Effects on soybean seed yield by members of 123 serocluster and USDA 110 in the greenhouse and in soils low in indigenous Bradyrhizobium japonicum

Abstract

USDA 123spc and USDA 110str were inoculated on three soybean cultivars in a pot experiment in the greenhouse. USDA 110str yielded 33% more seed than USDA 123spc (P < 0.01). In a low-Bradyrhizobium soil (10 cells/g) at Arlington, WI, three members of the 123 serocluster (USDA 123spc, NJ2-lastr, and I-123spc), USDA 110, and USDA 138 were inoculated at a rate of 1 × 108 cells/2.5-cm row on two soybean cultivars. The inoculum strains formed 100% of the nodules. There was no difference (P < 0.05) in seed yield between any of the inoculum strains on either cultivar. In a low-Bradyrhizobium (102 cells/g), low-N soil, in Georgia, USDA 110, USDA 110str, and two members of the 123 serocluster (USDA 123spc and NJ2-lastr) were inoculated at an inoculum rate of 1 × 108 cell/2.5-cm row on two soybean cultivars. Plots were fertilized with 156 kg of N ha−1, or no N was applied. Serogroup 110 formed 59–90% of the nodules and serocluster 123 formed 48–82% of the nodules on the cultivars. There were no differences in seed yield between the inoculum strains, except that on cv. Gordon with added N, USDA 110 resulted in higher seed yield than USDA 123spc. The uninoculated control plots with cv. Braxton (without added N) also had a better seed yield (P < 0.05) than plots inoculated with USDA 123spc. In summary, inoculation with USDA 110str resulted in higher soybean seed yield than inoculation with USDA 123spc under greenhouse conditions, but not always under field conditions. Key words: Bradyrhizobium japonicum, field trials, seed yield.