Model-based technique to determine variable rate nitrogen for corn

Past efforts to correlate yield from small field plots to soil type, elevat ion, fertility, and other factors have been only partially successful for c haracterizing spatial variability in corn (Zea mays L.) yield. Furthermore, methods to determine optimum nitrogen rate in grids across fields depend u pon the ability to accurately predict yield variability and corn response t o nitrogen. In this paper, we developed a technique to use the CERES-Maize crop growth model to characterize corn yield variability. The model was cal ibrated using 3 years of data from 224 grids in a 16 ha field near Boone, I A. The model gave excellent predictions of yield trends along transects in the field, explaining approximately 57% of the yield variability. Once the model was calibrated for each grid cell, optimum nitrogen rate to maximize net return was computed for each location using 22 years of historical weat her data. Results show high spatial distribution of optimum nitrogen fertil izer prescription for grids across the field. Grid-level nitrogen fertilize r management used lower amounts of fertilizer, produced higher yields and w as more profitable than either transect- or field-level (single rate) ferti lizer application. (C) 1999 Elsevier Science Ltd. All rights reserved.