Identification of bacterial communities, structure, and dynamics during cattle and poultry manure composting

Biochar-assisted composting has emerged as a promising strategy for improving the stabilization of animal manure and modifying composting conditions. This study evaluated the physicochemical performance and temporal bacterial succession during in vessel composting of cattle and poultry manure under different manure ratios and biochar amendment conditions. Six treatments were established using three cattle-to-poultry manure ratios (1:3, 1:1, and 3:1), with and without 10% organic biochar (OB). Composting performance was monitored through temperature, pH, and bacterial population analyses. The treatment showing the most favorable overall physicochemical performance was subsequently selected for temporal 16S rRNA gene sequencing. Among the investigated treatments, the 10% OB treatment containing a 1:3 cattle-to-poultry manure ratio (M4) achieved the highest maximum temperature (61 °C), the longest thermophilic phase, and the highest cumulative temperature (1007 °C). Compost pH increased from near-neutral values to an alkaline range of 7.6–8.47 during maturation, with higher values observed in OB-amended treatments. Bacterial populations increased during the active composting phase and subsequently declined during the later stages. Temporal sequencing of M4 revealed stage-dependent changes in bacterial community composition, with Proteobacteria-associated taxa predominating during the early stage and Firmicutes becoming more prominent during the thermophilic and maturation phases. Members of the genera Bacillus and Staphylococcus were among the prominent taxa detected during the composting process. Overall, manure ratio and OB amendment were associated with differences in physicochemical composting performance, whereas sequencing of M4 revealed temporal changes in bacterial community composition within the selected treatment. Because sequencing was restricted to M4, these microbial succession patterns cannot be independently attributed to OB amendment or manure ratio. These findings provide a basis for further comparative studies of microbial community responses to biochar-assisted manure composting.