Studies of field populations of rhizobium: Effectiveness of strains of rhizobium trifolii associated with trifolium subterraneum L. pastures in South-Eastern Australia

Field populations of Rhizobiuin trifollii from eight regions in south-eastern Australia were sampled over a period of 5 years from 1966 to 1970. The R. trifolii isolates were tested under bacteriologically-and environmentally-controlled conditions for effectiveness of nitrogen fixation in combination with Trifalium subterraneum L. cv. Bacchus Marsh; the effective strain TA1 was used as a standard of comparison.Mean effectiveness of the R. trifolii populations for any region at any sampling varied between 62 and 93 percent of the effectiveness of the standard strain. The principal feature was the large variability within sampling sites, between sites within paddocks, and between paddocks within regions. In addition there was some variability with time in the range of effectiveness values of isolates within a site and in the absolute values for both sites and paddocks. Effectiveness values were not related to soil pH, size of population of R. trifolii, inoculation procedure at sowing, age of pasture, annual rate of fertilizer application, or mean annual rainfall.