ASSESSMENT OF THE PHOSPHATE MOBILIZING ACTIVITY OF RHIZOSPHERIC BACTERIA ISOLATED FROM THE SOILS OF THE ASTRAKHAN REGION

Nitrogen and phosphorus are the most important macronutrients that affect the growth, development and yield of plants. Currently, in various types of soils, there is often a shortage of available forms of these elements for plants. An alternative solution to this problem may be the use of bacteria capable of converting nitrogen and phosphorus compounds into forms accessible to plants as a result of their vital activity. Nitrogen-fixing bacteria, which can exhibit a range of beneficial properties, attract special attention. Biologics based on these microorgan isms are economical, harmless, capable of self-reproduction and specific to specific conditions of the region and can become an alternative to the use of chemical fertilizers, the level of use of which is steadily increasing world wide. The purpose of this study was a comparative assessment of the phosphate-mobilizing activity of nitrogen fixing bacteria on dense and liquid nutrient media. The study of the intensity of nitrogen fixation by the Nessler method allowed us to select 11 of the most productive bacterial isolates for further studies (the concentration of free NH4+ in the culture fluid was 10.5–95.9 micrograms/ml). In laboratory experiments in vitro, it was found that only 9 isolates showed a different degree of phosphate-dissolving activity on dense media, while most of them are capable of mobilizing phosphorus mainly from inorganic than organic compounds. It was revealed that high val ues of Kg are typical for isolates KA-31 (6.38) and YUYA-13 (2.64), the average is for PA-7 (0.69). In a liquid medium containing Ca3(PO4)2, the maximum content of phosphate anion in the culture liquid of the PA-7 isolate is 128 mg/dm3, which corresponds to the mobilization of 69.6% of the introduced calcium phosphate after 7 days of the experiment. The three studied isolates YUYA-13, KA-10 and KA-31 showed high and medium phosphate mobilizing activity, dissolving 64.4, 48.1 and 42.0% Ca3(PO4)2, respectively. The conducted studies made it pos sible to select 4 isolates of nitrogen-fixing bacteria exhibiting phosphate-mobilizing properties that are promising for the creation of biological products for agricultural purposes in the arid climate of the Astrakhan region.