Soil water content varies spatially across fields, and the discontinuity of soil water contents in the vegetated surface can cause mesoscale features involving with triggering and development of convective clouds, and boundary layer growth. However, it is very difficult to predict the soil water balance components, such as soil water content, subsurface tile drainage, evaporation and so on, especially in the real Midwest crop field.
A hydrologic model has been incorporated into a recent version of the crop growth and development (CROPGRO-soybean) model. The coupled model is calibrated and validated using four years of data from the Water Quality Research site in northern Iowa. The data consisted of measurements of soil water contents at different depths and times, and cumulative monthly subsurface tile drainage from 36 different 0.41 ha plots that were individually tile drained. The results indicate that predicted soil water contents and subsurface tile drainage matched measured values very well over all years for these two soil types. We also give the results of the evaportranspiration and soil evaporation during these four years. The results of this study show that the modified CROPGRO model with coupling the hydrologic model does a very good job in simulating soil water movement and water dynamics in the Midwest crop field.