The Wisconsin Phosphorus Index (P Index) is a planning and assessment tool for managing runoff phosphorus losses from cropland. It uses information that is readily available to farmers and agricultural consultants to evaluate the potential for phosphorus in runoff from a specific field entering a nearby stream or lake. The P Index is used in nutrient management planning. It is also being used as a targeting and assessment tool for water quality projects in Wisconsin.
The P Index is calculated by estimating average runoff P delivery from each field to the nearest surface water in a year given the field’s soil conditions, crops, tillage, manure and fertilizer applications, and long-term weather patterns. It is reported as a whole number – the higher the number, the greater the likelihood that that field is contributing P to local water bodies.
The equations for the P Index have been tested with monitoring date for Wisconsin: Testing the Wisconsin P Index at the Field Scale
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