Methodology to link production and environmental risks of precision nitrogen management strategies in corn

A new decision support system called Apollo, which runs the CERES-Maize crop growth model, was used to study the corn (Zea mays L.) yield response and the nitrogen (N) dynamics of a cornfield in central Iowa, USA. The model was calibrated to minimize error between simulated and measured yield over five growing seasons. Model simulations were then completed for 13 spring-applied N rates in each of 100 grid cells with varying soil properties. For each N rate and grid cell, simulations were repeated for 37 years of historical weather information collected near the study site. Model runs provided the crop yield and unused N in the soil at harvest for all combinations of N rate, grid cell, and weather year. Using these simulated datasets, a methodology involving cumulative probability distributions was developed such that the yield and unused N resulting from each N rate applied in each grid cell could be directly linked according to their probability of occurrence over the 37 simulated growing seasons. These cumulative probability distributions were used to evaluate the economic and environmental risks of two alternate precision N management strategies for the study area. In the first strategy, N rates were selected to maximize the producer's marginal net return in each grid cell. The environmental cost of this management strategy, in terms of N left behind, was determined to be 56.2 kg ha−1 on average over all grid cells. In the second strategy, N rates were selected to insure that the amount of N left in the soil at harvest would not exceed 40 kg ha−1 in 80% of growing seasons. The producer's opportunity cost for reducing N rates to achieve this environmental objective was calculated to be $48.12 ha−1 on average over all grid cells. The overall goal of this work was to develop a methodology for directly contrasting the production and environmental concerns of N management in agricultural systems. In this way, N management plans can be designed to achieve a proper balance between production and environmental goals.