Assessing long-term impacts of cover crops on soil carbon sequestration and crop yield in the U.S. Midwestern agroecosystems

Abstract:

Soil health and food productivity is vital for the U.S. Midwestern region, which produces one third of the global corn and soybean. Cover crops, one of the majority soil conservation practices, have been recommended for farmer adoption to improve soil health and reduce the loss of soil organic carbon (SOC) in the U.S. Midwestern. To assess the impacts of different cover crops on SOC sequestration and food production, we evaluated an advanced process-based agroecosystem model, Ecosys, in simulating cover crop and its impacts, benchmarked with the ground measurements from a rich amount of field trials/experiments around Illinois as well as literature meta-analysis. The validation results show that the Ecosys model can accurately simulate cover crops biomass, cash crop yield, and SOC, when compared with ground truth. We find from the simulation results that growing cover crops can add extra carbon biomass into the agroecosystem, and thus increasing SOC when compared with no cover crop scenarios. For non-legume cover crops (such as cereal rye and ryegrass), the simulated results show that they have a small negative influence on cash crops production (i.e. about 5% yield loss), as cover crops may use available water and nitrogen in the early spring before planting, which creates the resource competition with cash crops, i.e. corn and soybean in the Midwest. The negative effects of cover crops on cash crop yield can be mitigated by earlier termination (i.e. one month before cash crop planting), changing cover crops type (i.e. from non-legume to legume), or adding more fertilizer to cash crops. The long-term simulations show that the cover crops have the potential to mitigate the decreasing trend of SOC and bring benefits to crop yield in turn, though the impacts may take 20+ years to show the benefits. Our results confirm that cover crop is a promising practice to maintain the U.S. Midwestern region as a sustainable agroecosystem, though its benefits may not be as large as what has been suggested in the popular media about regenerative agriculture, and its benefits also will take a longer time (20+ years) to exhibit.