Effects of composite growth-promoting microbial agent addition on the growth and soil properties of three mixed grasses

In this study, we examined the effects of composite growth-promoting microbial agents on the growth and soil properties of a mixture of three grass, using 11 strains of effective plant growth-promoting rhizobacteria (PGPR), including those in the genera Bacillus, Pseudomonas, and Pseudarthrobacter. On the basis of the phosphorus solubilization, nitrogen fixation, plant growth hormone secretion, and other characteristics of the bacterial agents, we prepared six composite bacterial formulations (T₁, T₂, T₃, T₄, T₅, and T₆), which were added to a mixture of the three grasses Elymus nutans, Poa qinghaiensis, and Festuca sinensis, and measured growth indices of forage and stubble and selected chemical indices of soil. The results revealed that compared with the control treatment, all indicators showed different degrees of change, among which, the plant height of E. nutans, P. qinghaiensis. and F. sinensis increased by 1.49% to 15.07%, 1.65% to 25.89%, and 6.36% to 11.13%, respectively, compared with the control; the total above-ground biomass increased by 4.38% to 13.60%; the pH declined by 0.03 to 0.11 units; the electrical conductivity increased by 2.31% to 14.02%; the available phosphorus increased by 12.07% to 27.80%; and ammonium nitrogen and nitrate nitrogen increased by 7.93% to 28.45% and 9.78% to 142.64%, respectively. Furthermore, the gray correlation comprehensive analysis ranking for the assessed formulations was T₁ > T₄ > T₃ > T₅ > T₂ > T₆ > control, thereby indicting that among these formulations, the composite microbial agent T₁ had the best promotion effect, and thus potential for promotion and application.