Complex Inoculation of Soybeans With Nodule Bacteria Bradyrhizobium Japonicum as a Measure to Optimize Symbiotic Nitrogen Fixation

Abstract

Objective. Establish effective mixed inoculants for soybeans based on new active strains of Bradyrhizobium japonicum with different intensity and dynamics of nitrogen-fixing activity to improve nodulation processes and functional activity of legume-rhizobia symbiosis. Methods. Microbiological, physiological, statistical, gas chromatography. Legume-rhizobia systems based on Glycine max L. (Merill) soybean, variety Samorodok, were studied using recombinant strains of B. japonicum: B199, B201, Д47, Д48, Д52, Д60, Д63. Monoinoculation of soybean with B. japonicum 634б served as the control. Results. Mixed inoculation of B. japonicum ensured positive ontogenetic dynamics of root nodule formation in soybean. The indicator of the number of root nodules in experimental plants was 1.2–1.9 times higher versus the control plants from Day 18 to 45 of soybean vegetation. When soybeans were inoculated with B. japonicum 634б + B201 and 634б + Д 52, the mass of nodules at Day 45 of vegetation increased by 30.0–35.3 % versus the control and was the highest (1.10–1.15 g/plant) among the studied variants, as a result of the strengthening effect of complex bacterization. A positive synergistic effect of the combined use of strains was obtained — intensification of the nitrogen-fixing activity of soybean root nodules. In the phase of budding/beginning of flowering and full flowering under combined inoculation with active strains of B. japonicum 634б + Д47, 634б + Д52 and 634б + В201, nitrogen fixation of soybean nodules increased by 10.7–25.5 % (at Day 32), by 13.2–30.9 % (at Day 38), and was also 2.3–2.8 times higher in the phase of full flowering (Day 45 of soybean vegetation) versus the similar indicator of control plants. In the phase of full flowering of plants (Day 45 of vegetation), under mixed inoculation with strains of B. japonicum 634б + Д47, 634б + В201, 634б + Д52 and В201 + Д52, the aboveground mass of plants exceeded that of control plants by 8.3–17.2 % variant, which was probably provided by improved conditions of their nitrogen nutrition, due to enhanced assimilation of N2 by root nodules. The most developed root system was in soybeans inoculated with strains B. japonicum 634б and B. japonicum 634б + Д52, B. japonicum 634б + В201 and B. japonicum Д48 + Д52. Conclusion. Symbiotic features of active recombinant strains of B. japonicum and their variability in functional activity at different stages of soybean ontogenesis should be taken into account when creating complex nitrogen-fixing bacterial preparations for soybeans with the effect of microbiological synergy.