Studies on the efficiency of n2 fixation by bradyrhizobium japonicum isolated from root nodules of soybean grown under semiarid tropics of Tamil nadu

The competitive nodulation ability of a Bradyrhizobium strain is an important property, as strains must compete with other Bradyrhizobia in the rhizosphere for nodulation sites on the host plant. If inoculants strains are to succeed, they must have the ability of competitiveness as well as being effective in symbiosis. The establishment of effective nodulation of soybean plant can be enhanced by using effective and competitive strains of Bradyrhizobium. In the present study 30 isolates of Bradyrhizobium japonicum obtained from semiarid locations were compared for their N2 fixing efficiency based on IAA production, EPS production, nodulation, nodule ARA activity and nodule N content. The isolate obtained from Tiruchengodu SBJ-14 produced maximum of IAA, EPS and ARA activity and this isolate also recorded the highest number of 30.00 nodules plant-1 ARA activity of 215.00 n moles C2H4 formed h-1 g-1 and nodule nitrogen content of 7.44%.