Soil P fractions as affected by on-farm composts in a controlled incubation study

Information on the different forms and availability of P following compost addition to soil may help to better manage manure in respect to plant growth and the environment. An experiment was conducted to investigate through a sequential extraction procedure the availability of P of fresh dairy manure and several on-farm compost-soil mixtures after a 13 wk incubation in glass jars at 35degreesC. Materials were mixed at a rate of 200 mg N kg(-1) with an Arago sandy loam (Humo-Ferric Podzol), supplying from 64 to 301 mg P kg(-1). Fresh dairy manure gave the highest net increase of resin-P and labile P fractions in terms of percentage of total P added, whereas poultry litter compost was the most efficient in increasing NaHCO3-inorganic, P (-Pi). Among compost materials, poultry litter, vegetable residue and sheep manure increased labile P fraction the most. The contribution of the young dairy manure compost to this fraction was largely negative, and lower than those of fresh manure or partially and well-decomposed manure composts. A large part of added P was found in the moderately labile P fraction. The organic P (Po) fractions in the soil were less affected by manure or compost addition. This study indicated that the material P availability was reduced by composting, and was more affected by the origin of residue than by manure management.