Effect of Associative Nitrogen Fixation in the Rhizosphere on the Growth and Development of Spring Wheat

The photosynthetic activity of plants has a significant effect on the intensity of nitrogen fixation, as a result of which the productivity of crops increases. At the moment, there is a shortage of scientific data on the nitrogen fixation process and the quantitative assessment of its activity in agroecosystems. The true role of nitrogen fixing microorganisms in the nitrogen balance of soils has not been established. There is also insufficient data on nutrition, growth and development of plants against the background of atmospheric nitrogen fixation (due to associative nitrogen fixation). The relevance of the study lies in the biological assessment of the effect of seed inoculation with fungicide-stimulating biologics on the degree of associative nitrogen fixation in the rhizosphere, the survival rate of introduced diazotrophic strains, plant growth and development, and yield formation in the southern forest-steppe zone of Western Siberia. The work was carried out in field experiments on the varieties of spring soft wheat Omsk 42, Omsk 44, Tarskaya 12 and the variety of spring durum wheat Omsk coral. Pre-sowing bacterization of seeds was carried out with an inoculant of diazotrophic bacteria of the genus Arthrobacter mysorens 7 and an inoculant of fungicidal-stimulating bacteria of the genus Flavobacterium sp. L-30. Rhizosphere sampling was carried out in the following phenological phases: tillering (June), earing (July), grain filling (August). The activity of the associative nitrogen fixation process in the rhizosphere of cereals varied significantly depending on the use of biological products and the type of culture. During the growing season, when introducing Flavobacterium sp. bacteria and Arthrobacter mysorens 7, an increase in nitrogen-fixing ability in the rhizosphere and a high survival rate of introduced bacteria were found. The highest level of nitrogen-fixing activity was in the rhizosphere of soft wheat varieties Omsk 42 and durum wheat Omsk coral, amounting to 151–322 and 140–393 nM C₂H₂/100 g of soil during the introduction of bacteria of the genus Arthrobacter mysorens 7, 149–281 and 86.2–555 nM C₂H₂/100 g of soil when Flavobacterium sp. was introduced, accordingly. In parallel, an increase in the number of CFU introduced bacteria was observed, as a result of which the nitrogen fixation process was activated. The complex nature of the interaction of the studied indicators is noted – from the average direct to the average inverse conjugacy, depending on the phase of development. The activity of associative nitrogen fixation in the earing phase was characterized by a positive correlation with yield and the formation of the number of grains in the ear (r = 0.55 and 0.35), in the phases of tillering and filling of grain – with the weight of the ear grain (r = 0.36 and 0.75).