Tuesday, November 14, 2006

Modelling Phosphorus Transport Using the Wepp Model.

Mario Perez-Bidegain, Matthew Helmers, and Richard Cruse. Iowa State Univ, 209 Davidson Hall, Ames, IA 50011-1010

Phosphorus (P) is required to maintain plant growth and optimize crop yields. The agronomic benefit of P applications to achieve optimum plant performance is well documented. Raising P concentration in soil also increases the potential transfer of this nutrient to soil solution and eventually to surface water. This could affect the use of surface water for recreation, drinking, and wildlife. Determining the critical soil P level that optimize both crop production and water quality for a given location and land form is critical as evidenced by recent legislative actions. Empirically determining optimum soil P concentrations for a large range of combinations involving crops, tillage, soil slopes, soil types, and distance from surface water bodies is not feasible. The use of a model to evaluate different land use management practices and their effects on on-site and off –site resources is necessary. The Water Erosion Prediction model (WEPP) is a physical based, daily, continuous simulation model for predicting runoff and soil erosion from fields and small watersheds. WEPP has been widely tested for its ability to predict soil erosion, runoff and sediment delivery over a very wide range of conditions and scales for both hillslopes and watersheds. The objective of this work is present a WEPP phosphorus loss model component to simulate phosphorus transport at the watershed scale.  Algorithms are developed based on current input parameters required for WEPP and soil and water runoff parameters known to influence nutrient phosphorus concentration in sediments and runoff water. The phosphorus transport model is tested in a corn-soybean rotation and meadow for Central Iowa.