Survey of Water-Extractable Phosphorus in Livestock Manures

fate) reduced WEP concentrations in the litter relative to untreated chicken litter. Similarly, when alum-treated Water-extractable P (WEP) in manure is increasingly used as an and untreated litters were broadcast onto pastures, difenvironmental indicator as it is correlated with P in runoff from soils recently amended with manure. Little information exists on WEP ferences in dissolved P concentrations of runoff correvariability across livestock manures. A survey of 140 livestock manures sponded with differences in litter WEP. Withers et al. was conducted to assess trends in WEP (dry weight equivalent) related (2001) found that concentrations of dissolved P in runoff to livestock types and manure storage. Manure WEP ranged widely from soils amended with mineral fertilizer, cattle ma(0.2–16.8 g kg 1 ), with swine (Sus scrofa domestica L.) having the nure, and biosolids were proportional to the concentrahighest average concentrations (9.2 g kg 1 ), followed by turkey (Meltion of WEP in the different amendments. leagris gallopavo) (6.3 g kg 1 ), layer chickens (Gallus gallus domesWater-extractable P in manure can also serve as a ticus L.) (4.9 g kg 1 ), dairy cattle (Bos taurus) (4.0 g kg 1 ), broiler quantitative predictor of dissolved P in runoff when chickens (Gallus gallus domesticus L.) (3.2 g kg 1 ), and beef cattle expressed as a concentration (e.g., g kg 1) on a dry (Bos taurus) (2.3 g kg 1 ). Manure WEP also differed by general storage weight equivalent basis. Kleinman et al. (2002b) applied system; dry manures contained significantly lower WEP concentrations (3.9 g kg 1 ) than manure from liquid storage systems (5.4 g dairy, chicken, and swine manures at equivalent total P kg 1 ). Within liquid storages, no significant differences in WEP were (TP) rates (100 kg ha 1) to three acidic soils with differobserved between covered and uncovered storages or between botent P concentrations. They found that when manures tom-loaded and top-loaded storages. Dry-matter (DM) content of were broadcast, the WEP concentration of broadcast manure was weakly correlated to WEP across all manures (r 0.44), manure was strongly related to concentration of disbut strongly correlated with WEP in liquid swine manure (r 0.87) solved reactive P (DRP) in runoff (r 2 0.86). For all and dairy manure (r 0.72), suggesting dissolution of phosphate soils, slopes of the regressions between DRP in runoff compounds as manure solids are diluted in storage. Varying positive and WEP in manure were similar. In that study, manure correlations were observed between WEP in manure and water-extracWEP and runoff DRP were greatest in swine slurry, table Ca, Mg, and Fe, or total P, depending on livestock category. intermediate in layer chicken manure and lowest in Results of this study show that livestock manure can be categorized by WEP, a key step toward differential weighting of agricultural P dairy manure. Studies by Ebeling et al. (2002), Kleinman sources in P site assessment indices. and Sharpley (2003), Brandt and Elliott (2003), Vadas et al. (2004b) and Kleinman et al. (2004) have confirmed that WEP concentration in manure and biosolids is a consistent indicator of DRP in runoff when P sources A particularly livestock agriculture, has are recently applied to soil. While the fraction of total been implicated in the growing problem of accelerP that is water extractable (WEP TP 1) is correlated to ated eutrophication of surface waters (Carpenter et al., runoff dissolved P concentrations within certain catego1998; U.S. Geological Survey, 1999). Land application ries of manures (e.g., dry biosolids as shown by Brandt of manure generated under livestock production can and Elliott, 2003), expressing manure WEP on this basis improve soil fertility and tilth, but can also result in does not provide accurate estimation of runoff P concenelevated concentrations of P in runoff (Sharpley et al., trations across manures of varying properties. For in1994). As P is a primary control of freshwater eutrophistance, in Kleinman et al. (2002b, 2004), concentrations cation (Thomann and Mueller, 1987), concern over runof WEP (g kg 1) in dairy manure were lower than in off P losses from manured soils has prompted a broad layer chicken manure, corresponding with lower runoff array of guidelines and regulations at federal and local dissolved P concentrations when the two manures were levels (USEPA, 1996; USDA and USEPA, 1999). broadcast to soils at the same aerial rate of total P Water-extractable P in manure has been linked to disapplication (kg ha 1). However, because total P concensolved P ( 0.45 m) concentrations in runoff from matrations in dairy manure were also low, a higher propornure-amended soils. Moore et al. (2000) showed that tion of total P in dairy manure was water extractable treating broiler chicken litter with alum (aluminum sulthan in layer chicken manure. As a result, WEP TP 1 P.A. Kleinman, A.N. Sharpley, and L.S. Saporito, USDA-ARS, Pasture was higher in the dairy manure than in the layer chicken Systems and Watershed Management Research Unit, Curtin Road, manure, making WEP TP 1 a poor predictor of runoff University Park, PA 16802; A. Wolf, Agricultural Analytical Services dissolved P concentrations across these manure cateLaboratory, The Pennsylvania State University, University Park, PA gories. 16802; B.D. Beegle, Dep. of Crop and Soil Sciences, The Pennsylvania Given the strong relationship between manure P and State University, University Park, PA 16802. Mention of trade names does not imply recommendation or endorsement by USDA-ARS. Redissolved P in runoff, a number of U.S. states now inceived 10 Mar. 2004. Nutrient Management & Soil & Plant Analysis. clude P source coefficients, formerly termed P availabil*Corresponding author ([email protected]). ity coefficients, in site assessment indices (Sharpley et Published in Soil Sci. Soc. Am. J. 69:701–708 (2005). doi:10.2136/sssaj2004.0099 Abbreviations: DM, dry matter; DRP, dissolved reactive phosphorus; TN, total nitrogen; TP, total phosphorus; WEP, water-extractable © Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA phosphorus. 701 Published online April 11, 2005