THE CONCEPT AND NEED FOR A PHOSPHORUS ASSESSMENT-TOOL

Nonpoint sources of P leaving the agricultural landscape can cause eutrophication of surface water and the associated growth of undesirable aquatic plants. USDA is developing an indexing procedure for identifying soils, landforms, and management practices that could have unfavorable impacts on water bodies because of P movement. This indexing procedure uses the characteristic of the field site, including soil erosion rates, runoff, available P soil test levels, and fertilizer and organic P application rates and methods to assess the degree of vulnerability of P movement from the site. A weighting procedure has been developed to include the various contributions each site characteristic may have. A summation of the products of the weighted site characteristic yields a site vulnerability rating. An assessment tool using the Phosphorus Index will assist field staff working with landusers to identify sensitive areas and recommend management alternatives to reduce risk of P losses.