Influence of Rhizobium japonicum Strains and Inoculation Methods on Soybeans Grown in Rhizobia‐populated Soil1

Abstract

AbstractIndigenous rhizobia in field soils previously planted to soybeans (Glycine max L. Merr.) usually preclude the nodulation by rhizobia applied as inoculants. However, the introduction of superior N fixing strains is still considered an important management goal. This study was conducted in a rhizobia‐populated field soil (Fluvaquentic dystrochpepts) using three strains of R. japonicum (62, 76, and 110). Each strain was used at 1× and 10 × rates of peat inoculum applied to the seed and at 1×, 10× and 100× rates of liquid inoculum applied over the seeds in the row. The objective was to determine if applied strains could compete with indigenous rhizobia for nodule sites and enhance N fixation. Inoculation by either method or with any rate or strain did not effect nodulation or plant growth. However, when the level of strains 62 and 110 in broth was increased 10 and 100 times the initial rate, the recovery of applied strains increased. Peat inoculum applied at 10 times the initial rate did not appreciably change the serogroup distribution in nodules. Strain 76 did not form an appreciable percentage of the nodules at any rate or method of inoculation because it was less competitive than the predominant strains in the field soil. Increased inoculum rates applied by different methods, while only partially successful in displacing indigenous soil rhizobia, demonstrate the need for continued evaluation of innovative methods of applying efficient rhizobia which can compete for nodule sites in the field.