Balancing water quality, nitrogen management, and corn production goals in Illinois

Abstract

Nitrogen (N) fertilizer inputs are required to maintain corn production in high-yielding cropping systems across much of the U.S. Midwest. However, applied N can also increase N losses through nitrate-nitrogen (NO3-N) leaching and nitrous oxide (N2O) emissions, negatively impacting water and air quality, respectively. Given these competing demands, there is a pressing need to develop new strategies for maintaining grain yields and economic returns while decreasing the risk of environmental N pollution. Therefore, the overall objectives of this dissertation research were to (i) evaluate the effectiveness of in-field recommended management practices for improving water quality while also assessing potential agronomic and environmental tradeoffs of those practices, and (ii) explore how process-based modeling tools could be used as an integrative approach for linking sustainability outcomes with improved agronomic efficiencies. Results from a 3-yr field experiment highlighted potential environmental tradeoffs between water and air quality when pairing in-season split N application with a cereal rye cover crop. Combining these two practices reduced NO3-N losses by 37% compared to pre-season N application alone, but soil N2O emissions also increased by 27%. Corn yields were not significantly affected by in-field management practices, indicating no agronomic tradeoffs. An analysis of 32 site-years of crop and soil data found that soil mineral N provided moderately good predictions for achieving optimum grain yields (R2 = 0.46 – 0.61). While increasing soil mineral N from deficiency to sufficiency levels increase corn yields by 22%, it also increased the probability of environmental N losses. Together, these results show that N fertilizer management and cover cropping can greatly impact production and sustainable goals. The delicate balance between productivity and environmental N losses illustrates the importance of incorporating multiple N loss pathways when developing sustainable in-field management strategies in the region.