Phosphorus indices: why we need to take stock of how we are doing

J Environ Qual. Nov-Dec 2012;41(6):1711-9. doi: 10.2134/jeq2012.0040.


Many states have invested significant resources to identify components of their Phosphorus (P) Index that reliably estimate the relative risk of P loss and incentivize conservation management. However, differences in management recommendations and manure application guidelines for similar field conditions among state P Indices, coupled with minimal reductions in the extent of P-impaired surface waters and soil test P (STP) levels, led the U.S. Natural Resources Conservation Service (NRCS) to revise the 590 Nutrient Management Standard. In preparation for this revision, NRCS requested that a review of the scientific underpinnings and accuracy of current P Indices be undertaken. They also sought to standardize the interpretation and management implications of P Indices, including establishment of ratings above which P applications should be curtailed. Although some states have initiated STP thresholds above which no application of P is allowed, STP alone cannot define a site's risk of P loss. Phosphorus Indices are intended to account for all of the major factors leading to P loss. A rigorous evaluation of P Indices is needed to determine if they are directionally and magnitudinally correct. Although use of observed P loss data under various management scenarios is ideal, such data are spatially and temporally limited. Alternatively, the use of a locally validated water quality model that has been shown to provide accurate estimates of P loss may be the most expedient option to conduct Index assessments in the short time required by the newly revised 590 Standard.

MeSH terms

  • Conservation of Natural Resources
  • Ecosystem
  • Environmental Monitoring / methods*
  • Environmental Pollutants / chemistry*
  • Geological Phenomena
  • Phosphorus / chemistry*
  • Risk Factors
  • Soil / chemistry
  • Water / chemistry
  • Water Movements


  • Environmental Pollutants
  • Soil
  • Water
  • Phosphorus