Symbiotic competence of rose clover (Trifolium hirtum All.)

Rose clover (Trifolium hirtum All.) is a forage plant that is well adapted to acidic and mildly alkaline soils of low natural fertility in southern Australia and to climates with a winter-dominant annual rainfall of 300 mm and above. Reports of low concentrations of nitrogen in rose clover foliage have been attributed to poor N 2 fixation and may have discouraged its use in Australia. This investigation, conducted in tube culture, examined the ability of four lines of rose clover to nodulate and fix N 2 with effective strains of clover rhizobia (Rhizobium leguminosarum bv. trifolii) and with soils (as a source of naturalised rhizobia) collected from field sites in New South Wales and South Australia. Comparisons with other Trifolium spp. were also made. It was confirmed that there was a low concentration ofN in the shoots of the rose clover cvv. SARDI Rose and Hykon. This occurred even where rose clover nodulated and fixed N 2 effectively with well known inoculant strains of clover rhizobia and with soil samples collected in the field (provided that the populations of resident clover rhizobia in the soil were at least 150/g). Individual plants were uniform in response to inoculation. Rose clover cv. SARDI Rose was closely related to six of the nine other lines of clover with which it was compared. It was concluded that the registered cultivars of rose clover, cvv. SARDI Rose and Hykon, are symbiotically competent plants. It appears that low N in rose clover foliage is an intrinsic characteristic of the species unconnected with its symbiotic characteristics.