Biochar Effects on Carbon and Nitrogen Dynamics During Co‐Composting of Poultry Manure With Carbonized and Uncarbonized Organic Materials in Sub‐Saharan Africa

ABSTRACT Background Carbonized organic matter (biochar) and compost are both beneficial soil amendments and particularly meaningful for the restoration of degraded soils. Application of biochar adds stable carbon (C) but only little nitrogen (N) to the soil. Compost is rich in C and N, but losses of these elements during composting are large, and C stability is relatively low. The addition of biochar during composting has been reported to decrease N losses, accelerate the composting process, increase cation exchange capacity (CEC), and increase water‐holding capacity compared to composting without biochar. However, C and N dynamics during biochar co‐composting vary enormously depending on feedstock quality. Aims Therefore, the aims of this study were to find out if biochar addition will reduce C and N losses during composting of organic materials in a field trial in Sub‐Saharan Africa or not. Methods Six compost treatments, among them three compost mixtures with biochars made from rice husks (cRH), corn cobs (cCC) and wood (cWO) or their un‐carbonized feedstocks (RH, CC, and WO), were co‐composted with poultry manure (15 vol‐%) and rice straw (60 vol‐%) in randomly allocated 1 m 3 compost bins. Results After composting, biochar treatments had lower or similar C losses, lower contents of dissolved organic carbon (DOC), higher C decomposition rates, and higher or similar pH‐values compared with their non‐biochar treatments. Biochars that were stored in mesh bags during composting increased in DOC and effective CEC and decreased in surface area. Biochar retained N through accumulation and sorption of ammonium nitrogen (NH 4 ‐N). Microbial biomass and nitrate nitrogen (NO 3 ‐N) were similar among all treatments. Conclusions Overall, biochar positively affected C and N retention and compost quality.