Phosphorus Distribution in Sequentially Extracted Fractions of Biosolids, Poultry Litter, and Granulated Products

Abstract

Land application of biosolids and poultry litter can benefit crop production by providing phosphorus (P) and other nutrients and organic matter. However, the bioavailability of applied P in those waste materials is directly dependent on the presence of specific P forms. In this study, we comparatively examined the P forms in biosolids and broiler litter by sequential fractionation (i.e., H2O, 0.5 M NaHCO3, 0.1 M NaOH, and 1 M HCl fractions) coupled with enzymatic hydrolysis. Extractable P in broiler litter was found in the order of HCl > H2O > NaOH > NaHCO3. Biosolid P was found in the four fractions in the following order: HCl > NaOH > NaHCO3 > H2O. Correlation analysis indicated that P was coextracted with Ca, Mn, Zn, Fe, and Al, but not Mg. Whereas most P was Ca bound in broiler litter, Al, Mn, and Zn played more important roles in metal P species in biosolids. The relative abundance of P species was determined to be inorganic P > hydrolyzable organic P > nonhydrolyzable organic P in each fraction. Compared with the P levels in the samples stored in a freezer, storage of the broiler litter sample at room temperature transformed part of the phytate P in the HCl fraction to other forms, resulting in more labile P in the H2O fraction. Granulated products of poultry litter and biosolid could be used as off-farm nutrient sources. Data in this work show that granulation transformed moderate NaHCO3- and NaOH-extractable P bilaterally to labile water-soluble P and stable HCl-extractable P in the granulated poultry litter but did not remarkably change the distribution of H2O-, NaHCO3-, and NaOH-extractable P in granulated products containing both poultry litter and biosolids.