Greenhouse Gas Emissions from U.S. Agriculture and Forestry: A Review of Emission Sources, Controlling Factors, and Mitigation Potential

Excerpts from the report Introduction: Approximately 6% of all greenhouse gas (GHG) emissions originating in the United States come from agricultural activities (EPA, 2010). These gases are in the form of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). By employing improved management techniques, agricultural lands can both sequester carbon and reduce CO2, CH4, and N2O emissions, thereby reducing agriculture’s GHG footprint. Forestry activities in the U.S. are currently a net sink (CO2 removal from the atmosphere) of carbon (C) as a result of net forest growth, increasing forest area and net accumulation of carbon stocks in harvested wood pools (EPA, 2010). Several options exist to maintain and further increase C sequestration on forested lands in the U.S. This report is organized as follows: Section II describes the main sources, processes and factors controlling soil and biomass C losses and emissions of CO2, N2O and CH4 from agricultural and forest systems. It also discusses the effects of common land use and management practices on GHG emissions and provides a range of emission estimates from different empirical field studies. Section III provides a review and synthesis of the literature regarding mitigation technologies for GHG emissions relevant to U.S. agriculture and forestry, and provides quantitative emission reduction estimates for various practices based on empirical field studies. Section IV concludes by highlighting current knowledge gaps and further research needs to improve the accuracy and completeness of agricultural GHG accounting methods and resulting GHG emission estimates.