Phosphorus Indexes: A Comparison of PI Results with the USDA-ARS Aple Model.

Nitrogen (N), phosphorus (P) and sediment losses from fields to freshwater ecosystems is a well-documented challenge for agricultural producers. Most states use some version of a phosphorus index (PI) to assess P and sediment loss risk, but the algorithms, objectives and associated PI ratings for these first generation risk assessment tools vary widely from one state to the next. We compared PI ratings and associated P management strategies in nutrient management plans from 38 states to the mass of P loss calculated using the USDA-ARS annual phosphorus loss estimator (APLE). We will present the results of these comparisons and suggest a framework to improve P and sediment loss risk assessment for the next generation of PI tools that will be needed as watershed-based total maximum daily loads (TMDLs) become more widely adopted.