Objective. Investigate the influence of the microbial preparation Polimiksobakteryn on the formation of populations of phosphate-mobilizing bacteria and transformation of phosphorus compounds in the root zone of corn plants under cultivating cultures on leached chornozem.
 Methods. Field, microbiological, biochemical, agrochemical, statistical.
 Results. With the use of Polimiksobakteryn for the bacterization of corn seeds and processing of vegetative plants in the phase of 3-5 leaves or 7-9 leaves in the root zone, the number of bacteria that hydrolyze organic phosphates increases to 24.2 million/g soil (in control – 15.7 million/g soil), those dissolving mineral phosphates: calcium – up to 26.0 million/g soil (in control – 10.6 million/g soil, aluminium – up to 19.5 million/g soil (in control – 10.1 million/g soil), iron – up to 21.7 million/g soil (in control – 12.1 million/g soil) and phosphatase activity increases from 2.31 mg P2O5 to 3.68 mg P2O5/100 g soil per hour, the degree of mobility of phosphates increases depending on the phases of plant development, while the content of mobile phosphorus compounds in the rhizospheric soil of plants decreases compared with the control parameters as a result of their more intensive consumption by plants. During polymerization of seeds by Polimiksobakteryn and the use of the aqueous suspension of the preparation for treatment of vegetative plants, increase of phosphorus content in leaf mass and corn grain and increase of removal of element with a crop yield by 44.4 % compared with the control parameters is observed.
 Conclusion. In corn growing technologies, seed bacterization and superficial treatment of vegetative plants in the phase of 3-5 leaves or 7-9 leaves with microbial preparation Polimiksobakteryn – a plant growth stimulator, the bioagent of which is phosphate-mobilizing bacteria Paenibacillus polymyxa KB is an effective method for optimizing phosphorus nutrition of plants and increasing crop yields.