Simulating Long-Term Impacts of Cover Crops and Climate Change on Crop Production and Environmental Outcomes in the Midwestern United States.

It is critical to evaluate conservation practices that protect soil and water resources from climate change in the Midwestern United States, a region that produces one-quarter of the world’s soybeans and one-third of the world’s maize.  An over-winter cover crop in a maize-soybean rotation offers multiple benefits that might reduce the impacts of higher temperatures and more variable rainfall, some of the anticipated climate changes in the Midwest.  In this experiment we used the Agricultural Production Systems sIMulator (APSIM) to quantify how winter rye cover crops impact crop production and environmental outcomes, given future climate change. We first tested APSIM with data from a long-term maize-soybean-winter rye field site.  Our modeling work predicted that the winter rye cover crop has a neutral effect on maize and soybean yields over the 45 year simulation period but that a warmer climate decreased yields by 1.6%-2.7% by decade.  Soil carbon decreased in both the cover crop and no cover crop simulations, although the cover crop is able to significantly offset (3% less loss) this decline compared to the no cover crop simulation.  Our predictions showed that the cover crop led to an 11-29% reduction in erosion and up to a 34% decrease in nitrous oxide emissions (N₂O).  Although the cover crop is predicted to reduce erosion losses and decrease N₂O emissions compared to having no cover crop, the cover crop is unable to offset future predicted yield declines and does not increase the overall carbon balance relative to current soil conditions.  This research illustrates that it will be challenging to develop cropping systems that can mitigate multiple climate change impacts.