Long-term depositions of animal manures affect P dynamics in soils and can pose environmental risks associated with P losses. Laboratory studies investigated P solubility characteristics in a manure-impacted Spodosol (sandy, siliceous, hyperthermic Arenic Alaquod) and the effectiveness of an Al-water treatment residual (WTR) amendment in controlling P leaching. Soil samples with contrasting total P concentrations were prepared by mixing samples of a manure-impacted A horizon and a minimally P-impacted E horizon. We examined the effects of mixing various ratios of A and E horizons, amendment rates (0, 25, 50, and 100 g kg^-1), and depths of amendment incorporation (mixed throughout the soil column or partially incorporated) on P leaching in a column leaching experiment. Between 62 and 77% of total P was released from the untreated soil mixes in successive water extractions, suggesting the considerable buffering capacity of the manure-impacted soil to re-supply P into solution. Between 224 to 408 mg kg^-1 P was leached over the 36-wk leaching period in the untreated soils. WTR amendment of soil columns reduced soluble P concentration in leachates by as much as 99.8%. Thoroughly mixing WTR with the entire soil column (15 cm) was much more effective than mixing WTR with only the top 7.5 cm of soil because of incomplete contact of the amendment with the soluble P in the soil. Thus, WTR should be in direct contact with soluble P, and applied at the soil depth where most of the soluble P is present. Data suggest the long-term stability of the P immobilized by the WTR.