Abstract
Water treatment residuals (WTR) can adsorb tremendous amounts of phosphorus (P). A soil that had biosolids applied eight times over 16 years at a rate of 6.7 Mg ha−1 y−1 contained 28 mg kg−1 ammonium–bicarbonate diethylenetriaminepentaacetic acid (AB‐DTPA), 57 mg kg−1 Olsen, 95 mg kg−1 Bray‐1, and 53 mg kg−1 Mehlich‐III extractable P. To 10 g of soil, WTRs were added at rates of 0, 0.1, 1, 2, 4, 6, 8, and 10 g, then 20 mL of distilled deionized H20 (DI) were added and the mixtures were shaken for 1 week, filtered, and analyzed for soluble (ortho‐P) and total soluble P. The soil–WTR mixtures were dried and P extracted using DI, AB‐DTPA, Olsen, Bray‐1, and Mehlich‐III. Results indicated that all methods except AB‐DTPA showed reduced extractable‐P concentrations with increasing WTR. The AB‐DTPA extractable P increased with increasing WTR rate. The water‐extractable method predicted P reduction best, followed by Bray‐1 and Mehlich‐III, and finally Olsen.