Quantifying the potential for cover crops to reduce GHG emissions in the US Midwest
Cover crops are widely considered to reduce GHG emissions from agriculture, but a comprehensive quantification of these ecosystem service benefits has not previously been reported. Here, I estimate the potential for cover crops in the Midwest United States to reduce GHG emissions if adopted over 7.6 million hectares. I synthesized published estimates of cover crop influence on soil carbon, CO2 emissions associated with fertilizer production, a meta-analysis of in-field N2O emissions, modeled N leaching in specific geographies, and IPCC tier 1 estimates of N2O emissions associated with leached N.
If adopted across 7.6 million Ha in 5 midwestern states, in farming systems where this practice is feasible given current rotations and practice used, cover crops could reduce emissions by 550-26,000 Gg CO2e per year, up to 4% of U.S. on-field agricultural emissions. The wide range reflects mainly the influence of cover crops on soil carbon. Considering only GHG emission reductions associated with embodied emissions in fertilizer and with N2O emissions from soil, I estimate GHG reductions as high as 3,500 Gg per year. Previous analysis showed that of 1,768 counties in the Upper Mississippi Basin, 162 account for 25 percent of N loss; targeting cover crop adoption in those counties would maximize reductions in N-related GHG emissions.
Initiatives like the Global Alliance for Climate Smart Agriculture highlight the need to ididentify practices that reduce emissions. Carbon registries have omitted cover crops from their protocols because estimates of cover crop affects are not sufficiently robust and because registries typically avoid crediting carbon benefits associated with reduced fertilizer dedemand. A complete accounting of emission benefits associated with cover crop adoption may apply more readily to sustainability indexes and incentive programs.