Abstract: Treatment of slow growing Bradyrhizobium japonicum “005” and inoculated plants with consistant magnetic field revealed that the efficiency of nitrogen fixation could be increased by 4–5 times under an appropriate magnetic intensity. The average number and weight of root nodules per experimental group were also increased by 2–3 times respectively. The change in growth phenotype of rhizobia isolated from the nodules of treated plants showed that the fast growing type of Rhizobium appeared with the frequency of about 17% among 100 plants. The generation time and pH value of the fast growing isolates obtained were similar to those of Rhizobium USDA 191 but different from Rhizobium “005”. The magnetic field dfect on nitrogenase activity and the change of growing rate of Rhizobium are also discussed.

Key words: Magnetic field, Soybean, Rhizobium, Nitrogen fixation