Effect of Soybean Co-inoculation with Bradyrhizobium japonicum and Azotobacter chroococcum and the Seeds Produced under Drought Stress on Nodule and Plant Characteristics

To study the effect of Bradyrhizobium japonicum and Azotobacter chroococcum on characteristics of plants grown by the seeds produced under drought stress, a study was conducted under laboratory and greenhouse conditions. The pot experiment was conducted with three variables in factorial form in a completely randomized design and the field experiment was split factorial in randomized complete block design with three replications. The treatments included different irrigation intervals based on 50, 100, and 150mm evaporation from class A pan, three different cultivars, namely, Manokin, Williams, and SRF×T3 Line, and inoculation treatment that consisted of inoculation with Bradyrhizobium japonicum, Bradyrhizobium japonicum co-inoculated with Azotobacter chroococcum, and no seed inoculation (check). In the pot experiments, plants were irrigated with nutrient solutions free of nitrogen. The result of the pot experiments indicated that, in all cultivars, the dry weight of the above-ground parts, the roots, and the whole plant were higher by, respectively, 16%, 23%, and 18% in plants of medium stress condition (100mm irrigation interval) compared with the plants grown by seeds of normal irrigation. Also plants of drought stress seeds had higher number and dry weight of nods. Addition of Azotobater chroococcum to Bradyrhizobium japonicum increased the number and fresh weight of nods compared to inoculation with Bradyrhizobium japonicum. Results of the field experiments showed that seedlings grown from medium stress seeds of Williams cultivar and inoculated with Bradyrhizobium japonicum had 46% higher plant dry weight than the control.