• Extended water extraction of 8 organic amendments (OA) removed 65 ± 8% of total P. • OA Origin and stability determined P extractability and Hedley's-P distribution. • TP extraction in water was 3–4 times more in untreated OAs than in composts. • Organic P depletion was 74%; by mineralization or dissolution, seldom by both. • WEP highly significantly correlated to TP, ON, and several Hedley's parameters. Phosphorous dissolution and ensuing chemical redistribution of P in organic amendments (OA) were studied by applying a modified Hedley selective fractionation to eight water-extracted and unextracted OAs. Nine 7-day, repeated extractions were applied using a 60:1 water:dry OA (v:w) ratio at pH 8. Eight OAs were tested including five biosolids, broiler litter, dairy manure compost and municipal solid waste compost. The average PWEP 9 (percent water-extractable P following nine water-extraction cycles) for the OAs was 65 ± 9% and all of the fractions, with almost no exceptions, contributed to that figure. Organic P was depleted by mineralization (in non-stabilized sludges and broiler litter) or dissolution (stabilized composts) or both (in lime-treated biosolids) and that depletion was completed within 1–2 extraction cycles. Only the organic P of the MSWC remained undepleted. Strong linear correlations were observed between the WEP 9 values of the OAs (0.8–21 g P kg−1) and several more easily determined properties, including total P content (r 2 = 0.84), organic N content (r 2 = 0.82), the sum of Hedley's more easily dissolved SRP (soluble reactive P) and OP (r 2 = 0.95), and the total P and SRP extracted by 16 h of shaking with the bicarbonate reagent (r 2 ≥ 0.90). These findings indicate that if greater P availability is desired, the stabilization of biosolids and biowastes should be minimized. These insights into the relationships between OA characteristics and P solubility may benefit the use of OAs in agricultural systems and aid assessments of the environmental significance of their use. [ABSTRACT FROM AUTHOR]