Inoculation and co-inoculation of Bradyrhizobium japonicum and Azospirillum brasilense in soybean crop with the use of soil bio-activator

Abstract

In view of the high nitrogen availability required by soybean, inoculation with nitrogen fixing bacteria, such as Bradyrhizobium japonicum, is an economically viable option. Moreover, the co-inoculation of these microorganisms with plant growth promoting bacteria, such as Azospirillum brasilense, presents high efficiency compared to the isolated use of these microorganisms. Given the above, the study aimed to determine the effects of applying a soil bio-activator associated with the inoculation of Bradyrhizobium japonicum and Azospirillum brasilense bacteria, on morphometric, physiological and productive variables of soybean crop. The experiment was conducted in the field, in a randomized block design with four replicates. The treatments were: control; seed inoculation with Bradyrhizobium japonicum; seed inoculation with Azospirillum brasilense; application of soil bio-activator; seed inoculation with B. japonicum and A. brasilense; seed inoculation with B. japonicum and application of soil bio-activator; seed inoculation with A. brasilense and application of soil bioactivator; and seed inoculation with B. japonicum and A. brasilense and application of soil bioactivator. In the morphometric analysis, plants inoculated with B. japonicum presented a greater number of nodules compared to the control. The co-inoculation associated with use of soil bio-activator increased the chlorophyll relative content, at the beginning of the cycle, in 6.37% in relation to the control. In gas exchange analysis, the isolated use of soil bio-activator obtained higher intrinsic water use efficiency (iWUE) in V4. No increases in relation to the control were observed in the other variables evaluated, rejecting the hypothesis that coinoculation associated with the use of soil bio-activator would promote increases in morphometric, physiological and productive characteristics of the soybean crop. Highlighted Conclusion1. The use of soil bio-activator associated with inoculation and coinoculation of Bradyrhizobium japonicum and Azospirillum brasilense does not provide increases in morphometric, physiological, and productive variables of the soybean crop. 2. Further studies are needed on the influence of soil bio-activators on the bacteria used in this study, enabling further verification of their applicability.