Nitrogen leaching sensitivity to evapotranspiration and soil water storage estimates in EPIC

ABSTRACT:

Two major influences on the soil water balance—potential evapotranspiration, and soil water storage capacity—are estimated in the Erosion/Productivity Impact Calculator (EPIC) model based upon soil and weather conditions. The EPIC model contains a choice of five methods to estimate potential evapotranspiration (Penman-Monteith, Penman, Priestley-Taylol, Hargreaves and Modified Hargreaves). There are four methods for estimating soil water storage capacity (Ritchie, Rawls, Baumer, and Manrique). Combinations of methods of estimating these two variables were used to determine if water and nitrogen percolation loss estimates varied with the method selected. Simulations were performed for five locations throughout the United States to determine differences due to climate and soils. Consistent differences in water percolation and N leaching occurred within a given location with different potential evapotranspiration and soil water storage capacity models. Across locations, however, percolation and N leaching usually varied more with local weather and soil conditions than among estimation methods. Care should be taken to select the most appropriate models for a given location if more than relative results are needed.