Irshad, M., Saleem, A., Faridullah, Hassan, A., Pervez, A. and Egrinya Eneji, A. 2012. Phosphorus solubility and bioavailability from poultry litter supplemented with gypsum and lime. Can. J. Soil Sci. 92: 893-900. Gypsum and lime are often used as amendments for the regulation of soil reaction (pH), which has an immense influence on soil nutrient availability. We determined the release and bioavailability of phosphorus (P) to spinach (Spinacia oleracea L.) from soils amended with gypsum and lime supplemented with poultry litter (PL). Four types of poultry litter (i.e., broiler litter, breeder litter, layer litter and duck litter) were mixed separately with lime and gypsum at the rates of 0, 2.5 and 5% and incubated at room temperature for 8 wk. The incubated materials were sampled at 4 and 8 wk and analyzed for water-extractable P. Prior to incubation, non-supplemented litter samples were also analyzed for total element contents (P, Ca, Mg, K, Mn, Cu, Zn and Fe). Total P varied in the order duck >broiler >layer >breeder. Water soluble P concentration was highly dependent on the type of PL as well as chemical amendment used. With the application of both gypsum and lime, P concentration decreased with increasing rate of application. There was less water-soluble P with lime than gypsum supplementation for all PL. Time of incubation slightly reduced water-soluble P concentration. Non-supplemented PL had greater P concentration after 8 wk, but soluble P was in the order duck >broiler >breeder >layer. At the 8th week of incubation with 5% gypsum, the soluble P decreased by 28% in duck, 22% in broiler, 17% in breeder and 16% in layer. The 5% lime treatment reduced P solubility by 26% in duck, 23% in broiler, 16% in breeder and 20% in layer. The addition of the supplemented PL to soil significantly reduced water-soluble P, especially with the lime treatment. Application of non-supplemented PL produced greater spinach biomass yield than PL supplemented with gypsum or lime, possibly on account of higher soluble P and micro elements (Zn, Cu, Mn and Fe). Although chemical amendments such as gypsum and lime lowered P concentration and even spinach yield, it may help reduce eutrophication of surface waters in areas where large amounts of PL are applied regularly.