Phosphorus availability is a major nutritional problem in several northern Idaho soils. Traditionally, fertilizers containing P have been applied to improve availability in soils; however, organic materials added to soils have the ability to provide large quantities of labile P via mineralization processes and to reduce sorption of P. Using this concept, plant residues applied to soils would increase P availability for future plant needs. This research evaluated the effect of plant residue, incorporated into a Northern Idaho soil, on P availability under controlled laboratory conditions. Alfalfa (Medicago sativa), pea (Pisum sativum) and wheat (Triticum aestivum) plant residues were incorporated into soil collected from the Ap horizon of a Latahco silt loam (fine‐silty, mixed, frigid Argiaquic Xeric Argialboll) at rates of 0, 1, 5 and 10% (w/w). The soils were incubated at soil water potentials of ‐0.05, ‐0.15 and ‐0.40 MPa, and temperatures of 10, 20 and 30°C over a 20 week period. Soils were sampled at 2, 4, 8, 12, 16 and 20 weeks for determination of NaOAc extractable P. Data were analyzed by SAS‐GLM and Omega squared (ω2) values were used to identify the impact of each main effect and interaction. A significant 4‐factor interaction of plant residue x amendment rate x water potential x incubation time, four 3‐factor interactions, six 2‐factor interactions and four main effects were observed at each of the three incubation temperatures. Since all interactions and main effects significantly affected P availability, ω2values were used to assess their relative importance. Amendment rate was the most important factor and plant residue material was the second most important factor observed affecting extractable P levels. In general, NaOAc extractable P increased with increasing amendment rates and incubation time‐period. Increasing incubation temperature and soil water potential also positively affected the extracted P level. The greatest amount of P was mineralized from alfalfa residue material while the smallest amount was released from wheat residue. Pea residue contributed an intermediate quantity of extractable P. This study demonstrated that residues applied to northern Idaho soils have the ability to enhance P availability in addition to providing a usable N source.