Competition for Nodule Sites Between Strains of Rhizobium japonicum Applied as Inoculum and Strains in the Soil¹

Abstract

Synopsis Strains of Rhizobium japonicum applied as inoculum at different rates and by different methods differed greatly in the proportion of nodules produced on soybeans (Glycine max (L.) Merr.) grown in soils containing effective soybean rhizobia. The percentage of nodules produced by all strains applied at the standard rate of inoculation was low and averaged 5%. Increasing the amount of inoculum applied increased the percentage of nodules produced by some strains but had little effect on others.

Populations of Rhizobium japonicum in Iowa soils and inoculum level needed for nodulation of Glycine max (L.) Merrill

“…Johnson and Means (1964) observed that strains of soybean rhizobia tested in the greenhouse for relative com petitiveness had the same relative competitiveness to each other when used as inoculum for soybeans planted in rhizobia free soil in the field. However, Johnson et al (1965) found that strains previously shown to be of similar competitiveness in the greenhouse did not maintain the same relationship when added to soils with established populations of R. japonicum. For instance, 2 strains of lower competi tiveness than a third strain in the greenhouse formed 82% and 8% of the nodules on soybeans in competition against a native population in the field.…”

“…Burton (1967) reported that approximately 73,000 rhizobia were supplied per seed by the commercial rate of inoculation. Johnson et al (1965) found that the recovery of inoculum strains in the nodules of soybeans was higher in a green house experiment than it was in the field. The field ex periment was performed during the summer but soil was collected in the winter from the same field for the green house experiment.…”

“…japonicum resulted in from 0 to 100% of the nodules being formed by the inoculum strain Johnson et al, 1965;and Ham, 1967). All of the nodules on field grown soybeans were determined to be of the inoculum type by Johnson and Means (1964) and Ham (1967) when fewer than 3 nodules per plant were on the uninoculated plants.…”

“…However, less than 10% of the nodules were formed by the inoculum strain when the uninoculated control was well nodulated and the commercial rate of inoculation was used (Johnson et al, 1965). By increasing the inoculum size to 800 times the commercial rate some inoculum strains of R. japonicum formed up to 50% of the nodules (Johnson et al, 1965).…”

“…By increasing the inoculum size to 800 times the commercial rate some inoculum strains of R. japonicum formed up to 50% of the nodules (Johnson et al, 1965). Burton (1967) reported that approximately 73,000 rhizobia were supplied per seed by the commercial rate of inoculation.…”