|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.