Using a phosphorus loss model to evaluate and improve phosphorus indices

J Environ Qual. Nov-Dec 2012;41(6):1758-66. doi: 10.2134/jeq2011.0457.


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.

MeSH terms

  • Agriculture
  • Computer Simulation
  • Environmental Monitoring / methods*
  • Models, Theoretical*
  • Monte Carlo Method
  • Phosphorus / chemistry*
  • Water Pollutants, Chemical / chemistry*


  • Water Pollutants, Chemical
  • Phosphorus