Relationships between biosolids treatment process and soil phosphorus availability

Laws mandating phosphorus (P) based nutrient management plans have been pas sed in several U.S. Mid-Atlantic states. Biosolids (sewage sludge) are freq uently applied to agricultural land and in this study we evaluated how bios olids treatment processes and biosolids P tests were related to P behavior in biosolids amended soils. Eight biosolids generated by different treatmen t processes, with respect to digestion and iron (Fe), aluminum (Al), and li me addition, and a poultry litter (PL), were incubated with an Elkton silt loam (finesilty, mixed, active, mesic Typic Endoaquult) and a Suffolk sandy loam (tine-loamy, siliceous, semiactive, thermic Typic Hapludult) for 51 d . The amended soils were analyzed at 1 and 51 d for water-soluble phosphoru s (WSP), iron-oxide strip-extractable phosphorus (FeO-P), Mehlich-1 P and p H. The biosolids and PL were analyzed for P, Fe, and Al by USEPA 3050 acid- peroxide digestion and acid ammonium oxalate, Mehlich-1, and Mehlich-3 extr actions. Biosolids and PL amendments increased extractable P in the Suffolk sandy loam to a greater extent than in the Elkton silt loam throughout the 51 d of the incubation. The trend of extractable WSP, FeO-P, and Mehlich-1 P generally followed the pattern: [soils amended with biosolids produced w ithout the use of Fe or Al] > [PL and biosolids produced using Fe or Al and lime] > [biosolids produced using only Fe and Al salts]. Mehlich-3 P and t he molar ratio of P to [Al + Fe] by either the USEPA 3050 digestion or oxal ate extraction of the biosolids were good predictors of changes in soil-ext ractable P following biosolids but not PL amendment. Therefore, the testing of biosolids for P availability, rather than total P, is a more appropriat e fool for predicting extractable P Com the biosolids-amended soils used in this study.