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United States Department of Agriculture

Agricultural Research Service


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

Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/1/2007
Publication Date: 7/17/2007
Citation: Kleinman, P.J., Sullivan, D., Wolf, A., Brandt, R., Dou, Z., Elliott, H., Kovar, J.L., Leytem, A.B., Maguire, R., Moore Jr, P.A., Sharpley, A.N., Shober, A., Sims, T., Toth, J., Toor, G., Zhang, H., Zhang, T., Saporito, L.S. 2007. Selection of a Water-Extractable Phosphorus Test for Manures and Biosolids as an Indicator of Runoff Loss Potential. Journal of Environmental Quality. 36(5):1357-1367.

Interpretive Summary: The water extractable phosphorus content of manures and biosolids is a key indicator of their potential to release phosphorus to runoff. To-date, no single test has been recommended for water extractable P. Consequently, comparison of research findings and management recommendations has been hampered by the lack of a consistent water extractable phosphorus protocol. A collaborative study was implemented across North America involving 10 laboratories to determine whether a single test for water extractable P could be recommended for manures and biosolids of highly varied properties. Laboratory extraction experiments and runoff experiments were conducted on a wide range of manures and biosolids. The result of this study is a single, recommended protocol for measuring water extractable phosphorus in manures and biosolids.

Technical Abstract: Water extractable P (WEP) is increasingly used as an indicator of the potential for manure and biosolids to release dissolved P to runoff. No consensus has existed on whether a single WEP method is sufficient to meet the analytical standards and production requirements of commercial laboratories while remaining a consistent indicator of P loss potential across materials of varying properties. A multi-laboratory (10) extraction study was implemented to quantify error associated with WEP protocols on 20 manures and biosolids. A supplemental runoff study was conducted with 15 of the manures and biosolids to assess whether protocol changes affect the prediction of dissolved P in runoff from WEP. Relative standard deviations (RSDs) in inter-laboratory findings were comparable to established manure tests (7.6-20.7 %). The 10:1 extraction ratio had the highest RSD when extract P was determined by colorimetry, and was too low to obtain uniform suspensions and sufficient extract volumes for some dairy manures and biosolids. Protocols based upon higher extraction ratios (100:1, 200:1) necessitate the extraction of small samples in conventional laboratory ware (volume < 500 mL). Smaller samples did not increase within-lab variability in WEP, however, they did produce greater recoveries of P from some materials than did larger samples highlighting the potential for sampling bias. Results of the runoff study showed WEP to be correlated with dissolved P in runoff for all methods, whether derived from a single laboratory (r = 0.79-0.93) or multiple laboratories (r = 0.56-0.83). As the strongest correlations with dissolved P in runoff were associated with the 100:1 extraction ratio and the fewest laboratory complaints were associated with this ratio, this study points to a single recommended protocol for measuring WEP in manures and biosolids.

Last Modified: 8/24/2016
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