Lignite drove phenol precursors to participate in the formation of humic acid during chicken manure composting

This study set out to explore the impact of lignite on preserving organic matter and promoting the formation of humic acid (HA) during chicken manure composting. Composting test was carried out for control (CK), 5 % lignite addition treatment (L1), 10 % addition treatment (L2) and 15 % addition treatment (L3). The results demonstrated that lignite addition effectively reduced the loss of organic matter. The HA content of all lignite-added groups was higher than that of CK, and the highest was 45.44 %. L1 and L2 increased the richness of bacterial community. Network analysis showed higher diversity of HA-associated bacteria in L2 and L3 treatments. Structural equation models revealed that reducing sugar and amino acid contributed to the formation of HA during CK and L1 composting, while polyphenol contributed more to the HA formation during L2 and L3 composting. Furthermore, lignite addition also could promote the direct effect of microorganisms on HA formation. Therefore, the addition of lignite had practical significance to enhance compost quality. [Display omitted] •Addition of lignite fixed carbon fraction.•Addition of lignite increased the HA content significantly.•Addition of lignite significantly enhanced the diversity of HA related bacteria.•Higher additions of lignite promoted the involvement of polyphenols in HA formation.•The addition of lignite promoted the direct effect of microorganisms on HA formation.