The evaluation of plant growth promoting rhizobacteria effect for improving soybean growth indices

The use of plant growth promoting rhizobacteria, is a solution to reduce the application of chemical fertilizers. In this research, first 51 rhizobacteria isolated from alfalfa rhizosphere, were screened from plant growth promoting point of view. According to the results of the screening of bacteria, 2 Rhizobium isolates, 2 Bacillus isolates and 4 Pseudomonas isolates were selected as superior strains to prepare the inoculums. To evaluate the effect of selected isolates on soybean growth indices, a completely randomized block design was carried out with 12 treatments and 3 replications. Treatments were included 4 Pseudomonas isolates, 2 Bacilli isolates and 2 Rhizobium isolates, mix of Bacillus, Rhizobium and Pseudomonas, control without Fertilizer and bacteria, half of fertilizer recommendation and Fertilizer recommendation. All Plant Growth Promoting Rhizobacteria treatments were accompany with Bradyrhizobium. The results indicated that bacteria inoculation significantly increased soybean growth indices, such shoot dry weight, root dry weight, root nodules, pods, seed weight, Fe, Zn, Mn, concentration of shoot, shoot nitrogen and phosphorus uptake compared to the control and the highest shoot Mn concentration was related to T8 treatment and the highest shoot N and P concentrations resulted from T5 (Bacillus), T8 (Rhizobium) and T1 (Pseudomonas) treatments. Generally, Pseudomonas bacteria were more effective than Bacillus and Rhizobium, to increase soybean growth indices and it can be attributed to high plant growth promoting properties of bacteria. According to the results, the usage of plant growth promoting rhizobacteria (PGPR), can decrease consumption of chemical fertilizers, especially N and P fertilizers. However, their use in field conditions requires further investigation.