Introduction and Survival of an Inoculant Strain of Rhizobium japonicumin Soil¹

A 7‐year experiment was begun in 1976 to determine if a nonindigenous inoculant strain of Rhizobium japonicum could be introduced into, and survive in a soil in Louisiana. The soil was an Olivier silt loam (fine‐silty, mixed, thermic Aquic Fragiudalf) located at Baton Rouge. Inoculation rates were 10 4 or 10 8 R . japonicum strain 110 cells cm −1 of row. The inoculum was applied directly into the furrow as a liquid suspension. The same plots were inoculated for 3 consecutive years. In 1978, a third treatment, 10 8 rhizobia cm −1 of row was used as the inoculant and 250 kg NH 4 NO 3 ‐N ha −1 was applied in five equal split applications. None of the plots were inoculated after 1978. ‘Lee’ cultivar was planted in the first 3 years while ‘Dare’, ‘Lee’, ‘Bragg’, and ‘Coker 338’ cultivars were planted in each plot from 1979 through 1982. The cultivars represented Maturity Groups V through VIII. Recovery of the inoculant rhizobia from the soybean ( Glycine max L. Merr.) nodules was quite low during the first 4 years. General recoveries were within the range of 0 to 17% as reported by other researchers for 1 year studies. In 1980 and thereafter, recovery of the inoculant rhizobia increased considerably. Average recoveries over all rates of inoculation ranged from 29 to 33% in 1980 and were up to 54% by 1982. Individual treatment values were as high as 60% from the 10 8 R . japonicum cm −1 of row plots in 1982. Results of this study were interpreted to indicate that 3 years of massive soil inoculation with a nonindigenous strain of R . japonicum allowed the permanent establishment of this strain into the soil. Once established, this strain became competitive with the native rhizobia in the soil, and each year formed a higher percentage of the nodules on the soybean roots.