Introduction and Survival of an Inoculant Strain of Rhizobium japonicumin Soil1

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Abstract
A 7‐year experiment was begun in 1976 to determine if a nonindigenous inoculant strain of Rhizobium japonicumcould 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 104or 108R. japonicumstrain 110 cells cm−1of 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, 108rhizobia cm−1of row was used as the inoculant and 250 kg NH4NO3‐N ha−1was 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 maxL. 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 108R. japonicumcm−1of 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. japonicumallowed 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.