Co-inoculation of Bradyrhizobium japonicum and Azospirillum brasilense in the soybean crop

Abstract

In soybean, the combined use of Bradyrhizobium japonicum and Azospirillum brasilense may be a promising strategy, joining biological nitrogen fixation (BNF) and phytohormone production. In this context, the aim of this study was to evaluate the effect of co-inoculation at different application rates of Bradyrhizobium japonicum and Azospirillum brasilense on the morphophysiological development and nodulation of soybean. The experiment was carried out in a greenhouse at the Federal University of Lavras (UFLA), in the Field Crop sector of the Department of Agriculture, Lavras, MG state, Brazil. A completely randomized experimental design was used with four replications in a 5 x 2 factorial arrangement consisting of five application rates of Azospirillum brasilense (0, 0.5, 1.0, 1.5 and 2.0 mL kg-1 of seed) and two application rates of Bradyrhizobium japonicum (0 and 3.0 mL kg-1 of seed), both transmitted via seeds. The soybean cultivar used was BRS Favorita RR , grown in 5 dm3 pots. At the beginning of flowering (R1), the following features were determined: plant height, number of trifoliate leaves, shoot dry matter, root dry matter, nodules dry matter, root volume, leaf chlorophyll content, and leaf nitrogen content. Application of Bradyrhizobium japonicum at the rate of 3 mL kg-1 of seed led to the best morphophysiological performance and the greatest nodulation in the potted soybean crop. The use of Azospirillum brasilense alone and in co-inoculation with Bradyrhizobium japonicum did not have a significant effect on the parameters evaluated.