Submitted to: Soil Science Society of America Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/4/2001
Publication Date: 11/20/2002
Citation: KLEINMAN, P.J., SHARPLEY, A.N., WOLF, A.M., BEEGLE, D., MOORE JR, P.A. MEASURING WATER EXTRACTABLE PHOSPHORUS IN MANURE. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL. 2002. V. 66. P. 2009-2015. Interpretive Summary: Water extractable phosphorus in manure is correlated with phosphorus concentration in runoff from soils amended with manure and is, thus, an effective indicator of environmental phosphorus loss. Despite the importance of water extractable phosphorus as an environmental indicator, no method to measure water extractable phosphorus in manure has been developed that can be readily adopted by agricultural analytical laboratories. This study examines factors affecting the measurement of water extractable phosphorus in manure, evaluates existing methods with regard to their suitability in predicting runoff phosphorus losses, and proposes a single, simple test for water extractable phosphorus.
Technical Abstract: Water extractable phosphorus (WEP) in manure is correlated with phosphorus concentration in runoff from soils amended with manure and is, thus, an effective indicator of environmental phosphorus loss. This study sought to elucidate methodological factors affecting WEP measurement in manure and to quantify errors related to two established methods of manure WEP determination. Dairy cow manure, poultry (layer) manure and swine slurry were used. Varying dry matter to distilled water ratios (1 to 20:200) revealed greater dilution of manure dry matter increased WEP (average 1.8 to 5.4 g kg-1), likely due to the dissolution of calcium-phosphates. Increasing shaking time from 1 minute to 24 hours, increased manure WEP concentration (average 3.7 to 8.2 g kg-1). Filtration with Whatman 1 paper filters resulted in significantly higher WEP measurements in dairy and poultry manure (4.1 g kg-1) than with a 0.45 um filtration (3.7 g kg-1). No osignificant difference was observed in the swine slurry. A rainfall-runoff experiment using simulated rainfall was conducted to determine the effect of the individual factors on predicting dissolved reactive phosphorus concentration in runoff. Comparison of regression coefficients relating manure WEP to runoff dissolved reactive phosphorus concentration revealed an optimum shaking time between 30 min and 2 hr, but did not support any single manure-to-water ratio or filtration method. Replication of two established methods of manure WEP measurement resulted in coefficients of variation of 0.01 to 0.12. Results of this study support the use of a single method for WEP measurement for liquid and dry manures.