Investigation the Effeciency of Different Bradyrhizobium Japonicum Strains as Pure and Mixed Form on the Nitrogen Fixation Using Isotope Dilution Method and Its Effect on Yield of Soybean (Cv. Sahar)

In order to evaluate the nitrogen fixation ability of soybean (cv. Sahar)، in symbiosis with Bradyrhizobium japonicum، a complete randomized block design with 3 replications was conducted in 2006 in greenhouse of Nuclear Agricultural Research Station. Experimental treatments were consisted of three strains of Bradyrhizobium japonicum including Gold coat، RS-130 and USDA110، as pure and mixture of two and three strains with a treatments without inoculation (control). Each pot was filled with 4 Kg soil، lacking local symbiotic bacteria with low nitrogen، mixed with 2ml related strain and 5ml marked Ammonium Nitrate (10 atom% 15N excess). Nitrogen fixation was estimated by isotopic dilution method after harvest. According to the results، the effect of different strains treatments was significant on all criteria (p≤0. 01). Among various strain treatments، the one inoculated with equal ratio of three strains mixture was superior to the others in the most criteria such as the quantity of fixed nitrogen (431. 5 mg per plant)، nitrogen percentage in plant (3. 53 percent)، dry weight of shoot (14. 07 g) and nodules (300. 6 mg per plant)، total dry weight of plant (16. 6g per plant) and seed dry weight (9. 87 g per plant). In addition، in all inoculated treatments، about 70% of plant nitrogen requirement was provided by symbiosis.