Abstract
The objectives of this study were: 1) to investigate the phosphate (P) composition of swine and layer and broiler manure composts; and 2) to evaluate the effects of compost production conditions on the P composition of manure composts. Total P contents in swine, layer, and broiler manure composts were significantly higher than those in cattle manure composts. Among the swine manure composts, compost produced with subsidiary materials had a lower total P content than compost without subsidiary materials and compost manufactured in an open-type composting facility had a higher P content than that produced in a closed-type compost depot. The readily soluble P fraction (the sum of water- and NaHCO_3-extractable inorganic P) as a percentage of the total P in layer and broiler manure composts (30% to 31%) was significantly lower than those in cattle manure composts (65% to 72%). In the all of manure composts, the percentage of readily soluble P fraction was negatively correlated with the calcium concentration (r=-0.703^<**>). The low P solubility in the layer manure compost was probably caused by a high calcium concentration and hydroxyapatite formation. In the broiler manure compost, a high percentage of organic P resulted in a low percentage of readily soluble P fraction. Layer manure compost made in a closed-type composting facility had a significantly higher percentage of organic P than that made by other composting methods, resulting in a lower ratio of readily soluble P fraction. Thus, in some cases, dividing manure composts into some groups according to the production method and raw materials enables easy estimation of the available P content in each group of manure compost. We discussed the validity of assessment of available P in manure composts using the readily soluble P contents and the importance of P-based manure compost application.
