Evaluation of Rhizobium japonicum Inoculants in Soils Containing Naturalized Populations of Rhizobia1

Abstract

AbstractAn important question in current soybean (Glycine max (L.) Merrill) production is whether inoculation is beneficial when seed is planted in soils where effectively nodulated plants have been produced previously. These studies were conducted to measure the effective of inoculating soybeans with commercial cultures of R. japonicum on seed yield and protein percentage when soybeans were grown on soils which had grown nodulated soybeans previously.Paired samples of different lots of soybean seed taken before and after commercial inoculation with R. japonicum were planted at two Minnesota locations in 1967. More extensive studies were conductedi in 1968 at five locations in cooperation with various inoculant companies. Seed from a common lot was sent to the participating companies to be inoculated. Two treated samples and an uninoculated check were returned from each company. Two samples were treated immediately prior to planting with humus samples from each inoculant company. Three humus cultures of single strains of R. japonicum, selected from the more effective strains in an inoculation study on rhizobia free soils in Minnesota, also were used as inoculants.Soybean seed yields and seed protein percentage were not significantly increased by inoculating soybean seeds with Rhizobium japonicum at planting time. The uninoculated checks were adequately nodulated by rhizobia which were in the soil from previous soybean crops. Serotyping of single strain inoculants indicated a substantial range of recovery (0–17%) depending on the strain and location.