Chemical and biochemical characterisation of biochar-blended composts prepared from poultry manure

► The addition of biochar enhances the organic matter quality of mature composts. ► Biochar improves compost maturity as shown by the classic stability indices. ► Urease, phosphatase and polyphenol oxidase were enhanced in biochar-blended composts. ► Biochar sorption capacity affects the determination of enzymatic activities. The aim of this study was to assess the effect of a 2% (v/v) addition of biochar on the quality of a composting mixture prepared with poultry manure and different local organic wastes (rice husk and apple pomace). Compost quality was evaluated in terms of typical stabilisation indices, the microbial biomass and selected enzymatic activities related to the C, N and P cycles. The main effects of biochar were a 10% increase in C captured by humic substance extraction and a 30% decrease of water-soluble C, due to an enhanced degradation rate and/or the sorption of these labile compounds into the biochar. The urease, phosphatase and polyphenol oxidase activities of the biochar-blended compost were enhanced by 30–40% despite the lower amount of microbial biomass. Denaturing gradient gel electrophoresis revealed a higher diversity of fungi in biochar-amended compost, suggesting a change in microbial composition compared to the unamended compost.