Climate-smart agriculture in Midwest cropping systems: evaluating the benefits and tradeoffs of cover crops
Climate-smart agriculture is a framework to develop and implement agricultural systems that facilitate reduced greenhouse gas emissions and increase resilience and productivity in the context of a changing climate. Winter cover crops are known to decrease soil erosion, increase soil carbon, improve water retention and have been hypothesized to reduce nitrous oxide emissions. Therefore they offer the potential to buffer projected climate change impacts for Midwestern agriculture, including increased rainfall variability. The overall objective of this dissertation research was to evaluate the mitigation and adaptation potential of cover crops in determining their efficacy as a climate-smart agricultural practice. In a global meta-analysis, it was found that cover crops do not universally reduce nitrous oxide emissions from the soil surface but that grass species and chemical termination methods are less likely to increase emissions. An analysis of seven years of crop and soil data found that the long-term use of a winter rye cover crop in a no-till maize-soybean rotation improved water retained in the soil profile and increased plant available water content by 21-22%, without sacrificing maize or soybean growth and yields. Finally, the simulation of a winter rye cover crop in a future climate predicted the practice’s ability to reduce nitrous oxide emissions by up to 34%, offset soil carbon decline by 3% and decrease erosion losses by 11-29% without significantly impacting maize or soybean yields. However, the cover crop is not predicted to offset crop yield declines that may occur because of temperature and water stressors. Taken together, this research illustrates that in the context of climate adaptation and mitigation, the greatest potential benefits from a winter rye cover crop in this region are preventing soil erosion, improving soil water retention, and potentially reducing nitrous oxide emissions from the soil surface.