Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2004
Publication Date: 5/1/2005
Citation: Kleinman, P.J., Wolf, A.M., Sharpley, A.N., Beegle, D.B., Saporito, L.S. 2005. Survey of water extractable phosphorus in livestock manures. Soil Science Society of America Journal. 69:701-708. Interpretive Summary: Water extractable phosphorus in manure is correlated with dissolved phosphorus concentration in runoff from soils amended with manure. As a result, a growing number of states use results of a water extractable phosphorus test for manures as an environmental indicator in phosphorus site assessment indices. This survey examines trends in water extractable phosphorus in manure related to livestock species and storage systems. Significant differences in water extractable phosphorus were detected between swine, dairy, beef, chicken and turkey manures, as well as between dry and liquid manure storage systems. This survey shows that distinction among manure storage systems within certain livestock categories is needed to accurately reflect water extractable phosphorus. The survey also points to the need for continued monitoring of water extractable phosphorus in manures to ensure that changes in livestock nutrient management are accurately reflected in agricultural guidelines.
Technical Abstract: Water extractable P (WEP) in manure is highly correlated with P concentration in runoff from soils amended with manure. A survey of 140 livestock manures was conducted to assess trends in WEP related to livestock and storage. Manure WEP ranged widely (0.2 to 16.8 g kg-1), with swine having the highest average concentrations (8.7 g kg-1), followed by turkey (6.3 g kg-1), layer chickens (4.8 g kg-1), dairy cattle (3.9 g kg-1), broiler chickens (3.2 g kg-1) and beef cattle (2.3 g kg-1). Manure WEP differed by storage and handling system, with dry manures containing significantly lower WEP concentrations than manure from liquid storage systems. Within liquid storages, no significant differences in WEP were observed between covered and uncovered storages or between bottom-loaded and top-loaded storages. Dry matter content of manure was weakly correlated to WEP across all manures (r = -0.30), but strongly correlated with WEP in liquid swine manure (r = -0.87) and dairy manure (r = -0.72), signifying dissolution of phosphate compounds as manure solids are diluted. Varying positive correlations between WEP in manure and water extractable Ca, Mg or Fe point to these cations as important controls of P solubility in manure. Total P was also correlated with WEP in some manures, pointing to the potential to control WEP through dietary P adjustments that affect fecal TP. Results of this study show that livestock manure can be categorized by WEP, a key step toward differential weighting of agricultural P sources in P site assessment indices.