Daycent Model Estimates of Greenhouse Gas Mitigation Potential of Cropped Soils in the USA

Agricultural soils in the USA are currently thought to be a net CO₂ sink but these soils remain a strong source of N₂O. N₂O is a potent greenhouse gas and also contributes to stratospheric ozone depletion. Reducing N₂O emissions thus represents an opportunity to reduce overall greenhouse gas emissions that complements C sequestration in soil and biofuel production. Practices that increase N availability in soils ensure high cop yields but N not used by plants can be lost as N₂O, NO_x, and NH₃ gasses, and as leached NO₃. Soil N₂O losses are referred to as direct N₂O emissions while NO_x and NH₃ gas emissions and NO₃ leaching contribute to indirect N₂O emissions. Strategies to minimize N losses and/or maintain or enhance soil C levels include the following: timing fertilizer application to be more synchronous with plant demand, use of nitrification and urease inhibitors, planting non-growing season cover crops, and reducing tillage intensity. The DAYCENT biogeochemical model has the ability to simulate the impacts of these land use options on N gas emissions, NO₃ leaching, crop yields, and soil C levels. Using data from GRACEnet and other sources, we tested the ability of DAYCENT to simulate C and N fluxes for different cropped systems under typical and improved land management. Comparisons of measured and simulated values for annual crop yields, N₂O emissions, and NO₃ leaching produced r² values of 0.72, 0.68, and 0.61, respectively. Land use options that decrease N₂O emissions and maintain or enhance soil C levels can reduce total greenhouse gas emissions from cropped soils by 20-40% for major cropped regions in the USA.