SYMBIOTIC EFFECTIVENESS OF RHIZOBIUM-LEGUMINOSARUM BV TRIFOLII COLLECTED FROM PASTURES IN SOUTH-WESTERN VICTORIA

The whole-soil inoculation method was used to assess the symbiotic eff ectiveness of rhizobia populations in soils collected from Is randomly -selected pastures in south-western Victoria. This was part of a large r study which described the condition of pasture within this region. B ased on the shoot weights of test subterranean clover plants, cv. Moun t Barker, effectiveness varied from 36 to 94% depending on the site of rhizobia collection. This range was wider than that found in an earli er survey of rhizobia effectiveness conducted nearby. WU95, the commer cial inoculant for subterranean clover, was significantly more effecti ve than 9 of the rhizobia samples. Rhizobia from 2 sites were especial ly poor and their effectiveness (37%) was not significantly different from the nil inoculum control (28%). Symbiotic effectiveness was not r elated to soil pH, available sulfur, available phosphorus, total nitro gen or mean annual rainfall for each site where rhizobia were collecte d. After pooling data for all sites, the shoot weights were significan tly related to the proportions of plants with nodules assigned high no dulation scores. In contrast, low scores, within 1 of 6 categories, di d not significantly affect shoot weight. The technique of using mean n odulation score was less capable of discriminating differences in symb iotic effectiveness, compared with assessment based on test plant weig ht.