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TECHNICAL REPORTS

Waste Management

Evaluating Phosphorus Release from Biosolids and Manure-Amended Soils under Anoxic Conditions

^a Soil and Water Science Dep., Univ. Florida Gulf Coast REC, Wimauma, FL 33598
^b Dep. of Plant and Soil Sciences, Univ. Delaware, Newark, DE 19716-2170

^* Corresponding author (alshober{at}ufl.edu).

Received for publication December 20, 2007. The solubility of P in biosolids and manures has been shown to influence the potential for dissolved P losses in runoff and leachate when these materials are land applied. As a result, some Mid-Atlantic US states have developed P source coefficients (PSCs) to account for differences in P solubility between fertilizers, manures, and biosolids in P risk assessment tools. The reliability of these PSCs has not been evaluated under anoxic conditions, where environmental changes may affect the P solubility of biosolids or manures. The objective of this study was to assess the effects of anoxic conditions on the release of P from a range of Mid-Atlantic soils amended with manures and biosolids. The concentration of dissolved P released into solution (0.01 mol L^–1 NaCl) from the Pamunkey, Berks, and Manor soils was significantly lower under reducing conditions than under oxidized conditions (median P = –0.70, –0.49, and –0.07 mg L^–1, respectively; all significant at the 0.001 probability level). There was no significant P source effect on dissolved P released into solution after anoxic incubation of soils. Calculated solubility diagrams and increases in oxalate-extractable Fe and P sorption index under reducing conditions for all soils suggest the precipitation of (i) an Fe(II)-oxide that increased the P sorption capacity of the soils or (ii) an Fe(II)-phosphate that decreased the solubility of P. We propose that current PSCs do not need alteration to account for differences in P solubility of organic sources under reducing conditions under relatively static conditions (e.g., seasonable high water table, periodically submerged soils, stagnant drainage ditches).

Abbreviations: Al_CD, citrate-dithionite extractable Al • Al_OX, oxalate-extractable Al • APL, alum-treated poultry litter • BPR, biological P removal • B-BPR/L, biological P removal/lime-treated biosolids • B-Fe, Fe-treated/anaerobically digested biosolids • B-Fe/L, Fe-treated/lime-stabilized biosolids • DM, liquid slurry pit dairy manure • DPS, degree of P saturation • DRP, dissolved reactive P • Eh, redox potential • F, inorganic P fertilizer • Fe_CD, citrate-dithionite extractable Fe • Fe_OX, oxalate-extractable Fe • ICP–AES, inductively coupled plasma atomic emission spectroscopy • M3-P, Mehlich-3 P • NPL, normal poultry litter • P_OX, oxalate-extractable P • PSC, P source coefficient • PSI, P sorption index • SM, liquid swine manure • WSP, water-soluble P