Selection of a water-extractable phosphorus test for manures and biosolids as an indicator of runoff loss potential.
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.
Kleinman
Peter
P
USDA-ARS, Pasture Systems and Watershed Management Research Unit, University Park, PA 16802, USA. Peter.Kleinman@ars.usda.gov
Sullivan
Dan
D
Wolf
Ann
A
Brandt
Robin
R
Dou
Zhengxia
Z
Elliott
Herschel
H
Kovar
John
J
Leytem
April
A
Maguire
Rory
R
Moore
Philip
P
Saporito
Lou
L
Sharpley
Andrew
A
Shober
Amy
A
Sims
Tom
T
Toth
John
J
Toor
Gurpal
G
Zhang
Hailin
H
Zhang
Tiequan
T
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
D008372:Manure; D014867:Water; D010758:Phosphorus