Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2005
Publication Date: 2/1/2006
Citation: Baum, K., Pierzynski, G., Kleinman, P.J., Kovar, J.L., Maguire, R., Moore Jr, P.A., Zhang, T. 2006. Evaluating the influence of storage time, sample handling method, and filter paper on the measurement of water extractable phosphorus in animal manures. Communications in Soil Science and Plant Analysis. 37:451-463.
Interpretive Summary: Although studies have shown that water extractable phosphorus (P) in manures applied to crop production areas is well correlated with P concentrations in runoff water, there is no single standardized protocol for measuring this form of P in manures. Several protocols have been published and are in use, but none have gained widespread adoption. In this interlaboratory study, we evaluated the influence of holding time, sample handling procedure, and filtration method, and found that the effect of sample holding time and sample handling method were quite variable. However, water extractable P measurements were usually higher from more coarse filter papers than from membrane filters. In general, these findings support the adoption of a standardized protocol for water extractable P in manures. Further studies are needed that explore correlations between P concentrations in runoff and results of different procedures. Ultimately, a method will have to be chosen that will have a strong correlation to P concentrations in runoff but can be conducted in a practical manner. This information is a valuable resource for any laboratory that analyzes manures for nutrient content.
Technical Abstract: Surface-applied manures create a potential phosphorus (P) runoff hazard, especially when unincorporated. In such cases, the concentration of water extractable P in the manure has been correlated to soluble P concentrations in runoff. This study evaluated the influence of holding time, sample handling procedure, and filtration method on measurement of the water extractable P content of manures in a 3 X 3 X 2 factorial arrangement of treatments. A two-way interaction between holding time and sample handling procedure occurred for most samples. Six samples had water extractable P concentrations that were less than or equal to dried and dried/ground treatments. Only one sample had higher water extractable P concentrations for fresh compared to dried and dried/ground treatments. When significant differences occurred as a result of the filtration method, results for Whatman 40 filters, with a larger pore size than 0.45mm nitrocellulose membranes, were usually higher. There was no significant difference in the coefficient of variation across sample handling procedures, suggesting that efforts to dry and/or grind samples were not needed. These results support the adoption of a standardized protocol for measuring water extractable P in manures that represents the appropriate balance between the ease of implementation and the strength of the correlation to P runoff concentrations.