Location: Dairy Forage ResearchTitle: Measuring Water-Extractable Phosphorus in Manures to Predict Phosphorus Concentrations in Runoff ) Author
|Powell, J Mark|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2008
Publication Date: N/A
Citation: Interpretive Summary: Water-extractable phosphorus (WEP) in livestock manure influences phosphorus (P) losses in runoff after manure has been land-applied. There is uncertainty however about how manure WEP should be determined. We evaluated relationships between various methods to determine manure WEP and dissolved reactive P (DRP) in runoff. Manure WEP concentrations determined by a 1:1000 extraction ratio provided the best prediction of DRP concentration in spring runoff. Manure WEP application rate rather than concentration provided the best prediction of DRP in fall runoff. With dairy manure, drying and grinding before WEP analysis decreased WEP concentrations. With poultry manure, drying and grinding before WEP analysis increased WEP. Regulatory agencies, labs, and researchers can use this information to standardize procedures for determining manure WEP, and this should improve our abilities to predict P losses in runoff after manure has been land-applied.
Technical Abstract: Water-extractable phosphorus (WEP) in manures can influence the risk of P losses in runoff when manures are land applied. There is some uncertainty about how WEP in manures should be determined. Information on the effects of manure sample handling before analysis on WEP values and appropriate manure extraction procedures for determining WEP are needed to assess the value of WEP measurements for predicting potential P runoff losses after manure application. We evaluated several manure handling and extraction variables in determinations of WEP in manures from several completed land application experiments. In each study, soluble P (DRP) concentrations in simulated rainfall runoff following surface application of the same manures were measured in field experiments. We related manure WEP determinations to DRP concentration in runoff to evaluate WEP as a predictor of soluble P runoff losses follow-ing land application of manures. Pre-analysis manure handling variables including fresh (no preparation), frozen and thawed, and dried and ground and manure:water extraction ratios ranging from 1:100 to 1:1000 with shaking times of 1 and 2 h were evaluated for their effects on WEP measurements in selected dairy and poultry manures. WEP concentrations increased with extraction ratio and shaking time. The best prediction of DRP concentration in spring runoff experiments was with manure WEP concentration at the 1:1000 extraction ratio. With fall runoff studies, DRP concentrations were best predicted with WEP application rate rather than concentration. Although pre-analysis manure handling methods significantly affected manure WEP measurements, these effects were minimized and often were negligible at the 1:1000 extraction ratio. With dairy manures, drying and grinding before WEP analysis usually decreased WEP concentrations, while WEP in poultry manures was often increased by drying and grinding. Manure WEP measurements have potential for predicting the risk of soluble P losses in runoff from land applied manures. Standardization of methods for manure sample handing and for measuring WEP is important for reliable interpretation of manure WEP data.