Inoculation for successful establishment of Caucasian clover

Abstract

Results from oversowing trials in the tussock grasslands have shown that nodulation problems can limit the establishment of Caucasian clover (Trifolium ambiguum). They also strongly suggest that previously reported difficulties with establishment of Caucasian clover, in areas where white clover (T. repens) had established sucessfully, were likely to be due to inoculation failures due to low numbers of rhizobia on the seed, or in the case of tetraploid cultivars, to the use of an unsatisfactory strain. With the tetraploid cultivar Treeline, inoculation with the recommended strain ICMP4074b resulted in low levels of effective seedling nodulation even with very high levels of rhizobia/seed at sowing (149 000). Treeline seedling nodulation was increased when inoculated with strain ICMP4073b, the approved strain for hexaploid cultivars, and the strain was effective at symbiotic nitrogen fixation. Effective seedling nodulation of both tetraploid Treeline and hexaploid Monaro cultivars inoculated with ICMP4073b increased as the number of rhizobia on the seed at sowing was increased. Low levels of seedling nodulation occurred when populations of rhizobia on the seed were in the range likely to be present when seed is slurry inoculated, or inoculated and pelleted and stored for several days before oversowing. To maximise effective nodulation, seed should be inoculated at least 5 times the recommended rate, with the incorporation of gum arabic in the slurry or pellet and oversown within one day. Keywords: Caucasian clover, establishment, inoculation, nodulation, rhizobia, Trifolium ambiguum