PHOSPHORUS COMPONENT IN ANNAGNPS

Abstract

The USDA Annualized Agricultural Non-Point Source Pollution model (AnnAGNPS) has been developed to aidin evaluation of watershed response to agricultural management practices. Previous studies have demonstrated the capabilityof the model to simulate runoff and sediment, but not phosphorus (P). The main purpose of this article is to evaluate theperformance of AnnAGNPS on P simulation using comparisons with measurements from the Deep Hollow watershed of theMississippi Delta Management Systems Evaluation Area (MDMSEA) project. A sensitivity analysis was performed to identifyinput parameters whose impact is the greatest on P yields. Sensitivity analysis results indicate that the most sensitive variablesof those selected are initial soil P contents, P application rate, and plant P uptake. AnnAGNPS simulations of dissolved Pyield do not agree well with observed dissolved P yield (Nash-Sutcliffe coefficient of efficiency of 0.34, R2 of 0.51, and slopeof 0.24); however, AnnAGNPS simulations of total P yield agree well with observed total P yield (Nash-Sutcliffe coefficientof efficiency of 0.85, R2 of 0.88, and slope of 0.83). The difference in dissolved P yield may be attributed to limitations in modelsimulation of P processes. Uncertainties in input parameter selections also affect the models performance.