Evaluating management zone optimal nitrogen rates with a crop growth model

Determining MZ (management zone)-specific optimal N rate is a challenge in precision crop management. The objective of this study was to evaluate the potential of applying a crop growth model to simulate corn (Zea mays L.) yield at various N levels in different MZs and estimate optimal N rates based on long-term weather conditions. Three years of corn yield data were used to calibrate a modified version of the CERES-Maize (Version 3.5) model for a commercial field previously divided into four MZs in eastern Illinois. The model performance in simulating corn yield for two hybrids (33G26 and 33J24) at five N levels in two independent years was evaluated. Economically optimum N rates (EONRs) were estimated based on 15 yr of simulation (1989-2003). The model explained approximately 59 and 93% of yield variability during calibration and validation, respectively. The model performed well at non-zero N rates, with most of the simulation errors being <10%. Model-estimated EONR varied from 70 to 250 kg ha^-1. Economic analyses indicated that applying N fertilizer at year-, hybrid-, and MZ-specific EONR had the potential to increase net return by an average of US$49 (33G26) or US$52 (33J24) ha^-1 over a URN (uniform rate N) application at 170 kg ha ^-1. Applying average hybrid- and MZ-specific EONRs across years did not consistently improve economic returns over URN application; however, applying the hybrid- and MZ-specific N rates that maximized long-term net returns would improve economic return by an average of US$22 (33G26) and US$14 (33J24) ha^-1.