Effects of fertilizer timing and variable rate N on nitrate-N losses from a tile drained corn-soybean rotation simulated using DRAINMOD-NII

摘要

Nitrogen (N) from farm fields is a source of pollution to fresh and marine waters. Modifying N fertilizer application rate and timing to consider the spatial and temporal variability in plant N requirements could reduce N losses from farmlands, resulting in improvements to surface water quality. In this study, the field-scale hydrologic and N simulation model DRAINMOD-NII was used to predict nitrate-N losses from fields planted in a corn-soybean rotation at Waseca, Minnesota, USA, over a 15-year period (2003-2017) for two fertilizer application treatments. The N fertilizer treatments simulated included a single uniform fertilizer application in the spring before planting and a variable rate N practice (VRN) where fertilizer was applied as a split pre-plant, side-dress application, based on in-season monitoring of plant N requirements to determine fertilizer rate. Measured discharge (2003-2008) and nitrate-N concentrations in subsurface drainage (2003-2008 and 2016-2017) at the site were used to calibrate discharge and nitrate-N losses in model simulations and validate model performance for uniform vs VRN fertilizer management. Measured nitrate-N concentrations in weekly samples were 13% lower for fields utilizing VRN versus a single spring application in 2016, and 18% lower in 2017. Model predictions of nitrate concentrations based on daily predictions of discharge accurately matched observed data for these years, predicting reductions of 23% and 19% for the years 2016 and 2017, respectively. The results of model simulation for the 15-year period indicated that changing the timing of fertilizer application from a single application to a VRN application could reduce annual N loads lost in drainage by 40%.