Effect of Growth-Promoting Bacteria on Soybean Nodulation and its Oil and Protein Yields

In order to investigate the effects of biological and chemical nitrogen and phosphorous fertilizers on soybean nodulation and grain yield، a factorial experiment based on Randomized Complete Block Design with three replications was carried out at the University of Tabriz Research Farm، Iran، during 2011 and 2012. Biological fertilizer consisted of seed inoculation with phosphate solubilizing bacteria، nitrogen fixing bacteria، co-inoculation with the two types of bacteria and non-inoculated seeds (control). Chemical fertilizers were control (0%)، 16. 5 Kg/ha urea + 49. 5 Kg/ha triple superphosphate (33%)، 33. 3 Kg/ha urea + 99 Kg/ha triple superphosphate (66%)، 50 Kg/ha urea + 150 Kg/ha triple superphosphate (100%). Nodule production was only seen in plots that their seeds were inoculated by nitrogen fixing bacteria lonely and dually. Level of 33% chemical fertilizers significantly produced the highest number and wet weight of nodules and adding more fertilizers led to reduction their values. For seeds inoculated with phosphate solubilizing bacteria and non-inoculated، protein percent and yields of grain، protein and oil per unit were increased as increasing chemical fertilizers but oil percent not affected noticeably. For seeds inoculated with nitrogen fixing bacteria، chemical fertilizer application in contrast to control not influenced protein percent but decreased oil percent. Seeds inoculated by nitrogen fixing bacteria، produced highest grain، protein and oil yield per unit at 33% fertilization and increased fertilization reduced their values. Co-inoculated seeds produced higher yields than seeds inoculated by nitrogen fixing bacteria at 33% fertilization. Inoculated seeds by nitrogen fixing bacteria solely and dually produced more grain yield، oil yield، protein yield and protein percent and lower oil percent than seeds non inoculated and inoculated with phosphate solubilizing bacteria، but produced lower oil percent.