Objectives The effects of inoculation of self-made and commercial compound microbial inoculants on the humification degree and enzyme activities during composting procession of planting and breeding waste were studied, so as to provide efficient compound microbial inoculants for their utilization as resources.

Methods Cow dung, mushroom chaff and tail vegetables (wet weight ratio of 5∶4∶1) were used as raw materials for mixed composting. The initial compost had a C/N ratio of about 30∶1, and was 1.5 t in weight, 100−200 cm in height. Two microbial inoculum CDS and XY4 were prepared in our lab for the experiment. CDS was mainly composed of Acinetobacter pittii, Bacillus subtilis subsp. Stercoris and Bacillus altitudinis. XY4 was mainly composed of Bacillus pumilus, Bacillus amyloliquefaciens and Streptomyces thermovulgaris. The two homemade microbial inoculum CDS, XY4, a commercial microbial inoculum (EM), and inactivated medium (CK) were used as treatments, with an inoculum ratio of 1.5% by mass. During the composting procession, compost temperature was daily monitored. On the 1st, 12th, 28th and 36th day of composting, samples were collected for the determination of seed germination index (GI), C/N ratio, pH, humic and fulvic acid content, and enzyme activities.

Results A high-temperature phase (>50.0℃) lasted more than 20 days in all the four treatment composts. After 28 days of composting, the compost extract from the XY4 treatment was recorded a germination index exceeding 80.0%. With the elongation of composting process, the C/N ratio decreased from 30 at initial to about 14.6. Compared with CK, CDS and XY4 treatments were tested higher fulvic acid content from 1 to 36 days, and higher humic acid content on day 36 (P<0.05). CDS and XY4 treatments were also tested higher enzyme activities than the other two treatments: the urease activity was as high as 28.0 mg/(g·d) on day 28 and the sucrase activity was as high as 97.6 mg/(g·d) on day 12 under XY4 treatment; CDS treatment exhibited the highest alkaline phosphatase activity on day 12 and 28, with values of 40.0 and 32.1 mg/(g·d), respectively. Correlation and redundancy analyses showed that catalase had an important role in humic acid formation in CDS and XY4 compared to CK, explained 17.3% and 26.7% of the difference. For all the CDS, XY4 to EM treatments, humic acid was significantly and negatively correlated with alkaline phosphatase (P<0.05).

Conclusions Compared to commercial microbial inoculants, XY4 homemade microbial preparations could significantly enhance the activities of alkaline phosphatase and sucrase during the composting maturation process. These inoculants not only accelerate the rapid decomposition and humification of organic matter in the compost, but also increase the compost temperature and the duration of the high-temperature phase, effectively shortening the compost maturation period. Consequently, the homemade inoculants XY4 expedites the compost maturation process.