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The USDA Annualized Agricultural Non-Point Source Pollution model (AnnAGNPS) has been developed to aid in the evaluation of watershed response to agricultural management practices. The main purpose of this paper is to introduce AnnAGNPS P component and test the performance of AnnAGNPS on P loading using comparisons with measurements from the Deep Hollow watershed of the Mississippi Delta Management Systems Evaluation Area (MDMSEA) project. Previous studies by Yuan et al. have demonstrated the capability of the model to simulate runoff and sediment. From sensitivity analyses in this study, parameters on initial P concentration in the soil and crop P uptake had the most impact on the P loadings. AnnAGNPS over-predicted the dissolved P loss (121%) and under-predicted the sediment attached P loss (64%) over four year period of simulation. AnnAGNPS simulations of monthly dissolved P and sediment attached P do not agree well with observed respectively because of the simplification of P processes during modeling and uncertainties in choosing input parameters. However, statistical test (t-Test) showed that the predicted monthly dissolved P loading is not significantly different from observed monthly dissolved P at the 95% level of confidence (the same as sediment attached). AnnAGNPS simulation of monthly total P was reasonable to the observed total P (R-square of 0.81 and slope of 0.71).