K-humate as an agricultural alternative to increase nodulation of soybeans inoculated with Bradyrhizobium

The use of products based on humic substances (HS), such as K-humate (KH), and the implementation of soybean seed inoculation technology can provide positive impacts on biological nitrogen fixation (BNF). In this work, different KH concentrations (0, 50, 100, 150, 200 and 4000 mg kH L-1) were applied to soybean seeds inoculated with Bradyrhizobium, and the effects of this compound on Bradyrhizobium seed survival, root morphology, nodulation, biomass increase and nitrogen content were evaluated. KH concentrations of 50, 100 and 4000 mg kH L-1 increased (p < 0.05) the survival of Bradyrhizobium in seeds after 25 days of storage. The application of KH showed superior effects compared to the control in relation to the length of primary roots (50 and 4000 mg kH L-1), total length of the roots (50, 100 and 150 mg kH L-1), volume (all concentrations), diameter (50, 100 and 4000 mg kH L-1) and root area (50, 100 and 200 mg kH L-1). In the soil experiment, a KH concentration of 50 mg L-1 was able to provide greater increments (p < 0.05) in nodulation (number and weight of nodules), biomass and N content in the shoots than the control. All KH doses increased the number of nodules in relation to inoculation with Bradyrhizobium. A KH concentration of 50 mg L-1 was the most promising considering the N input to the leaves.