Selection of a water-extractable phosphorus test for manures and biosolids as an indicator of runoff loss potential

Peter Kleinman, Dan Sullivan, Ann Wolf, Robin Brandt, Zhengxia Dou, Herschel Elliott, John Kovar, April Leytem, Rory Maguire, Philip Moore, Lou Saporito, Andrew Sharpley, Amy Shober, Tom Sims, John Toth, Gurpal Toor, Hailin Zhang, Tiequan Zhang

Research output: Contribution to journalArticlepeer-review

91 Scopus citations


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 1500 x g (filter with Whatman #1 paper if necessary); and determining P by inductively coupled plasma-atomic emission spectrometry or colorimetric methods.

Original languageEnglish (US)
Pages (from-to)1357-1367
Number of pages11
JournalJournal of Environmental Quality
Issue number5
StatePublished - Sep 2007

All Science Journal Classification (ASJC) codes

  • Environmental Engineering
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution
  • Management, Monitoring, Policy and Law


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