Objective Structural and functional improvements of microbial community in compost of pig manure mixed with spent straws by tossing and turning-over the pile during fermentation were examined.

Method Mixture of pig manure and spent straws were composted without disturbance (G) or with occasional tossing and turning-over (F) under ambient conditions. Temperature and nutrient content of the composts were monitored, and microbial abundance, structure, metabolic functions, and enzyme activities analyzed using metagenomics.

Result By tossing and turning over the compost pile occasionally during fermentation, F significantly promoted the composting process and quality. It allowed 8d earlier entrance of the compost to high-temperature and decomposition stages with a 6℃ higher maximum temperature and 29.53% more nutrient content than G. The numbers of microbial genes found in the F compost at the warming stage (F1), the high-temperature stage (F2), and the cooling stage (F3) were significantly higher than those in the G counterparts (i.e., G1, G2, and G3, respectively), but lower at the decomposition stage (i.e., F4 vs. G4). Bacillota, Pseudomonadales, Actinomycetota, Bacteroidete, and Deinococcota were the dominant microbial phylae in the composts. However, they differed on microbiota abundance, as Bacillota existed largely in F1 and F3, while Actinomycetota in G3 and G4; and the enrichment of Actinomycetota occurred gradually in F but only from G2 to G4 in the G compost. The microbial community structure and functions of the composts were highly similar between two adjacent fermentation stages, such as between F2 and G3 and between F3 and G4.

Conclusion By tossing and turning over the pig manure and straws mixture during composting, the fermentation process was significantly facilitated and the compost quality improved. The operation enriched microbial population in composts at the first three fermentation stages but reduced that at the 4^th stage which encouraged early formation of dominant functional microbial communities of Bacillota and Actinomycetota contributing to the advantages over the conventional practice it generated.