The Phosphorus Index
The Phosphorus Index is a tool used to assess the potential for phosphorus (P) to move from agricultural fields to surface water. It uses an integrated approach that considers soil and landscape features as well as soil conservation and P management practices in individual fields. These characteristics include source factors such as soil test P; total soil P; rate, method, and timing of P application from commercial fertilizer, manure, and other organic sources; and erosion. Transport factors include sediment delivery, relative field location in the watershed, soil conservation practices, precipitation, runoff, and tile flow/subsurface drainage. Erosion, runoff and drainage factors for a site or field are used in a mathematical equation to determine whether the phosphorus movement risk is very low, low, medium, high or very high.