Current maize simulation models (CORNF and CERES-Maize) are "source-oriented", in which kernel weight is predicted without simulating sink demand of the kernels. The major goal of this research is to develop a physiologically sound model to simulate vegetative and reproductive growth of maize;The objectives of this study are: (1) to develop a subroutine to predict maize vegetative development; (2) to develop mechanisms to calculate silk growth, fertilization of the silk, and kernel set; (3) to address some of the problems that CENTLI has and use it to simulate grain filling period; (4) to develop a mechanism to predict the impact of both temperature and water stresses on maize growth and development; (5) to test the physiological implication of the developed model;Maize-S was validated against field data collected from two locations in Iowa in 1995 and 1996 for two maize hybrids planted at two different planting dates were used. To evaluate accuracy of predictions, the mean root square error and percent error averaged over time were calculated for both Maize-S and CERES-Maize;Maize-S predictions for leaf and stem weight were more accurate than CERES-Maize. CERES-Maize predictions for kernel number were more accurate than Maize-S predictions in four locations. This might be attributed to the method that CERES-Maize uses to calculate kernel number, wherein a stress factor is used to reduce kernel number. Maize-S does not account for any stress during kernel set. CERES-Maize predictions for kernel number were more accurate than Maize-S at two locations;Sensitivity analysis using Maize-S with conditions of +5 or -5°C from observed air temperatures reveals major changes in plant behavior. Maize-S output shows that high temperature cause silking to occur earlier than normal with an average of 3.2 days for each 1°C increase in temperature. A reduction in leaf area, aboveground nongrain and grain weights were also observed. Whereas cool temperature prolongs the growing season, and consequently increasing both aboveground nongrain and grain weights and leaf area;Sensitivity analysis using Maize-S with the condition of 5% increase in solar radiation did not affect number of days to silking, but increase the number of days to maturity by an average of 6 days. Aboveground nongrain and grain weights were also increased, whereas leaf area was not affected;Furthermore, Maize-S output shows that when defoliation occurs on weekly intervals after silking up to three weeks reduced kernel yield, weight per kernel, and kernel number;Further improvement in estimating water stress is recommended. Other improvements would be the capability to simulate prolificacy, and the estimation of nitrogen stress effects on yield.