title: Selection of a water-extractable phosphorus test for manures and biosolids as an indicator of runoff loss potential.
abstract: The correlation of runoff phosphorus (P) with water-extractable phosphorus (WEP) in land-applied manures and biosolids has spurred wide use of WEP as a water quality indicator. Land managers, planners, and researchers need a common WEP protocol to consistently use WEP in nutrient management. Our objectives were to (i) identify a common WEP protocol with sufficient accuracy and precision to be adopted by commercial testing laboratories and (ii) confirm that the common protocol is a reliable index of runoff P. Ten laboratories across North America evaluated alternative protocols with an array of manure and biosolids samples. A single laboratory analyzed all samples and conducted a separate runoff study with the manures and biosolids. Extraction ratio (solution:solids) was the most important factor affecting WEP, with WEP increasing from 10:1 to 100:1 and increasing from 100:1 to 200:1. When WEP was measured by a single laboratory, correlations with runoff P from packed soil boxes amended with manure and biosolids ranged from 0.79 to 0.92 across all protocol combinations (extraction ratio, filtration method, and P determination method). Correlations with P in runoff were slightly lower but significant when WEP was measured by the 10 labs (r=0.56-0.86). Based on laboratory repeatability and water quality evaluation criteria, we recommend the following common protocol: 100:1 extraction ratio; 1-h shaking and centrifuge 10 min at 1500xg (filter with Whatman #1 paper if necessary); and determining P by inductively coupled plasma-atomic emission spectrometry or colorimetric methods.
authors.affiliation: USDA-ARS, Pasture Systems and Watershed Management Research Unit, University Park, PA 16802, USA. Peter.Kleinman@ars.usda.gov
authors.forename: Peter
authors.initials: P
authors.lastname: Kleinman
authors.forename: Dan
authors.initials: D
authors.lastname: Sullivan
authors.forename: Ann
authors.initials: A
authors.lastname: Wolf
authors.forename: Robin
authors.initials: R
authors.lastname: Brandt
authors.forename: Zhengxia
authors.initials: Z
authors.lastname: Dou
authors.forename: Herschel
authors.initials: H
authors.lastname: Elliott
authors.forename: John
authors.initials: J
authors.lastname: Kovar
authors.forename: April
authors.initials: A
authors.lastname: Leytem
authors.forename: Rory
authors.initials: R
authors.lastname: Maguire
authors.forename: Philip
authors.initials: P
authors.lastname: Moore
authors.forename: Lou
authors.initials: L
authors.lastname: Saporito
authors.forename: Andrew
authors.initials: A
authors.lastname: Sharpley
authors.forename: Amy
authors.initials: A
authors.lastname: Shober
authors.forename: Tom
authors.initials: T
authors.lastname: Sims
authors.forename: John
authors.initials: J
authors.lastname: Toth
authors.forename: Gurpal
authors.initials: G
authors.lastname: Toor
authors.forename: Hailin
authors.initials: H
authors.lastname: Zhang
authors.forename: Tiequan
authors.initials: T
authors.lastname: Zhang
mesh_terms: D000383:Agriculture; D000818:Animals; D003247:Conservation of Natural Resources; D004784:Environmental Monitoring / Q000379:methods*; D008372:Manure / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis* / Q000302:isolation & purification; D011891:Rain; D014867:Water / Q000737:chemistry*; D014876:Water Pollution / Q000517:prevention & control
chemical_list: D008372:Manure; D014867:Water; D010758:Phosphorus