Submitted to: Kentucky Water Resources Research Institute Symposium
Publication Type: Proceedings
Publication Acceptance Date: 2/12/2013
Publication Date: 3/18/2013
Citation: Bolster, C.H., Mehlhope, S., Horvath, T., Delgado, J.A., Higgins, S.F., Coffey, R.D., Coleman, S., Goodman, P., Lee, B., Renfro, C., Ritchey, E.L. 2013. Development and testing of a new phosphorus index for Kentucky. Kentucky Water Resources Research Institute Symposium. Abstract. Interpretive Summary:
Technical Abstract: The phosphorus index (PI) is a tool developed by USDA-NRCS to evaluate a field’s risk of P loss and has been adopted by most states, including KY, in their 590 Nutrient Management Standard. USDA-NRCS recently revised their 590 Standard, now requiring that states test the accuracy of their PI against measured P loss data or simulated P loss data generated from a P loss model. A recent study comparing output from the KY PI to output from an empirically-based P loss model highlighted several important deficiencies with the existing KY PI. To address these limitations, a committee consisting of scientists from federal, state, and local government agencies was formed to formulate a new PI for KY. Significant modifications to the KY PI include treating runoff as a continuous variable, development of county-specific relationships between curve number and runoff, inclusion of P application rates from both fertilizer and applied manures, and directly accounting for P loss through soil erosion. A good correlation (r2 = 0.76) between the updated KY PI and the observed P loss data was observed. Although output from the new KY PI was well correlated with P runoff data collected from a variety of sites through the U.S., the new PI still needs to be evaluated against P loss data collected in KY. To make it easier to use, the new PI was integrated into an existing GUI developed for a nitrogen index.