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The Virginia Phosphorus Index (P-Index) is a management tool for assessing risk of P delivery to surface waters. The P-Index considers the interaction of source and transport factors to estimate the average annual risk of P delivery to water bodies. Source factors include residual P in the soil and P applied via fertilization. Transport factors include edge-of-field soil loss, annual runoff, sediment and runoff delivery factors, annual percolation, and a soil texture/drainage factor. The risk of each of the three components of delivery, i.e., erosion, runoff, and subsurface, is computed separately and then combined to yield the overall risk for a field. The P-Index can be used to identify practices to reduce the potential for P losses from agricultural fields.