Effect of complex microbial preparation of free-living and symbiotic nitrogen-fixing bacteria for agricultural crops

The aim of this work was to study the newly developed biofertilizer and plant growth-promoting activity of a consortium of bacterial strains Azotobacter chroococcum MDC 6111, Paenibacillus polymyxa MDC 280 and symbiotic nitrogen-fixing bacteria Rhizobium leguminosarum MDC 5609, Mesorhizobium ciceri MDC 6048 and Bradyrhizobium japonicum MDC 5789. It should be noted that in the biofertilizer formula, the strains A. chroococcum and P. polymyxa are unaltered components, and the nodule bacteria are included depending on the type of crop, taking into account the specificity of these bacteria to plants. In this case, both the nitrogen-fixing capacity and the phosphate-mobilizing activity of these bacteria were taken into account. It was found that the increase in the organic layer content from 2.73 to 5.79% occurs with the active participation of microbial strains introduced into the soil. During the plant growth period, an increase in mobile nitrogen forms (NO3-) to 71.9 mg-eq/100 g and soil saturation with molecular nitrogen to 16.2 mg/100 g were detected. A decrease in the content of phosphorus salts (Р2О5, РО43-) and potassium (K+) to 2.86, 3.82 and 5.86 mg-eq/100 g, respectively, was shown. Thus, the content of the immobile form of potassium (K2O) decreases approximately 3 times, and the amount of immobile phosphorus (P2O5) - 3.63 times. These processes in the soil are due to the active activity of nitrogen-fixing and phosphate-solubilizing bacteria, as well as the use of these ions by plants. At the same time, the nitrogen (N) content increases by 2.38 times, and its mineralized form - NO3- by 3.0 times, respectively. As a result of the field experiments, it was found that the tested soil rhizobacteria actively adhere to seeds and seedlings, spreading in the rhizosphere of plants, contributing to the effective action of the biopreparation, thereby fixing more nitrogen. Microorganisms in the process of metabolism increase the efficiency of obtaining soluble salts of phosphorus, potassium and calcium by plants. In general, it was found that joint inoculation of rhizobacteria strains demonstrated higher growth parameters and plant biomass, and crop ripening is achieved 12-20 days earlier compared to the control options. The use of biopreparation in agriculture allows to improve the content of the organic component of the soil, thereby contributing to the restoration of the ecological balance of the soil.