Co-inoculation with Bradyrhizobium and Azospirillum Increases Yield and Quality of Soybean Seeds

Microorganisms are widely used in agriculture. Among them, the bacterial genus Bradyrhizobium is commonly found in cultivated soils, forming symbiotic relationships with legume species. This work aimed to evaluate whether co-inoculation with Bradyrhizobium japonicum and Azospirillum brasilense influences the components of production, yield, and physiological quality of soybean seeds. The experiment was conducted in three consecutive crop seasons (from 2014-2015 to 2016-2017), in the municipality of Chapadao do Sul, state of Mato Grosso do Sul, Brazil. The experiment consisted of a randomized complete block design, with seven treatments and four replications, using the following treatments: T1, control (without inoculation); T2, inoculation with B. japonicum (150 mL); T3, inoculation with A. brasilense (150 mL); T4, co-inoculation with B. japonicum + A. brasilense (75 mL + 75 mL); T5, co-inoculation with B. japonicum + A. brasilense (150 mL + 150 mL); T6, co-inoculation with B. japonicum + A. brasilense (225 mL+ 225 mL); and T7, co-inoculation with B. japonicum + A. brasilense (300 mL+ 300 mL). Each treatment (dose) was applied to 50 kg of soybean seeds. The study evaluated the agronomic variables number of nodules per plant, dry shoot biomass per plant, plant height, number of pods per plant, number of seeds per plant, mass of 100 seeds, and grain yield; and the seed quality variables first germination count, germination, emergence, emergence speed index, electric conductivity, accelerated aging, and tetrazolium. The co-inoculation of soybean seeds with B. japonicum and A. brasilense benefits the development of plants, increasing yield components, grain yield, and seed quality. The most efficient level was 225 mL of each inoculant for 50 kg of seed.