The alteration of easily available phosphorus (P) from the separated solid fraction of pig slurry by composting and thermal processing (pyrolysis or combustion at 300-1000 degrees C) was investigated by water and acidic extractions and the diffusive gradients in thin films (DGT) technique. Temporal changes in P availability were monitored by repeated DGT application in three amended temperate soils over 16 weeks. P availability was found to decrease in the order: drying > composting > pyrolysis > combustion with increasing degree of processing. Water extractions suggested that no P would be available after pyrolysis above 700 degrees C or combustion above 400 degrees C, respectively, but during soil incubation, even char and ash, processed at 800 degrees C, increased P availability. Low-temperature pyrolysis vs. combustion was found to favor P availability as did application to acidic vs. neutral soil. Composting and thermal treatment produced a slow-release P fertilizer, with P availability being governed by abiotic and biotic mechanisms. (C) 2014 Elsevier Ltd. All rights reserved.