Kozar S. Theoretical Justification and Management of Diazotroph Activity Under Their Introduction Into Soybean Agrocenoses

The thesis paper is devoted to the theoretical justification and management of growth and functional activity of nitrogen-fixing bacteria for their efficient introduction into soybean agrocenosis by implementing a strategy that involves combination of diazotrophs of different species, selection of the conditions for their co-cultivation and use after stabilization of the number of viable bacterial cells. According to the parameters of symbiotic index and growth activity of nodule soybean bacteria and azospirilla, reasonability of combining these microorganisms has been proved. A new digest medium for B. japonicum and A. brasilense was proposed, and the conditions of the co-cultivation of these diazotrophs have been studied. A method for maintaining the viability of nodule bacteria by using sodium alginate has been developed. The composition of the polysaccharide-protein complex was selected to extend viability of the bacteria on the seeds. Functional activity and efficacy of combined use of B. japonicum and A. brasilense under their introduction into soybean agrocenoses were studied. It has been proved that the combined use of diazotrophs forms an efficient symbiotic legume-rhizobial system, which provides additional biological nitrogen. According to the analysis of the content of extracellular phytohormones, synthesized by soil microorganisms, it was shown that co-cultivation of nodule soybean bacteria and azospirilla increases the intensity of production of cytokinins and gibberellins by microorganisms, reduces the amount of abscisic acid and auxin/cytokine ratio compared with pure cultures of studied nitrogen-fixing bacteria. It was shown that the combined cultivation of B. japonicum and A. brasilense increases the pectolytic activity of bacteria. Pre-sowing inoculation of soybean with mixed culture of B. japonicum and A. brasilense showed an increase in plant mass, chlorophyll content in soybean leaves, protein and oil content in the products. Combined use of diazotrophs increases soybean yields by an average of 9–16 % compared with inoculation of pure culture of nodule bacteria. It was found that inoculation of soybean with mixed culture contributes to the reduction of the leaching intensity of water-soluble humus and compounds of biogenic elements by soil profile. The implementation of the proposed strategy for regulating the activity of diazotrophs under their introduction into agrocenoses provides an increase in the level of both economic and energy efficiency of soybean cultivation.