Determining phosphorus runoff from cropland just got easier, based on an updated version of the Nebraska Phosphorus Index (NPI).

That's good news because fields designated under concentrated feeding operation (CAFO) regulations as sites where manure is to be applied need to be assessed for the potential of phosphorus loss in runoff and erosion, says Charlie Wortmann, University of Nebraska nutrient management specialist. After Jan. 1, this assessment needs to be made with a phosphorus index before any manure can be applied to the field, he adds.

"Most information needed to assess a field with a phosphorus index is easily available to a producer," Wortmann says. "However, the estimate of sheet and rill erosion is the most important information and relatively difficult to determine."

The NPI has a build-in calculator for estimating sheet and rill erosion. The erosion calculator, developed by UNL in cooperation with NRCS, does not require any additional information than that needed for the previous version of the phosphorus index, according to Wortmann. When estimating erosion loss, it accounts for soil type, slope, rainfall, land use and crop rotation, tillage crop yield and conservation practice. It is calibrated against USDA’s RUSLE2 erosion calculator.

The new NPI version is free and can be downloaded at cnmp.unl.edu. Background information and instructions for its use also are available.