A combined crop growth (SOYGRO 5.4) and water management (DRAINMOD 3.4) modeling system was developed using an expert system shell to coordinate input and output between the models. An iterative simulation procedure was used to keep the models intact and modular for inclusion of additional crop growth, pest, economic, and environmental impact models in the future. DRAINMOD 3.4 was modified to accept evapotranspiration and effective rooting depths from SOYGRO and allow feedback control. The feedback control system performed satisfactorily. SOYGRO 5.4 was enhanced to accept from DRAINMOD water movement due to upward flux from a water table. In addition, the model was modified to account for the crop stress due to oxygen deprivation caused by a water table extending into the rooting zone. Simulated soybean yields and root length densities were greatly affected by a raised water table and by climatic variations for the tested conditions. However, if the water table was maintained within 90 cm of the soil surface during the entire growing season, weather patterns had only a minor influence on root length densities and yield.