Carbon Sequestration and Greenhouse Gas Fluxesin Agriculture: Challenges and Opportunities Council for Agricultural Science and TechnologyAmes, Iowa, USACouncil for Agricultural Science and Technology, Ames, Iowa, USAPrinted in the United States of AmericaCover design, graphics, and layout by Rich Beachler, Studio 2172, Boone, IowaCover photo: Shutterstock Images LLC, New YorkISBN 978-1-887383-33-2ISSN 0194-408814 13 12 11 4 3 2 1Library of Congress Cataloging-in-Publication DataInformation available from CAST Task Force Report No. 142 October 2011Ronald Follett (Cochair), USDA–ARS–NPA, Soil Plant Nutrient Research, Ft. Collins, ColoradoSian Mooney (Cochair), Department of Economics, Boise State University, IdahoJack Morgan (Cochair), USDA–ARS–NPA, Rangeland Resources Research Unit, Ft. Collins, ColoradoKeith Paustian (Cochair), Department of Soil and Crop Sciences, Colorado State University, Ft. CollinsLeon Hartwell Allen, Jr., USDA–ARS–SAA, CMAVE, Chemistry Research Unit, Gainesville, FloridaShawn Archibeque, Department of Animal Sciences, Colorado State University, Ft. CollinsJohn M. Baker, USDA–ARS, University of Minnesota, St. PaulStephen J. Del Grosso, USDA–ARS–NPA, Soil Plant Nutrient Research, Ft. Collins, ColoradoJustin Derner, USDA–ARS–NPA, Rangeland Resources Research Unit, Cheyenne, WyomingFeike Dijkstra, Faculty of Agriculture, Food and Natural Resources, The University of Sydney, AustraliaAlan J. Franzluebbers, USDA–ARS–SAA, J. Phil Campbell Sr. Natural Resource Conservation Center, Watkinsville, GeorgiaHenry Janzen, Lethbridge Research Station, Alberta, CanadaLyubov A. Kurkalova, Department of Economics and Finance, North Carolina A&T State University, GreensboroBruce A. McCarl, Department of Agricultural Economics, Texas A&M University, College StationStephen Ogle, National Resource Ecology Laboratory, Colorado State University, Ft. CollinsWilliam J. Parton, National Resource Ecology Laboratory, Colorado State University, Ft. CollinsJeffrey M. Peterson, Department of Agricultural Economics, Kansas State University, ManhattanCharles W. Rice, Department of Agronomy, Kansas State University, ManhattanG. Philip Robertson, Department of Crop and Soil Sciences, Michigan State University, Hickory CornersMichele Schoeneberger, U.S. Forest Service, USDA National Agroforestry Center, Lincoln, NebraskaTristram O. West, Pacific Northwest National Laboratory and University of Maryland, College ParkJeff Williams, Department of Agricultural Economics, Kansas State University, ManhattanTask Force MembersiiCAST LiaisonKeith Newhouse, Land O’Lakes, Shoreview, MinnesotaContentsInterpretive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3The Science and Uncertainties Important to Climate Change, 3The Role of Agriculture, 3Mitigation Options, 4Impacts on Society, Including on Agriculture, 51 Introduction: Climate Change and Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8Background, 8Climate Change, 9Climate Change and Society, 12Agriculture’s Greenhouse Gas Emissions, 12Climate Change and Agriculture, 14 Basic Plant Response to Carbon Dioxide and Climate Change, 142 Science of Greenhouse Gas Emissions from Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17Processes, Sources, and Sinks of Carbon Dioxide, Nitrous Oxide, and Methane and the Drivers, 17 Carbon Dioxide, 17 Nitrous Oxide, 19 Methane, 20Measuring Carbon Dioxide, Nitrous Oxide, and Methane Fluxes, 24Agricultural Greenhouse Gas Flux Estimates for the United States, 25Feedbacks between Climate Change and Greenhouse Gas Emissions, and Implications for Future Emissions, 27 Impacts of Rising Carbon Dioxide and Climate Change on Plant Productivity, 27 Responses of Soil Carbon to Climate Change, 28 Responses of Non-Carbon Dioxide Greenhouse Gases, 283 Mitigation Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30Mitigation Principles, 30Annual Cropland, 32 Soil Carbon and Carbon Dioxide Mitigation, 32 Mitigating Nitrous Oxide Emissions from Soil, 34Grazinglands, 36 Background, 36 Management Considerations, 36 Environmental Considerations, 38 Ecosystem Services Associated with Soil Organic Carbon, 38 Knowledge Gaps, 39Horticultural Crops, 39 Vegetable Agriculture, 39 Orchards and Vineyards, 39Turfgrass, 40iiiAgroforestry, 40 Introduction, 40 Greenhouse Gas Mitigation by Agroforestry, 42 Soil Carbon in Agroforests, 42 Other Greenhouse Gas Dynamics in Agroforests, 43 Other Impacts of Agroforestry on Greenhouse Gas Dynamics and Emissions, 44 Agroforestry’s Cobenefits, 44 Inventory and Other Accounting Needs in Agroforestry, 45Wetlands Agriculture and Organic Soils, 45 Wetlands Agriculture, 45 Organic Soils, 46Set-aside (Conservation Reserve Program) Programs, 48 Legislation, 48 Impact, 49Confined Livestock, 50 Scale, 51 Other Impacts, 524 Bioenergy Feedstock Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Introduction, 53Basis for Bioenergy Carbon Benefits, 54Potential Feedstocks, 54Carbon Sequestration versus Carbon Loss and Debt, 56Land Use Conversion, 56Tillage, 57Residue Management, 57Biochar, 57The Importance of Nitrous Oxide and Methane in the Net Greenhouse Gas Benefit of Biofuel Systems, 57Indirect Land Use Costs, 58Other Environmental Considerations, 59Model Scenarios, 60Conclusions and Future Considerations, 615 Economics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .