MICROBIOLOGICAL TRANSFORMATION OF PHOSPHORUS IN THE ROOT ZONE OF SUNFLOWER UNDER THE ACTION OF BACILLUS SP. 2473 AND DIFFERENT DEGREES OF CROP FERTILIZATION

Abstract

Objective. To study the peculiarities of the microbiological transformation of phosphorus compounds in the root zone of sunflower plants under the action of Bacillus sp. 2473 and different degrees of crop fertilization. Methods. Field experiment; microbiological (accounting for bacteria capable of dissolving insoluble phosphate complexes with Ca2+, Al3+, Fe3+ and hydrolysing organic phosphates in the rhizosphere soil of sunflower plants); biochemical (determination of soil phosphatase activity); chemical (determination of phosphorus content in soil and plants); statistical. Results. Under the conditions of the field experiment on leached chornozem, it was established that during the growing season of sunflower in the soil after the introduction of Bacillus sp. 2473 into the agrocenosis, the number of bacteria capable of dissolving insoluble complexes of phosphates with Ca2+, Al3+, Fe3+ and bacteria hydrolysing organic forms of phosphates increases compared to the indicators of the control variants. Phosphatase activity increases during the growing season of plants and reaches the highest values during the seed ripening phase. The lowest levels of phosphorus content in the rhizosphere soil of sunflower plants were registered after presowing inoculation with Bacillus sp. 2473. The content of Р2О5 decreased from 0.25 mg Р2О5/dm3 of the soil solution (in the control) to 0.21 mg Р2О5/dm3 in the phase of 7–8 leaves under the action of the inoculant; from 0.42 mg Р2О5/dm3 to 0.31 mg Р2О5/dm3 in the flowering phase; from 0.24 mg Р2О5/dm3 to 0.21 mg Р2О5/dm3 in the seed ripening phase, respectively, which indicates the strengthening of phosphorus assimilation by bacterized plants. The optimal agricultural background, taking into account the effect of fertilizers on the development of phosphate-mobilizing microorganisms, is the use of mineral fertilizers in a rate not exceeding N90P90K90. Conclusion. Under the influence of the phosphate-mobilizing bacterium Bacillus sp. 2473, the processes of phosphorus transformation are activated in the root zone of sunflower plants, which is indicated by an increase in the number of phosphate-mobilizing bacteria, phosphatase activity and the degree of phosphate mobility in the rhizosphere soil of plants. As a result, the assimilation of phosphorus by plants is enhanced, which is confirmed by the increase in its removal with crop yield from 47.3 kg/ha to 74.8 kg/ha, while the efficiency of phosphorus nutrition of plants is 53.8 % (against the background of N90P90K90).