title: Using a phosphorus loss model to evaluate and improve phosphorus indices.
abstract: In most states, the phosphorus (P) index (PI) is the adopted strategy for assessing a field'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 field 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 first objective was to compare two different 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 modified 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. The 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.
authors.affiliation: USDA-ARS, Bowling Green, KY, USA. carl.bolster@ars.usda.gov
authors.forename: Carl H
authors.initials: CH
authors.lastname: Bolster
authors.forename: Peter A
authors.initials: PA
authors.lastname: Vadas
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Sharpley
authors.forename: John A
authors.initials: JA
authors.lastname: Lory
mesh_terms: D000383:Agriculture; D003198:Computer Simulation; D004784:Environmental Monitoring / Q000379:methods*; D008962:Models, Theoretical; D009010:Monte Carlo Method; D010758:Phosphorus / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D014874:Water Pollutants, Chemical; D010758:Phosphorus