title: Phosphorus indices: why we need to take stock of how we are doing.
abstract: 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.
authors.affiliation: Department of Crop, Soli and Environmental Sciences, University of Arkansas, Fayetteville, AR, USA. sharpley@uark.edu
authors.forename: Andrew
authors.initials: A
authors.lastname: Sharpley
authors.forename: Doug
authors.initials: D
authors.lastname: Beegle
authors.forename: Carl
authors.initials: C
authors.lastname: Bolster
authors.forename: Laura
authors.initials: L
authors.lastname: Good
authors.forename: Brad
authors.initials: B
authors.lastname: Joern
authors.forename: Quirine
authors.initials: Q
authors.lastname: Ketterings
authors.forename: John
authors.initials: J
authors.lastname: Lory
authors.forename: Rob
authors.initials: R
authors.lastname: Mikkelsen
authors.forename: Deanna
authors.initials: D
authors.lastname: Osmond
authors.forename: Peter
authors.initials: P
authors.lastname: Vadas
mesh_terms: D003247:Conservation of Natural Resources; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods*; D004785:Environmental Pollutants / Q000737:chemistry*; D055593:Geological Phenomena; D010758:Phosphorus / Q000737:chemistry*; D012307:Risk Factors; D012987:Soil / Q000737:chemistry; D014867:Water / Q000737:chemistry; D014872:Water Movements
chemical_list: D004785:Environmental Pollutants; D012987:Soil; D014867:Water; D010758:Phosphorus