Competition between inoculum strains ofRhizobium japonicum in the process of soybean nodulation during three planting periods

Competition between inoculum strains ofRhizobium japonicum D 216 and 311 B applied to soybean seeds in mixed inocula depended, especially in the year of inoculation, directly on the ratio of the cell numbers of the two inoculum strains in mixtures. Uninoculated plants grown in original soil contaminated in August 1969 by inoculated seed and stored subsequently in original pots without watering for 8 months displayed, after the spring (May) and summer (August) sowing in 1970, a statistically significant nodulation shift in favour of the D 216 strain. The highest nodulatiou was achieved with all inoculation treatments during spring sowing in 1970.