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Using a Phosphorus Loss Model to Evaluate and Improve Phosphorus Indices
- Bolster, Carl H., Vadas, Peter A., Sharpley, Andrew N., Lory, John A.
- Journal of Environmental Quality 2012 v.41 pp. 1758
- agricultural land, agricultural management models, losses from soil, nonpoint source pollution, phosphorus, risk
- In most states, the phosphorus (P) index (PI) is the adopted strategy for assessing a fi eld’s vulnerability to P loss; however, many state PIs have not been rigorously evaluated against measured P loss data to determine how well the PI assigns P loss risk—a major reason being the lack of fi eld data available for such an analysis. Given the lack of P loss data available for PI evaluation, our goal was to demonstrate how a P loss model can be used to evaluate and revise a PI using the Pennsylvania (PA) PI as an example. Our fi rst objective was to compare two diff erent formulations—multiplicative and component—for calculating a PI. Our second objective was to evaluate whether output from a P loss model can be used to improve PI weighting by calculating weights for modifi ed versions of the PA PI from model-generated P loss data. Our results indicate that several potential limitations exist with the original multiplicative index formulation and that a component formulation is more consistent with how P loss is calculated with P loss models and generally provides more accurate estimates of P loss. Moreover, using the PI weights calculated from the model-generated data noticeably improved the correlation between PI values and a large and diverse measured P loss data set. Th e approach we use here can be used with any P loss model and PI and thus can serve as a guide to assist states in evaluating and modifying their PI.