintaining a gene pool; providing a source of raw material for products such as bricks and tiles; regulating climate and hydrology; and providing an archive of cultural heritage. Soils provide ecosystem goods and services directly but some soil processes can have an adverse impact on the delivery of ecosystem goods and services. The ability of soils to function can be threatened by human activity (on this, see the Soil Thematic Strategy, SEC, 2006). A growing population, resource extraction, agricultural production, land use change and climate change all contribute to this threat. As population increases, food security is becoming more important in the global agenda. Our historical solution to producing more food has been to mechanize, cultivate more land, and increase the application of plant nutrients and water. This has led to an almost linear increase in production over time (Pretty, 2008). However, the rate of increase is likely to plateau, as has already been seen with wheat in Northern Europe and with rice in Korea and China (Cassman, Grassini and Wart, 2010). In addition, agricultural growth comes with environmental costs or externalities, which are costs not accounted for in the cost of production. The degradation caused can adversely affect everyone, and even the production systems themselves - for instance, et al. , 2014). declines in pollinators can threaten future production (Deguines Figure 7.1 The 11 dimensions of society’s ‘social foundation’ and the nine dimensions of the ‘environmental ceiling’ of the planet. Source: Vince and Raworth, 2012. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 170 170

213 et al. (2009) suggest we are approaching the limits of the planet’s cultivatable land, while Rockström the addition of nutrients, especially nitrogen, continues to overload many terrestrial-aquatic systems (Diaz and Rosenberg, 2008). At the same time, arable production has seen declines in the carbon content of soils - the largest terrestrial carbon reservoir – and these declines are affecting other soil functions, including et al. water and nutrient retention (Reynolds , 2013). Food production systems will need to change to create multifunctional agro-ecosystems capable of maintaining a balance between yields, soil functions and biological diversity. Within the field of ecology, this challenge has led to a rigorous debate concerning the loss of natural species from agricultural lands - often termed, the ‘land sparing, land sharing’ debate (Green et al. , 2005). This debate has now been integrated within the broad ecosystem services discussion whose central ten also focuses on human interaction with ecosystems and their long-term sustainability and continued functionality (MA, 2005). et al. (2005) proposed that a natural ecosystem provides a range of goods and services Conceptually, Foley (2) while on intensively farmed agricultural land, crop production dominates at the expense of all other goods and services. They proposed that an ideal situation would be one of balance, with the system producing a range of goods and services including food – the ‘sharing’ side of the land sparing/ land sharing debate. Organic agriculture has been seen as a model of this sharing or balance. However, organic agriculture has so far generally failed to maintain productivity levels in either crop or livestock systems (Pretty, 2008). The implication is that organic agriculture does not yet promise balance, because it requires more land and more use of natural capital to maintain production levels. Determining if there are viable ‘sharing’ systems should continue to be an important research goal but for the moment ‘sparing’ appears to have the upper hand in the debate (Phalan et al. , 2011). But how do we achieve sustainable intensification? While the viability of sharing remains in question, should we focus on a narrow-minded, single service supply management strategy, e.g. arable soils for crop production or peat soils for carbon storage? Sustainable intensification research, which seeks to find ways of optimizing production while blending in new strategies for multifunctional ecosystem , 2013). service management, is being championed as a way forward (Firbank et al. There is no single solution. Foley’s conceptual diagram (2) highlights the challenges and possible trade- offs: a natural ecosystem delivers a wide range of ecosystem services but scant production; and an intensive cropland system delivers royally on production but precious little on ecosystem services. A balanced system of cropland with restored ecosystem services would deliver on all services, including production. A recent synthesis and analysis of data from the Countryside Survey, a national survey of Great Britain, suggests that Foley’s conceptual diagram of intensive cropland (2) is the current situation. Different services reach optimums at different points along the productivity gradient, but we cannot have everything (3). The ecosystem service indicators alter, often in a non-linear way with the proportion of intensive land use – but with exception of production, they all decline with intensification. 3 b and c go on to show that changes in moisture inputs or moisture regime, or alteration of soil pH would change the service delivery balance. At no point do we get everything, so we will need to choose priorities with our current systems. Figure 7.2 Conceptual framework for comparing land use and trade-offs of ecosystem services. Source: Foley et al., 2005. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 171 171

214 The land sparing, land sharing approach can also been framed in terms of resilience (sharing) and efficiency (sparing). Efficient systems by their very nature will prioritise the performance of one function over that of others. The degree to which others are affected will depend on whether they perform well under similar management or not. Currently, the data in 3 indicate that the choice lies between efficiency and redundancy. We can have an efficient carbon storage system, e.g. peat development, which may also perform well as a climate thermal buffer because the conditions for peat accumulation require lots of water, but it will not be productive for crops in that state, nor will the arable system have high biodiversity as this is inefficient. Choices need to be made as to what types of systems we wish to promote. In light of this, the focus of this chapter is to assess the global scientific literature and understand how soil change discussed in Chapters 5 and 6 is likely to impact soil functions and the likely consequences for ecosystem service delivery. Each section of this chapter outlines key soil processes involved with the delivery of goods and services and how these are changing or - where evidence permits - may change. Each section then reviews how this change impacts soil function and affects ecosystem service delivery. Some soil change does not produce an ecosystem service, but does impact it; these impacts are considered when assessed as important and adverse. The focus is on the local, regional and global scales and follows the general reporting categories of the MA (2005) modified by TEEB (2014) to provisioning, regulating and cultural services. Towards the end of the section there is a focus on the links with policy, institutions and management. 7. 2 | Soil change and food security Keating et al. (2014) provide a useful frame for examining the main roles of soils in food supply through their development of the food wedge concept. The food wedge is the triangular area between the level of food demand in 2010 and the upper bound of food demand in 2050 (suggested by Keating and Carberry (2010) as a wedge equal to approximately 127 x 1015 kcal). The food wedge presented by Keating et al. (2014) assumes that food supply and demand were broadly in balance in 2010. Increases in food supply (through, for example, the strategies suggested by Foley et al. , 2011) would increase the supply to meet the rising demand for food. Either the incremental loss of productivity from current agricultural land or the total loss of agricultural land due to degradation in the future would cause the lower boundary of the wedge to decrease and hence increase the gap between food supply and demand (Figure 7.4). This decrease (or total loss) could occur if the services for plant production supplied by the soil decreased due to a significant impairment of one or more of the soil functions. Alternatively the restoration of productivity to previously degraded land would increase plant production in addition to addressing the yield gap or increases in food delivery. Therefore a key soil- focused strategy is to reduce future productivity loss from agricultural soils due to degradation to a minimum and to restore productivity to soils that have previously experienced productivity losses. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 172 172

215 Figure 7.3 Response curves of mean ecosystem service 1.0 2 across Great Britain. Source: Maskell et indicators per 1-km al., 2013. cSLA The curves are fitted using generalized additive models to ordination axes constrained by; (a) proportion of intensive land (arable and Water quality improved grassland habitats) within each 1-km square from CS field survey data; (b) mean long-term annual average rainfall (1978–2005); and (c) mean soil pH from five random sampling locations in each 1-km Soil diversity square. All X axes are scaled to the units of each constraining variable Pollination (B'flies) Plant diversity Cultural Response Pollination (Bee) Freshwater diversity Soil C storage 0.0 Proportion of intensive land in 1km square 1.0 0.0 1.2 Freshwater diversity cSLA Soil C storage Plant diversity Butt Response Soil diversity 0 50 Rainfall (mm) 5000 Soil C storage 1.0 cSLA Water quality Soil diversity Pollination (Bee) Pollination (B'flies) Response Cultural Freshwater diversity Plant diversity 0.0 2.0 9.0 Mean Soil pH Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 173 173

216 The restoration of productivity on degraded soils can be complex insofar as soils may have been degraded to the point where they cannot readily respond to fertility-improving management techniques. These complex interactions among inherent soil properties, management history and the response to inputs is (2013) on maize production intensification on smallholder well illustrated in the work of Rusinamhodzi et al. farms in Zimbabwe. In this region two major controls of productivity exist – significant differences in yield between sandy and clay soils (e.g. inherent soil properties); and pronounced fertility gradients between more productive fields close to the homestead and more degraded soils in outfields further from the homestead (a management-induced fertility gradient common in many areas of Africa). The sandy soils required long- term additions of manure to restore soil functions before the benefit of the mineral fertilizer additions could begin to be realized; however even after nine years of substantial organic inputs, the highly degraded sandy outfields did not recover their productivity. The authors speculate that the initial soil organic carbon levels in the sandy outfields were too low for yields to recover. Moreover at the village scale, the overall amount of manure produced is insufficient to apply the required amounts of manure in all fields. Figure 7.4 The food wedge and the effect of soil change on the area of the wedge. Source: Keating et al., 2014. The relative sizes of the effects of soil change on the food wedge are not drawn to scale. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 1 74 1 74

217 One approach to maintaining soil health is ‘conservation agriculture’, which comprises a range of agricultural practices that include reduced tillage and no-till, greater retention of crop residues, and crop rotations. However, the lack of organic inputs which constrained productivity in the Zimbabwe example above also limits the ability of conservation agriculture to restore fertility in sub-Saharan Africa generally. Palm et al. (2014) found that the greatest obstacle to improving soil functions and other ecosystem services in Sub-Saharan Africa region is the lack of residues produced due to the low productivity of the soils. The limited supply of crop residues also highlights the need to make optimum use of all sources of organic inputs, such as animal manure and properly processed human wastes. These studies emphasize the inability of mineral fertilizers alone to significantly increase food production in regions where the yield gap is greatest. Removing the nutrient limitations through additions of mineral O emission from N-fertilizer, fertilizers alone will also exacerbate the range of environmental issues (e.g. N 2 surface and groundwater contamination) in all food-producing regions unless the efficiency of crop use of agricultural inputs can be increased. Additionally the fraction of P available as mineable phosphate rock is finite. Recent concerns that the world’s supply of phosphorus was being rapidly depleted and that ‘peak phosphorus’ was only a few decades away (Cordell and White, 2010) have been dispelled, due to recent upward revisions of world phosphate rock reserves and resources (Van Kauwenbergh, 2010). However, the world supply of phosphorus is limited, and rising prices and market volatility are inevitable. More efficient use of phosphorus is therefore essential. This overall issue is termed the ‘Goldilocks’ problem by Foley et al. (2011) – there are many regions with too much or too little fertilizer but few that are ‘just right’. A final strategy is to minimize diversion of agricultural soils to production of non-food crops. Recent large- scale bioenergy production on land previously used for food production has driven a significant land use change and represents a major shift of agricultural soils away from food production. Demand for soybean, maize and oil palm for biofuel has been a driver of agricultural land conversion in recent years particularly in Latin America. Conversion of existing cropland or the development of new cropland for bioethanol and biodiesel production competes with food production and carbon returns to the soil (Foley et al. , 2011) and thus constitutes a threat to soil and food security. Biofuels produced from crops using conventional agricultural practices will exacerbate stresses on water supplies, water quality and land use. In any case, biofuels are not expected to mitigate the impact of climate change as compared with petroleum (Delucchi, 2011). Threats to the food security dimension ‘availability’ are mainly (but not only) caused by soil and land , 2009). This is particularly the situation when the degradation and associated water resources (Khan et al. degradation is irreversible or very hard to reverse. This may, for example, be the case with severe topsoil losses caused by wind or water erosion, terrain deformation by gully erosion or mass movement, acidification, alkalinization/salinization, soil sealing, or contamination with toxic substances (Scherr, 1999; Palm et al. , 2007; Mullan, 2013). The resulting loss of productivity will reduce yields from a site, leading to reduced returns to producers and, in some cases, abandonment of production at the site. Productivity may be restored, but economic considerations may limit the adoption of restorative measures. The impact of each threat on specific soil functions relevant to crop production has been covered in Chapter 6 and is summarized in Figure 7.5. The present chapter will focus on the implications for food security of the trends in each threat. 7.2.1 | Soil erosion A summary by den Biggelaar et al. (2003) suggests that global mean rates of erosion are between 12 to 15 -1 -1 -1 (see Table 7.1), very similar yr (Table 7.1). The mid-point of this range yields a soil loss of 0.9 mm yr tonnes ha -1 calculated by Montgomery (2007). Overall these rates are substantially to the mean soil loss of 0.95 mm yr higher than rates of soil formation, and hence pose a long-term global threat to soils (Montgomery, 2007; see also Section 6.1 above). Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 175 175

218 Our understanding of the rates for the three erosion agents (wind, water and tillage) is uneven. Erosion -1 -1 yr ) in cropland in many agricultural regions rates due to water erosion remain very high (> ca. 20 tonnes ha (Figure 7.2); essentially any cropped area with hilly land and sufficient precipitation is at risk. No reliable global estimates for current wind erosion rates exist, and the estimates of the human contribution to current dust emissions range from only 8 percent in North Africa to approximately 75 percent in Australia (see also Section 6.1 above). Tillage erosion primarily results in in-field redistribution of soil, and decreases the productivity of soils in convex slope elements and near-upslope field or terrace borders. Global-scale summaries also require consideration of the fate of eroded soil – in some regions deposition of eroded soil in river floodplains and deltas creates areas of very high and enduring fertility. The effect of soil erosion on individual soil properties related to crop production is well documented, but the aggregate effect of soil loss on crop yields themselves is less firmly established. The four integrative studies summarized in Table 7.1 are based on data sources which range from experimental plot data to re- interpretation of GLASOD data. The range of estimates of annual crop loss due to erosion ranges from 0.1 percent to 0.4 percent, with two studies estimating 0.3 percent yield reduction. If the median value of 0.3 percent annual crop loss is valid for the period from 2015 to 2050, a total reduction of 10.25 percent could be projected to 2050 (assuming no other changes such as the adoption of additional et al. conservation measures by farmers). Foley (2011) cite a value of 1.53 billion ha for cropland globally; the loss of 10.25 percent of yield due to erosion would be equivalent to the removal of 150 million ha from crop production or 4.5 million ha per year. Figure 7.5 Direct impacts of soil threats on specific soil functions of relevance to plant production. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 176 176

219 Database Used Estimates Extent Author den Biggelarr Erosion: 179 plot-level et al. Global (37 countries) Erosion: Average rates -1 -1 yr (2003) studies between 12 – 15 t ha 1 (0.8 to 1.0 mm per year) Crop yield-erosion: 362 Relative annual crop yield reduction due to erosion: 0.3 percent per year (for six major crops) Bakker, Govers and Erosion-yield: 24 Primarily North America Yield reductions of experimental studies Rounsevell (2004) + Europe approximately 4 percent per 10 cm soil loss (= 1 0.36 percent per year) 28 regional studies Scherr (2003) Productivity losses Global and 54 national or since WWII of about sub-national studies 0.3 percent per year for on soil degradation cropland and 0.1—0.2 (many GLASOD based, percent for pasture. primarily soil erosion) Crosson (2003) Re-analysis of GLASOD Global Cumulative loss of 5 and Dregne and Chou percent of productivity (1992) on 4.7 billion ha of cropland and permanent pasture -1 990 period; in 1945 average annual rate of loss of 0.1 percent Table 7.1 Erosion and crop yield reduction estimates from post-2000 review articles -1 -3 -1 yr (den Biggelaar et al., 2003) and average erosion rate of 13.5 tonnes ha Calculated using average bulk density of 1.5 tonnes m 1 (mid-point of den Biggelaar et al., 2003 range) The regional differences in crop response to erosion are, however, major. There are great disparities in the sensitivity of soils to erosion – soils with growth-limiting sub-soil layers (e.g. shallow soils over bedrock, soils with high sodium and/or dense B horizons) are inherently more susceptible to yield reductions due to soil loss (Bakker et al. , 2007). In a study modelling the impact of erosion in Europe over the next century, Bakker et al. (2007) predicted yield reductions on the order of 6 to 12 percent in southern Europe and reductions of only 0 to 1 percent in much of northern Europe. The overall impact on European food production is, however, relatively small as the yields from southern Europe are lower to begin with. In addition, increases in climatic extremes associated with human-induced climate change may lead to enhanced levels of wind and water erosion, but the impact of these changes will differ greatly among regions. Finally, the crop yield/soil erosion relationship may be a less critical reason to reduce soil erosion than the off-site impacts of erosion, especially the transport of agricultural inputs such as N and P to waterways et al. (Steffen , 2015). Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 177 177

220 7.2.2 | Soil sealing Soil sealing is most commonly associated with the expansion of urban areas and leads to a permanent, non-reversible loss of agricultural land. Yields are eliminated, not just reduced and the soil, if completely sealed, becomes effectively non-soil. Urbanization of agricultural land should thus be considered as a threat to future food production, not only for the loss of good quality agricultural land but also because of the risk of soil pollution through waste disposal and acid deposition from urban air pollution (Chen, 2007; Hubacek et al. , 2009; Clavero, Villero and Brotons, 2011). Blum and Nortcliff (2013) provide a very rough estimate of 2 , and suggest this rate could increase due daily losses of soil due to sealing at the global scale of 250-300 km to continuing migration of rural dwellers to urban areas. Thus, new policies that favour sustainable rural development, oriented to avoid rural-urban migration as well as to support the return to rural areas of people living in the cities, could avoid soil degradation and promote food security. 7.2.3 | Soil contamination Soil contamination reduces food security both by reducing yields of crops due to toxic levels of contaminants and by causing the crops that are produced to be unsafe to consume. As summarized in Chapter 6 (Section 6.3), there are worldwide tens of thousands of known contaminated sites due to local or point-source contamination. In regions with a long-standing industrial base, the expansion of contamination is limited, but in countries undergoing rapid industrialization or resource development the potential for the further spread of contamination is great. The tremendous expansion of industry in China is one example of this: 20 million ha of China’s farmland (approximately one fifth of China’s total farmland) is estimated to be contaminated by heavy metals, and this may lead to a significant reduction in food availability (see also Section 6.3 above). Contamination is also severe due to point sources such as Cs pollution from the Fukushima Dai-ichi nuclear power plant and the Chernobyl disaster of 1983. Diffuse soil contamination occurs in many regions (Blum and Nortcliff, 2013), but is more commonly linked with concerns about food safety rather than significant decreases in crop yields. 7.2.4 | Acidification Acidification of agricultural soils is primarily associated with the net removal of base cations (e.g. product removal without replacement with ameliorants such as lime) and the direct addition of acidifying inputs (e.g. ammonium-based N fertilizer) to inherently low-pH soils, which have a low capacity to buffer added acidity. It is most prevalent on ancient, highly weathered soils. Acidification is a significant regional threat in countries such as Australia and Vietnam (see Chapters 10 and 15). Liming is an effective response to control acidity of surface horizons, but rates of lime addition lag behind required levels even in developed countries like Australia (SOE, 2011) and continuing loss of yield occurs. 7.2.5 | Salinization Salinization in a soil progressively reduces crop yields; beyond a certain crop-specific threshold, growth of a given crop may fail entirely. The regional summaries in Chapters 9 to 16 illustrate how difficult it often is to separate the causes of salinization: whether the saline soils are naturally occurring (primary salinization) or the salinization has been caused by inappropriate management, which is often the case with poorly executed irrigation programmes (secondary salinization). Estimates from the 1990s place the land area affected by primary salinization at approximately one billion ha, and the area of land with secondary salinization at 77 million ha (Ghassemi, Jakeman and Nix, 1995). Salinization is typically associated with arid and semi-arid areas, and may be exacerbated by climate change (see also Section 6.5). An increase in irrigated land is commonly suggested as a means to increase food production, but poorly designed and implemented irrigation schemes can readily cause an increase in Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 178 178

221 salinization. Safe design and operation of irrigation systems requires a high level of managerial expertise. Irrigation expansion can contribute to increases in food production but great care is needed in planning and design to avoid negative effects such as salinization. 7.2.6 | Compaction Compaction impairs soil functions by impeding root penetration and limiting water and gas exchange. In soils where it occurs, it can reduce crop yields but it rarely eliminates plant growth entirely. The susceptibility of different crops to compaction differs greatly (see also Section 6.9 above). Good soil management requires care in minimizing soil compaction and the adoption of management practices which alleviate existing compaction. The effect of soil compaction on output and hence on food security is, however, difficult to assess, especially in tropical areas (Lal, 2003). 7.2.7 | Nutrient imbalance The problems associated with under-supply of nutrients in regions such as Sub-Saharan Africa will be discussed in Chapter 8 in the context of closing the yield gap. Foley et al. (2015) clearly (2011) and Steffen et al. indicates the regions where over-supply of nutrients is occurring: mid-west United States, western Europe, northern India, and the coastal areas of China. Foley et al. (2011) emphasize the need to address the economic and environmental issues in nutrient over-supply by increasing the efficiency of nutrient uptake by plants. This, coupled with reductions in transport of nutrients to waterways by minimizing erosion, would substantially reduce eutrophication. It would also allow the redistribution of N and P to areas of nutrient-poor soils without , 2015). exceeding the planetary boundaries for the elements (Steffen et al. 7.2.8 | Changes to soil organic carbon and soil biodiversity Soil organic carbon (SOC) and soil biodiversity are commonly linked to three dimensions of food security: increases in food availability, restoration of productivity in degraded soils, and the resilience of food production systems. Soil C is not itself a direct control on food production but is a proxy for soil organic matter (SOM), which is one of the key attributes associated with many soil functions. Soil microbial C is normally included in aggregate measures of SOC, and soil microbes are a component of the soil organic matter; hence in terms of mass, SOC/SOM and soil microorganisms are directly related. The focus on SOC, rather than SOM, occurs because of the ease of measurement of C as a proxy for SOM, and because of the direct connection between SOC and atmospheric C. The roles of SOC and soil biodiversity in increasing food availability are also inextricably bound together. Increases in SOC and in soil biodiversity are believed to be beneficial for crop production, and decreases in both are equally believed to be deleterious for crops; however providing evidence for these qualitative statements , 2009; Bommarco, Kleijn and Potts, and establishing predictive relationships has been difficult (Naeem et al. 2013; Palm et al. , 2014). The more readily understood relationship between soil C storage and atmospheric C levels has driven much of the work in the past 15 years on soil carbon dynamics, but the secondary benefit of increasing SOC levels for crop production is commonly cited, if rarely quantified. Efforts to determine a threshold SOC value for maximum crop production in temperate soils have not been successful as it depends on management and on other factors such as soil limitations and precipitation (Loveland and Webb, 2003). Lal (2006) estimates yield -1 -1 -1 gain in SOC in the tropics and sub-tropics ranging from 20-70 kg ha for yr gains associated with a 1 Mg ha -1 -1 for maize. However, the study acknowledges that the data are meagre and that yr wheat to 30-300 kg ha functional relationships between SOC pool and crop yield are not available, especially for degraded soils in the tropics and subtropics. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 179 179

222 Research in tropical and semi-tropical lands has established that inputs of organic material through the return of residues and manure to the soil are essential for fertility restoration in degraded soils, but that low residue production and competing uses for residues and manure limit the adoption of these SOC-aggrading 2014). Sustainable soil management that approaches (e.g. Lal, 2006; Rusinamhodzi et al. , 2013; Palm et al. increases SOM levels will assist in maintaining productivity, but the specific measures taken to increase SOM must be locally developed. Establishing a direct, quantitative link between soil biodiversity and increasing food production is even more elusive. Sylvain and Wall (2011) observe that “the total invertebrates found in a soil will interact to provide many services and participate in several ecosystem functions, but it is unlikely that a single species will influence all services and functions that influence plant growth or composition at the same time or in the same manner”. Biodiversity beyond the soil plays an important role in regulating services such as biological pest control and crop pollination (Bommarco, Kleijn and Potts, 2013), and public concerns about the effects of pesticides on key species continues to grow. A final role for SOC enhancement and maintenance of soil biodiversity is to increase the resilience of the soil for food production, especially its ability to withstand disruption due to human-induced climate change. SOC buffers the impact of climate extremes on soils and crops by: (i) regulating water supply by reducing runoff and increasing soil-water holding capacity; (ii) reducing erosion through runoff reductions and improved aggregation; and (iii) providing sites for nutrient retention and release (Loveland and Webb, 2003; Lal, 2006). The combined role of soil organic matter and biodiversity in nutrient cycling ensures a continuing supply of nutrients for crop growth. It is difficult to quantify this relationship, especially in the light of the uncertainties associated with human-induced climate change, but the existing qualitative understanding is sufficient to establish the importance of SOC and biodiversity in sustainable soil management. Summary The importance of soil degradation and soil rehabilitation are highlighted in principles eight and nine of the proposed World Soil Charter: Soil degradation inherently reduces or eliminates soil functions and their ability to support ecosystem services essential for human well-being. Minimizing or eliminating significant soil degradation is essential to maintain the services provided by all soils and is substantially more cost-effective than rehabilitating soils after degradation has occurred. Soils that have experienced degradation can, in some cases, have their core functions and their contributions to ecosystem services restored through the application of appropriate rehabilitation techniques. This increases the area available for the provision of services without necessitating land use conversion. Our ability to predict the effect of soil degradation on food security is very limited for two main reasons. First, there is a lack of up-to-date knowledge both on the area affected by degradation and on the linkages between degradation and soil functions (and ultimately plant production). The research community continues to cite research summaries on the effects of soil degradation on crop yields from the 1990s based on data gathered in the 1980s. Yet crop production in many regions has undergone profound change since the 1980s – for example, the widespread adoption of conservation tillage in many regions occurred during the 1990s and 2000s. There is a pressing need for meta-analyses on all of the soil threats discussed here. This in-depth review of existing work needs to be complemented by new research to address major information gaps, and in particular to prove more conclusively the functional relationships between soil attributes and plant production. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 180 180

223 The second limitation to predictions is that farmers are not simply passive observers of inexorable degradation processes – farmers in all regions, including the tropics, are willing to invest in the future to protect soils and the essential services that they provide (Stocking, 2003). For example, the adoption of conservation tillage in heavily mechanized systems such as those in North America has substantially lowered erosion rates (Montgomery, 2007). The general applicability of conservation tillage in other regions may be et al. , 2014) but the principle that farmers are active participants in soil change is essential to limited (Palm recognize and encourage. 7. 3 | Soil change and climate regulation Soils play a fundamental role in the maintenance of a climate favourable to life. A range of soil processes and O, CO , CH helps regulate climate, including the thermal and moisture balance, greenhouse gases (H 2 4 2 O) and particulates in the atmosphere. Soils can also adversely impact the maintenance of air quality. N 2 7. 3 .1 | Soil carbon Although it is hard to estimate quantities, it is certain that soils contain vast reserves of carbon. Recent estimates range between 1200 and 3000 Pg C depending on the depth to which estimates extend, and on the way in which wetland soils are counted (Hiederer and Köchy, 2012). Roughly 1670 Pg of C is stored in peatlands , 2008). Hence soil organic matter is a large et al. and permafrost soils in high northern latitudes (Tarnocai . Soils also pool. Consequently, only small changes in soil C storage can have a large effect on atmospheric CO 2 contain approx. 950 PgC in the form of pedogenic carbonates to 2 m depth (Batjes, 1996). Carbon respired from soils and derived from decomposition of organic matter in soils approximately balances annual net primary production of carbon by biomass. Carbon dioxide derived from plant roots and from soils to the atmosphere, which in total is ~10 their symbionts below ground adds to the total flux of CO 2 to the atmosphere by fossil fuel burning (Schimel, 1995). Hence times larger than the current release of CO 2 . relatively small changes in the cycling of soil C can lead to large changes in atmospheric CO 2 Management that changes C inputs or tillage that alters the stability of soil organic matter through changes in soil aeration or structure measurably alter soil C storage. Historically, the expansion of agriculture has led to losses of soil C to the atmosphere, estimated globally to be of order 40-90 PgC, some of which has remained in the atmosphere (Smith, 2004, 2012). In terms of climate change, most projections suggest soil carbon changes driven by future climate change will range from small losses to moderate gains, but these global trends show considerable regional variation (Smith, 2012). The response of soil C in future will be determined by two factors: (i) the impacts of increased temperature and altered soil moisture on decomposition rates; and (ii) the balance between increases in C losses resulting from accelerated decomposition and predicted C gains through enhanced productivity under and nutrient deposition (Smith, 2012). elevated CO 2 Soil organic matter (SOM) is considered dynamic and has importance beyond its climate role. Plant residues added to soils provide energy for a cascade of heterotrophic organisms. A key outcome of organic matter (OM) breakdown is the release of essential nutrients into the soil. If the breakdown of OM exceeds the supply of , e.g. under high moisture conditions, the degradation of OM using other electron acceptors drives the O 2 production and consumption of other important greenhouse gases such as methane and nitrous oxide. The degradation of OM also indirectly affects greenhouse gases like troposphere ozone by altering the emission of reactive trace gases. In addition to climate effects through regulation of greenhouse gases, SOM determines properties such as nutrient retention, water retention, and the structure and size of the microbial community in soils. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 181 181

224 SOM feedbacks to climate change (Figure 7.6) include direct responses such as: (i) the alteration of microbial relative to , 2011); and (ii) moisture-related changes in the supply of O et al. activity with temperature (Conant 2 other electron acceptors that reflect precipitation change. In this context, probably the biggest concern is the thawing of large stores of C in permafrost at high northern latitudes, which will make organic C that has been frozen for millennia available for decomposition. This response is predicted to create a significant positive feedback to climate change (Schuur et al. , 2008). and its effect Another direct response of soil organic carbon pools is predicted in response to elevated CO 2 on ecosystem productivity. Free Air Carbon Dioxide Enrichment (FACE) studies have shown that belowground productivity can be strongly affected, with cascading and mixed consequences for SOM storage. However indirect effects are such as altered stabilization of older C associated with the increased inputs of fresh fertilization, plant inputs (‘priming’) add uncertainty to the prediction of future soil C responses. As with CO 2 increased deposition of reactive N associated with regional air pollution affects production, quality and spatial distribution of plant inputs (e.g. above- versus belowground) and can alter the decomposition rates through changes in the soil microbial community (Berg and Matzner, 1997). Hence the net effects on soil C storage are difficult to predict, though the combined effects of climate change and fertilization are expected to result in net losses of soil C overall from temperate forest soils (Hopkins, Torn and Trumbore, 2012) Many of the processes affecting SOM over the past century have been dominated by human management of vegetation, which in turn affects the inputs and status of SOM. Changes in vegetation cover, including those occurring in response to climate as well as to land use or management, influence soil organic matter by altering the rates, quality and location of plant litter inputs to soils. In turn, litter inputs influence the amount and composition of the decomposer organisms, including soil fauna, as well as the soil microbial community. Studies of a number of vegetation transitions – for example the replacement of forests with agriculture or pasture – have shown that these transitions have led to a loss of soil C to the atmosphere. However, the , are not trajectory of vegetation change in response to climate, and the consequences for atmospheric CO 2 well known, as soils will in turn determine what kind of vegetation will take over. For example, C from thawing permafrost soils may eventually be sequestered in the biomass of forests that can grow in the warmer climate. Evidently the time lags required for these transitions are an important part of understanding the net effect of soil C on the carbon cycle. In addition to direct effects of changes in plant litter addition to soils, management or vegetation change also alters the chemical and physical framework of soil and thereby the organisms inhabiting it. For example, ploughing can break up soil aggregates and make organic matter that was previously protected available to decomposers. Changes in evapotranspiration can change local and regional water resources. Addition of fertilizers increases plant productivity but also alters soil microbial communities and can stimulate production O. of reactive N gases and N 2 Large-scale soil erosion is thought to slow decomposition of buried, eroded organic matter, while growth of vegetation on the remaining soil will tend to increase soil C storage. However, these effects have been shown to be relatively small (Van Oost et al. , 2007). By removing topsoil that is generally high in organic matter, erosion can have profound effects on physical and chemical soil properties such as water retention and cation exchange capacity. Global increases in carbon stocks have a large, cost-competitive potential for climate change mitigation et al. , 2008). Mechanisms include reduced soil disturbance, improved rotations and residue/organic (Smith input management, and restoration of degraded soils. Nevertheless, limitations on soil C sequestration include time limitation, non-permanence, displacement and difficulties in verification (Smith, 2012). Despite these limitations, soil C sequestration can be useful to meet short- to medium-term targets. In addition, soil C sequestration confers a number of co-benefits on soils. It is thus a viable option for reducing the atmospheric Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 182 182

225 Figure 7.6 Some soil-related feedbacks to global climate change to illustrate the complexity and potential number of response pathways. Source: Heimann and Reichstein, 2008. concentration in the shorter term, buying time to develop longer term emission reduction solutions CO 2 across all sectors of the global economy (Smith, 2012). Just as reductions in soil C stocks are associated with negative consequences for soil function, increased soil carbon stocks are associated with increased soil fertility, workability, water holding capacity, reductions in greenhouse gas emissions and reduced erosion risk (Lal, 2004). Increasing soil carbon stocks can thus reduce the vulnerability of managed soils to future global warming (Smith and Olesen, 2010). Management practices effective in increasing SOC stocks include: (i) improved plant productivity through nutrient management, rotations and improved farming practices; (ii) reduced or conservation tillage and residue management; (iii) more effective use of organic amendments; (iv) land use change, for example from crops to grass or trees; (v) set-aside; (vi) agroforestry; (vii) optimizing livestock densities; and (viii) planting legumes or improving the crop mix (Smith et al. , 2008). While these measures have the technical potential to increase SOC stocks by -1 (Smith et al. , 2007a, 2008), they are dependent on economics: the economic potential for about 1 – 1.3 Pg C yr -1 at carbon prices of up to US$20, $50 and $100 SOC sequestration was estimated to be 0.4, 0.6 and 0.7 Pg C yr -eq. yr–1, respectively (Smith et al. , 2008). In addition, the size of the potential sequestration per tonnes CO 2 is relatively small in comparison to the threats: only a small loss of C from permafrost or peatlands could offset this potential sequestration ( Joosten et al. , 2014). However, an increase in SOC through improved management is expected to also reduce vulnerability of the soils to future SOC loss under global warming. As such, soil carbon sequestration can, in many respects, be regarded as a ‘win-win’ and a ‘no regrets’ option (Smith et al. , 2007b). 7.3.2 | Nitrous oxide emissions Soils emit nitrous oxide (N O), a greenhouse gas that is around 300 times more potent for radiative forcing 2 O-N yr–1 emitted globally in the . Of the approximately 16 Tg N (climate warming) over 100 years than CO 2 2 1990s, between 40 and 50 percent was a result of human activities (Reay , 2012). The main sources were et al. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 183 183

226 agriculture, industry, biomass burning and indirect emissions from reactive nitrogen, such as leaching, runoff and atmospheric deposition (Reay , 2012). Of these sources, agricultural soils are the dominant source, et al. et al. , 2007a). O emissions during the 1990s (Smith contributing over 80 percent of global anthropogenic N 2 O emissions from agricultural soils have increased from just under 4 Tg N O-N yr–1 in 1990, to over 4 Tg N 2 2 O-N yr–1 in 2010. Emissions are projected to increase to over 5 Tg N O-N yr–1 by 2030 (Reay et al. , 2012). N 2 2 Nitrous oxide is emitted from soils through two processes, nitrification and denitrification. Any mineral N available in the soil is subject to loss through one of these processes. The processes depend on soil environmental conditions such as the availability of mineral N, soil temperature and soil water content, soil pH, organic matter content and soil type. Nitrification tends to be favoured under aerobic conditions and denitrification under anaerobic conditions (Galloway et al. , 2003). Subject to mineral N being available, O through mineralisation of soil organic matter. However, the majority of emissions are any soil can emit N 2 driven by sources of N added to the soil as fertiliser, either as synthetic fertilizer, or as organic amendments O (e.g. manures, slurries, composts). So close is the relationship between N addition and emission, that N 2 O et al. , 2012). Emissions of N emissions are often calculated as a direct function of N added to the soil (Reay 2 -1 -eq. yr in 1961, from agricultural soils driven by addition of synthetic fertilizers have increased from 67 MtCO 2 -1 et al. , 2013). in 2010 (Tubiello -eq. yr to 683 MtCO 2 Given the close association between N inputs and N O emissions, soil management strategies to reduce 2 O emissions, and thereby improve this aspect of their climate regulation function, are mostly centred on N 2 removing surplus N in the soil. This is mainly accomplished by improving N-use efficiency to reduce the N surplus, either by reducing inputs or by better matching applications (timing and amount) to plant demand O emissions can be reduced by et al. (Snyder (2014) noted that soil N , 2014). In a recent review, Snyder et al. 2 selecting the right source, rate, time and place of N application and that new technologies and greater farmer/ adviser skills can improve N input management. They estimate that crop N recovery could be increased by >20 O emissions by >20–30 percent (Snyder et al. , 2014). percent, reducing risks of N 2 Beyond these technical measures, N O emissions could also be reduced through demand-side management, 2 for example through reduced food waste. Another demand-side measure could be to encourage dietary change away from less efficiently produced food products such as meat and other livestock products, or foods with very high energy inputs, such as heated glasshouses during winter (Reay et al. , 2012). O emissions, and a number of In summary, managed soils can play a key role in climate regulation via N 2 options exist to improve the soil’s delivery of its climate regulation service both by enhanced N management et al. , 2012; Snyder and by wider systemic changes in agriculture (Flynn and Smith, 2010; Reay , 2014). et al. 7.3.3 | Methane emissions Methane (CH ) is a greenhouse gas that is around 20–35 times more potent for radiative forcing (climate 4 . Soils often emit methane through methanogenesis when decomposition warming) over 100 years than CO 2 of organic matter occurs in anaerobic soil layers. Methane is also oxidised by methanotrophy in aerobic layers, so the emission is a balance between methanogenesis and methanotrophy (Le Mer and Roger, 2001). emissions are natural (including the natural wetland flux), and around About 30 percent of total global CH 4 70 percent anthropogenic (Le Mer and Roger, 2001). Given that methanogenesis occurs under anaerobic conditions, waterlogged soils, particularly wetlands, peatlands and rice paddies, are the largest source of methane emissions (Le Mer and Roger, 2001). Since much of the methane flux from wetland and peatland Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 184 184

227 soils occurs on largely unmanaged areas, the emissions are not considered anthropogenic, so are not routinely included in greenhouse gas inventories. This means that the quantification of soil methane emissions over O. Nonetheless, some global estimates time from peatlands and wetlands is not as well documented as for N 2 emissions from wetlands do exist: in 1998, total global emissions of CH from wetlands were estimated of CH 4 4 -1 -1 -1 came from natural wetlands and 53 Tg yr , of which 92 Tg yr from rice paddies (Cao, Gregson to be 145 Tg yr and Marshall, 1998), with some estimates a little higher (Le Mer and Roger, 2001). Emissions from rice paddies, emissions from rice paddies were estimated to have increased from however, are included in inventories: CH 4 -1 -1 et al. in 1961 to 499 MtCO -eq. yr -eq. yr in 2010 (Tubiello , 2013). 366 MtCO 2 2 By contrast, aerobic soils tend to act as sinks for CH , thereby having a positive impact on climate regulation. 4 usually exhibit Temperate and tropical aerobic soils that are exposed to atmospheric concentrations of CH 4 oxidation but, since they cover large areas, they are estimated to consume ~10 low levels of atmospheric CH 4 (Le Mer and Roger, 2001). Forest soils are the strongest CH sink, followed by percent of the atmospheric CH 4 4 , et al. grasslands, with the sink capacity of cultivated land much lower than that of undisturbed soils (Steudler oxidation also occurs in extreme environments such as deserts and et al. , 1997). Atmospheric CH 1996; Priemé 4 glaciers, in the floodwater of submerged soils and in river waters (Le Mer and Roger, 2001). Potter, Davidson consumption to be 17–23 Tg yr−1. and Verchot (1996) estimated global soil CH 4 Soil management strategies to reduce CH emissions or enhance CH uptake can improve this aspect of the 4 4 soil’s climate regulation function. Enhancing uptake in managed soils is difficult, so most mitigation options emission reduction, and since wetlands or often unmanaged, most mitigation options have been occur for CH 4 developed for rice paddies. These include draining the wetland rice once or several times during the growing season, selection of rice cultivars with low exudation rates, off-rice season water management, fertilizer management and the timing and composting of organic residue additions (Smith et al. , 2008). For managed peatlands and wetlands (e.g. those used for forestry or agriculture), methane emissions can be reduced by fertilizer, water and tillage management (Le Mer and Roger, 2001). Rewetting of drained or cultivated emissions, but the peatlands to restore wetland function and maintain carbon stocks is likely to increase CH 4 overall impact on climate will vary between systems and depending on the time horizon considered ( Joosten et al. , 2014). 7. 3 . 4 | Heat and moisture transfer Soils play an essential role in storage of water. Soil moisture strongly affects water, energy and carbon exchanges, leading to major forcings and feedbacks within the climate system (Seneviratne et al. , 2010). Soil moisture generally refers to the amount of water stored in the unsaturated soil zone. The most important soil moisture storage is that affecting plant transpiration, e.g. the water available within the root zone. Land evapotranspiration is an essential component of the continental water cycle, since it returns as much as 60 percent of precipitated land water back to the atmosphere (e.g. Dirmeyer et al. , 2006; Oki and Kanae, 2006; van der Ent et al. , 2010). Soil moisture is the main water source for this process, through plant transpiration and bare soil evaporation. Plant transpiration contributes about 60 percent of all land evapotranspiration (Schlesinger and Jasechko, 2014). et al. , 2010). This Evapotranspiration is itself a function of soil moisture (Koster et al. , 2004; Seneviratne dependency is conceptually illustrated in Figure 7.7, which builds upon the classical Budyko framework (Budyko, 1956, 1974). It shows that three main soil moisture regimes can be distinguished: (i) a wet soil moisture regime in which evapotranspiration is solely limited by the availability of energy; (ii) a transitional soil moisture regime in which evapotranspiration is strongly sensitive to the availability of soil moisture; and (iii) a dry soil moisture regime in which soil moisture is at or below the wilting point and for which evapotranspiration is negligible. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 185 185

228 The geographical distribution of these soil moisture and evapotranspiration regimes can be estimated (2010). As an illustration, Figure 7.8 displays the et al. with various methods, as discussed in Seneviratne correlation of annual mean evapotranspiration with radiation and precipitation in an observation-driven land surface model using a two-dimensional colour map. This analysis illustrates the existence of distinct evapotranspiration regimes, with most regions clearly displaying either the characteristics of a soil moisture- or energy-limited evapotranspiration regime. One should note that the relationship displayed in Figure 7.7 is qualitative, and is affected (both in space and et al. , 2010; time) by variations in soil parameters, land cover characteristics, and other factors (e.g. Teuling et al. , 2013). Koster and Mahanama, 2012; Guillod The water and energy balances of land are tightly connected through the process of evapotranspiration. It follows that the soil moisture effects on evapotranspiration (illustrated in Figure 7.8) are also highly relevant for land energy exchanges at the land surface. This link makes soil moisture a strong control of temperature variability and temperature extremes on land (e.g. Seneviratne et al. , 2006; Fischer et al. , 2007; Vautard et al. , 2007; Mueller and Seneviratne, 2012). Modelling estimates suggest that soil moisture feedbacks affect about 60 percent of temperature variability in the present Mediterranean climate in summer (Seneviratne et al. , 2006) and that they induced additional temperature anomalies of the order of 2°C in Central Europe during the 2003 European summer heat wave (Fischer , 2007). Observation-based analyses also confirm the et al. existence of strong correlations between the occurrence of hot extremes in regional hottest months and prior precipitation deficits in regions with soil moisture-limited evapotranspiration regimes (Hirschi et al. , 2011; Quesada et al. , 2012; Mueller and Seneviratne, 2012). The example of the European summer heat wave shows, moreover, that these feedbacks can be relevant in extreme years even in regions like Central Europe which have a dominant energy-limited evapotranspiration regime under the present climate. For present climate conditions, the relationship between soil moisture deficits and hot extremes implies that information on soil moisture deficits could be used for improved forecasting of temperature mean and Transitional Dry Wet Soil Moisture Limited Energy limited EF max EF=λE/R n 0 Soil moisture content θ θ CRIT WILT Seneviratne et al., 2010. Figure 7.7 Definition of soil moisture regimes and corresponding evapotranspiration regimes. Source: EF denotes the evaporative fraction, and EFmax its maximal value. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 186 186

229 extremes several weeks in advance (e.g. Koster , 2010a; Mueller and Seneviratne, 2010). Such early soil et al. moisture information can be either provided by an offline land surface model driven with observation-based et al. , 2006), by remote sensing products (e.g. Wagner et al. , 2007; De Jeu et al. , 2008), forcing (e.g. Dirmeyer or by the assimilation of remote sensing products in land surface models (e.g. Reichle, 2008). However, the scarcity of precipitation and soil moisture observations still limits the derivation of reliable soil moisture estimates and the evaluation of satellite approaches on most continents (e.g. Koster et al. , 2010b; Dorigo et al. , 2013). Figure 7.8 Estimation of evapotranspiration drivers (moisture and radiation) based on observation-driven land surface model simulation. Source: Seneviratne et al., 2010. The figure displays yearly correlations of evapotranspiration with global radiation Rg and precipitation P in simulations from the 2nd phase of the Global Soil Wetness Project (GSWP, Dirmeyer et al., 2006) using a two-dimensional color map, based on Teuling et al. 2009, redrawn for the whole globe. (Seneviratne et al., 2010) Climate models project that several regions will be affected by more frequent drought conditions in the future as a consequence of enhanced greenhouse gas concentrations (e.g. Wang, 2005; Sheffield and Wood, , 2012). This implies shifts in climate and soil moisture regimes, with important impacts 2007; Seneviratne et al. on temperature projections (e.g. Seneviratne et al. , 2012), in particular for temperature et al. , 2006; Dirmeyer et al. , 2013). extremes (Seneviratne Another feedback of soil moisture on climate is the possible impact of droughts on plant carbon uptake et al. , , 2006; Sitch emissions (Ciais et al. , 2005; Friedlingstein et al. and a resulting decreased sink for CO 2 2008; Reichstein et al. , 2013). One particularly important region for this feedback is the Amazon rainforest, which is projected in some models to dry substantially (e.g. Mahli et al. , 2008). However, these projections are associated with high uncertainty in current climate models (Orlowsky and Seneviratne, 2013), and the resulting effects on carbon uptake could also be affected by the representation of plant physiology in the land surface schemes (Huntingford et al. , 2012). Finally, the combined effects of soil moisture on near-surface humidity and temperature are also relevant , 2004; Taylor et for boundary layer development and precipitation occurrence (e.g. Betts, 2004; Koster et al. al. , 2012). More details on these feedbacks are provided in Sections 7.5 and 7.6 below. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 187 187

230 7. 4 | Air quality regulation http://www.who.int/topics/air_pollution/en /), air pollution According to the World Health Organisation ( is “contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere”. The status of air pollution is often referred to as air quality (Monks et al. , 2009). Air quality affects human health through exposure to toxic inorganic compounds (e.g. HBr, elemental Hg vapour), toxic organic compounds (e.g. organic pesticides), and particulate matter , CH , (PM). Air quality also affects the climate system through changes in greenhouse gas concentrations (CO 4 2 O) – as discussed in Section 7.3 − and through aerosols (e.g. mineral particles, black carbon or ‘BC’). After N 2 deposition of atmospheric pollutants (e.g. N and S compounds, or compounds containing trace elements) on land or water, acidification, eutrophication, and contamination might occur (see Section 4.4), which can have harmful effects on ecosystem function and structure, particularly where deposition exceeds the ‘critical load’ that a particular soil can buffer (Nilsson and Grennfelt, 1988). Specific compounds in the atmosphere, such as ), can result in a host of environmental problems (e.g. impacts on human health, odour, climate ammonia (NH 3 change, soil acidification, eutrophication, biodiversity). The magnitude of the problems would depend on interactions with other compounds (Aneja, Schlesinger and Erisman, 2009). 7.4.2 | Ammonia emissions Agriculture accounts for 80–99 percent of all NH emissions (FAO, 2014). In Europe, agriculture accounts 3 for 94 percent (EEA, 2012). These emissions mainly come from animal manure and fertiliser application (Olivier reductions are voluntary and there are neither federal nor national et al. , 1998). In the United States, NH 3 regulations controlling its emission (Aneja, Schlesinger and Erisman, 2009; Greaver et al. , 2012). In Europe, emissions have been an important policy issue (van der Hoek, 1998) and regulation has led however, NH 3 emissions decreased in the EU-27 by emissions. Between 1990 and 2010, NH to an overall reduction in NH 3 3 28 percent (EEA, 2012), with especially large reductions in Poland, the Netherlands and Germany. Ammonia emission reductions have been associated with a reduction in the number of livestock (especially cattle), improvement of manure management, and the lower input of nitrogenous fertilisers to soils (EEA, 2011, 2012). The effectiveness of manure injection to decrease emissions is under debate, as a result of its effect on pollutant leaching (Erisman but an increase in N O emissions and/or NO swapping, as there may be a reduction in NH 2 3 3 as a precursor of PM concentrations, et al. , 2008). A better understanding is needed on the contribution of NH 3 both emissions of primary PM 10 (particulate matter with a size < 10 μm) and secondary formation of PM 2.5 (particulate matter with a size < 2.5 μm) (Aneja, Schlesinger and Erisman, 2009). It is worth mentioning that and NOx interactions occur with other compounds in the atmosphere, to the extent that reductions in SO 2 reductions (Erisman and are only effective in the reduction of PM 2.5 if carried out simultaneously with NH 3 Schaap, 2004). 7. 4 . 3 | Aerosols Mineral dust, sulphate aerosols, and organic C and black C (BC) aerosols from fossil fuel and biomass burning have a significant effect on radiative forcing (Forster et al. , 2007). Mineral dust is mainly emitted from deep and extensive alluvial flood deposits emplaced during the Pleistocene, for example in the Sahara, East Asia, the Arabian deserts, and Central Australia (Prospero et al. , 2002). The largest sources are located in the Northern Hemisphere, in the so-called ‘global dust belt’ that extends from the west coast of North Africa, through the Middle East, into Central Asia. Outside this belt, areas with remarkable persistent dust activity include the Great Basin in south-western North America, the Lake Eyre Basinin Australia, some areas of South America (predominantly in Argentina), and southern Africa (Prospero et al. , 2002) (Figure 6.2). The ‘Red Dawn’ dust storm that affected Sydney, Australia in September 2009 is described in Chapter 15. Mineral dust originating in the Sahel has been reported to be regularly carried over large areas of the Atlantic and the Caribbean; the largest export occurs during years of low rainfall in the source region (Prospero and Lamb, 2003). Although this process might have been exacerbated by anthropogenic activities (Prospero and Nees, 1978), recent evidence indicates that vegetation cover in the region has not changed substantially in the past 20 years and that, on a , 2002). et al. global scale, dust mobilisation is probably mostly driven by natural events (Prospero Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 188 188

231 The direct effect of aerosols on the climatic system is mainly through the reflection and absorption of solar radiation (Miller and Tegen, 1998). The indirect effect involves the modification of cloud properties (Kaufman, Tanre and Boucher, 2002). Greenhouse gases, in contrast, reduce the outgoing thermal radiation to space. Differences in lifetime and spatial distribution between greenhouse gases and aerosols are also considerable: et al. , 2007), greenhouse gases have a lifetime of more than 100 years and a homogeneous distribution (Forster whereas aerosols have a lifetime of about a week and a rather heterogeneous distribution (Andreae , et al. 1986). Soil dust aerosols have also been reported to modify the lifetime of some greenhouse gases (Dentener et al. , 1996). They also provide essential nutrients to ocean ecosystems that may increase the efficiency of the in the deep ocean (Martin, 1990). This is specially the case of ocean’s biological pump and help sequester CO 2 iron, which is an important micronutrient for phytoplankton (Falkowski, Barber and Smetacek, 1998). Most aerosols are highly reflective, thus raising the albedo of our planet and having a cooling effect. However, aerosols containing BC are dark and strongly absorb the incoming sunlight (Kaufman, Tanre and Boucher, 2002). This warms the atmosphere and cools the Earth’s surface before a redistribution of the energy occurs in the atmosphere column (Ramanathan and Carmichael, 2008). Black C alters the radiative forcing through different processes: (i) the presence of BC in the atmosphere above surfaces with high albedo such as snow or clouds may cause a significant positive radiative forcing (Ramaswamy et al. , 2001); (ii) BC aerosols deposited on snow may promote melting (Warren and Wiscombe, 1980; Hansen and Nazarenko, 2004); and (iii) BC influences evaporation and cloud formation by modifying the atmosphere’s vertical temperature gradient (Ackerman et al. , 2000; Raufman and Fraser, 1997). However, the exact radiative forcing depends on how BC is mixed with other aerosol constituents ( Jacobson, 2001). Carbonaceous aerosol emission inventories suggest that approximately 34-38 percent of these emissions , 2007). come from biomass burning sources, the remainder from fossil fuel burning sources (Forster et al. Fossil-fuel-dominated BC emissions are approximately 100 percent more efficient warming agents than biomass-burning-dominated plumes (Ramana et al. , 2010). The type of smoke is also largely influenced by et al. the type of biomass being burned (Takemura , 2002). In savannah ecosystems, about 85 percent of the biomass (mostly grasses) is consumed by flaming during fire events. In forest fires this value decreases to 50 percent or less, as the flaming stage is followed by a long, cooler smouldering stage in which the thicker wood, , 2002). not completely consumed, emits smoke composed of organic particles without BC (Takemura et al. Black C is thus mostly emitted during the hot, flaming stage of the fire (Kaufman et al. , 2002). The intense surface heating caused by fires can further cause a rapid uplift of heated air, known as pyro-convection, which can considerably disturb the chemical conditions in the free and upper troposphere and, in some cases, in the , 2009). Aerosols from fires are more likely to be injected at higher altitudes and are stratosphere (Monks et al. likely to experience long-range transport. Aerosol emissions from large boreal fires in Alaska and Russia have , 2007). been shown to be transported very efficiently over long distances (Damoah et al. , 2006; Petzold et al. | Soil change and water quality regulation 7. 5 Soils provide a biogeochemically activated filtration and cleaning service that transforms or retains materials deposited at the land surface. These materials include not only nitrogen and phosphorous, elements from grey water used for irrigation, and acidic compounds, but also inorganic and organic toxins. If the capacity of the soil to retain, transform or filter these materials is exceeded, there can be severe environmental consequences for water quality. Soils also adversely impact the provision of clean water through erosion into water courses, through salinization and through redox cycling and the release of metals such as arsenic. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 189 189

232 7. 5 .1 | Nitrogen and phosphorous retention and transformation By increasing fertilizer production and crop N fixation, human activities have doubled nitrogen (N) fixation -1 -1 ) of global nitrogen fixation (413 Tg N yr ) is from the atmosphere during the last century. Half (210 Tg N yr human-driven (Fowler et al. , 2013). Mining and erosion have increased the phosphorus (P) flow from land into -1 ; Carpenter and Bennett, the ocean by at least ten-fold (preindustrial value of 1 to current estimate of 9-32 Tg P yr 2011). A recent inventory indicates that approximately 60 percent of the nitrogen fixed by human activities is et al. released back into the environment without being incorporated into food or products (Houlton , 2013). Increases in the release of reactive nitrogen (N) and phosphorus (P) to the environment are associated with many significant environmental concerns, including surface water contamination, harmful algal blooms, hypoxia, air pollution, nitrogen saturation in forests, drinking water contamination, stratospheric ozone depletion and climate change (Bennett, Carpenter and Caraco, 2001; Sutton et al. , 2011; Davidson et al. , 2012). Soils serve as an important regulator of the leakage of this anthropogenic N and P back into the air or to surface and ground water, since much of the release occurs from fertilizers or atmospheric deposition. Soil is the largest pool of N and P within terrestrial ecosystems (Cole and Rapp, 1981), illustrating the magnitude and stability of soil N and P storage. Review of 15N tracer studies reinforces that idea that soils are the strongest sink for nitrogen in the short and medium term (Fenn et al. , 1998; Templer et al. , 2012). Flows of N through et al. , 2003). the landscape and the consequences of excess N can be represented by the N cascade (Galloway Nitrogen and phosphorus removal occurs through plant or microbial uptake, storage in soil organic matter, by complexation, and sorption or exchange. Nitrogen is cycled biologically through plant uptake, litterfall and microbial cycling, and is stored in organic forms except in areas with substantial rock-derived N (Morford, Houlton and Dahlgren, 2011). By contrast, soil P is mainly found in an inorganic form, sorbed or complexed by soil minerals and the exchanger. Organic P is a smaller pool in most soils, found in a review of global soil P to range from 5-40 percent (Yang and Post, 2011). For N, there are also significant gaseous losses via NOx or NH 3 or N O. Storage in soils or perennial plants and conversion into other inert and through denitrification as N 2 2 for N or stable inorganic complexes for P) represent stable sinks that remove N and P from flowpaths forms (N 2 and the N cascade for a period of time determined by the residence time of those sinks. An important service provided by soils is to remove N and P along flowpaths, preventing mobile nitrate and phosphate from moving from terrestrial ecosystems into surface waters and groundwater. Global models indicate that soils are responsible for the largest portion of landscape N removal - 22 percent of global N removal et al. , 2006). Riparian soils or wetlands as denitrification - second only to coastal ocean sediments (Seitzinger can remove N that has leaked from forests, farms, rangelands or the built environment (Peterjohn and Correll, 1984), as long as riparian zones are downgradient of the N source (Weller and Baker, 2014). One study indicates that replacement of 10 percent of historical riparian buffers could substantially reduce N loading to the Gulf of Mexico (Mitsch et al. , 2001). Phosphorus cycling has important distinctions from N cycling. In particular, the dominant inorganic form of phosphorus, orthophosphate, binds strongly to soil particles via sorption or complexation as inorganic P, in contrast to nitrate, which is quite mobile. Phosphorus can be displaced under reducing conditions, and thus efforts to target N removal may in fact cause unanticipated increases in dissolved P concentrations (Ardón et al. , 2010). While we do not have a parallel conceptual P cascade, P availability can drive the formation of harmful algal blooms, and recent work indicates that joint management of N and P is critical (Conley et al. , 2009). In efforts to reduce effects on ecosystems and water quality, it is important to consider the soil processes involved in removal of both elements and their interactions. Perturbations that increase the mobility of N and P may saturate the retention capacity of soils such that the ability to remove these elements declines as inputs increase. Disturbances that affect soil structure, rooting patterns and organic matter also decrease N and P retention capacity. At the ecosystem scale, N removal Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 190 190

233 capacity declines as N loads increase above a point where N can be taken up by plants and soil processes et al. , 1989). While studies illustrate that the rate of N removal does generally decline with increasing N (Aber inputs (e.g. Perakis, Compton and Hedin, 2005), there are still questions about the ability of soils to retain N over time. The saturation point may vary by ecosystem and soil type. For example, wetland ecosystems have a tremendous capacity to retain N – a recent meta-analysis indicates that wetland N removal is linear with N loading, removing about 47 percent of N inputs even at very high loads ( Jordan, Stoffer and Nestlerode, 2011). O production increases with increased N loading However, recent work on agricultural soils found that N 2 (Shcherbak, Millar and Robertson, 2014). This reinforces the pattern of decline in capacity of soils to serve as a O production should target areas of stable N sink under high N inputs, and suggests that efforts to reduce N 2 high N loads where larger benefits will be seen per unit N. The connection between ecosystem services and soil processes is sometimes distant. The benefit of N uptake in a riparian soil in Iowa might be most appreciated in distant coastal fisheries. In addition, ecosystem services do not turn on or off with the flick of a switch; for example, it may take decades to recover water , 2010). Our perspectives about soils and quality after a widespread land use change (Hart, 2003; Howden et al. ecosystem services should include these distant connections and time lags. Removal of N from the cascade has implications for many aspects of human health and well-being (Figure 1; , 2011), and an increasing number of studies are including soil processes in Brauman et al. , 2007; Compton et al. ecosystem service assessments and valuation frameworks (De Groot, Wilson and Boumans, 2002; Robinson , 2013). Soil N and P removal is generally seen as an intermediate service or a supporting or regulating et al. service in current ecosystem services classification schemes, as it affects a number of final ecosystem goods and services (Boyd and Banzhaf, 2007). Impacts of nitrogen on ecosystem services (ES), on the economy and on human well-being have been examined in a number of studies (Birch et al. , 2010; Compton et al. , 2011; van Grinsven et al. , 2013). Soil N and P storage could have implications for many benefits, including the following: (i) avoidance of consequences to ecosystem services provided by freshwater, groundwater and coastal waters from reduced quality for swimming, drinking, recreation or fishing; (ii) avoidance of air quality problems associated with N such as those affecting human respiratory health or visibility (NOx, NHy); (iii) avoidance of damage from climate change and O); and (iv) maintenance of soil fertility and ecosystem production (both N stratospheric ozone depletion (N 2 and P). Eutrophication of coastal areas and associated hypoxia can result in physiological and behavioural impacts on important coastal organisms, populations and ecosystems that result in lowered fitness and productivity. However, there is a good deal of uncertainty about the economic damages associated with et al. coastal eutrophication in many areas (Rabotyagov , 2014). Efforts to inform policy should bring together ecologists and economists to study the impacts of N and P on ecosystem services all along the cascade. 7.5.2 | Acidification buffering Soil acidity is controlled by both biota (plant roots and microorganisms) and particles (soil minerals and organic matter). Production of carbon dioxide, organic matter decomposition, and the excretion of acidic compounds by biota increase soil acidity, while binding of acidic compounds to root and particle surfaces, as well as mineral weathering, decrease it (Sposito, 2008). Over periods ranging from centuries to millennia, while most of the less resistant minerals become depleted through weathering reactions with rainwater and subsequent leaching, highly acidic soils are produced naturally. They now occupy about one-third of the ice- et al. free land area on Earth (Guo , 2010), mainly in the humid tropics and in the forested regions of temperate zones. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 191 191

234 Industrial effluents (for example, sulphur and nitrogen oxide gases dissolved in atmospheric precipitation or transformed to particles, or acidic wastewaters) and nitrogenous fertilizers, such as urea, are typical anthropogenic inputs of acidity to soils. If these two acidic inputs exceed about 15 percent of the capacity of soil to neutralize them, acidification increases markedly, with a variety of serious problems arising for both plant and microbial growth. The potential for generating polluted runoff or drainage water also increases markedly. Over a 20 year period Guo et al. (2010) documented such increases of acidity in Chinese topsoils, caused by nitrogen fertilization and acidic deposition. The topsoils investigated showed an average pH decrease of 0.50, which is quite serious. Other long-term studies document decadal changes in soil acidity that are even larger (Richter and Markewitz, 2001). Acidic deposition is an important problem in China, but the acidification caused by nitrogen fertilization was found to be 10 to 100 times greater than that caused by acid rain. In the principal double-cropping cereal systems of China (wheat-maize, rice-wheat, and rice-rice), nitrogen fertilizer use efficiencies are only 30 to 50 percent. The progressive acidification of topsoil – as well as nitrogen pollution of agricultural runoff and drainage – will remain unchecked as long as this low nitrogen use efficiency is not addressed. Guo et al. (2010) noted that optimal nutrient-management strategies can significantly reduce nitrogen fertilization rates without decreasing crop yield, thus providing benefits to both agriculture and water quality. 7.5.3 | Filtering of reused grey water -1 Nearly 80 percent of urban ‘blue water’ becomes wastewater. At about 100 m3yr per household in the developed world, wastewater thus represents a rapidly expanding environmental and health challenge, particularly in urban centres. The ecological footprint of untreated wastewater is unsustainable even in regions where water is plentiful (e.g. South East Asia), as it may either increase nutrient loads in rivers and coastal regions or represent a direct hazard to human health. By contrast, arid regions increasingly rely on treated wastewater for irrigation, often practiced with little consideration of long-term impacts on the soil, hydrology and ecology of the producing area. The sustainability of this coupled agro-urban hydrological cycle hinges on proper management to mitigate adverse impacts of long-term wastewater use and avoid potential collapse of soil ecological functions. Various studies (e.g. Bond, 1998; Assouline and Narkis, 2013) have shown that, over the long term, even irrigation with wastewater results in significantly increased soil ESP that can adversely impact soil structure and hydraulic properties. In the absence of proper regulation, irrigation with wastewater may pose a range of human health and other ecological risks associated with introduction of pathogenic microorganism into the soil and crop (del Mar et al. , 2012). The sustainable management of wastewater irrigation requires new management strategies including water source mixing, proper selection and rotation of crops, and avoidance of sensitive soils. 7. 5 . 4 | Processes impacting service provision Trace elements Elevated concentrations of potentially toxic trace elements can affect provision of the services that depend on soils. Trace elements – such as arsenic, cadmium, chromium, lead, mercury, and selenium – naturally occur in low quantities within soils. They may also be introduced and concentrated through anthropogenic activities like waste disposal, fertilizer and pesticide application, and atmospheric particulate emission and deposition (Sparks, 2003; Pierzynski, Vance and Sims, 2005). Even when at low concentrations in soils, they can have pronounced impacts on water quality. This is particularly the case where the capacity of soils to store trace elements is exceeded or where there are changes in the soil chemical, physical and/or biological environment that influence the partitioning of trace elements between the solid and aqueous phases. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 192 192

235 The concept of the critical load of a specific trace element enables a precautionary assessment of the risks its input causes to food quality and of the eco-toxicological effects on organisms in soils and surface waters et al. et al. , 2013b). The critical load of trace elements is defined as “the load resulting (Lofts , 2007; de Vries at steady state in a concentration in a compartment (e.g. soil solution, plant, fish) that equals the critical et al. , 2007; de Vries et al. , 2013b). The critical limit is a receptor-specific limit for that compartment” (Lofts concentration below which significant effect on the receptor is assumed not to occur (Lofts et al. , 2007). The concept of critical loads – specifically the critical loads of acidity − was key in gaining acceptance of the need for reduction of atmospheric deposition of N and S (Section 4.4.1 above). However, the usefulness of the concept of critical loads of trace elements in international negotiations aimed at reducing trace element deposition is not equally evident. This is mainly owing to two factors that distinguish trace elements from the case of acidity and acid rain: (i) the time needed for a specific trace element in a specific scenario to attain steady state is much longer than for N and S; and (ii) other changes in the environment, notably acidification, may have a greater influence on the exposure and effects of a specific trace element than the particular amount entering the system (de Vries et al. , 2013b). In fact, problems associated with trace elements in soils are commonly exacerbated by changes in land use that alter environmental conditions and increase the potential for exposure to trace elements through food and water consumption. Because of this, in addition to applying the concept of critical loads, the assessment of the future risks of trace elements needs to employ dynamic et al. , 2013b). models (de Vries Salinity Salinization of soil and water resources remains a chronic problem in many parts of the world, mostly in arid regions where evapotranspiration exceeds rainfall. The increased frequency of extreme climate events (droughts, intense rainfall events) together with the expansion of irrigated agriculture are expected to increase the range of soils affected by salinity. In addition to the effects of hotter and drier climate patterns, the primary causes of salinity risk include: (i) increasing salt loads due to use of marginal water sources such as waste water; (ii) over exploitation of coastal aquifers and related sea water intrusion (Várallyay, 1994); (iii) overpumping and degradation of slowly replenishing inland aquifers (Ogallala); (iv) sea level rise impacting coastal wetlands (e.g. Mexico pacific coastline); (v) mismanagement of rapidly expanding irrigation in arid regions, particularly inadequate leaching and drainage and (vi) clearing of perennial vegetation in landscapes with significant salt stores in soils and deeper regolith. One solution is to reduce the salt content of irrigation water through desalination. Recent advances in desalination techniques have resulted in a dramatic reduction in costs. Irrigation experiments with desalinated water show substantial increase in yield with less water used and less salt leaching to groundwater resources. However, the use of desalinated water requires careful management to avoid soil and ecological damage (e.g. , 2007; Tal, 2006). clay dispersion) due to irrigation with extremely pure water (Yermiyahu et al. Erosion Intensification of agriculture, changes in rainfall patterns with more intense rain events, and potentially more compacted soil surfaces may all contribute to increased rates of surface soil erosion. In addition to the removal of the top layer of productive soil and the incision of stream channels, the potential increase in et al. (1995) soil transport to surface water may cause a cascade of adverse effects downstream. Pimentel list impacts on stream and lake ecology, dam siltation and effects on waterways, and of course, potential for enhanced pollution by agrochemicals and colloid-facilitated transport of phosphorous and carbon. Soil erosion is also linked to climate change as it mobilizes large amounts of soil organic carbon (SOC). Since the industrial revolution and associated land use changes, SOC has been estimated to contribute 78±12 Gt of C to the atmosphere, of which about one-third is due to accelerated erosion and two-thirds to mineralization (WMO, 2005). Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 193 193

236 The WMO (2005) report estimates that 25 percent of African soils are prone to risk of water erosion (excluding deserts that comprise about 46 percent of the African land surface), and that 50 percent of cropland in Australia is susceptible to water erosion. Drier conditions associated with future climate extremes (droughts) may limit rates of soil carbon accumulation and reduce soil aggregation, thereby enhancing vulnerability to wind erosion. WMO (2005) estimate that about 22 percent of the African land surface is prone to wind erosion, and 15 percent of the cropland in Australia. A host of soil conservation strategies for combating land degradation due to soil erosion also offer co-benefits such as enhanced water storage in the soil profile (Pimentel et al. , 1995; Troeh, Hobbs and Donahue, 1991). Eroded landscapes may take centuries to millennia before their abilities to provide quality ecosystem services are restored. 7. 6 | Soil change and water quantity regulation Soil moisture regulation of precipitation Soil moisture acts as a buffer for precipitation anomalies. As long as the soil is not saturated, it can reduce the direct impact of flooding. Similarly, soil moisture acts as a buffer against dry anomalies in the onset of meteorological droughts, before soil moisture or streamflow droughts are noticeable. However, if pre- event soil moisture is anomalously wet or dry, these same properties can also lead to significant flooding and droughts even where precipitation is not abnormally high or low. For these reasons, the monitoring of soil moisture conditions (as well as of snow and groundwater) is valuable for the forecasting of floods and droughts (e.g. Koster et al. , 2010b; Fundel, Jörg-Hess and Zappa, 2013; Orth and Seneviratne, 2013; Reager, Thomas and Famiglietti, 2014). In addition to effects related to the buffering or persistence of soil moisture, several studies suggest that soil moisture also affects the regional water cycle through impacts of evapotranspiration on precipitation (e.g. , 2012). However, the underlying Beljaars et al. , 1996; Koster et al. , 2004; Seneviratne et al. , 2010; Taylor et al. feedbacks, including their sign, are strongly model-dependent (e.g. Koster , , 2004; Hohenegger et al. et al. 2008). Also observational studies diverge with respect to inferred soil moisture-precipitation feedbacks. Some suggest the presence of positive (temporal) feedbacks while others identify mostly negative (spatial) feedbacks (Findell et al. , 2011; Taylor et al. , 2012). In addition, causality is very difficult to establish based on observations (e.g. Salvucci, Saleem and Kaufmann, 2002). Precipitation persistence could, for example, lead to some confounding effects (Guillod et al. , 2014). Overall, effects of soil moisture on precipitation are still uncertain. Human land and water use strongly affects soil moisture variations and the resulting land water balance, et al. , 2010; Wei for instance through irrigation (Wisser , 2013) or other changes in agricultural practices et al. , 2014). These effects are generally not considered in present day climate models, et al. , 2014; Jeong et al. (Davin although they could substantially affect soil moisture and hydrological drought projections, including feedbacks to the atmosphere. 7.6.2 | Precipitation interception by soils Together with vegetation, soils help to regulate water quantity by intercepting water, reducing floods and maintaining the soil moisture buffer. Precipitation arriving at the Earth’s surface can be intercepted by vegetation canopies and returned directly to the atmosphere through evaporation, never reaching the soil moisture pool. Typically, trees can intercept 25-50 percent of precipitation and shrubs 10-25 percent, while interception by grass is significantly less (Calder, 1999). The rest of the precipitation arrives at the soil surface, the characteristics of which control the partitioning between what infiltrates and what runs off into surface (2013) have shown that K is largely dependent on bulk density, et al. water. In a recent meta-analysis, Jarvis organic carbon content and land use. This has important consequences for ecosystem service delivery by soils, Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 194 194

237 as it indicates that management and land-use change will affect the soil infiltration service temporally as well as spatially. This analysis by Jarvis et al. (2013) corresponds to an increasing number of studies that show the importance of vegetation in determining soil K values on similar soils. Because of their large root systems, trees in particular create conduits for conducting water into soil. Both dead and living roots can create flow networks. Beven and Germann (1982) cited work suggesting that as much as 35 percent of the volume of a forest soil may contain macropores formed by roots. Chandler and Chappell (2008) demonstrated that K was highest near the trunk of single oak trees and decreased toward the edge of the canopy. The ratio of K geometric mean values under the tree at 3 metres from the trunk to the adjacent pasture was 3.4 times higher, similar to results compiled from the literature in the same paper. Gonzalez-Sosa et al. (2010) presented conductivity data for a range of land use types in France, with trees being generally higher, and crops and pasture lower for the same soil. In the tropics, deforestation results in a major reduction in infiltration, whether the forest is recently cleared or has been turned into pasture (Zimmermann, Elsenbeer and De Moraes, 2006). Soil macrofauna - worms, ants and termites etc. - also play an important role in determining infiltration at local scales (Beven and Germann, 1982; Lal, 1988), and perhaps also regionally and globally given the prevalence of these organisms. There are typically two modes of macrofauna action impacting hydraulic properties. The first is the creation of burrows forming macropores; the other is the turnover of soil and aggregation which impacts infiltration and water retention, generally increasing both. Soils might offer potential for slowing , 2009). However, et al. water movement across landscapes under certain precipitation conditions (Marshall once runoff is generated and large quantities of precipitation fall, the role of soils is likely to be less important. Above a certain threshold, massive floods can occur in almost any landscape Although often cited as an important ecosystem service, the impact of land use on altering flood risk remains hard to quantify with any precision (Pattison and Lane, 2011). The link between land management and flood risk is complex and scale dependent as conceptualized by Bloschl et al. (2007). Many studies have demonstrated how land or soil management impact infiltration and runoff generation at the plot to hillslope scale (Wheater and Evans, 2009). These tend to be local effects in temperate zones, but can be large scale in the tropics. Beven et al. (2008) found a distinct land use signal hard to detect, and also pointed out that “adequate information about past land management changes and soil conditions is not readily available but will need to be collected and made available in future for different land use categories if improved understanding of the links between runoff and land management is to be gained and used at catchment scales.” 7.6.3 | Surface water regulation Soils provide a maintenance service that contributes to the regulation of base flow and water supply in rivers. Groundwater, lakes and soil drainage all play a role in setting base flow in surface waters (Price, 2011). Groundwater dominates in the lowlands, but soil drainage dominates upland catchments. Changes to the hydraulic characteristics of upland catchments and to the quantity of water stored by soils will have distinct implications for water supply downstream. Again, the soil water retention characteristics and hydraulic conductivity play a crucial role in the regulation of drainage. 7.7 | Soil change and natural hazard regulation Soil and its characteristics (depth, hydro-mechanical properties, mineralogy, ecological function, and position in the landscape) play an important role in several natural hazards including: landslides, debris flows, floods, dam failure, droughts, shrink and swell damage to roads and infrastructure, and more. The United Nations International Strategy for Disaster Reduction (UNISDR, 2009) defines a natural hazard as a “natural Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 195 195

238 process or phenomenon that may cause loss of life, injury or other health impacts, property damage, loss of livelihoods and services, social and economic disruption, or environmental damage”. Projected human population expansion, agricultural intensification, and greater human presence and infrastructure in mountainous regions combined with projected changes in climate extremes (IPCC, 2012) are expected to jointly contribute to enhanced vulnerability to soil-mediated natural hazards (Figure 7.9). The extent of the vulnerability and exposure to a particular type of hazard vary considerably among regions (ESPON, 2013). For example, floods may increase in flat terrains with increasing mean precipitation or rapid snowmelt, and landslides may become more common in mountainous areas with changes in the seasonality and intensity of rainfall (Huggel, Clague and Korup, 2012). Figure 7.9 A conceptual sketch of how vulnerability, exposure and external events (climate, weather, geophysical) contribute to the risk of a natural hazard. Source: IPCC, 2012. The past few decades have been marked by an increase in the frequency and magnitude of damages caused by soil-climate related hazards such as landslides (Figure 7.10, FAO 2011). In part this increase may be simply attributed to more timely and accurate reporting, and also to deeper human penetration into soil-hazard prone regions, facilitated by increases in mobility and personal wealth (Keiler, 2013; Papathoma-Köhle et al. , 2015). The reports of EM-DAT ( http://www.emdat.be/publications ) provide a global perspective of all aspects of 1 report estimates global damages natural disasters and their human and economic impacts. The 2013 EM-DAT by natural hazard attributed to hydrological and geophysical causes (most closely related to soil) in excess of US$ 60 billion, with impacts on the lives of 40 million people in 2013 alone. It is instructive to place the various natural hazards in their soil-human-climate context to enable general inferences and detection of future trends with global change (population growth, land use, and climate change). 1 http://www.emdat.be/publications Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 196 196

239 Ten-year frequency of landslides and associated mortality in Asia 7000 120 6000 100 Frequency 5000 80 Mortalities 4000 60 Mortalities 3000 10-year frequency 40 2000 20 1000 0 0 1970 - 1979 1990 - 1999 1960 - 1969 1980 - 1989 1950 - 1959 2000 - 2009 Figure 7.10 Trends in landslide frequency and mortality on Asia. Source: FAO, 2011; EM-DAT, 2010. 7.7.1 | Soil landslide hazard The depth of the soil mantle forming over mountainous topography reflects a natural balance between soil production and soil erosion processes (Trustrum and De Rose, 1988; Heimsath et al. , 1997). The primary soil removal process in mountainous regions is landsliding, driven by the topographic relief and triggered by climatic forcing such as rainfall or snowmelt (Iverson, 2000; Larsen, Montgomery and Korup, 2010; Kawagoe, Kazama and Sarukkalige, 2009) or by earthquakes (Huang and Fan, 2013). Landslide damage is costly: Sidle and Ochiai (2006) estimated the direct costs associated with rebuilding or replacing infrastructure at several billion dollars per year, even without considering indirect costs related to construction and temporary loss of , 2015). site functionality. Similar estimates have been made just for Europe (Papathoma-Köhle et al. Rainfall is the most common trigger for shallow landslides (Iverson, 2000). The strong relationship between rainfall intensity-duration and landslide triggering conditions has prompted the use of rainfall characteristics for early warning (Guzzetti et al. , 2008; von Ruette, Lehmann and Or, 2014). The observed increase in precipitation variability and in extreme events attributed to climate change has been linked to the observed increase in landslide frequency in mountainous regions (Huggel, Clague and Korup, 2012). The recent IPCC report (IPCC, 2012) lists evidence for the contiguous United States confirming statistically significant increases in heavy (upper 5 percent) and very heavy (upper 1 percent) precipitation of 14 and 20 percent, respectively. Moreover, evidence from Europe and the United States suggests that the relative increase in precipitation extremes is larger than the increase in mean precipitation. Schmidt and Dikau (2004) found that climatic scenarios representing unstable conditions of transition from more humid to a dryer climate produced the highest slope instabilities. Soil hydraulic properties play an important in imparting mechanical sensitivity. Indeed, the soil plays multiple roles in the landslide hazard, not only as the mass that slides down the slope, but also through its own mechanical strength and through its modulation of local hydrology via infiltration capacity, base flow, macropore flow and ground cover (Iverson, 2000; Sidle and Ochiai, 2006; Lehmann and Or, 2012). The partitioning of precipitation between infiltration, overland flows and base flows is critical to the loading of the soil and to the ultimate soil failure. The mechanical reinforcement by plant roots helps to stabilize the soil mantle (Abe and Ziemer, 1991; Schwarz, Cohen and Or, 2012), and bulk soil mechanical and hydraulic properties affect the susceptibility to failure. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 197 197

240 Recent widespread drought-induced forest die-offs highlight how climate change could accelerate forest et mortality. This has potential consequences for the carbon cycle and for ecosystem services (Anderegg al. , 2013). Through loss of root reinforcement, die-off may also increase landslide hazard. Rapid landslide processes have also been observed in Southeast Asia and the Western Pacific where large tropical cyclones induce numerous landslides and remove significant amounts of soil and particular carbon through the river systems to the ocean (Hilton et al. , 2008). These extreme tropical precipitation events are likely to increase in frequency and magnitude (Huang et al. , 2013). 7.7. 2 | Soil hazard due to earthquakes Keefer (2002) provides a historical overview of the study of earthquake-induced landslides. These are often extensive in their size and occurrence and cause more significant damage than hydrologically-induced shallow landslides. For example, the 2008 Wenchuan earthquake in Sichuan province in China triggered more than 2 causing about one-third of the total number of fatalities in the 60 000 landslides over an area of 35 000 km earthquake disaster (Huang and Fan, 2013). In addition to the direct damages, the Wenchuan earthquake induced an unprecedented number of secondary geohazards such as heightened subsequent landslide frequency, causing river damming and consequent floods as well as debris flows. The links between seismic activity and landslide characteristics were systematically investigated by Malamud et al. (2004) based on landslide inventory data of landslide size-frequency distribution in the affected landscape. These analyses are useful for deriving large-scale soil erosion rates enhanced by seismic activity. Erosion rates in active subduction -1 . Hazard schemes often classify earthquake-induced landslides as ‘geophysical’ zones are around 0.2–7 mm yr or ‘dry’ events to indicate they do not require water for mass movement initiation, unlike hydrological ‘wet’ landslides. On March 11, 2011, a seaquake followed by an enormous tsunami and by the destruction of the Fukushima Atomic Power Plant, Japan, brought about additional soil changes such as liquefaction, tsunami sedimentation and radio isotope contamination, all of which affected the local population. Liquefaction brought about by the earthquake occurred mainly on soil-banked lands or soil-dressed lands, causing extreme damage to housing and structural facilities. The tsunami carried massive deposits from the bottom of the sea onto farmlands along the seashore. This sedimentation contained considerable quantities of arsenic (Kozak and Niedzielski, 2013). The explosion of the atomic power plant resulted in soil contamination (mainly with Cesium 137) of an area as large as 800 square kilometres (Steinhauser, 2014; Itoha et al. , 2014). Cleaning these contaminants is vital before the population can return. More broadly, although a variety of soil hazard regulation techniques et al. , 2011; Esteves have been developed (Gasso et al. , 2013; Delgado , 2012) there is a need for both more et al. research and more regulation related to soil hazards than hitherto. 7.7. 3 | Soil and drought hazard Droughts limit primary production and thus the accumulation rates of organic matter. Reduced accumulation rates contribute to soil vulnerability to water and wind erosion. Recent meso-scale strategies for combating drought damage and reducing risk in agro ecosystems have proposed landscape-scale vegetation management. This can, for example, take the form of patches or bands of perennial vegetation to promote feedbacks that are conducive to recycling of water vapour, soil moisture and nutrients (Ryan, McAlpine and Ludwig, 2010). An often ignored consequence of prolonged drought and soil water depletion is soil subsidence (2011) presented a systematic et al. and related damage to buildings and infrastructure (Corti et al. , 2011). Corti study of damage costs from drought-induced soil subsidence applicable across different climate regimes. The primary variables include drought severity, soil type (shrink/swell properties), land use, and vegetation. Prolonged droughts and drier climate patterns accentuate damages due to soil shrink/swell properties. The insurance industry reports that damage to infrastructure often peaks following extreme drought events, especially in the densely built up regions of Europe and United States. Dry climate also induces other Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 198 198

241 phenomena such as the onset of massive dust storms. Dust storms can arise either from destabilization of vulnerable surface soils (the Dust Bowl), or from the drying of lake beds, or from desertification and loss of vegetation and similar soil destabilizing activities over large scales. The rates of wind erosion associated with -1 in sensitive regions in the Sahel. Prolonged exposure is known to sand storms may exceed 100 mm topsoil yr pose respiratory health hazards to human population. | Soil and flood hazard 7.7. 4 Agricultural intensification has been linked to alteration of runoff mechanisms and to increased risk and burden of floods (Marshall et al. , 2014). Some of the primary changes in land management documented in the United Kingdom and elsewhere that affect soils include: heavy traffic contributing to soil compaction, tillage operation and consequent loss of soil structure, the formation of larger fields, choice of cover crops in rainy seasons, and increased livestock densities (O’Connell et al. , 2007). However, establishing rigorous causal links between changes in land management practices, local runoff generation and catchment scale flood et al. , 2013). Nevertheless, mounting evidence suggests that soil and behaviour remains a challenge (Ewen land management contribution to flood risk is not limited to management of lowland agricultural regions. Management of upland soils and related impacts on runoff generation mechanisms cascade and also have impacts on flood risk downstream (Wheater and Evans, 2009; Marshall et al. , 2009). A recent review by Hall et al. (2014) on flood trends in Europe (including climatic effects) confirms the important role of land use changes (urbanization, afforestation, etc.) as key factors in modifying large scale flood risk. Some of the strategies for reducing flood risk include afforestation in upland catchments (Ewen et al. , 2013), creation of retention basins, and adding floodplains by lowering levees (Hall et al. , 2014). 7.7. 5 | Hazards induced by thawing of permafrost soil et Permafrost is perennially frozen soil remaining at or below 0°C for at least two consecutive years (Brown , 1998). Permafrost regions occupy about 24 percent of the exposed land area in the Northern Hemisphere al. and in some high mountainous regions (UNEP, 2012). Expected thawing of permafrost is projected to induce alterations in soil hydrology and biological activity, and to have an impact on the global carbon cycle (Schuur et al. , 2008). In addition, the thawing of permafrost is expected to change vegetation species and reshape many ecosystem functions. The mechanical weakening of the previously frozen soil is likely to result in foundation settling, with damage to buildings, roads, pipelines, railways and power lines (Nelson, Anisimov and Shiklomonov, 2001; Jorgenson, Shur and Pullman, 2006). Estimates of infrastructure repair in Alaska up to 2030 are in the range of US$ 6 billion (UNEP, 2012). Changes in mean temperature and snow cover also affect sensitive permafrost in high mountains, and contribute to a higher risk of landslides and avalanches (Gruber and Haeberli, 2007; Harris et al. , 2009). Schoeneich et al. (2011) present an extensive report and case studies, largely from the European Alps, on various slope movement hazards (landslides, rock fall, and debris flow initiation) associated with degrading permafrost. Evidence suggests accelerated erosion rates of the thawed permafrost, especially along coastlines and rivers banks as documented by Schreiner, Bianchi and Rosenheim (2014) and Vonk et al. (2012), with subsequent transport of the carbon-rich sediment through river systems to the ocean. 7.8 | Soil biota regulation Soil biodiversity is vulnerable to many anthropogenic disturbances, including land use and climate change, nitrogen enrichment, soil pollution, invasive species and the sealing of soil. A recent sensitivity analysis revealed that increasing land use intensity and associated soil organic matter loss are placing the greatest pressure on soil biodiversity (Gardi, Jeffery and Saltelli, 2013). Numerous studies report soil biodiversity declines et al. et al. , 1997; Eggleton , 2002; Dlamini as result of the conversion of natural lands to agriculture (Bloemers Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 199 199

242 and Haynes, 2004), and as a result of agricultural intensification (Mulder et al. et al. , , 2005; Postma-Blaauw et al. 2010; De Vries , 2013a). In particular, studies show larger bodied soil animals, such as earthworms and termites are especially vulnerable, but intensive land use can also reduce the abundance and variety of species of nematodes, mites and collembolans. Climate change also poses a considerable threat to soil biodiversity through direct effects of warming and et al. altered precipitation (e.g. drought and flooding) on the availability of moisture in soil (Bardgett , 2008). Indirect climate change effects of warming and elevated atmospheric carbon dioxide may also have an impact on the quantity and quality of organic matter in soil (Blankinship, Niklaus and Hungate, 2011; van Groenigen et al. , 2014). Although poorly understood, predicted increases in the frequency of erosive rainfall events (Nearing et al. , 2005) and climate-induced shifts in land use (Mullan, 2013) could pose a considerable future threat to soil biodiversity. Other threats to soil biodiversity include nitrogen enrichment, which negatively impacts soil fungi (Treseder, 2008), soil sealing, which effectively stops the natural functioning of soil (Gardi, Jeffery and Saltelli, 2013), and invasive species, which affect native soil biodiversity through a range of mechanisms, including altered resource supply, competitive interactions and predation, and physical and chemical modification of the soil environment (Wardle et al. , 2011). Although it is well known that soil organisms play key roles in many ecosystem processes, our understanding of the functional consequences of belowground diversity loss is limited, at least compared to what is known about aboveground losses (Cardinale et al. , 2012). Recent synthesis of experimental studies on soil diversity- function relationships indicate that diversity effects on processes of nutrient and carbon cycling are highly variable, but effects of species loss are most pronounced at the low end of the diversity spectrum (Nielsen et al. , 2011). There is also a general consensus that changes in the functional composition of belowground communities, rather than species diversity per se, are of most importance for ecosystem functioning (Nielsen et al. , 2011). Consistent with this, laboratory studies with low numbers of species have shown the functional composition of soil macrofauna communities to be a better predictor of litter decomposition than species richness (Heemsbergen , 2004). The selective removal of different groups of soil organisms has been shown et al. et al. to impair soil functioning (Wagg , 2014). Likewise, a recent cross-biome field experiment showed that the loss of key components of the decomposer communities consistently slowed rates of litter decomposition and et al. , 2014). carbon and nitrogen cycling, indicating negative effects of diversity loss on soil functions (Handa A field-based study of different sites across Europe also showed that changes in soil food web composition resulting from intensive agriculture consistently strongly affected processes of carbon and nitrogen cycling (De Vries et al. , 2013a). At one site, high intensity management reduced the resistance and resilience of the soil food web to drought, increasing soil carbon and nitrogen loss as greenhouse gases and in leachates (De Vries et al. , 2012a, 2012b, 2012c). Changes in soil biodiversity can also modify vegetation dynamics, both directly through associations of symbionts and pathogens with plant roots, and indirectly, by modifying nutrient availability to plants (van der Putten et al. , 2013). For example, mycorrhizal fungi, which form symbiotic associations with roots of most plant species and are very vulnerable to soil disturbances, can enhance plant species diversity by relaxing plant competition intensity and promoting more equitable distribution of resources within the plant community (van der Heijden, Bardgett and van Straalen, 2008). Also, plant diversity and productivity have been shown, in some situations, to be positively related to arbuscular mycorrhizal fungal diversity due to more efficient use of soil phosphorus (van der Heijden et al. , 1998). Soil pathogens, which cause considerable problems for agricultural crops, have also been shown to impact vegetation dynamics in natural settings, by suppressing the growth of their host plant species more than their neighbours, thereby contributing to vegetation change (Bever, Westover and Antonovics, 1997; Packer and Clay, 2000; Klironomos, 2002). The spread of invasive plant species has also been linked to release from their natural soil enemies in their new territories, giving the invasive plant a competitive edge over native species. This often leads to declines in plant diversity and to , 2013). et al. et al. , 2011; van der Putten shifts in the functioning of the soil (Wardle Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 200 200

243 Although poorly explored, diversity changes in soil are likely to impact soil physical properties, with consequences for ecosystem services related to soil formation and water regulation. Diversity effects on soil physical properties have not been explicitly studied, but they are likely to be important given the potential for different groups of soil organisms to differentially impact soil structure through different routes. For example, fungi promote soil aggregate stability through the physical enmeshment of soil particles by their extensive networks of mycelia, whereas bacteria produce metabolic products, mainly polysaccharides, which bind et al. soil particles together (Hallett , 2009). Mycorrhizal infection can also influence soil aggregate stability through physical enmeshment of soil particles by their extensive networks of mycelium, but also through the binding of soil particles via the production of extracellular polysaccharides and proteins, including the protein glomalin, which alters the wetting behaviour of soil (Rillig and Mulley, 2006). Finally, soil animals, especially ecosystem engineers such as earthworms and termites, impact soil structure by creating macropores and channels, thereby improving water movement through soil (Bardgett, 2005). While evidence is mounting that shifts in soil biodiversity resulting from human activities have significant consequences for ecosystem functions and the services that they underpin, there is still much to be learned. The mechanisms by which soil biodiversity change can impact ecosystem are enormous, involving a range of ecological and evolutionary processes at different spatial and temporal scales, and links between aboveground and soil communities. Moreover, impacts of soil biodiversity change on soil functions are likely to be context dependent, varying with soil abiotic properties and vegetation type. Unravelling this complexity in order to make better predictions about the consequences of soil biodiversity change for the services that ecosystems provide is a major challenge. 7.9 | Soils and human health regulation The linkage between soils and human health is increasingly being recognized (Abrahams, 2006, 2013; Baumgardner, 2012; Brevik and Burgess, 2013; Jeffrey and van der Putten, 2011; Oliver, 1997). A central understanding is that soils form an integral link in a holistic view of human health that includes physical, mental and social dimensions. The soil acts as a natural filter, it can kill off pathogens, it can biodegrade organics and, in general, it does a wonderful job of protecting us from human health threats. However, soil is not able to protect itself against all the insults it is subject to on a regular basis. Soils aid in the regulation of human health. They do this by keeping in check, or balancing, the beneficial versus deleterious concentrations of elements and moderating disease-causing organisms. For example, soils regulate human health by impacting the nutrient quality or nutrient density of foods. Too little of an essential nutrient in soil can lead to human diseases such as Keshan disease caused by selenium deficiencies in the human diet (Chen, 2012). Conversely, health problems can be caused by an excess amount of organics or trace elements such as the arsenic released by soils into the drinking and irrigation waters of Bangladesh (Khan, Hamra and Mu, 2009) (Section 7.3). Soil is a natural source of radiation that can adversely affect human health, and soil can also affect human health by directly interacting with people. One example is the disease of podoconiosis or Mossy Foot disease (Mossy Foot Project, 2014). Mossy Foot disease affects about 5 percent of the population in highland tropical areas with volcanic soils and lots of rainfall. These soils are rich in silicates that can penetrate the skin of susceptible people as they go barefoot about their daily business. Soils can also act as a reservoir of all kinds of introduced materials that can impact human health. The dioxin at Love Canal in New York, United States is a classic example (Silkworth, Culter and Sack, 1989). There are large quantities of industrial and agricultural products and by-products added to soil every year that have the potential to impact human health. Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 201 201

244 Vast numbers of people, primarily women, infants and children, are afflicted with trace element deficiencies (notably Fe, I, Se, and Zn), mostly in the resource-poor countries of the developing world. A diet with low boron (B) has been found to lead to a number of general health problems and to increase cancer risk. The most common symptoms of B deficiency include arthritis, memory loss, osteoporosis, degenerative and soft cartilage diseases, hormonal disequilibria and a drop in libido (Scorei and Popa, 2010). According to one et al. , 2003). hypothesis, the low cervical cancer incidence in Turkey correlates with its B-enriched soil (Simsek et al. , 2007). In a survey Indeed, the ingestion of B via drinking water prevents cervical cancer risk (Korkmaz -1 ) in the drinking water was associated with in northern France, exposure to high levels of boron (>0.3 mg L et al. , 2005). a significantly lower mortality rate as compared to that of a low-boron reference area (Yazbeck Silicon is the second most abundant element in the Earth’s crust. Dietary silicon intake is positively associated with bone mineral density in men and premenopausal women of the Framingham Offspring cohort ( Jugdaohsingh et al. , 2004). Silicon is bound to glycosaminoglycans and has an important role in the formation of cross-links between collagen and proteoglycans (Carlisle, 1976). In vitro studies have demonstrated that silicon stimulates type 1 collagen synthesis and osteoblast differentiation (Reffitt et al. , 2003). Many physicians have believed that zinc deficiency is a rare occurrence in Japan. Nevertheless, One study found many zinc-deficient patients at a clinic in Japan since 2002 (Kurasawa, Kubori and Okuizumi, 2010). Their complaints were anorexia, general fatigue, impaired sense of taste, burning mouth, various types of skin lesion, delayed wound healing and emotional instability. Based on dietary intake recommendations, subclinical or marginal Mg deficiency (50 percent to <100 percent of requirement) commonly occurs throughout the world (Nielsen, 2010). Yet, pathological conditions attributed specifically to dietary Mg deficiency alone are considered rare. However, epidemiological and correlation studies indicate that a low Mg status is linked to numerous pathological conditions associated with aging, including atherosclerosis and hypertension (Ma , 1995), osteoporosis (Rude, Singer and et al. et al. , 2003), and some cancers (Dai Gruber, 2009), diabetes mellitus (Barbagallo , 2007). Magnesium et al. (Mg) deficiency increases genomic instability and Mg intake has been reported to be inversely associated with a risk of colorectal cancer (CRC). An experiment designed to determine whether Mg in drinking water suppresses inflammation-associated colon carcinogenesis in mice showed Mg at all doses caused a significant inhibition of CRC development (Kuno et al. , 2012). The role of soil in contributing to human health is considerable. Soils rich in biodiversity produce healthier and more nutritious foods and control the proliferation of any pathogenic microorganisms that affect both plant and human health. Biodiversity is a result of a highly functioning, high quality soil with a good balance of nutrients and good water infiltration and aeration. An example of how imbalance in a soil, for example improper soil water balance, causes human and animal disease comes from Australia (Hampton et al. , 2011; Creswell, 2012). Birds and people were being infected and some died due to a disease, melioidiosis, caused by the bacteria Burkholderia pseudomalle. This microorganism is normally found only at low levels in soil, mostly in subsoils. However, after heavy rains, pools or puddles of water provide a suitable habitat for the bacteria to proliferate. It enters the body via a cut or graze or through the lungs by inhalation. Soil that is properly drained and aerated regulates the prevalence of this bacteria and keep it in check. Soils also serve as a source of many medicines. For example, soil microorganisms still account for many of et al. , 2006; Pepper , 2009). It is therefore important the current clinically relevant antibiotics (D’Costa et al. to maintain the vast diversity of microorganisms in soil in order preserve the untapped potential for future discoveries important to human health. We are just now beginning to understand how the chemical, physical and biological properties of soil can Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 202 202

245 affect the health of humans and animals and entire ecosystems. The same techniques that are available to map the human microbiome can also be applied to map the soil microbiome. We are thus on the verge of understanding what constitutes a healthy soil microbiome and how a degraded or unhealthy soil microbiome may affect our food production and overall human health. 7.10 | Soil and cultural services The soil is one of the main sources of information on the prehistoric culture of humankind. Indeed, soil is an excellent medium for preserving artefacts. Different soil types have particular characteristics to preserve remains. For instance, in permanently or seasonally wet soils, the lack of oxygen slows down the decomposition of organic matters. Sometimes the remains of animals can be found with hunting marks from arrows or spears. Well-preserved human bodies have been excavated from moors and bogs. The anaerobic conditions preserve the bodies very well and several thousands of years later they are excavated with skin, flesh and clothes still present. Wooden constructions, such as poles for bridges, boats and wooden tools may also be preserved, giving us valuable information on the level of technology at that time. Past farming practices can also be recognized in the soil profile, particularly in Anthrosols. For example, in northwest Europe, notably in the Netherlands and Germany, a human-made soil type, known as plaggen soil, has developed as a result of a specialized agricultural system. On the strongly leached, acid sandy outwash plains and moraines, Podzols developed underneath a vegetation cover of heather. Farmers used the heather and the uppermost level of the soil as bedding in the stables. The droppings from the animals, mixed with the bedding, were later used as manure on the nearby fields, slowly building up a thick soil layer rich in organic matter and high in nutrients and with a good soil water retention. These fields provide a relatively high and stable crop production compared to the surrounding land (European Soil Bureau Network, 2005). In the Amazon basin, the Terra Preta soil owes its name to its very high charcoal content. It was created by the addition of a mixture of charcoal, bone and manure to the otherwise relatively infertile Amazonian soil. Terra Preta soils were created by indigenous peoples in the pre-Columbian era between 450 BC and AD 950 (Sombroek et al. , 2002). Technosols are modern examples of soils that store artefacts or are strongly influenced by (modern) humankind. They include soils from wastes (landfills, sludge, cinders, mine spoils and ashes), pavements with their underlying unconsolidated materials, and constructed soils in human-made materials (FAO, 2014). Soils provide aesthetic and recreational value through the landscape, particularly in Globally Important Agricultural Heritage Systems (Koohafkan and Altieri, 2011). They have also been used as an aesthetic approach to raise soil awareness in contemporary art (Toland and Wessolek, 2014). Churchman and Landa (2014) provide a comprehensive treatment of the topic. References Abe, K. & Ziemer, R.R. 1991. Effects of tree roots on a shear zone: Modelling reinforced shear stress. Can. J. For. Res., 21: 1012–1019.. Aber, J.D., Nadelhoffer, K. J., Steudler, P. & Melillo, J.M. 1989. Nitrogen saturation in northern forest ecosystems. BioScience , 39: 378-286. Abrahams , P.W. 2006. Soil, geography and human disease: A critical review of the importance of medical cartography. Progress in Physical Geography , 30: 490-512. , P.W. 2013. Soils: Their implication to human health. ., 291: 1-32. Abrahams Sci. Total Environ Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services 203 203

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265 8 | Governance and policy responses to soil change 8.1 | Introduction This chapter provides an overview of policy and governance responses to soil change. While most attention is given to issues at the global, regional and national levels, it is emphasized that effective responses nearly always have a basis in local action by individual land managers. Indeed, understanding the interconnectedness and the consequences of actions at each level is central to effective governance and policy. This book, and in particular the regional assessments of soil change (Chapters 9 to 16), demonstrate that at the global scale there is a qualitative appreciation of the pressures on soil resources but limited consistent evidence on their condition and trajectories of change. These assessments reveal that some of the world’s soil management challenges are immediate, obvious and serious – they arise partly because of the nature of soils in different regions and their associated history of land management. Other problems are more subtle but equally important in the long term – they require vigilance and a sustained policy response over decades. At present, few countries have effective policies to deal with these problems. In short, the world’s soils need to support at least a 70 percent increase in food production by 2050 (FAO, 2011) but there are some fundamental uncertainties. For example: Is there enough arable land with suitable soils to feed the world in coming decades? Are soil constraints partly responsible for the apparent yield plateau for major crops? Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 223 223

266 Can changes to soil management have a significant impact on the seemingly unsustainable global demand for nutrients? Can changes to soil management have a significant impact on atmospheric concentrations of greenhouse gases without jeopardising other functions such as food and fibre production? Will the extent and rate of soil degradation threaten food security and the provision of ecosystem services in the coming decades? Can water-use efficiency be improved through better soil management in key regions facing water scarcity? How will climate change interact with the distribution of soils to produce new patterns of land use? A comprehensive global view is needed to respond to these questions. A comprehensive view is also needed to deal with the trans-national aspects of food security and soil degradation. Through trade, most urbanised people are protected from local resource depletion. The area of land and water used to support a global citizen is scattered all over the planet. As a consequence, soil degradation and loss of production are not just local or national issues – they are genuinely international. The consideration of soil in policy formulation has been weak in most parts of the world. Reasons for this weakness include the following. Lack of ready access to the evidence needed for policy action. The challenge of dealing with a natural resource that is often privately owned but is at the same time an important public good. The long-time scales involved in soil change – some of the most important changes take place over decades and they can be difficult to detect. As a result, communities and institutions may not respond until critical and irreversible thresholds have been exceeded. Perhaps even more significant for policy makers is the disconnection between our increasingly urbanized human societies and the soil. The task of developing effective policies to ensure sustainable soil management is neither simple to articulate nor easy to implement. This is true regardless of a country’s stage of development, its natural endowment of soil resources, or the threats to its soil function. 8.2 | Soils as part of global natural resources management In setting the stage, it is useful to examine the major drivers, pressures and institutional responses to land use and then set these within the broader international sustainable development agenda (see Table 8.1). 8.2.1 | Historical context The ‘Great Dust Bowl’ of the 1930s in the United States of America was pivotal because it triggered widespread public concern about land use, degradation and the need for sustainable management. Severe wind erosion resulted from the opening up of vast areas for cereal production through mechanisation, with associated loss of protective vegetation cover. In response, the Soil Conservation Service of the USDA was established in 1935. This served as a model for many other countries facing similar issues (Young, 1994). In 1937, the United States President Franklin D. Roosevelt famously stated ‘The nation that destroys its soil destroys itself.’ This is perhaps the most succinct and sharpest challenge for policy makers and it remains an all-too-real Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 224 224

267 contemporary challenge for policy makers in many countries. After World War Two, many countries experienced food shortages and governments responded by increasing their investments in agricultural research. Understandably, most of this research focussed on increasing crop yields and food production. During this period there was also a large investment in soil and land resource surveys, particularly in Africa and Asia. In the following decades, soil science was strongly supported, with diverse institutional responses emerging in different regions. In some countries, there was close integration with other aspects of natural resource management while in others, separate soil agencies were established. The FAO played an important role in developing influential technical standards (e.g. FAO, 1976) and supporting within-country programs that aimed to establish sustainable soil and land management. The production of the FAO-UNESCO (1980) Soil Map of the World was a landmark achievement. The success of the Green Revolution (Borlaug, 2000) along with large increases in crop yields in North America and Europe eventually led to less investment by public agencies in agricultural science and related activities. The emphasis shifted to environmental issues, a transition which occurred during the 1970s and 1980s, particularly in developed western countries. During the 1990s and 2000s, disinvestment in soil science was widespread and many soil departments in universities or governments were either closed or incorporated into natural resource or environmental units. The UN commitment to soil resources through the FAO and related agencies was also scaled back dramatically. The food price rises in 2007 and 2008 shocked many policymakers out of the belief that stable or declining , 2012). This period also marked et al. food prices and assured supplies could be taken for granted (Beddington the start of a critical re-examination of the capacity of the world’s soil resources to support sustainable agriculture, assist with climate regulation, and safeguard ecosystem services and biodiversity. Before exploring this topic in more detail, it is useful to review some of the key global agreements relating to soils that emerged from the 1980s onwards. 8.2.2 | Global agreements relating to soils In 1982, the FAO adopted the World Soil Charter and UNEP published the World Soils Policy (FAO, 1982; UNEP, 1982). It has been difficult to assess the practical impact of these initiatives. Nevertheless, the principles and definitions provided useful guidance for national governments that pursued actions on sustainable soil management. The first United Nations Conference on Environment and Development (UNCED, 1992, also known as the ‘Earth Summit’) launched the global environmental agenda (Table 8.1). The UN Convention to Combat Desertification (UNCCD) addressed issues of desertification, land degradation and drought; the UN Framework to Combat Climate Change (UNFCCC) was to tackle climate change; and the Convention on Biological Diversity (CBD) dealt with the challenges of biodiversity conservation and sustainable use (CBD). Supported by the Global Environment Facility (GEF), these conventions have raised awareness and mobilised increased efforts by countries and partners to generate global environmental benefits. These conventions also cover, albeit with less prominence, issues of soil conservation, sustainable land management and land use change, taking into account human as well as ecological perspectives (Hurni et al. , 2006). The ecosystem approach promoted by the CBD between 1998 and 2004 (CBD, 2014), recognised that human management is central to biodiversity conservation and sustainable use. This ecosystem approach was further developed in the Millennium Ecosystem Assessment of 2005. This paved the way amongst international agencies and donor funds for more integrated ecosystem approaches in agriculture. These approaches emphasized the need for sectoral integration, with increased attention given to the benefits of mixed agroforestry and agro-silvo-pastoral systems. Similar approaches had already been developed in many countries. Globally, there was a trend towards the use of incentive measures to encourage land users to adopt sustainable practices which not only enhance production but also maintain biodiversity and ecosystem services (FAO, 2007; MA, 2005; UNEP, 2004). Soils came to be seen in relation to the services they provide for human well-being and poverty reduction. However, compared to other functions, soil-related matters did not Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 225 225

268 feature prominently in policy or programmes. Following the food crisis in 2008, policy makers at the international level began to appreciate that soils were finite and an important factor that had to be considered in the debate on food security. Within the framework of UNCCD’s ‘Zero Net Land Degradation’, discussions were initiated about the need for quantitative targets and indicators to measure soil degradation (UNCCD, 2012). Concerns over food insecurity, water scarcity, climate change and increasing pressures on limited land and water resources led to much greater dialogue, advocacy and partnerships supporting integrated approaches to this complex set of issues (Beddington et al. , 2012; Steffen et al. , 2015). The UN Conference on Sustainable Development (Rio+20), took place in June 2012, two decades after the Earth Summit. In the resulting document, The Future We Want, the international community agreed on the need to achieve a land degradation neutral world in the context of sustainable development (UN, 2012). The conference also initiated the process of developing universal Sustainable Development Goals (SDGs). All of the above developments relating to soils and land degradation are framed by the broader issue of climate change. Again, there is a long institutional history but it is useful to start with the establishment of the Intergovernmental Panel on Climate Change (IPCC) in 1988 by the UN Environment Programme (UNEP) and the World Meteorological Organization (WMO). The IPCC provides the world with scientific and technical information on climate change and its socio-economic impacts. The next major development was adoption of the Kyoto Protocol in 1997 by the UNFCCC. The Protocol, which entered into force in 2005, committed ). The Protocol industrialized countries to stabilize greenhouse gas emissions, in particular carbon dioxide (CO 2 started as a non-binding agreement but later progressed to legally binding agreements on emission reduction targets. The Protocol is of great importance for soils and land management because soils are important carbon sinks. The Protocol recognized opportunities for better management of carbon stores and for the enhancement of carbon sequestration in forestry and agriculture. There was thus clear recognition that soil management can be a vehicle to achieve climate goals – and conversely, that soils can be managed to avoid the loss of carbon through land degradation. Because of the climate system’s sensitivity to soil processes, soil- related issues are set to attract increasing attention in future climate agreements. In recent years, FAO and its member countries have made significant progress in supporting strategies and policies to improve global governance of soil resources. In order to meet the need for a multilateral agreement focusing specifically on soil challenges, and to advocate for sustainable soil and land management at global level, the Global Soil Partnership1 (GSP) was proposed by FAO and the EU and then established in September 2011. The GSP strives to raise awareness among decision makers on the role of soil resources in relation to food security, climate change, and the provision of ecosystem services (Montanarella and Vargas, 2012). Technical and scientific guidance is provided by the Intergovernmental Technical Panel on Soils (ITPS). The ITPS complements related scientific advisory panels including the Intergovernmental Panel on Climate Change (IPCC), the Intergovernmental Panel on Biodiversity and Ecosystem Services (IPBES), and the UNCCD’s Science-Policy Interface (SPI). The ITPS has been key to the development of the Plans of Action for the five pillars of the Global Soil Partnership (Table 8.2). It has also been engaged in the development of the Sustainable Development Goals and the initiation of formal reporting mechanisms, including the present book. An indication of the emerging priority accorded to soils and a measure of the impact of the GSP was the declaration by the United Nations General Assembly of 2015 as the International Year of Soils. 1 www.fao.org/globalsoilpartnership Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 226 226

269 Year FAO World Soil Charter 1982 1988 Intergovernmental Panel on Climate Change (IPCC) UN Conference on Environment and Development Rio Declaration Agenda 21 Global Environmental Facility 1992 UN Convention to Combat Desertification (UNCCD) UN Framework to Combat Climate Change (UNFCCC) Convention on Biological Diversity (CBD) 1997 Kyoto Protocol 2000 Millennium Development Goals (MDGs) 2005 Millennium Ecosystem Assessment 2008 UNCCD’s Zero Net Land Degradation 2011 Global Soil Partnership initiated (FAO/EU) Rio+20 2012 Sustainable Development Goals (SDGs) and Post-2015 Development Agenda Intergovernmental Technical Panel on Soils (ITPS) of the GSP Updated FAO World Soil Charter 2013 Land and Soils integrated in the Open Working Group of the Sustainable Development Goals Regional Soil Partnerships of the GSP International Year of Soils declared by the UN General Assembly 2015 Table 8.1 Recent Milestones in soil governance and sustainable development Pillar No. Action Promote sustainable management of soil resources for soil protection, 1 conservation and sustainable productivity Encourage investment, technical cooperation, policy, education awareness 2 and extension in soil Promote targeted soil research and development focusing on identified gaps and priorities 3 and on synergies with related productive, environmental and social development actions Enhance the quantity and quality of soil data and information: data collection, analysis, 4 validation, reporting, monitoring and integration with other disciplines Harmonize methods, measurements and indicators for the sustainable management 5 and protection of soil resources Table 8.2 The 5 Pillars of Action of the Global Soil Partnership. Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 227 227

270 | National and regional soil policies 8.3 8.3.1 | Sustainable soil management – criteria and supporting practices International agreements on soil and land resources are helpful but they are all to no avail unless there are complementary policies and coordinated activities at regional, national, district and local levels. Appropriate and effective policies need to reflect the local context in terms of the natural resource issues, culturally acceptability and economic feasibility. However, a unifying scientific narrative is also needed. In broad terms, the criteria for determining whether a landscape is functioning effectively and whether soils are being managed sustainably are as follows. Leakage of nutrients is low. Biological production is high relative to the potential limits set by climate and water availability. Levels of biodiversity within and above the soil are relatively high. Rainfall is efficiently captured and held within the root zone. Rates of soil erosion and deposition are low, with only small quantities being transferred out of the system. Contaminants are not introduced into the landscape and existing contaminants are not concentrated to levels that cause harm. Systems for producing food and fibre for human consumption do not rely on large net inputs of energy Net emissions of Greenhouse Gases are zero or less. We can manage what we can measure, so the task is to ensure that the above criteria can be measured against locally appropriate benchmarks. Without this information, policy makers and land managers do not have indicators of whether they are moving towards sustainability or going backwards. Policy makers also require an appreciation of how soil and land management practices can be applied to achieve desired outcomes. Regardless of the level of mechanization and technological sophistication, farming practices in general need to (FAO, 2013): Minimize soil disturbance by avoiding mechanical tillage in order to maintain soil organic matter, soil structure and overall soil function. Enhance and maintain a protective organic cover on the soil surface, using cover crops and crop residues, in order to protect the soil surface, conserve water and nutrients and promote soil biological activity. Cultivate a wide range of plant species – both annuals and perennials – in associations, sequences and rotations that include trees, shrubs, pastures and crops, in order to enhance crop nutrition and improve system resilience. Use well-adapted varieties with resistance to biotic and abiotic stresses and with improved nutritional quality, and to plant them at an appropriate time, seedling age and spacing. Enhance crop nutrition and soil function through crop rotations and judicious use of organic and inorganic fertilizer. Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 228 228

271 Ensure integrated management of pests, diseases and weeds using appropriate practices, biodiversity and selective, low-risk pesticides when needed. Manage water efficiently. Control machines and field traffic to avoid soil compaction. Thousands of different soil and land management practices have been developed around the world in response to local biophysical, social and cultural settings (e.g. WOCAT, 2007). Most cultures have deep connections with the land, and soil is venerated in diverse ways (Churchman and Land, 2014). In many regions, traditional knowledge still plays an important role in determining land management. However, most traditional systems have been disrupted or modified for a wide range of reasons. The two most common reasons have been the loss of access to land (e.g. invasion and displacement; increasing population densities causing shorter fallow periods on smaller areas; loss of access to grazing lands) and the arrival of new technologies. 8.3.2 | Education about soil and land use Regardless of the culture or landscape setting, knowledge of soil and land resources is the foundation for achieving sustainable soil management (Dalal-Clayton and Dent, 2001). Spreading knowledge about soils requires formal education, preferably at all levels of schooling. Some countries are developing comprehensive and imaginative curricula that use an understanding of soils as a basis for teaching a wide range of cultural, social, scientific and economic subjects. At a more advanced level, training is needed in a range of soil science sub-disciplines (e.g. soil physics, soil chemistry, soil biology and pedology), Training in soil science needs to be linked to related disciplines including geology, ecology, forestry, agronomy, hydrology and other environmental sciences. Mechanisms for outreach, vocational training and extension are also needed. Policy makers need to ensure that education systems provide sufficient understanding and training for a nation to achieve sustainable soil management. In particular, farmers and others directly involved in soil management require sufficient knowledge to manage their soils profitably and sustainably. | Soil research, development and extension 8.3.3 The second key area where policy makers have responsibility is in relation to research, development and extension. The pioneering work of the Soil Conservation Service in the United States and the technical innovations of the Green Revolution are two examples that demonstrate the power of agricultural science and technology. The Green Revolution also highlights how trade-offs are required when there is a focus on a single ecosystem service (food production) at the expense of others (e.g. water quality). Contemporary science policy often focuses on impact and public benefit. In this regard, soil research is often considered simply as a means to an end. Although soil science is vital to several important ends, notably agriculture, environment, water management and climate change, it is often overlooked in priority setting exercises. More formal recognition of soil resources as a cross-cutting issue in science policy is necessary to ensure it receives sufficient support. The recent Australian initiative to achieve a more integrated view of soil research, development and extension is instructive in this regard (Australian Government, 2014). 8.3.4 | Private benefits, public goods and payments for ecosystem services The amount of regulation on land use and management varies substantially between countries depending largely on the degree of government intervention. Effective regulations on land use and management require a good information base for setting critical limits, implementing various zoning schemes and monitoring Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 229 229

272 compliance. In practice, regulating soil management practices (e.g. application of manure, moderating or increasing fertilizer use, control of dryland salinity) and implementing zoning systems (e.g. to protect the best agricultural soils) involves complex technical, institutional and policy challenges. Countries that rely less on regulation often opt for incentive schemes to achieve outcomes. Incentives can range from subsidy systems (e.g. for fertilizer in poor countries or for equipment for conservation tillage in developed countries) through to various forms of certification for the adoption of specified soil management practices (e.g. organic farming). Some of these systems have strong economic drivers because they are mandatory for market access (e.g. participation in supply chains to supermarkets). Implementing effective policies requires organized systems for monitoring soil conditions and an understanding of the relationship between soils and land management. Without this basic information, policy makers have no way of knowing whether regulations and incentive schemes are achieving the desired result. | Intergenerational equity 8.3.5 Ensuring intergenerational equity is becoming more difficult as human pressures on soil resources reach critical limits. Most traditional cultures and systems of family farming have strong cultural norms that ensure tribal lands or family farms are passed to the next generation in the same or better condition than when they were inherited. However, dramatic changes to land management associated with intensive agriculture, the adoption of Green Revolution technologies, and intensification of land use more generally, are having a major impact on soil resources. The area of arable land per capita is decreasing sharply (0.45 ha in 1961, 0.25 ha in 2000 and a forecast of 0.19 ha in 2050). Future generations will inherit a radically modified land and soil resource. Many countries have sophisticated reporting systems for assessing issues relating to intergenerational equity (e.g. long-term forecasts to determine the viability of pension and health systems; decadal plans for critical infrastructure). Scenario analysis and futures forecasting are essential to national preparedness and long-term sustainability. There is now an imperative for policy makers to assess the current trends in soil condition and natural resource scarcity summarised in this book and to factor in the consequences to scenario analysis and futures forecasting. 8.3.6 | Land degradation and conflict Land degradation and resource scarcity can play a role in the rise of conflicts, but these conflicts are rarely purely resource driven. Where tensions about access and use of natural resources do exist, they depend on a variety of factors – the outcomes of which may sometimes cascade from tension into violent conflict, but certainly not always. More often than not, natural resource degradation is a result of conflict rather than a cause. The existence of land degradation can also lead people to seek cooperative solutions. Policy makers and others involved in land management can not only act to resolve resource conflicts but also help to prevent et al. them and to find peaceful mutually acceptable solutions (Frerks , 2014; Bernauer, Böhmelt and Koubi, 2012). Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 230 230

273 | Regional soil policies 8.4 8.4.1 | Africa Africa has a diverse range of soils and land use systems. However, very large areas, particularly in West Africa, are infertile or of low fertility, and unsustainable systems of land use are widespread. A leading cause of low fertility is nutrient depletion (Smaling, 1993; Stoorvogel, Smaling and Janssen, 1993). This is considered to be the chief biophysical factor limiting small-scale farm production (Drechsel, Giordano and Gyiele, 2004) although other factors including limited organic matter and erosion are significant as well (Bossio, Geheb and Critchley, 2010). Mounting concern over these issues contributed to the creation of the New Partnership for Africa’s Development (NEPAD). This is a vision and policy framework produced by the African Union (AU) that aims to provide member countries with guidance over their development agenda. Within NEPAD, the Comprehensive Africa Agriculture Development Programme (CAADP) sets out an agenda targeting annual growth of 6 percent in agricultural production. The Abuja Declaration on Fertilizers, agreed in 2006, laid out the vision for an African Green Revolution. Central to this was the aim of increasing the level of fertilizer -1 -1 to 50 kg ha . However, only slow progress has been made in implementing this application from 8 kg ha agenda at regional and country level (NEPAD, 2012). Food policy and agricultural development in Africa pose challenges beyond the scope of this book. However, there are some promising developments even for countries facing the most daunting difficulties owing to rapid population growth, very low incomes, weathered and infertile landscapes, low levels of literacy, vulnerability to climate variability and change, disease and significant potential for social unrest. Two of these promising developments have been supported by the Bill and Melinda Gates Foundation. First is the AGRA Soil Health Programme which aims to increase income and food security by promoting the wide adoption of integrated soil fertility management (ISFM) practices among smallholder farmers and creating an enabling environment for wide adoption of these improved practices across sub-Saharan Africa. The objective is to improve supply and access to appropriate fertilizers, as well as access to knowledge on IFSM for over four million smallholders and to strengthen extension and advisory capacity. The Programme also seeks to influence national policy in favour of investment in fertilizer and ISFM. Some 1.8 million smallholders are reported to be using ISFM, including fertilizer micro-dosing, manure and legumes in crop rotations, with yields in the Sahel up three to fourfold in good seasons. The second promising initiative is the AgWaterSolutions Project. The project concept builds on the existence of sizable untapped groundwater systems in the region and on the recent availability of small affordable motorized water pumps. The project promotes small-scale distributed irrigation systems that rely primarily on groundwater. In these systems, the access point for water, the distribution system and the irrigated crop all occur at or near the same location. These systems are typically privately owned and managed by individuals or small groups. The potential in countries such as Burkina Faso is large. This initiative is helping to shift the attention of policy makers and planners away from large scale irrigation developments. There are many other significant soil policy issues facing the region. Examples include: the costs and benefits of subsidy schemes for fertilizers; the growing pressure on land resources and the consequent shortening of fallow periods; the challenge of making inputs affordable and ensuring market access in areas where poverty is prevalent; and addressing urban and peri-urban planning so that more intensive and safe food production systems can develop in and around the rapidly growing African cities. Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 231 231

274 Asia 8.4.2 | In regions of rapid development in Asia, urbanization, industrialization and intensive land use lead to unbalanced use of agro-chemicals, poor waste management and acid deposition caused by urban air pollution. These factors have contributed to increasing soil contamination and acidification. In China, for example, a soil pollution survey found that 6.4 million square kilometres of arable land are contaminated and that this represents an alarming threat to human health (Yue, 2014). In consequence, China’s Environmental Protection Law was revised and strengthened in 2014. However, in China and all across the region the greatest environmental challenges arise from the gap between legislation and implementation (Mu et al. , 2014). In recent years government policy responses across the region have encouraged improved land use practices that increased tree cover for carbon sequestration. Carbon-financing schemes have been implemented. However, government policies have been less effective in dealing with the issue of foreign investment in agricultural land. In some countries, foreign companies have begun a variety of contractual arrangements with local farmers, resulting in some cases in the loss of land for smallholders (Fox et al. , 2011). 8.4.3 | Europe Europe has well-established and strong formal governance mechanisms to address environmental issues at regional, national and sub-national levels. European Union (EU) environmental policies are agreed at central level but legislated and implemented at the national level. However, the experience with soils policy has been more complex and only a handful of member states have specific legislation on soil protection. With the objective of protecting soils across Europe, the European Commission adopted a Soil Thematic Strategy in 2006 which consists of a communication, a proposal for a framework directive (under European Union legislation) and an impact assessment (EC, 2006). The proposal for a Soil Framework Directive would require member states to adopt a systematic approach to identifying and combating soil degradation. However, this could not be agreed by the required majority in the European Council and the draft Directive was consequently withdrawn by the European Commission at the end of 2014. The failure to adopt the directive was largely due to concerns about subsidiarity, with some member states maintaining that soil was not a matter to be negotiated at the European level. Others felt that the cost of the directive would be too high, and that the burden of implementation would be too heavy. However, the Seventh EU Environment Action Plan, which entered into force in 2014, recognises the severe challenge of soil degradation. It provides that by 2020 land in the EU should be managed sustainably, soil should be adequately protected, and the remediation of contaminated sites should be well underway. Furthermore it commits the EU and its member states to increasing efforts to reduce soil erosion, to increase soil organic matter and to remediate contaminated sites (EC, 2013). 8.4.4 | Eurasia Eurasian countries have well-developed environmental policies and regulations. However following the break-up of the Soviet Union, the system of environmental monitoring and conservation collapsed and has only recently been partially restored. Countries all across the region have maintained and even improved environmental and soil conservation legislation in recent years, but in most countries the mechanisms for quality control and environmental monitoring have been weakened. For example, only Belarus and Uzbekistan maintain their soil survey institutes, and even there soil monitoring has been discontinued. Ukraine, Russia and Kazakhstan are the countries with the largest under- or unused agricultural lands in the world. The World Bank (2011) states that these countries have the capacity to meet the growing global demand for food. In Russia in 2002 the area of abandoned land reached 70 million ha. Since then there has been a slow decrease in the area of unused land (Nefedova, 2013). However, it should be noted that most land abandonment occurred in badlands, wetlands, steep slopes and areas with an unfavourable climate, Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 232 232

275 while in areas with fertile soils the investment in land management increased. In countries such as Ukraine and Georgia, where land tenure legislation allows land ownership by non-residents, foreign capital is being invested in farmland. Non-transparent land grabs on a large scale are expected to increase, and might have far reaching consequences for the livelihoods of the rural population (Visser and Spoor, 2010). 8.4.5 | Latin America and the Caribbean (LAC) This region is one of the richest in the world in terms of natural resources. However, rapid exploitation and export of these resources (minerals, gas, forests, and pastures) is occurring with associated dramatic land use changes and widespread land degradation. Nonetheless, some countries in the region have developed and implemented good policies and approaches to mitigate land degradation. These policies, implemented at national and sub-national levels, are good practice examples that could be replicated in other countries in the region (UNEP, 2012). Uruguay provides a good example of soil and land conservation policies: here the soil conservation policy was designed by the Ministry of Livestock, Agriculture and Fisheries (MGAP) within a programme promoting agricultural intensification, with the objective of implementing a sustainable intensification model. Under this policy, crop producers must submit soil management plans and state the rotation sequence on each plot. They must stay within the maximum tolerable soil erosion amount based on local soil characteristics (Hill, Mondelli and Carrazzone, 2014). Another example is Cuba’s National Environmental Strategy of 2011/2015 which characterizes soil degradation as one of the fundamental environmental challenges in the country. The Cuban government has also implemented action plans to fight desertification and, since 2001, has undertaken programmes for soil conservation (CITMA, 2011). Brazil’s Forest Code was updated in 2012: it establishes general standards for protection of forests and other native resources, including soil and water resources. The Forest Code also integrates legal and economic incentives to promote sustainable production activities. However, closer analysis of the updated Forest Code suggests that it may in fact allow more deforestation than the previous version, in response to the demands of agricultural intensification (Soares-Filho et al. , 2014). 8.4.6 | The Near East and North Africa (NENA) This region is considered as the most water scarce and arid region in the world. Moreover, given the scarcity of land and water resources, this region is particularly vulnerable to the impacts of climate change, increasing drought, declining soil fertility and consequently declining agricultural production (Wingkvist and Drakenberg, 2010; Drine, 2011). There are government programs to improve land management in several countries, especially countries that are party to international agreements and are in receipt of donor support. Most actions promoting sustainable land management have been to combat desertification under the framework of the UNCCD (UNCCD, 2012). Despite significant improvements in the region in tackling the root cause of land degradation, there are still challenges in enforcing environmental regulations and implementing environmental conservation policies. The main implementation constraints are: the weakness of institutions at all levels; the difficulty of coordinating action across sectors, themes, donors and stakeholders; the lack of participation of the local communities; and tenure insecurity. MENARID (Integrated Natural Resources Management in the Middle East and North Africa) is a partnership working for improvement of the governance of natural resources, including water. MENARID supports restoration of natural resources. In particular, the programme aims to improve the livelihoods of target communities through the restoration of degraded natural resources, including land and soils. It offers a platform for coordination between stakeholders and information sharing in the countries (ICARDA, 2013). Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 233 233

276 The NENA region is endowed with oil and gas reserves. In areas of rapid urbanization and oil production, soil pollution and soil sealing are associated challenges. Parts of the region are extremely sensitive to political conflicts, and peace and post-conflict are the main focus. Land degradation issues become more pronounced, but inevitably they have to take second place to other concerns. 8.4.7 | North America In the United States, federal policies favour market-based instruments within an overall environmental governance framework, and these instruments have superseded traditional regulatory instruments. Land use is a priority issue on the political agenda, due to its contribution to GDP through forestry and agriculture. Governments diminish environmental impacts by paying land managers to implement sustainable land management practices and soil conservation. Taxes and incentives encourage land and farmland preservation programmes through payment for ecosystem services (UNEP, 2012). The United States Conservation Reserve Program (CRP) pays farmers to remove land from agricultural production in order to prevent soil erosion and improve ecosystem functions. This set-aside generates economic benefits of around US$1.3 billion per year (Hellerstein, 2010). However, high prices have made agriculture more profitable and the rates of payment from CRP have not risen so fast. The amount of land enrolled in the programme is therefore expected to decline (Wu and Weber, 2012). The Environmental Quality Incentives Program and the Observation Security Program of 2002 are other programmes that reward farmers for applying sustainable land management practices. It has been estimated that soil erosion could be reduced by 17 percent, saving around 36 million tonnes of soil annually. Valued at US$2 per tonne, the cost of conservation would thus be US$34 million annually, compared to the cost of restoring the soils, estimated at up to US$332 million (Hellerstein, 2010). In Canada land-use planning is a provincial responsibility and legislation differs widely among provinces. British Columbia has a long-standing Agricultural Land Reserve Program that prohibits development on approximately 4.7 million ha of agricultural land throughout the province. In the early 2000s Ontario created a Greenbelt that protects 0.7 million ha of agricultural and natural lands in the most populated region surrounding Toronto. Generally in Canada the implementation of Payment for Ecosystem Services needs still to be complemented with land use planning frameworks in order to become more effective at all levels of government (Calbick, Day and Gunton, 2003). 8.4.8 | Southwest Pacific The scale of land degradation across the countries of the Southwest Pacific has given rise to a range of significant policy responses all with a strong emphasis on participative engagement and local action. Perhaps most significant has been the rise of the Landcare Movement in Australia. It began with an unlikely alliance between traditional opponents (conservationists and farmers) and grew into a movement with thousands of groups in Australia and in other countries. The activities of Landcare Groups transformed many landscapes with large areas being revegetated and restored. Youl et al. (2006) provide a good outline of the history and factors that were important for success. They conclude that the strength of Australian Landcare is that community groups and networks, with government and corporate support, conceive their own visions and set goals for local and regional environmental action. Working from the ground up to achieve these goals creates freedom and flexibility, giving communities a great sense of purpose. The Secretariat of the Pacific Community (SPC) is a regional intergovernmental organisation whose membership includes both nations and territories in the Pacific Ocean and their metropolitan powers. The Land Resources Division assists the Pacific Community to improve food, nutritional and income security and sustainable management and development of land, agriculture and forestry resources. Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 234 234

277 In New Zealand, there are few regulatory instruments directly related to soil. Where they exist, they focus on soil conservation. However there is an increasing number of national policy instruments that legislate against the impacts of unwise soil use. The Resource Management Act is given effect at regional level and regulates activities not outcomes (through regional policy statements, plans and resource consents). These regulatory instruments typically focus on ensuring soil intactness. However, new initiatives are increasingly looking at the consenting of land use according to soil capability. New Zealand has also used non-regulatory approaches to achieve good soil management. These approaches include direct payments, support to the development of industry codes of practice, and certification schemes to ensure market access. 8.5 | Information systems, accounting and forecasting The distribution and characteristics of the soils in any district or nation are neither obvious nor easy to monitor. As a consequence, understanding whether a land use is well-matched to the qualities of the soil requires some form of diagnostic system to identify the most appropriate form of management and to monitor how the soil is functioning. Important components of the diagnostic system necessary for sustainable land use and management are: an understanding of spatial variations in soil function (e.g. maps and spatial information) an ability to detect and interpret soil change with time (e.g. via monitoring sites, long-term experiments, environmental proxies) a capacity to forecast the likely state of soils under specified systems of land management and climates (e.g. through the use of simulation models) an understanding of the edaphic requirements of plants Preparation of this book was severely constrained by the lack of relevant information. Soil map coverages are variable and, in some regions, out-of-date. The capacity to monitor and forecast soil change is also rudimentary. All nations require coordinated soil information systems that parallel those that exist in many countries for economic data, weather and water resources. Action on soil information systems is enshrined in the World Soil Charter’s guidelines for action for governments (Sections VIII and IX) and international organizations (Sections I and II). However, creating appropriate institutional systems for soil information gathering and dissemination is challenging for the following reasons: All levels of government need reliable information on soil resources but often no single level of government or department has responsibility for collecting this information on behalf of other public sector agencies. Public and private interests in soil are large and overlapping – mechanisms for co-investment by public and private agencies are therefore needed. Market failure in relation to the supply and demand of soil information is a significant and widespread problem. Simply stated, beneficiaries of soil information do not usually pay for its collection and this reduces the pool of investment for new survey, monitoring and experimental programmes. Partly as a result of the above, soil-information gathering activities in many countries are currently funded through short-term government programmes, private companies or individuals or are produced in response to specific regulatory requirements. This piecemeal approach does not result in the kind of enduring, accessible and broadly applicable information systems that are needed to meet the requirements of stakeholders. The following sections outline some specific requirements that policy makers have of soil information systems. Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 235 235

278 8.5.1 | Soil information for markets The various types of markets regulated by governments and other institutions need to be sufficiently informed to ensure economic efficiency and the desired allocation of resources. These markets include: traditional real-estate markets where information is needed on the capital value of soil resources (e.g. the nutrient status of a farm, presence of contaminants, and options for improved soil management) carbon trading schemes cap-and-trade systems for nutrient loading or other pollutants forecasting of within-season production of agricultural commodities insurance (e.g. crop insurance, disaster insurance, risk analysis of supply chains). Oversight and regulation of market activities is a central function of governments in most countries. A key responsibility for policy makers is to ensure the availability of reliable soil information. 8.5.2 | Environmental accounting A closely related area where policy makers are starting to need better information is environmental accounting. Globally, national accounts of economic activity are recorded and indicators such as gross domestic product (GDP) are widely used in government and policy to assess economic activity and progress. However, indicators such as GDP measure mainly market-based transactions and are not a good indicator of welfare; GDP ignores social costs, environmental impacts and income inequality (Costanza et al. , 2014). GDP also does not deduct the direct cost of the depletion of natural resources on national income nor does it take into account the impact that our resource extraction and use of nature has on the continued functioning of the Earth system for life support. In light of these limitations of the current national economic accounting system, the ecosystem services approach seeks to include nature in our accounting and acknowledge that it has value and its use is not simply free and limitless (Westman, 1977; Daily, 1997; Costanza et al. , 1997; M et al. , 2014). In this context, soils make an important contribution to the supply of A, 2005; Robinson ecosystem services (Daily et al. , 1997; Wall, 2004; Robinson, Lebron and Vereecken, 2009; Dominati, Patterson , 2013). and Mackay, 2010; Robinson et al. One proposal to address the deficiency of the current national accounts is to have a set of complementary accounts. Since the early 1990s, the international official statistics community has been developing such a set of accounts, named the System of Environmental Economic Accounting (SEEA). The over-arching objective of the SEEA approach is to develop an accounting structure that integrates environmental information with the standard national accounts and hence to mainstream environmental information in economic and development policy discussion. The SEEA accounts are presented in two volumes. First, the SEEA Central Framework (UN et al. , 2014) which was adopted as an international statistical standard in 2012, and second, SEEA Experimental Ecosystem et al. , 2014) which was endorsed in 2013. The SEEA Central Framework deals with individual Accounting (UN environmental assets (minerals, timber, fish, water, soil, etc.), the flows of mass and energy between the environment and the economy, and the space in which this occurs (Obst and Vardon, 2014). SEEA Experimental Ecosystem Accounting is focused on the function of ecosystems and the generation of ecosystem services which is dependent on ecosystem extent, condition and quality. Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 236 236

279 The SEEA Central Framework identifies seven individual components of the environment as environmental assets; mineral and energy resources, land, soil resources, timber resources, aquatic resources, other biological resources (excluding timber and aquatic resources, for example, livestock, orchards, wild plants for medicine, wild animals that are hunted), and water resources. SEEA Experimental Ecosystem Accounting uses the same definition of environmental assets but rather than considering individual components as assets, it seeks to consider the way in which these components function jointly as ecosystems. To apply this logic it defines spatial areas, such as different vegetation habitats (forests, wetlands, agricultural land etc.) as ecosystem accounting units. In this approach soil is considered a component within a broader ecosystem rather than being considered as a distinct ecosystem. Soils form an important part of the Central Framework, being recognized as an environmental asset in their own right. An important distinction is made between land and soil resources. Land is considered in terms of space and location often referred to as Ricardian land (Daly and Farley, 2011). Soil resources are the volume of biologically active topsoil, and its composition in the form of nutrients, soil water and organic matter. The accounts are structured to recognize, and distinguish between, the use of an asset (e.g. soil volume and area within the asset accounts); and the use of the soil resource or elements of the soil resource (e.g. carbon, nutrients and soil moisture in the physical flow accounts). Fundamental to the accounting process is the measurement of change for both the environmental and ecosystem accounts, which is underpinned by the availability of good quality data (Obst, Edens and Hein, 2013). The major aspects of soil of interest for the environmental accounts are: the volume of soil moved or extracted; the area of soil under different land uses; carbon, nutrient and moisture stocks; and changes in these three aspects. Hence the understanding and quantification of soil change is central to environmental accounting (Robinson, 2015).There is still no agreed set of soil indicators, although soil carbon content is widely seen as being perhaps the main indicator. There is still much work to do to synthesize soil quality work into the SEEA framework for the creation of useful, informative accounts, and to encourage countries to adopt this unified approach. 8.5.3 | Assessments of the soil resource It is essential to have some form of regular reporting on the rate and extent of soil change along with the likely consequences for society at local, national and global scales. Some countries now have various forms of audits and state-of-the-environment reports. However, most countries do not produce regular assessments showing where land management systems can operate sustainably within the constraints set by changing climate, weather and soils. These are necessary given the economic and environmental significance of soil resources. Regular reporting forces policy makers to impose an operational discipline on the management of soil information. Systems for collecting and analysing data can be progressively improved and a body of knowledge will be developed over several cycles of reporting. The assessments need to adopt a highly participative mode of engagement so that all stakeholders are represented and then empowered to make the necessary changes to land management. The World Soil Charter addresses this issue directly. It encourages governments to develop a national institutional framework for monitoring implementation of sustainable soil management and overall state of soil resources. International organizations are encouraged to facilitate the compilation and dissemination of authoritative reports on the state of the global soil resources and sustainable soil management protocols. This book is a sign that progress is being made in relation to regular assessment and reporting. Further Enhance progress will depend on successful implementation of Pillar Four of the Global Soil Partnership - – and of Pillar Five - the quantity and quality of soil data and information Harmonize methods, measurements and indicators for the sustainable management and protection of soil resources. Status of the World’s Soil Resources | Main Report Governance and policy responses to soil change 237 237

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284 9 | Regional Assessment of Soil Changes in Africa South of the Sahara Regional Coordinator : Victor Chude (ITPS/Nigeria) : Ayoade Ogunkunle (Nigeria) Regional Lead Author Contributing Authors : Victor Chude (ITPS/Nigeria), Isaurinda Dos Santos (ITPS/Cape Verde), Tekalign Mamo (ITPS/Ethiopia), Garry Paterson (South Africa), Ndaye Soumare (Senegal), Liesl Wiese (South Africa), and Martin Yemefack (ITPS/Cameroon). Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 242 242 in Africa South of the Sahara

285 9.1 | Introduction Land degradation in sub-Saharan Africa (SSA) is believed to be expanding at an alarming rate, accompanied by the lowest agriculture and livestock yields of any region in the world. While cereal production has increased marginally over the past two decades, more than 70 percent of this growth is due to area expansion rather than yield increases. The region also suffers from the world’s highest rate of deforestation, with some countries having lost more than 10 percent of their forest cover in the fiveyears up to 2009 (IFAD, 2009) and is most likely continuing at the same rate to this day. There is a growing and long-standing recognition among both policy-makers and soil specialists that soil degradation is one of the root causes of declining agricultural productivity in sub-Saharan Africa and that, unless the process of degradation is controlled, many parts of the continent will suffer increasingly from food insecurity (e.g. see Lal, 1990; UNEP, 1982). The consequences of allowing the productivity of Africa’s soil resources to continue on its present downward spiral will be severe, not only for the economies of individual countries, but for the welfare of the millions of rural households across the continent who are dependent on agriculture (FAO, 1999). Soil degradation is the decline in soil quality caused its improper use by humans, usually for agricultural, pastoral, industrial or urban purposes. Soil degradation may be exacerbated by climate change and encompasses physical, chemical and biological deterioration. Examples of soil degradation cited by Charman and Murphy (2005) are: loss of organic matter; decline in soil fertility; decline in structural condition; topsoil loss and erosion; adverse changes in salinity, acidity or alkalinity; and the effects of toxic chemicals, pollutants and excessive flooding. There is no consensus on the exact extent and severity of land degradation or its impacts in SSA as a whole (Reich et al. , 2001; GEF, 2006). Lack of information and knowledge is considered to be one of the major obstacles for reducing land degradation, improving agricultural productivity, and facilitating the adoption of , 2011). The recent publication sustainable land management (SLM) among smallholder farmers (Liniger et al. of the first Soil Atlas of Africa has provided a first comprehensive overview of the soil resources of Africa ( Jones , 2013). et al. Four continental-scale studies have assessed the extent of soil degradation in Africa. A literature review by Dregne (1990) of 33 countries found compelling evidence of serious land degradation in sub-regions of 13 countries: Algeria, Ethiopia, Ghana, Kenya, Lesotho, Mali, Morocco, Nigeria, Swaziland, Tanzania, Tunisia, Uganda, and Zimbabwe. In another literature review, focused on drylands only, Dregne and Chou (1992) estimated that 73 percent of drylands were degraded and 51 percent severely degraded. They concluded that 18 percent of irrigated lands, 61 percent of rainfed lands, and 74 percent of rangelands located in SSA drylands are degraded. The Global Assessment of Soil Degradation (GLASOD) expert survey found that 65 percent of soils on agricultural lands in Africa had become degraded since the middle of the twentieth century, as had 31 percent of permanent pastures, and 19 percent of woodlands and forests (Oldeman, Hakkeling and Sombroek, 1991). Serious degradation affected 19 percent of agricultural land. A high proportion (72 percent) of degraded land was in drylands. The most widespread cause of degradation was water erosion, followed by wind erosion, chemical degradation (three-quarters from nutrient loss, the rest from salinization), and physical degradation. In terms of causes of degradation, overgrazing was responsible for half of all degradation, followed by agricultural activities, deforestation, and overexploitation. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 243 243 in Africa South of the Sahara

286 The Land Degradation Assessment in Drylands project (LADA) started in 2006 with the general purpose of creating the basis for informed policy advice on land degradation at global, national and local levels. This goal is being reached through the assessment of land degradation at different spatial and temporal scales in six countries and through the creation of a baseline at global level for future monitoring (FAO, 2010). Two of the six countries involved (Senegal and South Africa) are within SSA and national results are reported at the end of this chapter. Lal (1995) calculated continent-wide soil erosion rates from water using data from the mid to late 1980s, and then used these rates to compute cumulative soil erosion for 1970-90. The highest erosion rates occurred in the Maghreb region of Northwest Africa, the East African highlands, eastern Madagascar, and parts of Southern Africa. Excluding the 42.5 percent of arid lands and deserts with no measurable water erosion, Lal found that the land area affected by erosion fell into the following six classes of erosion hazard: none, 8 percent; slight, 49 percent; low, 17 percent; moderate, 7 percent; high, 13 percent; and severe, 6 percent. Soils host the majority of the world’s biodiversity and healthy soils are essential to securing food and fibre production. Soils assure an adequate and clean water supply over the long term, as well as providing cultural functions. Ecosystem services provided by soils are integral to the carbon and water cycles. Major increases in agricultural production have been associated with different kinds of soil degradation, especially since the agricultural growth came in part from extensive clearing of new agricultural lands. Yet, even with this expansion, arable land per capita in Africa declined from just under 0.5 ha in 1950 to just under 0.3 ha in 1990 (FAO, 1993). During this time period, yield increases on land already in production thus contributed far more to the total production. For example, more than 90 percent of the growth in developing country cereal production between 1961 and 1990 came from yield growth (World Bank, 1992). Agricultural expansion and yield growth at such a scale is inevitably associated with some degradation of soil resources. However, the type and extent of degradation vary in the different ecological/farming systems (IFPRI, 1999). 9.2 | Stratification of the Region The region is diverse in terms of relief, climate, lithology, soils and agricultural systems. A combination of some et al. , 2002; Global of these have been used to stratify the region into agro-ecological zones (AEZs) (Fischer HarvestChoice, 2010). Table 9.1 shows the AEZs into which the region has been grouped and some of their characteristics, while Figure 9.1 shows the distribution of the AEZs in the region. 9.2.1 | Arid zone The arid zone occupies 36 percent of the land area of SSA, most of which is in West and East Africa. Rainfall is low and extremely variable in this zone. The annual rainfall of less than 500 mm, combined with high temperatures and consequent high rates of evapotranspiration, make this zone capable of sustaining plant life for less than 90 plant growth days (or length of growing season). Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 244 244 in Africa South of the Sahara

287 Figure 9.1 Agro-ecological zones in Africa South of the Sahara. Source: Otte and Chilonda, 2002. Area (percent) Rainfall Area Zone Definition range Southern East Central West of zone (mm) Africa Africa Africa Africa (percent) Arid <90 pgda 36 20 52 1 0–500 54 90–180 500– Semi-arid 18 34 18 7 20 1000 pgd 180–270 1000– Sub-humid 29 38 16 22 16 1500 pgd Humid 2 7 19 1500+ 10 59 >270 pgd Highlandsb 0 n.a.c <20°C 1 4 12 5 100 100 100 100 100 Total Total area 7.3 3.2 5.8 5.3 2 6 ) km (10 Table 9.1 Characteristics and distribution of agro-ecological zones in Africa a b c : n.a. = not available. Source: ILCA, 1987, after pgd = plant growth days; Areas with mean daily temperature during the growing period less than 20°C; Jahnke, 1982. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 245 245 in Africa South of the Sahara

288 The arid zone is mostly associated with sandy soils (Arenosols, Psamments) which are weakly differentiated and are often of aeolian origin. Water and air move freely through these soils, which are low in all nutrients. The accompanying vegetation consists of short annual grasses, legumes, scattered shrubs and trees. Mobile herds of sheep, goats, cattle and camels browse the herbage and shrubs, while farmers use most of the trees and shrubs for fuel. The low rainfall and its erratic distribution make cropping uncertain in most years. Owing to this unreliability, arable farming is mostly restricted to opportunistic cultivation of short-season millets, except in topographically favourable sites such as oases or irrigated areas. Opportunities for livestock development are limited but existing techniques could be improved upon, if not to increase productivity, then at least to sustain it. 9.2.2 | Semi-arid zone The semi-arid zone receives 500 to 1000 mm of rainfall annually which can be capable of sustaining 90 to 180 plant growing days. This zone occupies 18 percent of the land area of SSA. Semi-arid lands are found in all regions of SSA except central Africa. The low rainfall and the long dry season make the semi-arid zone a relatively healthy environment for humans and livestock. Arenosols (Psamments) and Cambisols (Inceptisols) are widespread and include coarse sandy soils, fine sands, and loamy sandy soils. Water retention is poor and nutrient contents, including N, P and S levels, are generally low. The permeability of the undisturbed soil is good, but algal skins contribute to the formation of surface crusts. The natural vegetation is an open low-tree grassland but this has been severely modified in many regions. The lower rainfall areas of this zone are used for grazing. Cropping and crop–livestock systems dominate the areas with higher rainfall where farmers commonly grow millet, sorghum, groundnut, maize and cowpeas. 9.2.3 | Sub-humid zone The sub-humid zone occupies 22 percent of SSA, mainly in southern and central Africa. The zone receives 1 000 to 1 500 mm of rain annually which can sustain plants for 180 to 270 plant growing days. Within the climatic definition, this is a very varied zone in terms of climate, soils and land use. Luvisols (Alfisols) and Cambisols (Inceptisols) occur widely, parent material is often strongly weathered, and the levels of mineral nutrients as well as the clay fraction are low. Cambisols (Inceptisols) have fewer constraints to plant production than the older, more weathered soils, since their high base status provides adequate Ca and eliminates constraints related to low pH levels. The fertility of many soils in this zone is low, especially due to leaching of –, accompanied by the loss of cations and P adsorbtion. In addition, structural stability in these soils can NO 3 be poor, with crusting and hardening occurring when soils are dry. The natural vegetation is typically medium height or low woodland with understory shrubs and a ground cover of medium to tall, mainly perennial, grasses; Hyparrhenia spp. are common. Food and cash crops are grown, including cassava, yams, maize, fruits, vegetables, rice, millet, groundnut, cowpeas and cotton. From these crops, products such as cottonseed cakes and the residues of the crops are available as feed for livestock. In some areas of this zone farmers grow soybean and leguminous forage crops. The humid zone occupies 19 percent of SSA mostly in central and west Africa. The zone receives more than 1 500 mm of rainfall annually which can sustain plants for 270 to 365 plant growing days. The zone is found at low latitudes north and south of the equator. Soils in this zone include Ferralsols (Oxisols), Acrisols (Ultisols) and Luvisols (Alfisols), the last of which are commonly encountered at the forest-savannah boundary. Vegetation consists of rain forest and derived savannahs with natural vegetation dominated by tall, closed forest which may be evergreen or semi-deciduous and which is often floristically rich. The herbaceous vegetation often contains large amounts of the major nutrients. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 246 246 in Africa South of the Sahara

289 The soils are strongly weathered and hence have high levels of iron and aluminium oxides and low levels of phosphorous. The organic matter content is therefore generally low and the soils are fragile and easily degraded when the vegetative cover is lost. This zone has limited potential for livestock development, particularly because of the threat of the trypanosomiasis-transmitting tsetse fly. 9.2.5 | Highlands zone The highland zone represents 5 percent of the land area of SSA, most of which is in eastern Africa, and half in Ethiopia. This zone occupies areas above 1 500 m altitude that have a mean daily temperature of less than 20 ºC. The main highland areas in sub-Saharan Africa (SSA) are in Ethiopia, Kenya, Uganda, Rwanda, Burundi, western Zaire, Tanzania, Angola and Lesotho. There are also many other areas above the 1500 m contour and some of these afford tsetse-free grazing (e.g. Fouta Djallon and Bamenda). The highland areas vary in climate, topography, soils and land use. Topography varies from gently rolling hills to deeply incised valleys and steep slopes. Soils are sometimes deep and fertile Vertisols and Nitosols, but shallow soils of inherently low fertility are widespread. In many mountain grassland areas, soils only have a very shallow surface horizon that is fertile. Undisturbed upland areas are normally stable, although some soils exhibit ‘slumping’ even where undisturbed. Cultivating the so- and soils that form a surface crust on slopes results in high run-off. Unless soil conservation called ‘duplex’ soils 5 measures are taken and soils are sufficiently covered with vegetation, overland flow removes large amounts of soil. The zone receives bimodal rainfall (>1000 mm annually) and there are two growing seasons. Livestock rearing is widespread: farmers grow fodder, and animal traction is of increasing importance. Population pressure is encouraging crop–livestock integration, for which the cool highlands have high potential 9.3 | General soil threats in the region The various threats to soil health and ecosystem services in SSA include: (1) erosion by water or wind; (2) loss of soil organic matter; (3) soil nutrient depletion; (4) loss of soil biodiversity; (5) soil contamination; (6) soil acidification; (7) salinization and sodification; (8) waterlogging; and (9) compaction, crusting and sealing/ capping (Mabogunje, 1995; Oldeman, 1991; Meadows and Hoffman, 2002; World Bank, 1997; IFPRI, 1999). | Erosion by water and wind 9.3.1 About 77 percent of SSA is affected by erosion, with the most serious erosion areas in the Republic of South Africa, Sierra Leone, Guinea, Ghana, Liberia, Kenya, Zaire, Central African Republic, Ethiopia, Senegal, Mauritania, Nigeria, Niger, Sudan and Somalia. According to the GLASOD results (ISRIC/UNEP, 1990), about 494 million ha of the land in SSA is affected by one form of degradation or another. Of this, 227 million ha (46 percent) is by water erosion, 187 million ha (38 percent) by wind erosion, 62 million ha (12 percent) by chemical degradation and 18 million ha (4 percent) by physical degradation. The intensity of water erosion has been described as very high to extreme on about 102 million ha (45 percent of the total SSA area affected), moderate on about 67 million ha (30 percent) and slight on about 58 million ha (25 percent) (Oldeman, 1991). Water erosion : This is the most widespread soil degradation type in SSA. Water erosion increases on slopes where vegetation cover is reduced due to deforestation, overgrazing or cultivation that leaves the soil surface bare. It is further aggravated where there has been a loss of soil structure or infiltration rates have been reduced. The areas particularly affected are humid and sub-humid zones. Almost 70 percent of Uganda was degraded by soil erosion and soil nutrient depletion between 1945 and 1990. More than 20 percent of agricultural land and pastures in the country have been irreversibly degraded. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 247 247 in Africa South of the Sahara

290 Water erosion poses the greatest threat to soils in , where it affects over 80 percent of the land Nigeria (NEST, 1991). Wind, sheet, gully and beach erosion affect different parts of the country at varying intensities, but attention will focus here on the impact of erosion on agricultural land. While wind erosion is confined to the arid north, sheet erosion by water is ubiquitous throughout the country. Areas most prone to sheet erosion are where farming has cleared the original vegetation, and the soils became impoverished scrubland. Gully erosion is by far the most alarming type of erosion, particularly in the Eastern region, because it often threatens settlements and roads. Although it affects a small fraction (less than 0.1 percent) of Nigeria’s 2 of landmass, gully erosion claims large amounts of public funds annually for remedial action. 924 000 km Wind erosion: Wind erosion occurs most frequently in the arid and semi-arid parts of SSA, especially in areas with sandy or loamy soils. Wind erosion leads to loss of topsoil over extended areas causing soil fertility decline. Bielders, Michels and Rajot (1985) stated that wind erosion can remove up to 80 tonnes of soil from 1 ha in a givenyear. In SSA wind erosion is second in importance to water erosion, constituting 38 percent of the total erosion in the region (ISRIC/UNEP, 1990) and affecting about 186 million ha of land in the region. The intensity of wind erosion is strong on about 9 million ha (5 percent), moderate on 89 million ha (48 percent) and light on 89 million ha (48 percent) (Oldeman, 1991). Over 99 percent of wind erosion in Africa occurs in the dry land zone, with less than 1 percent affecting the humid zone. Wind erosion is a natural process that commonly occurs in deserts and on coastal sand dunes and beaches. During drought, it can also occur in agricultural regions where vegetation cover is reduced. If the climate becomes drier or windier, wind erosion is likely to increase. Climate change forecasts suggest that wind erosion will increase over the next 30 years due to more droughts and more variable climate. The combination of a changing climate and consequent increase in wind erosion will cause a series of changes affecting soils: less rain, which will support less vegetation • lower soil moisture, which will decrease the ability of soil particles to bind together into larger, heavier • aggregates increased wind speeds, which will result in more force exerted on the ground surface and more wind • erosion (if wind speed doubles, the erosion rate increases eight times) • large losses of soil and nutrients • more large dust storms, which will impact soils and the community • poorer air quality, increased respiratory health risks, and temperature and rainfall changes due to atmospheric pollution (all off-site effects). 9.3.2 | Loss of soil organic matter Land degradation leads to a release of carbon to the atmosphere through oxidation of soil organic matter (Oldeman, Hakkeling and Sombroek, 1991). Africa’s current major negative role in the global carbon cycle can be attributed to the substantial releases of carbon associated with land use conversion from forest or woodlands to agriculture (Smith, 2008). In the 1990s, these releases accounted for approximately 15 percent of the global net flux of carbon from land use changes (Hooper et al. , 2006). Land management following conversion also impacts carbon status, soil fertility, and agricultural sustainability – a point underlined by many including Lal (2006), Ringius (2002), Zivin and Lipper (2008) and Tieszen, Tappan and Toure (2004). Soils often continue to lose carbon over time following land conversion (Woomer, Toure and Sall, 2004; Tschakert, , 2014), resulting in further reductions in crop yields and impoverishment et al. Khouma and Sene, 2004; Liu of the farming population. However, these carbon stocks can be replenished with combinations of residue retention, manuring, nitrogen (N) fertilization, agroforestry, and conservation practices (Lal, 2006). In most sub-humid and semi-arid areas, much of the grazing land is burned annually during the dry season to remove the old and coarse vegetation and to encourage the growth of young and more nutritious grasses. ) and thus impairs agricultural productivity. Burning causes the loss of soil organic matter (released as CO 2 Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 248 248 in Africa South of the Sahara

291 It exposes the soil to the erosive forces of the wind during the dry season and of the rain during the rainy season. Furthermore, the annual burn of the vegetation severely reduces the return of organic matter to the soil. This results in loss of the benefits of soil organic matter, including fertility, structure, water retention and biodiversity. The soil becomes biologically, chemically and physically poorer (FAO, 2001). Land degradation further leads to a release of carbon to the atmosphere through the oxidation of soil organic matter which results from soil disturbance and from the consequent exposure of new soil surfaces to the weather. In agricultural land, the challenge has been to produce increasing quantities of food in an economic and institutional context where the means to improve productivity in a sustainable fashion are generally not available (e.g. lack of sustainable technological packages, absence of extension, training or affordable inputs etc.). Pressures to increase output in the absence of these supporting factors has led to: (i) the rapid expansion of agricultural land (over 65 percent in the last three decades); and (ii) the shortening of the fallow periods in traditional, extensive land use systems, which reduced the rehabilitation of soil fertility through natural processes. The increased use of fire as a clearing tool has led to the further loss of nutrients in many systems. Fertilizer consumption has not increased to compensate for the loss of soil nutrients resulting from the intensification of land use. Hence, there has been widespread mining of soil organic matter and nutrients. As a consequence of this poor land management combined with the vulnerable nature of many soils, much of SSA’s cropland is now characterized by low organic matter content, often in combination with a low pH and with aluminium toxicity. On degraded soils with low organic matter, inorganic fertilizers are also easily leached, which is likely to have negative long-term effects on agricultural productivity and on the quality of downstream water resources. 9.3.3 | Soil nutrient depletion Soils in a large part of SSA are strongly weathered and inherently low in organic matter. Because of the increasing pressure on land, natural replenishment of nutrients during fallow periods is now insufficient to maintain soil productivity over the long-term. Insufficient nutrient replacement in agricultural systems on land with poor to moderate potential results in soil degradation. Already soil moisture stress inherently constrains land productivity on 85 percent of soils in Africa (Eswaran, Reich and Beinroth, 1997). Now soil fertility degradation places an additional serious human-induced limitation on productivity. The low nutrient status of most soils in SSA is further exacerbated by insufficient use of fertilizers and -1 , the manure and by the practice of mono-cropping. Overall use of inorganic fertilizers in SSA is just 12 kg ha lowest in the World, and soil nutrient depletion is widespread in croplands. Approximately 25 percent of soils in Africa are acidic, and therefore deficient in phosphorus (P), calcium and magnesium with often toxic levels of aluminium (McCann, 2005). Use of fertilizer in the region involves average applications of less than 9 kg of nitrogen and 6 kg of phosphorus per ha, compared with typical crop requirements of 60 kg of nitrogen and 30 kg of phosphorus per ha. Recent research estimates that on average every country in SSA has a negative soil nutrient balance; in all countries studied, the amount of nitrogen, phosphorus and potassium (K) added as inputs was significantly less than the amount removed as harvest or lost by erosion and leaching (Swift and Shepherd, 2007). Although many farmers have developed soil management strategies to cope with the poor quality of their soil, low inputs of nutrients, including of organic matter, contribute to poor crop growth and to the depletion of soil nutrients. Stoorvogel, Smaling and Janssen (1993) calculated nutrient balances for arable soils in 38 sub-Saharan -1 983 and made forecasts for 2000. Subtracting values of the output (made countries and for 35 crops for 1982 up of harvest, removal of residues, leaching, denitrification and erosion) from the values of the input (made up of fertilizers, manures, rain, dust, biological N-fixation and sedimentation), the study reported alarming -1 983: 22 kg N, 2.5 kg P and 15 kg K; 2000: 26 kg N, 3 kg P and 19 average nutrient losses for SSA as follows: 1982 kg K. This indicated persistent nutrient mining over time (Bationo , 2012). Other estimations claim that et al. each year 4 million tonnes of nutrients are harvested annually in SSA against <0.25 million tonnes returned to the soils in the form of fertilizers. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 249 249 in Africa South of the Sahara

292 Sub-national studies of nutrient depletion found annual losses of 112 kg per ha of N, 2.5 kg of P, and 70 kg of K in the western Kisii highlands of Kenya. Significantly lower losses were, however, recorded in southern Mali (Smaling, 1993; Smaling, Nandwa and Janssen, 1997). Farm monitoring and modelling of nutrient cycles for the western highlands of Kenya found that more nitrogen (63 kg per ha) was being lost through leaching, nitrification, and volatilization than through removal of crop harvests (43 kg per ha). Depending on the type of farm management practice, net nitrogen balances on cropped land varied between -39 and 110 kg per ha peryear, and net phosphorus balances between -7 and 31 kg per ha per year (Shepherd and Soule, 1998). 9.3.4 | Loss of soil biodiversity Loss of soil biodiversity is considered the fourth major threat in SSA. Biodiversity loss occurs in a number of ways including destruction of habitat, land use change, introduction of new species, and harvesting and -1 980s in Sub-Saharan Africa (SSA), 65 hunting of individual wild species. It has been estimated that in the mid percent of the ‘original’ ecosystems had been converted (Perrings and Lovett, 1999). The most important factors affecting soil biodiversity are: (i) habitat fragmentation; (ii) resource availability – the amount and quality of nutrients and energy sources; (iii) temporal heterogeneity e.g. seasonal effects; (iv) spatial heterogeneity - spatial differences in the soil; (v) climate variability; and (vi) interactions within the biotic community. Habitat destruction and/or fragmentation remains the primary threat to soil biodiversity in SSA. For instance, the once great equatorial forest that stretched from western Africa into eastern Africa is now fragmented into pockets represented by Lamto forest in Ivory Coast, Mbalmayo forest in Cameroun, Congo forest in Democratic Republic Congo, Kabale, Budongo and Mabira forests in Uganda and Kakamega forest in Kenya. The surrounding communities still rely heavily on these forests for basic needs such as fuelwood, charcoal, timber, poles, and other building materials. Due to human encroachments, the forests are subject to a mosaic of different land uses. There are patches of secondary forest, fallow and arable fields amidst significant remnants of primary vegetation. In the process of conversion and change in land use, soil biota (2011) have shown that up to 50 percent of have not been spared. Studies by Okwakol (2000) and Ayuke et al. soil macrofauna species within the forest area have been lost due to habitat destruction or fragmentation. Other threats to soil biodiversity in SSA include land use and land cover change, mainly through conversion of natural ecosystems, particularly forests and grasslands, to agricultural land and urban areas. In a study conducted across different ecosystems of Eastern (Kenya), Western (Nigeria, Burkina Faso, Ghana, Niger) and Southern Africa (Malawi), Ayuke et al. (2011) demonstrated a substantial reduction in the number of species and abundance of soil macrofauna groups such as earthworms and termites because of conversion of native or undisturbed ecosystems into arable systems. Continuous cultivation also exacerbates soil biodiversity loss , 2011). It is because of loss of soil organic matter and hence of food resources for the soil organisms (Ayuke et al. likely that land clearing and deforestation will continue, further threatening genetic diversity as more species are lost (IAASTD, 2009). Sub-Saharan Africa suffers the world’s highest annual deforestation rate because of overexploitation of forest resources and conversion of forested land to agriculture. Although deforestation occurs throughout the continent, particularly affected areas are the moist forests of Western Africa and the , 2013). et al. highland forests of the Horn of Africa (FAO, 2007; Hansen Mulugeta (2004) reported that in Ethiopia deforestation and subsequent cultivation of the tropical dry Afromontane forest soils endangered the native forest biodiversity not only through the outright loss of habitat but also by impairing the soil seed banks. The results showed that the contribution of woody species to the soil seed bank declined from 5.7 percent after sevenyears to nil after 53 years of continuous cultivation. However, soil quality and native flora degradation are reversible through reforestation. In fact, reforestation of abandoned farm fields with fast-growing tree species was shown to restore soil quality. Tree plantations established on degraded sites also fostered the recolonization of diverse native forest flora under their canopies. An important result from studying the effects of reforestation is that good silviculture, particularly selection of appropriate tree species, can significantly affect the rate and magnitude of restoration processes for both soil quality and biodiversity. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 250 250 in Africa South of the Sahara

293 In many African cultures, harvesting of soil fauna groups such as the termite alates and queens, chafer grubs for food, and the use of earthworms as bait by fishermen can also be a threat to soil biodiversity, and may in the long run contribute to substantial loss of many species of soil fauna. Harsh climatic conditions and/or climate change may also contribute to changes in soil biodiversity in SSA. For example, a more than average numbers of earthworm and termite taxa are found under relatively warmer, drier conditions (Ayuke et al. , 2011). This is contrary to the observation that earthworm and termite diversity increases with increases in rainfall or soil moisture, as generally found in temperate climates (Bohlen et al. , 1995; Curry, 2004). However, seasonality of rainfall in the tropical regions means rainfall amounts per season may be more important than the annual total. Lower taxonomic richness among sites in Eastern Africa may be attributable to less favourable conditions arising from high rainfall and low temperatures at higher altitudes (Ayuke et al. , 2011). Intense management practices that include application of pesticides and frequent cultivation affect soil organisms, often altering community composition of soil fauna. Soil biological and physical properties (e.g., temperature, pH, and water-holding characteristics) and microhabitat are altered when natural habitat is converted for agricultural production (Crossley, Mueller and Perdue, 1992). Changes in these soil properties may be reflected in the distribution and diversity of soil meso fauna. Organisms adapted to high levels of physical disturbance become dominant within agricultural communities, thereby reducing the richness and diversity of soil fauna (Paoletti, Foissner and Coleman, 1993). The extent of soil sterilization and loss of soil biodiversity in SSA has yet to be quantified on a large-scale across the region. However, it is clear that unsustainable soil management practices have depleted soil organic matter, promoted soil degradation and may have caused soil fauna and flora imbalances. This land degradation will continue unless land users in SSA adopt an agro-biological approach to managing their soils (Van der Merwe et al. , 2002). 9.3.5 | Soil contamination and pollution Chemical fertilizers and pesticides have had negative effects on the environment in most SSA countries. However, soil pollution through agrochemical use in SSA has been of less concern compared to other regions of the world, mainly because of the low levels of application. However, with the increasing push towards higher use of fertilizer, pesticide and herbicide to boost productivity, efforts will be needed to reduce the associated negative impacts on soil quality (IAASTD, 2009). Chemical pollution has emerged as a threat to soil quality. According to a United Nations Environment Programme (UNEP, 2007) environmental assessment in ten communities in Ogoni land in southeastern Nigeria which had been affected by crude oil spills, drinking water, the air and agricultural soils contained over 900 times the permissible levels of hydrocarbon and heavy metals. The report acknowledged that, even if all its recommendations were implemented, recovery might take 30 years. Other published research work suggests that heavy metal pollution is occurring across SSA. Heavy metal (Pb, Cd, Hg, Cu, Co, Zn, Cr, Ni, As) pollution of soils has been reported in Nigeria, Kenya, Ghana and Angola (Fakayode and Onianwa, 2002; UNEP, 2007; Odai et al, 2008). Change of land use, particularly urbanization, is another factor in soil contamination. National data from South Africa indicate that areas under urban, forestry and mining land uses have all increased over the last decade, whereas the cultivated area has decreased. The urban area has increased from 0.8 percent of total area to 2 percent, forestry from 1.2 percent to 1.6 percent, and mining from 0.1 percent to 0.2 percent, while the cultivated area has decreased from 12.4 percent to 11.9 percent. The increase in the urban and mining areas is a major concern in terms of soil conservation and future use. Urban development involves soil sealing which irreversibly removes soils from other land uses. Mining results in serious chemical and physical soil degradation which subsequently can only be partially restored. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 251 251 in Africa South of the Sahara

294 | Soil acidification 9.3.6 In SSA, extremely acid soils, mainly potential or actual acid sulphate soils, occur only in a small area around the Niger delta and sporadically along the coastal plains of West Africa. Other acid soils occupy about 15 percent of the continent and are mainly found in the moist parts of the semi-arid zones and in sub-humid areas. Many of the Acrisols (Ultisols) and some Lixisols (Alfisols) have acid surface and subsurface horizons which, coupled with the moisture stress conditions, makes these soils extremely difficult to manage under low-input conditions. In West Africa, the annual additions of dust from the Sahara brought by the Harmattan winds raise the pH of the surface horizons. The problem is therefore less acute there, although subsoil acidity remains (Eswaran et al. , 1996). Another region of acid soils occurs south of the tropic of Capricorn and includes parts of South Africa (Beukes, Stronkhorst and Jezile, 2008a,b) where it poses a serious soil chemical problem and is in fact one of the greatest production-limiting factors. 9.3.7 | Salinization and sodification Salinization is defined as a change in the salinity status of the soil. This can be caused by improper management of irrigation schemes, particularly in the arid and semi-arid regions. Irrigation-induced soil acidity is aggravated when irrigation is practiced on soils unsuitable for irrigation (Barnard et al. , 2002). Salinization can also be caused if sea water intrudes into coastal regions either on the surface or into groundwater. It may also arise in closed basins when there is excessive abstraction of groundwater from aquifers of different salt content. Salinization also takes place where human activities lead to increased evapotranspiration from soils on salt-containing parent material or where saline ground water is being pumped out (Oldeman, 2002). In the arid and semi-arid parts of Africa, soil salinity and alkalinity are major problems affecting about 24 percent of the continent. Soils with pH>8.5 are designated as alkaline (Eswaran et al. , 1996). Soil salinity and sodicity problems are common in arid and semi-arid regions where rainfall is insufficient to leach salts and excess sodium ions out of the rhizosphere. More than 80 million ha of such soils are found in Africa. Increasing temperatures may result in high evaporative demands that may activate the capillary rise of salts, leading to soil salinization. The results of a study in Sudan showed a significant increase in salinity in the Dongla area in the north, where the annual rainfall is the lowest in the country. This increase is associated et al. , 2011). with fluctuation and erratic distribution of rainfall, as well as with a rise in temperature (Abdalla 9.3.8 | Waterlogging Human intervention in natural drainage systems may lead to waterlogging or flooding by river water. Most waterlogging threats are due to effects of human-induced hydromorphy. Causes include a rising water table (for example, due to construction of reservoirs or irrigation) or increased flooding caused by higher peak flows of rivers. The technology of flooding in paddy fields to provide a proper environment for paddy rice is generally not considered a threat to ecosystem services, although it may increase the emissions of GHG. It is estimated (Oldeman, Hakkeling and Sombroek, 1991) that waterlogging constitutes 1.5 percent of the non-erosion soil degradation threats in Africa. 9.3.9 | Compaction, crusting and sealing The population of the Sub-Saharan Africa (830 millions) is approximately 12 percent of the world population. SSA population has been growing at a rate of 2.6 percent year during the last decade, although the rate is now declining. The tendency in the region is towards the concentration of growing populations in moderately large cities (rather than mega-cities). Since the early 1970s, several SSA countries have experienced accelerated urban expansion, recording some of the highest urban growth rates in the world of up to 5 percent per year (Todaro, 2000). There are numerous examples of single-city dominance in the region. For instance, in Mozambique, Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 252 252 in Africa South of the Sahara

295 Maputo accounts for 83 percent of the country’s urban population, while the figures for Dakar, Lome, Kampala and Harare are 65, 60, 52 and 50 percent respectively (World Bank, 2002). Nigeria and South Africa represent exceptions to this single-city dominance, as they have several large and well distributed urban centres. South Africa and Nigeria are also the countries recording the highest amount of impervious surface area (ISA) in the region, and they have high Urbanization Indexes (the ratio between the total area of the country and the urbanized area) (Figure 9.2). 9.4 | The most important soil threats in Sub-Saharan Africa Of the threats to soils and related ecosystem functions in SSA listed in Section 9.3, the most critical are soil erosion, loss of soil organic matter and soil nutrient depletion (UNEP, 2013). Loss of soil biodiversity is also a significant threat in SSA. These four threats are interrelated. More is known about the first three and these are discussed in greater detail in this section. 1,2 10 Urban Area (SQKM) Urbanization index (%) 1 8 0,8 6 0,6 Urbanization index (%) 4 Urban Area (thousands SQKM) 0,4 2 0,2 0 0 Mali Togo Chad Niger Benin Kenya Sudan Eritrea Ghana Gabon Liberia Malawi Angola Nigeria Zambia Uganda Somalia Burundi Senegal Lesotho Rwanda Djibouti Ethiopia Reunion Namibia Morocco Mauritius Botswana Swaziland Cameroon Zimbabwe Mauritania The Gambia Madagascar South Africa Sierra Leone Cote d'Ivoire Burkina Faso Mozambique Guinea-Bissau Equatorial Guinea Republic of the Congo Central African Republic United Republic of Tanzania Democratic Republic of the Congo , Figure 9.2 Extent of urban areas and Urbanization Indexes for the Sub-Saharan African countries. Source: Schneider Friedl and Potere, 2010. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 253 253 in Africa South of the Sahara

296 9. 4.1 | Erosion by water and wind Direct causes of soil erosion Expansion of land for agriculture: Soil erosion can be a natural process but it is also often caused or accelerated by human activities that involve inappropriate land use. As discussed above (Section 9.3), much of the change in land use practices in SSA has been driven by the need to increase production and incomes in an economic and institutional context where the means to improve productivity in a sustainable fashion are generally not available. The processes involved - rapid expansion of agricultural land, shortening of fallow periods, increased use of fire – are discussed in full in Section 9.3.2 above. As fertilizer consumption did not increase to compensate for the loss of soil nutrients resulting from the intensification of land use, there has been widespread mining of soil nutrients and soil organic matter. As a consequence of the type of soils that occur in the region and because of generally poor land management, many SSA croplands now have low soil organic matter contents and soils that have a low pH and suffer from aluminium toxicity. On degraded soils with low organic matter, inorganic fertilizers are also easily leached, and this process has devastating long-term effects for agricultural productivity. Alternative means of maintaining soil fertility, such as crop rotation with biological nitrogen fixing (BNF) species, application of green manure, agroforestry, composting, rock phosphates, etc., have proved to be highly effective at the local scale. However, these technologies have not been applied widely enough to have an impact at a national let alone continental scale. Overgrazing: There has been much debate on the impacts in SSA of high grazing pressures on vegetation composition in rangelands. The current understanding is that continued high grazing pressure may affect rangeland productivity, particularly in the long term. Vegetation studies also show that high grazing pressures lead to changes in species composition, which may reduce the resilience of rangelands to drought (Hein and De Ridder, 2006). During a drought, degraded rangelands show a much stronger decline in productivity than non-degraded rangelands. Recentyears have seen droughts with severe impacts on livestock and local livelihoods in parts of Niger and in the East African drylands (Uganda and Kenya). Deforestation: Most forests and woodlands in SSA are experiencing rapid rates of deforestation. Deforestation is driven by a number of processes, in particular: (i) the continued demand for agricultural land; (ii) local use of wood for fuel, charcoal production and construction purposes; (iii) large-scale timber logging, often without effective institutional control of harvest rates and logging methods; and (iv) population movements and resettlement schemes in forested areas. The amount of cropped land in SSA has increased by about 40 million ha in 30 years (1975-2005), most of it at the expense of forests and woodlands (FAO, 2015). Further expansion of cropland would be at the expense of forests or rangeland. Socio-economic causes of soil erosion Population expansion: Behind these direct drivers of erosion lies the demographic driver of a continuously growing population (Figure 9.3). The rate of SSA population growth has moderated in recentyears and is currently 2.1 percent per year. Nonetheless, in the next 15 years SSA will have to accommodate at least 250 million additional people, a 33 percent increase (UNDP, 2005). With the increase in population comes an increased demand for living space and food which will directly affect soil use in the region. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 254 254 in Africa South of the Sahara

297 Poverty: General poverty of the farming population and the low potential of the farming systems characteristic of SSA pose considerable challenges to sustainable agricultural growth and poverty reduction. Poverty is particularly prevalent in the pastoral/agro-pastoral, highland perennial and forest based farming systems which constitute one-third of the total SSA production systems (FAO and World Bank, 2001). From Figure 9.4 it is clear that SSA has many countries where a large percentage of the population is living below the poverty line. Figure 9.3: The fertility rate (the number of children a woman is expected to bear during her lifetime) for 1970 and 2005. Source: Fooddesert.org Climate Change: Climate change is predicted to affect SSA agro-ecosystems on a significant scale in the coming decades. The continent has a long history of rainfall fluctuations of varying lengths and intensities. Severe droughts affected East and West Africa alike during the 1910s. Drought episodes were generally followed by increasing rainfall levels, but negative trends were observed again from the 1950 onwards, culminating in -1 980s. These droughts had an impact on the susceptibility of soils to the droughts of the early 1970s and mid erosion. Legend Population (%) 3 - 14 14 - 26 26 - 37 37 - 48 48 - 57 57 - 66 66 - 75 75 - 84 Figure 9.4 Percentage of population living below the poverty line. Source: CIA World Factbook, 2012. Regional Assessment of Soil Changes Status of the World’s Soil Resources | Main Report 255 255 in Africa South of the Sahara

298 Water erosion: its extent and distribution in the region Water erosion constitutes 46 percent of the land degradation types in SSA, and wind erosion accounts for a further 38 percent (FAO, 2005). The most recent continent-wide assessment shows that 494 million ha, or 22 percent of the agricultural land (including rangelands) in Africa, are affected by water erosion (Oldeman, Hakkeling and Sombroek, 1991). The assessment confirms common field observations that overgrazing is the main cause of soil erosion, followed by inappropriate cultivation techniques on arable land. In this context -1 994, while the it is important to note that the number of cattle in Africa almost doubled in the period 1961 area of grazing lands hardly increased (FAO, 2015). For the future, the expected intensification of use on currently cultivated lands, expansion of cultivation into more marginal areas, reduction in grazing lands and the increasing numbers of livestock are likely to increase vulnerability to erosion. As discussed above (9.3.1), severely eroded areas in Africa can be found in South Africa, Sierra Leone, Guinea, Ghana, Liberia, Kenya, Nigeria, Zaire, Central African Republic, Ethiopia, Senegal, Mauritania, Niger, Sudan and Somalia. More than 20 percent of SSA’s agricultural land and pasture has been irreversibly degraded, mainly by soil erosion (UNSO/SEED/BDP, 1999). Erosion has assumed a serious dimension in Nigeria, affecting every part of the country. In the eastern part of the country, erosion has ravaged wide areas. Active and inactive gullies have formed with surface areas 2 2 in Ohafia to 1.15 km in Abiriba in Abia State. The width of the gullies ranges between 0.4 ranging from 0.7 km km in Ohafia and 2.4 km in Abiriba. A gully with a depth of 120 m has been recorded at Abiriba (Ofomata, 1985). In addition, agricultural practices have contributed to the problems of widespread sheet erosion. Erosion is thus exerting major pressure on soil resources with far-reaching consequences for both the population and the environment ( Jimoh, 2000). In the northern areas of Nigeria, erosion is equally serious, especially in places like Shendam and Western Pankshin in Plateau State, as well as at Ankpa and Okene in Kogi State. Gully erosion is also prominent in Efon-Alaaye, Ekiti State in the western part of the country (Adeniran, 1993). The areas of Nigeria most affected by erosion are the Agulu and Nanka districts of the eastern part of Nigeria, and the Shendam and western Pankshin areas of Plateau State, Nigeria (Udo, 1970; Okigbo, 1977). 2 of land has been devastated Elsewhere, the Imo State government has estimated that about 120 000 km by gully erosion. As a result, eight villages have been destroyed and 30 000 people needed to be resettled. Erosion damage in Imo and Anambra states was estimated to cause the loss of over 20 tonnes of fertile soil per annum, at an economic cost of over 300 million naira per annum. Gullies extended to depths of over 120 m and widths up to 2 km wide (Adeleke and Leong, 1980). In 1994, about 5 000 people were rendered homeless due to erosion in Katsina State, Nigeria. Properties worth over 400 million naira were destroyed and many lives lost. Other areas affected by erosion include Auchi in Edo State, Efon Alaye in Ondo State, Ankpa and Okene in Kogi State, and Gombe in Bauchi State. In many areas, erosion has resulted in a physical loss of available land for cultivation. For example, about 1 000 ha of cultivable land has been lost to erosion at the Agulu-Nanka area of Nigeria. Thus the loss of homes and crops, disruption of communication routes, financial losses and attendant hydrological problems can all stem from erosion problems. Nearly 90 percent of rangelands and 80 percent of farmlands in the West African Sahel, Sudan, and northeast Ethiopia are seriously affected by land degradation, including soil erosion. More than 25 percent of South Africa is seriously degraded by erosion. Almost 70 percent of Uganda’s territory was degraded by soil erosion and soil nutrient depletion between 1945 and 1990. Across SSA, more than 20 percent of agricultural land and pastures has been irreversibly degraded, affecting more than 65 percent of Africa’s population (Global HarvestChoice, 2011). Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 256 256 in Africa South of the Sahara

299 Considering that over 80 percent of South Africa’s land surface is covered by natural vegetation, the estimated annual soil loss of 2.5 tonnes soil per ha is excessive. These rates of soil loss far exceed tolerance levels and are almost ten times the estimated rate of soil formation, which has been estimated at 0.31 tonnes -1 -1 yr in the case of a 1 m thick solum of a tropical soil (Van der Merwe, 1995; see Section 6.1). Soil organic ha matter (SOM) plays a major role in ensuring soil stability. There is a general decline in SOM in South African soils. An estimated 20 percent of the country’s total surface area is potentially highly erodible. Bearing in mind the country’s geology, rainfall and topographic characteristics in addition to declining SOM, soil erosion is likely to stay a dominant soil degradation process. Sediment movement by erosion contributes significantly to shifts in soil fertility. Sediment movement is widespread in South Africa as reflected by the annual losses of 3 300 tonnes N, 26 400 tonnes P and 363 000 tonnes K estimated by Du Plessis in 1986 (Van der Merwe, 1995). Periodic floods transport massive amounts of sediment and nutrients within catchments. The Demoina flood in 1984, for instance, deposited as much as 34 million tonnes of sediment in the Mfolozi flats (Scotney and Dijkhuis, 1990). One 1985 study used a siltation approach to estimate the siltation load carried by the Tugela River, finding soil loss from the catchment area -1 -1 et al. , 2002). It has been estimated that water erosion affects 6.1 (De Villiers yr as high as 4.4 tonnes ha million ha of cultivated soils in South Africa. Of this area, 15 percent of soils are seriously affected, 37 percent moderately affected, and the rest slightly affected. Wind erosion in the region Wind erosion physically removes the lighter, less dense soil constituents such as organic matter, clays and silts, thus removing the most fertile part of the soil and lowering soil productivity (Lyles, 1975). In SSA, soil erosion by wind occurs mainly in the arid and semiarid regions. The occurrence of wind erosion at any one site is a function of weather events interacting with soil and land management through the effects of weather on soil structure, tilth and vegetation cover. At the southern fringe of the Sahara Desert, a special dry and hot wind, locally termed Harmattan, occurs. These North-easterly or Easterly winds normally blow in the dry winter season under a high atmospheric pressure system. When the wind force of Harmattan is beyond the threshold value, sand particles and dust particles will be blown away from the land surface and transported for several hundreds of kilometres across the land and as far as the Atlantic Ocean (WMO, 2005). Areas in SSA most susceptible to wind erosion are the southern fringe areas of the Sahara, Botswana, Namibia, Zimbabwe, Tanzania and South Africa (Favis-Mortlock, 2005). It is estimated that 25 percent of South Africa is affected by wind erosion (Laker, 2005), amounting to an estimated 10.9 million ha. Of this area, 7 percent is seriously affected, 29 percent moderately and 64 percent , 2002). Wind erosion is particularly evident on drift sands in the coastal areas, but also slightly (Barnard et al. on cultivated land in the Highveld areas. The seriousness of wind erosion can be deduced from the situation in the Eastern Cape Province where there are over 14 000 ha of drift sand (Barnard et al. , 2002). Most of South Africa’s prime agricultural soils in the relatively arid western part of the country are wind-blown sand deposits , 2002). et al. (De Villiers Wind erosion may cause off-site effects, such as the covering of the terrain with wind-borne soil particles from distant sources. It is estimated that more than 100 million tonnes of dust per annum are blown westward from the African continent across the Atlantic. The amount of dust arising from the Sahel zone has been per reported to be around or above 270 million tonnes per year which corresponds to a loss of 30 mm per m 2 year or a layer of 20 mm of soil particles over the entire area (WMO, 2005). Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 257 257 in Africa South of the Sahara

300 9.4.2 | Loss of soil organic matter The loss of vegetative cover and decline in the level of soil organic matter (SOM) are the root cause of most soil degradation, since all the physical, chemical and biological problems follow a drop in SOM content. Soil organic matter is a key component of any terrestrial ecosystem, and any variation in its abundance and composition has important effects on many of the processes that occur within the system. The amount of organic matter and size of soil carbon stock results from an equilibrium between the inputs into the system, which are mostly from biomass detritus, and outputs from the system, largely decomposition and volatilization. These processes are driven by various parameters of natural or human origins (Schlesinger and Winkler, 2000; Amundson, 2001; Section 2.1). A decrease of organic matter in topsoil can have dramatic negative effects on the water holding capacity of the soil, on the soil structure stability and compactness, on nutrient storage and supply, and on soil biological components such as mycorrhizas and nitrogen-fixing bacteria (Sombroek, Nachtergaele and Hebel, 1993). Direct causes of SOM decline Apart from climatic factors that influence carbon changes in the soil, inappropriate land uses and practices are the main cause of decline in SOM. These uses and practices include: monoculture cereal production; intensive tillage; short to no fallow; and reduction or absence of crop rotation systems. The long-term effects of these management actions are now being experienced across SSA. The SSA experience is not unique. Across the globe, the carbon balance of terrestrial ecosystems is being changed markedly by the direct impact of human activities. Land use change was responsible for 20 percent emissions during the 1990s (IPCC, 2007). In SSA, land use change is the primary of global anthropogenic CO 2 source, much of it through burning of forests. The impact of land use change varies according to the land use types. The clearing of forests or woodlands and their conversion into farmland in tropical SSA reduces the soil carbon content mainly through reduced production of organic inputs, increased erosion rates and the accelerated decomposition of soil organic matter by oxidation. Various reviews agree that the loss amounts to 20 to 50 percent of the original carbon in the topsoil, with deeper layers less affected, if at all (Sombroek, Nachtergaele and Hebel, 1993; Murty et al. , 2002; Guo and Gifford, 2002). However, conversion of forests to pasture does not necessarily change soil carbon (Guo and Gifford, 2002) and may actually increase the soil organic matter content (Sombroek, Nachtergaele and Hebel, 1993). Where shifting cultivation is practiced, soil carbon has been found to reduce to half the level before the land was cleared for use (Detwiler, 1986). Surprisingly, studies suggest that commercial logging and tree harvesting do not result in long-term decreases in soil organic matter (Knoepp and Swank, 1997; Houghton et al. , 2003). Clearly many factors are at play: changes in the amount of soil organic matter , 2001; Yanai et al. following conversion of natural forests to other land uses depend on several factors such as the type of forest ecosystem undergoing change (Rhoades, Eckert and Coleman, 2000), the post conversion land management et al. practiced, the climate (Pastor and Post, 1986) and the soil type and texture (Schjønning , 1999). Socio-economic causes of SOM decline In Sub-Saharan Africa, socio-economic pressures to increase production and incomes create incentives for farmers to reduce the length of fallow periods, cultivate continuously, overgraze fields, or remove much of the above-ground biomass for fuel, animal fodder and building materials. These practices can result in the reduction of SOM, water holding capacity and nutrients. They also increase the soil’s vulnerability to erosion (Lal, 2004). Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 258 258 in Africa South of the Sahara

301 Extent of SOM decline in the region As with negative nutrient balances (see below, 9.4.3), SOM decline threatens soil productivity. In SSA, the -1 -1 for the humid zone, 7 mg kg concentration of organic carbon in the top soil is reported to average 12 mg kg -1 or less in the semi-arid zone (Williams et al. , 1993). These inherently low for the sub-humid zone and 4 mg kg concentrations of soil organic carbon are due not only to the low root growth of crops and natural vegetation but also to the rapid turnover rates of organic materials caused by high soil temperature associated with abundant micro-fauna, particularly termites (Bationo et al. 2003). There is considerable evidence for rapid decline in SSA of soil organic C levels where cultivation of crops is continuous (Bationo et al. , 1995). For sandy soils, average annual losses in soil organic C may be as high as 5 percent, whereas for sandy loam soils reported losses are much lower, averaging 2 percent (Pieri, 1989). Results from long-term soil fertility trials indicate that -1 -1 yr in the soil surface layers are common in Africa, even with high levels losses of up to 0.69 tonnes carbon ha of organic inputs (Nandwa, 2003; Bationo et al. , 2012). Responses to SOM decline Appropriate land management could reverse the trend of SOM decline and contribute to soil carbon sequestration. In fact, increasing the SOM content is crucial for future African agriculture and food production , 2007; Sanchez, 2000). Several studies on SSA have shown that a synergetic effect exists (Bationo et al. between mineral fertilizers and organic amendments and that this synergy leads to both higher yields and higher SOC content (Palm , 2007). , 2005; Bationo et al. et al. et al. , 2001, Vågen Barnard et al. (2002) emphasized the importance of establishing and maintaining an effective and intimate association between soils and growing plants. Biological measures for stabilizing slopes and decreasing the rate of runoff are essential. It is often necessary to undertake some form of land shaping prior to this, together with chemical amelioration and nutrient augmentation. There is abundant evidence that soil organic matter plays a major role in stabilizing soil and in preventing its physical, chemical and biological deterioration. This has been demonstrated under South African conditions et al. (2002). For example, Folscher (1984) pointed out that micro- by several scientists as reported by Barnard organisms played a vital role in the chemo-biological condition of soils. Under predominantly heterotrophic microbial activity, physical and chemical stability could be expected, while under autotrophic microbial activity, acidification and nutrient decline could be forecast. Much more attention therefore needs to be paid to the dynamic nature of soil and its physical, chemical and biological interactions. Because nitrogen dynamics are so important in establishing a stable C:N ratio in soil, alternative sources of natural forms of nitrogen such as suitable legumes should be included in rotations. Rhizobial and mycorrhizal associations need to be stimulated and soil organic carbon and nutrient levels need to be systematically monitored and evaluated. Other soil quality indicators relating to specific situations need to be developed and utilized, with emphasis on earthworm populations as an indicator of soil quality. Reduced, minimum and no-till systems also need to be investigated and implemented where possible. These have been introduced worldwide and are being adopted in many parts of South Africa (Van der Merwe et al. , 2000). Land degradation leads to a release of carbon to the atmosphere through oxidation of soil organic matter. , it has been suggested that With present concerns about climate change and the increase in atmospheric CO 2 this process could be reversed and that the soil could be used to capture and store carbon. Soil organic matter could be gradually built up again through carbon sequestration. Among the land use changes which could be promoted with this objective in mind are improved agricultural practices, the introduction of agroforestry, and reclamation of degraded land. By such means, the carbon stored in soils could be substantially increased by -1 . Thus land use changes which are beneficial to local communities amounts of the order of 30–50 tonnes ha would, in addition, fulfil a global environmental objective. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 259 259 in Africa South of the Sahara

302 9.4.3 | Soil nutrient depletion Nearly 3.3 percent of agricultural gross domestic product (Agricultural GDP) in Sub-Saharan Africa is lost annually due to soil and nutrient losses (Global HarvestChoice, 2011). In Africa, harvesting grains and crop residues from the land removes considerable quantities of soil carbon content. As lost nutrients in SSA are only very partially replaced with fertilizers, these losses contribute to negative nutrient balances (Gray, 2005). As a result, soil fertility decline has been described as the single most important constraint on food production and food security in SSA. Soil fertility decline (also described as soil productivity decline) is a deterioration of chemical, physical and biological soil properties. Besides soil erosion, the main processes contributing to nutrient depletion in SSA are: • Decline in organic matter and soil biological activity • Degradation of soil structure and loss of other soil physical qualities • Reduction in availability of major nutrients (N, P, K) and micro-nutrients • Increase in toxicity, due to acidification or pollution In the first assessment of the state of nutrient depletion in SSA, which was carried out in 1990, nutrient balances were calculated for the arable lands of 38 countries across the continent. Four classes of nutrient-loss rates were established (Table 9.2). As discussed above (9.3.3), the average nutrient loss in 1990 was estimated -1 O per year (10 kg N; 4 kg P O). Countries with the highest depletion rates, , 10 kg K to be 24 kg nutrients ha 5 2 2 such as Kenya and Ethiopia (Table 9.3), also have severe soil erosion. Moderate Very High High Class Low <10 >40 21-40 N 10-40 -1 4-7 O <4 8 5 >15 P 2 5 <10 10-40 21-40 >40 O K 2 -1 -1 yr ). Source: Stoorvogel and Smaling, 1990. Table 9.2 Classes of nutrient loss rate (kg ha Direct causes of nutrient decline Fertility decline is caused by a negative balance between output (harvesting, burning, leaching, and so on) and input of nutrients and organic matter (manure/fertilizers, returned crop residues, mineral deposition through flooding). The estimate of nutrient depletion in SSA cited above is worrying. However, some scientists (Roy et al. , 2003) have expressed concern about the approach used, as it is based on approximation and aggregation at country level which could be misleading, masking the ‘bright’ spots and the ‘hot’ spots where urgent nutrient replenishment is required. Assessment of fertility decline at micro-watershed or community level would be more appropriate. Socio-economic causes of nutrient decline There are various factors that indirectly influence nutrient depletion in SSA and they vary between ecological regions and amongst countries and locations within a given ecological region. The cost of buying mineral fertilizer can put it beyond the reach of many SSA smallholders (World Bank, 1998). Farm-level 2012). One metric tonne of urea, for fertilizer prices in Africa are among the highest in the world (Bationo et al. example, costs about US$ 90 in Europe, US$ 500 in Western Kenya and US$ 700 in Malawi. These high prices can be attributed to the removal of subsidies, high transaction costs, poor infrastructure, and poor market development, inadequate access to foreign exchange and credit facilities, transportation costs and lack of training to promote and utilize fertilizers. For example, it costs about US$ 15, US$ 30 and US$ 100 to move 1 et al. tonne of fertilizer 1 000 km in the United States, India and SSA respectively (Bationo , 2012). Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 260 260 in Africa South of the Sahara

303 Many farmers do not follow recommended fertilizer application rates because of cash or labour constraints. In much of Southern and Western Africa there is a dry season lasting 7 to 8 months. In the first weeks of the rainy season many farm operations such as planting, weeding, and fertilizing must take place in rapid succession. Farmers who weed maize twice at critical periods can achieve a higher yield with half the amount of fertilizer used by farmers who only weed once (Kabambe and Kumwenda, 1995), but many farmers do not have sufficient labour to weed more often. et Output price instability is an important factor posing risks for fertilizer users in Western Africa (Byerlee al. , 1994). When markets are sparse, as they are in many rural areas dominated by subsistence production, the variations in market prices of crops tend to be wider than in regions where markets are more fully developed. Overall, the economics of fertilizer use are often not sufficiently positive, especially under rainfed conditions; farmers are cash-poor and so cannot buy expensive inputs; and farmers are highly averse to making cash outlays in unpredictable climatic conditions and with uncertain commercial returns. Extent of nutrient decline in the region The results of an FAO study (1983-2000) (Lesschen et al. , 2003; Stoorvogel and Smaling, 1990) which assessed N, P and K balances by land use system and by country revealed a generally downward trend in soil fertility in Africa. Overall, the study suggests that all African countries except Mauritius, Reunion and Libya show negative nutrient balances every year. The result for 2000 showed a deteriorating nutrient balance for almost all countries. This was influenced by the FAO estimates for crop production in 2000 and an accompanying -1 in 1983 and -26 kg expected decrease in fallow areas. For SSA as a whole, the nutrient balances were: -22 kg ha -1 -1 -1 -1 -1 -1 in 2000 for N; -2.5 kg ha 9 kg ha in 1983 and in 1983 and -3.0 in 2000 for P; and 5 kg ha in 2000 for K. ha Table 9.3 lists nutrient balances for several SSA countries. The study found substantial differences between countries. In 1993-95 the difference between nutrient inputs and nutrient losses in the continent ranged from -1 4 kg of NPK per ha per year in South Africa to 136 kg in Rwanda. Burundi and Malawi also experienced rates of nutrient depletion above 100 kg of NPK per ha per year. Densely populated and hilly countries in the Rift Valley area (Kenya, Ethiopia, Rwanda and Malawi) had the most negative values, owing to high ratios of cultivated land to total arable land, relatively high crop yields, and significant erosion problems. In the semiarid, arid, and Sudano-Sahelian areas that are more densely -1 00 kg of nitrogen, phosphorus, and potassium (NPK) per ha each year. populated, soils were found to lose 60 The soils of these areas are shallow, highly weathered, and subject to intensive cultivation with low-level fertilizer use. Short growing seasons contribute to additional pressure on the land. In important agricultural areas in the sub-humid and humid regions and in the savannas and forest areas, nutrient losses vary greatly. Rates of nutrient depletion range from moderate (30 - 60 kg of NPK per ha per year) in the humid forests and wetlands in southern Central Africa, to high (> 60 kg NPK per ha per year) in the East African highlands. More countries fall into the high depletion range than the medium range. Nutrient imbalances are highest where fertilizer use is particularly low and nutrient loss, mainly from soil erosion, is high. The low gains in nutrients, inherently low mineral stocks in these soils, and the harsh climate of the interior plains and plateaus aggravate the consequences of nutrient depletion. The estimated net annual losses of nutrients vary considerably by sub-region: 384 800 metric tonnes for North Africa, 110 900 metric tonnes for South Africa, and 7 629 900 metric tonnes for Sub-Saharan Africa as a whole. This represents a total loss of US$ 1.5 billion per year in terms of the cost of nutrients as fertilizers. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 261 261 in Africa South of the Sahara

304 K P N 2000 2000 1982-84 2000 1982-84 Country 1982-84 -1 -1 ) yr (kg ha -1 -1 -1 -1 6 4 -2 -9 1 Benin 0 Botswana 0 -2 1 0 -2 -1 -1 3 2 -2 -2 -21 Cameroon -20 Ethiopia -47 -6 -7 -26 -32 -41 -1 7 -20 -3 -4 Ghana -30 -35 -1 -29 -36 Kenya -42 -46 -3 -1 -1 -48 0 0 -44 -68 -67 Malawi -1 -1 -1 0 -2 -7 1 -8 Mali Nigeria -34 -37 -4 -4 -24 -31 -1 1 -61 -47 -60 -54 Rwanda -9 -1 -1 -1 -1 2 6 -2 -2 4 0 Senegal -1 -21 8 -32 United Republic of Tanzania -27 -5 -4 2 Zimbabwe -31 -27 -2 -22 -26 Table 9.3 Estimated nutrient balance in some SSA countries in 1982-84 and forecasts for 2000. Surce: Stoorvogel and Smaling, 1990; Roy et al., 2003. More nitrogen and potassium than phosphorus get depleted from African soils. Nitrogen and potassium losses primarily arise from leaching and soil erosion. These soil problems result mainly from continuous cropping of cereals without rotation with legumes, inappropriate soil conservation practices, and inadequate amounts of fertilizer use. Among West African countries, Guinea Bissau and Nigeria experience the highest annual losses of nitrogen and potassium. Nitrogen loss in East Africa is highest in Burundi, Ethiopia, Malawi, Rwanda, and Uganda, and phosphorus loss is highest in Burundi, Malawi, and Rwanda (IFPRI, 1999). Responses to nutrient decline The negative nutrient balances clearly indicate that not enough nutrients are being applied in most areas (Bationo et al. , 2012). Annual application of nutrients in SSA averages about 10 kg of NPK per ha. Fertilizer tends to be used mostly on cash and plantation crops because of the higher profitability of fertilizer application in the production of cash crops. Food crops receive less fertilizer because of unfavourable crop/fertilizer price ratios and financial constraints faced by farmers. In addition, food crops are only partly commercialized. To maintain current average levels of crop production without depleting soil nutrients, Africa as a whole (including North Africa) would require approximately 11.7 million metric tonnes of NPK each year, roughly three times more than the continent currently uses (3.6 million metric tonnes) (Henao and Baanante, 1999). Of this quantity, Sub-Saharan Africa would need by far the largest proportion (76 percent) because the current average level of fertilizer use is so low. Total nutrient requirements per ha per year range from Botswana’s -1 -1 NPK (a figure 350 percent above current usage) to Reunion’s 437.3 kg ha NPK (about 20 NPK per 24.5 kg ha ha less than the country consumes). Burkina Faso would have to increase its NPK consumption more than 11 times to maintain crop production levels without depleting nutrients and Swaziland would have to double its consumption. Estimated average use for SSA as a whole would have to increase about 4 times to meet nutrient needs at the current level of production. Generally, more nitrogen is required than potassium, and more potassium than phosphorus. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 262 262 in Africa South of the Sahara

305 | Case studies 9.5 9.5.1 | Senegal Introduction The main objective of the national land resources assessment undertaken in Senegal between 2000 and 2010 was to identify for each land use system the status and trends of land degradation and the major sustainable land management interventions present in the country. This assessment used national and local technical expertise, including that of the land users themselves. The findings have been reported in several documents, maps and web-sites (Ndiaye and Dieng, 2013). The methodology was based on the premise that land degradation is largely driven by the way people use the environment in which they live. The level of degradation or sustainable use of a given land resource depends to a great extent on the needs and objectives of the land user, which are limited by technical knowledge and level of access to production factors (capital, labour etc.). Choices about land use take place within an integrated production system ( Jouve, 1992). Consequently, defining the units in which both degradation and sustainable land management are to be described requires the identification of areas with similar geographic characteristics and then the mapping of the different production or land use systems. In Senegal this mapping was carried out using the ‘Framework for characterization and mapping of agricultural land use’ (George and Petri, 2006). In Senegal the following major land use systems were identified and characterized: Aquaculture and fishing, which takes place in areas covered with mangrove and other aquatic 1. vegetation that are regularly flooded. Rainfed subsistence agriculture, which is characterized by the absence of livestock and minimal use of 2. inputs. Agropastoral systems, characterized by a significant presence of rainfed agriculture but with greater 3. levels of livestock activity. These systems are located in areas that receive between 400 and 700 mm of rainfall. 4. Riverbank agriculture, characterized by the use of receding floodwaters to produce crops. 5. Irrigated agriculture, characterized by intensive management and relatively high use of inputs. 6. Forest based systems that exploit trees for timber. 7. Conservation areas that are protected to preserve biodiversity 8. Peri-urban agriculture, characterised by a mix of activities aimed at producing high-value products close to urban markets. 9. Nomadic grazing, which takes place in the driest areas of the country and is characterized by shifting livestock and no permanent agriculture. The distribution of these land use systems and their extent within the country are given in Figures 9.5 and 9.6 respectively. The national assessment of land degradation and sustainable management was carried out using available , 2011). The et al. hard data and a questionnaire developed by FAO in collaboration with WOCAT (Liniger evaluation describes the actual situation and assesses the trends of land change over the last ten years. The method used local observations and measurements and expert opinion and covered the whole of Senegal. It has achieved the identification and characterization of land change in terms of degradation types, their Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 263 263 in Africa South of the Sahara

306 extent, degree, level, trend, causes and impacts on ecosystem services. Each of these parameters has been mapped and examples are given in Figure 9.7 (extent of dominant degradation type) and Figure 9.8 (rate of change of degradation). All information collected has been captured in a national database and analysed statistically (SOW-VU, 2010). Figure 9.5 Major land use systems in Senegal. Source: FAO, 2010. Figure 9.6 Proportional extent of major land use systems in the Senegal. Source: Ndiaye and Dieng, 2013. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 264 264 in Africa South of the Sahara

307 Figure 9.7 Extent of dominant degradation type in Senegal. Source: FAO, 2010. negal - Avera ge ra te of degra dation Land degra dation in Se Legend Rate of incr easi ng degradation no change 0.00 Mauritania 0.01 0.5 slowly increasing 1 1.5 2 moderately increasing 2.5 Senegal no data 2.5 Mali Atlantic Ocean Gambia Guinea-Bissau Guinea 25 km 0 50 100 Figure 9.8 Average rate of degradation in Senegal. Source: FAO, 2010. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 265 265 in Africa South of the Sahara

308 Some examples of analysis of the data show the value of the national assessment: 1. The analysis of the socio-economic drivers of land degradation in the country showed that poverty and population pressure are the main drivers, while governance and education are also significant. Land tenure and conflict situations were reported to be of minor importance as drivers of land degradation in Senegal. 2. It is population pressure and poverty which lead in a majority of cases to deforestation and overgrazing and which, together with lack of access to extension services, lead to unsustainable soil and crop management. Urbanisation and mining are minor pressures in the country. Impacts of land degradation on ecosystem goods and services fell mainly on the productive services 3. (affecting 15 percent of the area), while impacts on ecological services, in particular on biodiversity, were slightly less (13 percent). The influence on the socio-cultural provisioning services was the smallest, affecting only 6 percent of the area. 4. Further field and socio-economic studies were undertaken at the local level, both in areas that were considered ‘hotspots’ for degradation and in ‘bright spots’ where degradation was less prevalent and sustainable management was practiced. The analysis of results in these local areas is illustrated in Figure 9.9 which gives the impact of degradation on the various ecosystem services. There is a major impact on the net returns of the farmers in all areas, but there are also important differences according to the different situations in each zone. Figure 9.9 Impact of degradation on ecosystem services in the local study areas in Senegal. Source: Ndiaye and Dieng, 2013. Responses have included measures implemented by the government, NGOs, the communities themselves and local producers. The principal responses were: assisted natural regeneration, agro-forestry, application of organic amendments, introduction or extension of fallow periods, composting, and using a millet/groundnut rotation. Most of these responses have proved to be efficient, but their adoption by land users has been slow, affected by lack of information and by economic and/or political constraints. 9.5.2 | South Africa -1 5 percent. Of this arable Of South Africa’s total area of 123.4 million ha, arable land accounts for only 11 land, only about a quarter is high potential. This high potential land is thus a critical resource which needs to be protected. South Africa’s soils are diverse and complex as a result of varied soil formation and weathering processes. The largest proportion (81 percent) are slightly weathered and calcareous soils. More than 30 percent of soils are sandy (e.g. less than 10 percent clay content) and almost 60 percent of soils have low organic matter content (Scotney, Volschenk and Van Heerden, 1990). The most important soil limitations are shallow depth, extremes of texture, rockiness, severe wetness and high erosion hazard. In terms of soil Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 266 266 in Africa South of the Sahara

309 management, it is important to note that agriculture in South Africa has a dualistic nature, with a well- developed commercial sector on the one hand, and a predominantly subsistence or small-scale agricultural sector in communal areas on the other. The first, and to date only, nationwide study of soil distribution was done by the Land Type Survey Staff (2003) from 1970 to 2003. The study delineated areas known as ‘land types’ at 1:250 000 scale - land types were defined as areas displaying a marked degree of uniformity in terms of terrain form, soil pattern and climate. The study included an in-depth analysis of a number of soil profiles, termed modal profiles, selected to represent the range of soils encountered during the survey. Soils from 2 380 profiles across the country were described and analysed for morphological and chemical data and classified according to the binomial , 1977). Each land type includes a collection of et al. classification system developed for South Africa (MacVicar soils and their relative distribution in terms of area per landscape position, as well as their characteristics in terms of physical and chemical properties. The resultant national map of broad soil patterns is shown in Figure 9.10. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 267 267 in Africa South of the Sahara

310 Figure 9.10 Broad soil patterns of South Africa. Source: Land Type Survey Staff, 2003. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 268 268 in Africa South of the Sahara

311 From 2006, several further national studies were conducted to assess the status of soils, land use trends, land degradation and sustainable land management implementation in the country. Results are summarized in this section. There is much evidence of mismanagement of soil resources which has led to widespread erosion by both wind and water, loss of soil fertility, compaction and acidification. National land degradation assessment Since land use is considered the single most important driver of land (and soil) degradation, land degradation assessments were conducted based on land use categories. For this purpose, a national stratification map was developed for South Africa based on amendments to the Land Use System Approach as described by Nachtergaele and Petri (2008) as well as by Pretorius (2009). On this basis, the stratification map adopted the following 18 land use categories: • Desert • Azonal vegetation • Savanna • Forest • Grassland • Nama-Karoo Indian Ocean Coastal Belt • • Succulent Karoo • Fynbos • Albany Thicket • Open Water • Urban • Cultivated – commercial – rain-fed Cultivated – irrigated • • Cultivated – subsistence – rain-fed • Plantations Mines • • Protected areas By integrating the local municipality boundaries with those of land use, a total of 2 447 unique units were derived for further assessment, as illustrated in Figure 9.11. Land degradation and sustainable land management implementation were then assessed in each of the 2 447 mapping units. The assessment was carried out from 2008 to 2010 and was based on a participatory approach as part of a Land Degradation Assessment in Drylands (LADA) project. The approach relied strongly on the inputs from a range of experienced contributing specialists and land users who were conversant with the areas to be assessed. Data capturing was done through a series of 33 Participatory Expert Assessment (PEA) Workshops throughout the country, involving 728 contributing specialists (Wiese, Lindeque and Villiers, 2011). In terms of soil, the main forms of degradation at national level were soil erosion by water, biological degradation and chemical soil degradation. For soil erosion, sheet and gully erosion were considered the most serious threats, with river or stream bank erosion and off-site sedimentation considered less critical. Soil acidification and salinization were also highlighted, although their occurrence was more localized and area-specific. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 269 269 in Africa South of the Sahara

312 Figure 9.11 The national stratification used for land degradation assessment in South Africa, incorporating local municipality boundaries with 18 land use classes. Source: Pretorius, 2009. Erosion assessment A separate spatial study was conducted on the extent of gully erosion in South Africa (Le Roux et al. , 2008). The study also assessed national erosion potential in terms of soils, climate and topography (Le Roux, 2012). The assessment of water erosion susceptibility indicated that around 20 percent (26 million ha) of the country is classified as having a moderate to severe erosion risk (mainly based on sheet-rill erosion). The affected areas are concentrated in the south-eastern and north-eastern interior, mainly in the Eastern Cape, KwaZulu- Natal, Mpumalanga and Limpopo Provinces. All of these areas are characterized by a combination of high (often intense) rainfall, duplex soils derived from sodium-rich parent materials, and steep slopes (see Figure 9.12). These natural conditions are often exacerbated by poor land use practices, such as incorrect cultivation methods, overgrazing by livestock and high population density. Under such circumstances, potential soil loss -1 -1 (Le Roux yr , 2006). et al. can easily be in the ‘Very High’ class of more than 50 tonnes ha Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 270 270 in Africa South of the Sahara

313 Figure 9.12 Actual water erosion prediction map of South Africa. Source: Le Roux et al., 2012. The erosion process starts when the vegetation cover is disturbed or removed, allowing the rainfall to impact directly on bare soil. If measures to restrict surface run-off are not put in place, the effect is generally two-fold: firstly, the water flowing on the soil surface removes a significant amount of topsoil (‘sediment’), especially on steeper slopes; and secondly, the duplex nature of the soils (sandy topsoil abruptly overlying a structured clay subsoil) results in the formation of a surface seal. As a result, very little water is actually able to infiltrate the soil. Research in South Africa (Levy, 1988; Rapp, 1998; Bloem, 1992) indicated that exchangeable sodium percentage (ESP) values play an important role in erosion risk, with problematic values being over 12, although values as low as 5 or 6 (Bloem and Laker, 1994; Laker and D’Huyvetter, 1988) can also cause erosion under poor land use conditions. Combating soil erosion by water remains a huge challenge in many affected areas of the country due to a combination of lack of resources, poor knowledge or awareness and poor infrastructure, mainly roads. The challenges of treating erosion and the more difficult task of rehabilitating large areas of land, combined with the off-site effects such as silting up of dams, together pose one of the most serious soil management challenges in South Africa today. Soil nutrient depletion, acidity and organic matter Although soil erosion by water was confirmed as the main soil degradation type in the country, there are areas in South Africa affected by wind erosion, nutrient depletion, loss of organic matter, soil acidity, salinity and sodicity as well as pollution from mining and industrial sources. Desktop assessments of soil nutrient depletion, acidity and organic matter in South Africa were conducted during 2007-2008 (Beukes, Stronkhorst and Jezile, 2008a,b; Du Preez , 2010; Du Preez et al. , 2011a,b; Rantoa, Du Preez and Van Huyssteen, 2009). et al. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 271 271 in Africa South of the Sahara

314 Nutrient depletion and acidity A multitude of soil nutrient and acidity studies have been conducted over time in South Africa (Bierman, 2001; Bloem, 2002; Buhmann, Beukes and Turner, 2006; Conradie, 1994; Eweg, 2004; Farina, Manson and Johnston, 1993; Mandiringana et al. , 2005; Meyer et al. , 1998; Miles and Manson, 2000; Thibaud, 2005). These studies included extensive reviews of international and national documentation, interviews with experts from various national and provincial institutions, and processing of data available from a number of national databases and soil analytical laboratories. Detailed results have been reported for each of the nine provinces in South Africa, but only a national summary is presented here (Beukes, Stronkhorst and Jezile, 2008a,b) with a focus on the agricultural sector. The impact of the dualistic nature of South African agriculture on soil nutrient depletion was clearly resource-poor/small-scale/upcoming farmers generally being acidified, severely evident, with soils from the P depleted, and N, K, Ca and Mg deficient (Manson, 1996; Beukes, Stronkhorst and Jezile, 2008b). Within this group, two sub-groups can be distinguished, as these farmers produce crops at two levels. The first sub-group is the home garden where relatively high fertility levels are evident. This is mainly because these gardens are located next to the homesteads and are therefore easier to manage. The second sub-group consists of crop fields which are larger and further from the homesteads. As a result, these fields are less secure in terms of livestock access and there are transport constraints. In addition, most smallholder farmers are risk-averse due to their limited resources. These fields are therefore generally severely nutrient depleted, especially in terms of P and K deficiencies, while N, Mg and Ca deficiencies are also often noted. operates on a much larger scale and higher levels of management and By contrast, commercial agriculture inputs are maintained on these farms to ensure higher productivity. This is especially the case in the sugar, vine and fruit farming sectors due to higher costs for crop establishment and maintenance. Soils in the commercial sector generally exhibit P deficiency as the main nutrient concern, with K deficiency also occurring in many areas. Commercial pastures may have fewer deficiencies: for example in KwaZulu-Natal, P deficiency is almost negligible and K, Ca and Mg appear well supplied (Beukes, Stronkhorst and Jezile, 2008b). Naturally occurring acid soils are generally associated with high rainfall areas and certain geological materials which, in South Africa, are located in the western and southern Cape coastal belts, KwaZulu-Natal, Mpumalanga and Limpopo Province (see Figure 9.13). The extent of anthropogenic soil acidity in the country is not easy to estimate, but general trends can be observed. In the winter rainfall region, approximately 560 000 ha is under cultivation, and on 60 percent of this area soils indicate problems with acidity. In Kwa-Zulu-Natal, roughly 35 percent of the more than 660 000 ha of cultivated soils have acid saturation values above 15 percent. In the summer rainfall area west of the Drakensberg, 37 percent of topsoils in the cropped area are acidified (Beukes, 1995). Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 272 272 in Africa South of the Sahara

315 Figure 9.13 Topsoil pH derived from undisturbed (natural) soils. Source: Beukes, Stronkhorst and Jezile, 2008a. Soil organic matter Although data on soil organic carbon in South Africa are limited, fragmented and uncoordinated, general trends of SOC content can be derived from a range of studies conducted (Barnard et al. , 2000; McKean, 1993, , 2005; Mills and Fey, 2004; Prinsloo, Willshire and Du Proez, 1990; et al. Du Toit and Du Preez, 1993, Le Roux Van Antwerpen and Meyer, 1996; Birru, 2002; Du Preez, Mnkeni and Van Huyssteen, 2010, 2011a, b). A review of SOC research estimated that approximately 58 percent of South African soils contain < 0.5 percent organic C, 38 percent contain 0.5–2 percent organic C and 4 percent have > 2 percent organic C. These organic C contents vary greatly as a function of soil types, climate, vegetation, topography and soil texture, and are greatly influenced by management practices which result in organic C losses such as overgrazing, high levels of soil disturbance during cultivation, and the use of fire in rangeland management. Soil organic matter losses were generally associated with dryland cropping, but were less prevalent in irrigated agriculture. Increasing SOM is a slow process, but it has been achieved by implementing zero/minimum tillage, by mulching and through reversion of cropland to perennial pastures. Increases have mainly occurred in the upper 300 mm of soil, and in most instances, have been restricted to the upper 50 mm of soil. Loss of SOM has been found to result in lower nitrogen and sulphur reserves, but not necessarily in lower phosphorus reserves. Loss of SOM also coincided with changes in the composition of amino sugars, amino acids and lignin. It further resulted in a decline of water stable aggregates which are essential in the prevention of soil erosion. Rantoa, Du Preez and Van Huyssteen, (2009) used data from the approximately 2 200 modal profiles from the land type survey to estimate organic carbon stocks in South African soils with reference to master horizons, diagnostic horizons, soil forms and land cover classes. In summary, the average organic carbon content in the Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 273 273 in Africa South of the Sahara

316 master horizons ranges from 16 percent in the O horizon to 0.3 percent in the C horizons. In the diagnostic horizons, the highest average organic C in topsoils ranged from 21 percent in the O horizons to 1.4 percent in the orthic A horizons. In the diagnostic subsoil horizons, however, values ranged from 1.2 percent in podzol B to 0.2 percent in the dorbank horizons. Land Cover Change Assessment Land use trends give an indication of land conversion from one land use to another, which directly affects soil use properties as a function of management. A study of land-cover change was conducted in 2010 based on land-cover data from 1994/1995, 2000 and 2005 employing a cost-effective approach which used Earth Observation data. The study was based on changes in five land-cover classes: urban, mining, forestry, et al. cultivation, and other. These five classes are defined in Table 9.4 (Schoeman , 2010). Class definition Land-cover class Urban Human settlements, both rural and urban Areas covered by mining and related mining activities Mining (also includes mine dumps) All forestry and plantations including woodlots and clear fell areas Forestry and plantations (excludes indigenous natural forests) All areas used for agricultural activities, including old fields Cultivation and subsistence agriculture All other areas not covered by those listed above Other Table 9.4 Definitions of the five land-cover classes on which the land-cover change study was based. Source: Schoeman et al., 2010. The land-cover change results (Figure 9.14) indicated that at national level there was a total increase of 1.2 percent in transformed land, specifically associated with Urban, Cultivation, Forestry & Plantation and Mining. This represents an increase from 14.5 percent transformed land in 1994 to 15.7 percent in 2005 across South Africa. On a national basis the areas of Urban, Forestry & Plantation, and Mining have all increased over the 10-year period, whereas Cultivation areas have decreased. Urban has increased from 0.8 percent to 2 percent, Forestry & Plantation from 1.2 percent to 1.6 percent, and Mining from 0.1 percent to 0.2 percent, while Cultivation has decreased from 12.4 percent to 11.9 percent. The spatial patterns do, however, vary geographically across provinces in South Africa. The increase in urban and mining areas are the biggest concern in terms of soil conservation and future use since urban development involves soil sealing which irreversibly removes soils from other land uses, while mining results in serious chemical and physical soil degradation which can only be restored to a limited extent. For this reason, it is essential that soil suitability and potential for agricultural and environmental purposes be assessed in order to ensure that the high potential and environmentally important soils are reserved and conserved for food production purposes. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 274 274 in Africa South of the Sahara

317 Figure 9.14 Change in land-cover between 1994 and 2005 as part of the Five Class Land-cover of South Africa after logical corrections. Source: Schoeman et al., 2010. | Summary of conclusions and recommendations 9.6 Based on the above finding, an assessment is made of the status and trend of the ten soil threats in order of importance for the region. At the same time an indication is given of the reliability of these estimates (Table 9.5). Soil degradation is considered one of the root causes of stagnating or declining agricultural productivity in SSA. Unless soil degradation can be controlled, many parts of the continent are expected to suffer increasingly from food insecurity. If this decline in the productivity of Africa’s soil resources continues, the consequences will be severe, not only for the economies of individual countries, but also for the welfare of the millions of rural households dependent on agriculture for meeting their livelihood needs. There is an urgent need for proactive interventions to arrest and reverse soil degradation. Rehabilitation of degraded land and conservation of those not yet degraded is the most desirable step for every country in the region, but this can only be achieved if the characteristics of the soil resources are well defined and quantified and soil monitoring systems established in every country. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 275 275 in Africa South of the Sahara

318 Threat Condition and Trend Confidence Summary to soil function Very poor Poor Fair Good Very good In condition In trend Soil erosion constitutes >80% of land degradation in SSA, affecting about 22% of agricultural land and all countries in Soil erosion the region. The majority of causes related to the exposure of the bare soil surface by cultivation, deforestation overgrazing and drought. The replacement of the natural vegetation reduces nearly always the soil carbon level. Further carbon release from the soil is caused by Organic complete crop removal carbon from farmlands, the change high rate of organic mater decomposition by microbial decomposition accentuated by high soil temperature and termite activates in parts of SSA. Nutrient imbalance, which is generally manifested by the deficiency of key essential nutrients is mainly due to the fact that fertilization has not been soil and crop specific, Nutrient farmers are unable to pay imbalance the price for fertilizers and the inability to follow the rates that are recommended. Nearly all countries in the region show a negative nutrient balance. SSA suffers the world’s highest annual deforestation rate. The areas most affected are the in the moist areas of West Africa and the highland forests of the Loss of soil Horn of Africa. Cultivation, biodiversity introduction of new species, oil exploration and pollution reduce the population of soil organisms thus reducing faunal and microbial activities. Over 25% of soils in Africa are acidic. Most of these occur in the wetter parts of the Soil continent. In South Africa acidification it poses as a serious chemical problem and the greatest production- limiting factor. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 276 276 in Africa South of the Sahara

319 Most waterlogging threats are due to rise in water table due to poor infiltration/ drainage or occurrence Waterlogging of impervious layer in the subsoil. Waterlogging generally reduces crop productivity, but in paddy fields is deliberate and beneficial. The major cause of compaction is pressure on the soil from heavy machinery. It is more Compaction serious in forested regions where land clearing (and even other cultivation activities) cannot be done without mechanization. These constitute problems mainly in peri-urban Soil sealing agriculture and valley and land take sites used for dry season vegetable production. Soil contamination by chemicals (fertilizers, petroleum products, pesticides, herbicides, mining) has affected Soil pollution agricultural productivity and other ecosystem services negatively. Nigeria and South Africa are the most affected. Table 9.5 Summary of soil threats status, trends and uncertainties in Africa South of the Sahara. Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes 277 277 in Africa South of the Sahara

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