Past eorts to correlate yield from small ®eld plots to soil type, elevation, fertility, and other factors have been only
partially successful for characterizing spatial variability in corn (Zea mays L.) yield. Furthermore, methods to determine
optimum nitrogen rate in grids across ®elds depend upon the ability to accurately predict yield variability and
corn response to nitrogen. In this paper, we developed a technique to use the CERES-Maize crop growth model to
characterize corn yield variability. The model was calibrated using 3 years of data from 224 grids in a 16 ha ®eld near
Boone, IA. The model gave excellent predictions of yield trends along transects in the ®eld, 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 weather data. Results show high spatial distribution
of optimum nitrogen fertilizer prescription for grids across the ®eld. Grid-level nitrogen fertilizer management used
lower amounts of fertilizer, produced higher yields and was more pro®table than either transect- or ®eld-level (single
rate) fertilizer application. # 1999 Elsevier Science Ltd. All rights reserved.