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Crop yield-is affected by many factors, primarily encompassing soil and weather conditions,and-crop management practices. Crop modeling can. be used to help understand how multiple factors interact and impact yield. The CROPGRO modeling package has been used extensively to assess the effects of management practices arid environmental conditions on soybean growth and development. However, the model has not been thoroughly evaluated for some environments that have unique characteristics such as claypan soils in which the depth to the claypan horizon-can vary greatly within fields. The objectives of this-study were to evaluate the performance of the CROPGRO-Soybean model for simulating-site-specific crop growth, soil water content, and grain yield on claypan soils. Data were obtained during low. and average rainfall conditions from two sites over 3 years in central Missouri. Plant (e.g. yield, leaf area, root length density) and soil (e.g. topsoil thickness, moisture, texture) measurements were collected for calibrating and validating the model. Results indicated-that CROPGRO-simulated soil water contents in the 15-90 cm soil profile agreed well with measured values. Simulated leaf area index and grain yield also agreed well with measured values during-average precipitation years; but were under-estimated during extremely dry years. Within-season precipitation and claypan soil topsoil depth were shown to have greatest influence on soybean yield. Although we hypothesized it to be otherwise, field measurements in 1997 showed that the claypan did not negatively affect soybean root penetration. (C) 2002 Elsevier Science Ltd. All rights reserved.