Effects of winter and summer microbial inoculants on the physicochemical properties and microbial diversity of sunflower straw-cow dung compost.

To promote the utilization of sunflower straw resources, we conducted composting experiments in winter and summer with microbial inoculants to explore the effects of season and inoculant addition on physicochemical properties and microbial diversity during composting.The results indicated that both season and microbial agents significantly influenced the physicochemical characteristics of the compost, as well as the diversity and abundance of bacteria and fungi. On day 15 of composting, the application of the FAB (Commercial composite microbial inoculant+Candida utilis+Bacillus licheniformis) inoculant in the summer effectively promoted the humification of organic matter and enhanced nitrification. Furthermore, a distinct seasonal difference in its effect on phosphorus transformation was observed earlier, on day 5. While the FAB inoculant promoted phosphorus transformation in winter, it inhibited the process in summer. In the winter treatments, the relative abundance of Firmicutes ranged from 24.58 % to 30.70 %, which was higher than that in the summer treatments (12.49 %-28.16 %). In summer, the abundance of Proteobacteria followed the order FBX (Commercial composite microbial inoculant+Bacillus licheniformis) > FABX (Commercial composite microbial inoculant+Candida utilis+Bacillus licheniformis) > BX (Bacillus licheniformis) > ABX (Candida utilis+Bacillus licheniformis), with the relative abundance of Proteobacteria in the CKX group being 16.52 %. In contrast, all groups in winter exhibited the opposite trend, with the CK group showing the highest abundance. Certain fungal phyla exhibited contrasting seasonal distribution patterns: Basidiomycota was significantly enriched during winter, with its relative abundance reaching 27.36 % in the FB group, while Fungi_phy_Incertae_sedis predominated in summer, with a relative abundance of 19.38 % in the BX group. Correlation analysis further revealed that total potassium (TK), organic matter (OM), and nitrate nitrogen (NO3--N) were significantly correlated with bacterial community composition. The fungal community composition, on the other hand, was correlated with factors such as total nitrogen (TN), total phosphorus (TP), TK, ammonium nitrogen (NH4+-N), OM, the C/N ratio (C/N), and NO3--N.