Improving SWAT Auto-Irrigation Functions for Simulating Irrigation Management Using Lysimeter Field Data.

The Texas High Plains is one of the most productive U.S. agricultural regions. However, decreasing groundwater availability has resulted in the adoption of limited irrigation strategies such as the management allowed depletion (MAD) concept of plant available water. Simulation models such as the Soil and Water Assessment Tool are a cost-effective and time saving method commonly used to evaluate best management practices and their effect on water balance. However, some studies have suggested that the irrigation algorithms in SWAT are inadequate for evaluation of representative irrigation practices. Consequently, auto-irrigation algorithms were developed based on a 1) single season MAD level and 2) growth stage-specific MAD levels for seasonal crop growth partitioning based on both scheduled date and accumulated heat units. Comparisons with observed data from an irrigated lysimeter field at the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas resulted in improved representation and simulation of irrigation.