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The Hybrid-Maize model (Yang et al, 2004), which has been validated under optimal water conditions, was evaluated for its ability to simulate soil moisture dynamics in the root zone and effects of water deficits on maize development and final yields (Fig. 1). The experimental data for this evaluation were obtained from ongoing field studies of the Carbon Sequestration Program (CSP) at the University of Nebraska. The studies include three cropping systems, each located in a quarter-section field (57 ha), two of which are irrigated by central-pivots and the third is rainfed. One irrigated field is in continuous maize and the other two are maize-soybean rotation. In each field, detailed micro-meteorological measurements were made, and soil moisture is continuously monitored at 10, 25, 50 and 100cm depths year around. Maize crop phenological development, leaf area expansion and aboveground biomass were measured nine times each growing season from 2001-2003, and final grain yield and stover biomass were measured at physiological maturity.