In this study, the CERES-Maize crop model was used in conjunction with Apollo, a shell program, to evaluate potential improved yield in a central Iowa cornfield on a spatially and temporally variable basis. Five years of historical yield and weather data were used to calibrate the model over 100 spatially variable grid cells for non-irrigated conditions in the 20.25 ha field. This calibrated model then used 28 years of historical weather data to simulate three irrigation scenarios: no irrigation, scheduled uniform irrigation, and precision irrigation. Irrigation improved yield by at least 500 kg ha⁻¹ in half of the years simulated. Precision irrigation showed slightly lower yields than scheduled uniform irrigation. Assuming use of a center pivot system, irrigation showed economic returns in only one of the 28 years included in the study. High capital costs were the leading restrictor of economic feasibility.