Managing Global Resources for a Secure Future

Maintaining the balance between providing enough nitrogen (N) to crops while avoiding its environmental loss has proven difficult despite significant field research and modeling efforts. To inform nutrient loss reduction strategies that are being implemented in corn production systems of the US Midwest, information is needed on early-season soil N availability in response to different weather patterns and N fertilizer management scenarios. The objectives of this geospatial assessment were to i) evaluate the risk of early-season N losses, defined here as in-season soil N disappearance due to crop uptake and environmental N losses (leaching, denitrification, ammonia volatilization), and ii) develop watershed scale N management zones where split N applications are most effective in 1) reducing N losses only and 2) both in reducing N losses and increasing crop uptake. We applied a calibrated DSSAT model across 3000 field data points in Illinois during 2011–2016 using three N fertilizer management strategies: 200-S (200 kg N ha^-1 applied 2 weeks before planting), 200-Split1 (150 kg N ha^-1 applied 2 weeks before planting + 50 kg N ha^-1 side-dressed on June 1), 200-Split2 (50 kg N ha^-1 applied 2 weeks before planting + 150 kg N ha^-1 side-dressed on June 1). The results were aggregated to 53 watersheds (HUC-8). Our presentation will focus on identifying spatial hotspots with a high risk of soil N disappearance for the three different N timing treatments, and developing an early spring rainfall threshold for maintaining low N losses across soil types in Illinois.