Influence of Bradyrhizobium japonicum and phosphate solubilizing bacteria on soybean yield at different levels of nitrogen and phosphorus

In order to investigate the effects of biological and chemical fertilizers on soybean (Glycine max [L.] Merr. cv. Williams) yield, we carried out a factorial experiment based on Randomized Complete Block Design with three replications at the University of Tabriz Research Farm, Iran. Biological fertilizer consisted of non-inoculated (NI), phosphate solubilizing bacteria (PSB), bradyrhizobium japonicum (BJ) and B. japonicum + PSB (BJ + PSB). Different levels of chemical fertilizer were control (0%), 16.5 Kg/ha1 urea + 49.5 Kg/ha1 triple superphosphate (33%), 33.3 Kg/ha1 urea + 99 Kg/ha1 triple superphosphate (66%), 50 Kg/ha1 urea + 150 Kg/ha1 triple superphosphate (100%). One thousand grain weight was significantly affected by bio-fertilizer and inoculations with BJ and BJ + PSB were superior to NI and PSB. Also, grains per pod affected by bio-fertilizer and NI and BJ produced highest grains and lowest grains belonged to PSB and BJ+PSB. Plant biomass, grains per plant, and grain yield per plant at NI and PSB were enhanced as chemical fertilizers increased. In all chemical fertilizer levels, differences between NI and PSB were low, indicating that PSB was not able to improve the performance of soybean in contrast to NI. The highest Plant biomasses, grains per plant and grain yield were achieved at 33% × BJ+PSB. Maximum number of pods per plant was produced at 33% chemical fertilizer for BJ and BJ+PSB. Inoculation of seeds by BJ and BJ+PSB without chemical fertilizer application had equal or higher performance than non-inoculated seeds with 100% chemical fertilizer. Therefore, soybean seed inoculation by B. japonicum singly or dual with PSB, not only decreases chemical fertilizer application, but also improves soybean yield and yield components.