SUMMARY: Field trials were made at thirteen centres in varied localities to test whether a strain of clover Rhizobium used as a seed inoculum in the field could establish itself in the crop in competition with the native strains already present in the soil. Each experiment comprised four sets of plots, one uninoculated and the other three each sown with seed inoculated with a different strain of Rhizobium.
The difficulty in identifying a strain re-isolated from a nodule was met by using as inocula strains whose antigenic composition made them readily identifiable by agglutination tests. From each plot, twenty-five nodules were selected, and isolates from these tested against selected antisera. This method of identification enabled the percentage of nodules produced by each inoculant strain to be ascertained. Strains differed in their ability to establish themselves in the field: a suitable strain gave rise to 50% or more of the nodules. In sand culture competition between pairs of inoculant strains was not related to their ability to establish themselves in the field, but each strain whose establishment was superior also showed competitive dominance on at least one date of sampling.
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