Among the eight field isolates tested in a greenhouse for efficiency by comparison with eight lyophilized isolates, seven showed no significant difference for the total weight of soybean or seed yield but one field isolate showed a loss of efficiency corresponding to 27% less seed weight. With regards to agronomic characteristics, there were no important changes in the competitivity of the strains. In the two fields where the survival was high, the two strains remained at about the same relative level as at introduction, there was no detectable exchange of characters between them.
japonicum remained high during 4 years without soybeans, but a new inoculation would be necessary after 5 years. In this field, the number of introduced B. In the Toulouse field after the two initially introduced strains, inoculation of subsequent soybean crops with a new strain enabled this strain to occupy 70–80% of the nodules these results suggest that under such conditions the problem of competition can be solved by repeated inoculation. japonicum completely disappeared in the Montpellier field after 10 years under vineyard. In the Dijon location, the survival was high although soybean was never grown in the field. These strains were re-isolated 16 or 20 years later and compared with the parental strains kept lyophilized. Two strains of Bradyrhizobium japonicum, recognizable by their intrinsic resistance to high levels of antibiotics and their serological features were introduced into three calcareous soils under field conditions.
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