Effectiveness of endophytic-rhizobial seed inoculation of soybean (Glycine max (L.) Merr.) cultivated in irrigated soil

Abstract

Application of seed inoculation with active nodule bacteria strains increases crop productivity of legumes and reduces the impact of negative environmental factors. The effectiveness of complex inoculation has not been studied thoroughly. The purpose of the study was to determine the impact of complex seed inoculation with nodule and endophytic bacteria on plant growth and development, rhizosphere microbiota, and productivity of soybean in irrigated soil in the Southern Steppe of Ukraine. In field research, soybean seeds of the ultra-early maturing cultivar Diona and the medium-maturing cultivar Aratta were inoculated with the bioformulation RyzobinK (based on the association of Bradyrhizobium japonicum UCM B-6018, B-6023 and B-6035), and with its combination with endophytic bacteria. During the growing season, the number of phosphorus-mobilizing, pedotrophic, prototrophic, oligonitrotrophic, and nitrogen-fixing bacteria increased in the rhizosphere of soybean inoculated with RyzobinK, and combined with one of the endophytes − Bacillus sp. 4, Brevibacillus sp. 5 or Pseudomonas sp. 6. Under unfavorable conditions of high temperatures and droughts, endophytic-rhizobial inoculation contributed to an increase in the productivity of the soybean. On average in 2018-2020, under complex seed inoculation with RyzobinK combined with Bacillus sp. 4, the highest yields of soybean cultivars Diona and Aratta of 2.66 and 2.90 t/ha were obtained, that exceeded the yields of the bacteria-free treatment variants by almost 30% and 40% respectively, with a simultaneous increase in protein and fat content in the seeds.