Incorporation of a Subsurface Tile Drainage Component Into a Soybean Growth Model

A simple tile drainage model was incorporated into a recent version of the CROPGRO-soybean model. Themodel was calibrated and validated using four years of data from the Water Quality Research site, located at the IowaState University Northeast-Research Center near Nashua, Iowa having two soil types (Readlyn and Kenyon). The dataconsisted of measurements of soil water contents at different depths and times, cumulative monthly tile flow, and final cropyield from 36 different 0.41 ha plots that were individually tile drained. The model was calibrated to give the best fitbetween the predicted and measured tile flow, soil water content, and crop yield from 1993 and 1994 for each soil type. Itwas validated by using data from 1995 and 1996 for each soil type. Predicted soil water contents, tile drainage andsoybean yield matched measured values very well over all years for these two soil types. The results of this study showthat the modified CROPGRO model does a very good job in simulating soybean yields and water dynamics for Readlynand Kenyon soil in the experiment.