Abstract: To clarify the synergistic effects of Trichoderma harzianum (TH), Bacillus mucilaginosus (BM), and Glomus mosseae (GM) on soil quality improvement, three single application treatments, three two-bacterium mixed application treatments, one three-bacterium mixed application treatment and control treatment were set up. The growth index of alfalfa, soil nutrient content and soil microbial index were measured in a pot experiment. The results showed that the growth indices of alfalfa were significantly improved by single application and mixed application. The application of TH+BM had the strongest effect, with the biomass of alfalfa being significantly increased by 93.8% compared with that in the control. In terms of soil nutrients and microorganisms, among the single application treatments, BM treatment had the best comprehensive improvement effect on soil nutrients, increasing the contents of available P, available N, available K and microbial biomass nitrogen (MBN) by 58.1%, 8.9%, 13.1% and 77.6% respectively. Among the two-bacterium mixed application treatments, TH+BM had the strongest effect on soil comprehensive improvement, and increased available P, available N, available K contents, microbial biomass C and MBN by 93.1%, 26.7%, 23.1%, 78.7%, 143.3% respectively. The effect of the three-bacterium mixed application on soil substrate improvement was within the range of the three two-bacterium mixed application treatments. In general, the effects of two-bacterium mixed application on soil comprehensive improvement were better than that of single application and three-bacterium mixed application. The TH+BM  treatment had the best effect, which could be used for soil quality improvement.

Key words: Trichoderma harzianum, Bacillus mucilaginosus, Glomus mosseae, mixed application of microbial agent.