Objective By analyzing the succession of microbial community structure and function during the integrated tossing and turning composting process of pig manure and straw, this study aims to elucidate, from a microbiological perspective, the reasons for the advantages of this process in terms of temperature variation and nutrient content.

Method Two groups were established: Group F, using the integrated tossing and turning composting process of pig manure and straw, and Group G, using natural static composting. Temperature changes and total nutrient content were measured throughout the composting period. The composting progress and product quality of the two groups were compared. Metagenomic analysis was performed to examine differences between Group F and Group G in gene abundance, microbial community structure, metabolic functions, and enzymatic activities, thereby interpreting the observed variations in composting temperature and nutrient content.

Result  Compared with Group G, Group F entered the high-temperature and maturation stages 8 days earlier, had a 6 °C higher peak temperature, and showed a 29.53 percentage points higher rise in total nutrient content. Thus, the composting performance and product quality of Group F were markedly better than those of Group 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 The integrated tossing and turning composting process of pig manure and straw can significantly facilitate the composting process and improve compost quality. 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.