Composite bacterial agent increases microbial diversity and speeds up the composting procession of sheep manure and tailed vegetables on Tibetan Plateau

Objectives A composite bacterial agent was prepared using the strains screened in Tibetan Plateau. Its effect on the compost quality of sheep manure and tailed vegetables was studied, to provide an efficient tool for the utilization of sheep manure and tailed vegetables in Tibetan Plateau area.

Methods Three compost cones, each 1.5 m in height and 5 t in weight, were made by mixing sheep manure and tailed vegetables in mass ratio of 8∶1. One cone was under natural fermentation (CK), one was added with a commercial compost fermenter (T2), and one was added with self-prepared composite fungicide (T3). The fermentation lasted for 60 days, and the compost temperatures were monitored. At 0, 7, 14, 20, 25, 50, and 60 days of fermentation, the compost samples were collected for measurement of pH, electrical conductivity (EC), water content, total organic carbon (TOC), total N, NH₄⁺-N, NO₃⁻-N, and NO₂⁻-N content. At 0, 20 and 60 days of fermentation, composts were sampled for analysis of microbial community structure, combined with amplicon sequencing. Seed germination index (GI) was determined to assess the quality of compost.

Results T3 treatment was monitored the fastest warming rate, reaching 47.8℃ on the 3rd day, and reached high temperature period (>50℃) on the 17th day, which was 5 days earlier than the CK and T2 treatment did. In addition, T3 maintained high temperature period 6 days longer than the CK did. The composite fungi agent showed strong ability to utilize sheep manure and taille TOC, speed up their degradation. At the end of fermentation, the total N contents in CK, T2, and T3 treatments were 21.4, 23.1, and 19.7 g/kg, NH₄⁺-N contents were 155, 144, and 45.6 mg/kg, NO₃⁻-N contents were 218, 283, and 344 mg/kg. The addition of composite bacterial agents changed the community structure of microorganisms in the composting process, increased bacterial diversity and specific bacterial abundance, and found the dominance of Psychrobacter in the initial stage of composting. The Actinobacteriota level increased significantly in the T3 group.

Conclusions Compared with commercial agent, the addition of self-prepared composite bacterial agent could accelerate the composting process of sheep manure and tail vegetables, as the rapidly temperature increase and prolonged high-temperature period, and increase the available N content in compost product. Addition of the composite bacterial agent could cause the change of microbial community diversity and structures in the compost, as the relative higher abundance of contained Psychrobacter contributes to warming the composting at the initial stages, and the Streptomyces sp. with efficient cellulose degradation capacity contribute the cellulose degradation. Thus, the composite bacterial agent is recommended for the production of sheep manure and taille compost in Tibetan Plateau.