Extreme Precipitation Years Impact Soil N Loss in Mid-West Corn-Soybean Cropping System.

Nitrous oxide fluxes from agricultural croplands are prone to predicted severe precipitation pattern. However, these fluxes with changing precipitation pattern are not well estimated. Process based biogeochemical models that simulate soil C and N, can be used a tool to reliably estimate soil N₂O-N fluxes with changing precipitation pattern. DayCent is a process based ecosystem model that can be used to simulate C and N dynamics in soils. The objectives of this study were to validate DayCent and use this model to investigate the impact of extreme precipitation years on soil N (N₂O-N, NO₃^--N) loss in corn-soybean cropping system in the Midwest. To accomplish these objectives, we measured soil N₂O-N fluxes and NO₃^--N concentration over three years (2011-2013) in corn-soybean rotation with and without winter cereal rye cover crop with three N fertilizer rates (0 kg N ha^-1, the recommended rate of 135 kg N ha^-1, and a higher rate of 225 kg N ha^-1) applied to corn. Soybean received no fertilizer. DayCent model was used to predict soil N loss using three climate change precipitation scenarios for dry, normal, and wet years in corn-soybean rotation. The model reasonably approximated crop yield, soil N₂O-N fluxes, soil CO₂–C fluxes, soil temperature, soil moisture, and soil NO₃^--N. In the soybean phase of the crop rotation, yield scaled- N₂O-N fluxes decreased with cover crop and increased with higher N fertilizer rate. In the corn phase of the crop rotation, yield scaled- N₂O-N fluxes increased with cover crop and decreased with high N fertilizer treatments. The predicted N₂O-N fluxes increased from Dry to Normal year by 61-79%, Dry to Wet year by 83-104% and Normal to Wet year by 12-18%. The predicted NO₃^--N leaching increased from Dry to Normal year by 310-429%, Dry to Wet year by 708-1659% and Normal to Wet year by 97-232%. Cover crop significantly reduced yield-scaled- NO₃^--N leaching in both crops. These results reveal the importance of agricultural soil N loss in predicted severe climate changes.