Assessing the impacts of different nitrogen application strategies on crop productivity and environmental sustainability in the U.S. Midwest

Improving nitrogen (N) fertilizer management strategies is urgently needed to meet the economic and environmental objectives in increasing nitrogen use efficiency and reducing nitrogen loss. To systematically evaluate impacts of different nitrogen application strategies on crop productivity and environmental sustainability in the U.S. Midwestern agroecosystem, we simulated crop yield and N losses (i.e. N leaching and N2O emissions) at seven continuous corn fields in Illinois during 2000-2008 with different N application strategies using an advanced process-based model, ecosys. Specifically, we did simulations for 15 different fertilizer application strategies at each field, including fall applications with or without nitrification inhibitors, spring application, and 12 side-dress applications. For the side-dress applications, we applied part of the total N fertilizer before planting (25%, 50%, and 75%), and applied the remaining fertilizer to the field at different growth stages ranging from V1 to R2 stages. We found that (1) applying fertilizer in fall had the lowest N use efficiency compared with spring and side-dress applications, and adding nitrification inhibitors in fall application can offset N losses and increase crop yield compared with fall application without nitrification inhibitors. (2) Side-dress at earlier growth stages (V1-V12 stages) with higher side-dress-to-total proportion of fertilizers had larger crop yield than side-dress at later growth stages and spring application, except in the extreme year (e.g. heat stress in summer). (3) Compared with spring application, side-dress applications can reduce N leaching in normal years, but may increase N leaching when side-dress is followed by heavy precipitation events, especially for side-dress at later growth stages. (4) N2O emissions of side-dress applications is larger compared with fall and spring applications, which is due to the higher air temperature and precipitation (resulting lower O2 content) during the side-dress period (June-August). Our findings provide useful insights to improve N fertilizer management in the U.S. Midwestern agroecosystems.