Sub-field Variability of Nitrate Leaching in the Midwest: A Process Based Crop Simulation Approach

Abstract:

Given economic and environmental concerns regarding nitrate loss and pollution, it is important to improve our understanding of nitrate leaching and its relationship to climatic variability. One of the challenges in simulating nitrate leaching in agricultural fields across a region is the noted spatial and temporal variability in nitrogen cycling and crop yield at the sub-field scale. Using a process-based crop model (System Approach to Land Use Sustainability [SALUS]), gridded soil, gridded meteorological data, and a stability zone concept, calibrated on multiple years of crop monitor data, management data, remotely sensed imagery, in-situ soil, and plant samples across the Midwest, we simulated 41 years (1979-2019) of continuous maize production in 12 Midwestern states at the sub-field scale. Four zones based on multi-year yield stability were simulated for each field at ~30m x 30m resolution. Outputs were evaluated using a nitrogen balance approach to establish zone-specific statistical distributions of nitrate leaching across the 12 states, specifically highlighting periods with highly variable precipitation. Preliminary results indicate that low stable yield zones are associated with an outsized contribution to nitrate leaching and that unstable zones exhibit variable year-to-year response tied to their position in the landscape. Ultimately, the results from these simulations can be used to modify long-term precision management plans for individual agricultural fields and could be a useful tool for increasing agricultural sustainability through the upscaling of traditional point-based crop model simulations.