Influence of the number of rhizobia on the nodulation and establishment of Trifolium ambiguum

Rhizobium leguminosarum bv. trifolii in New Zealand soils is ineffective on Trifolium ambiguum and inoculation with an effective strain of rhizobia is essential for nodulation. We investigated the effect of inoculation on the establishment of oversown T. ambiguum (cv. Monaro) in different tussock grassland environments. Peat-based inoculant was applied to seed at a range of rates, in a gum arabic-lime pellet, and when sown 1 day after inoculation the number of rhizobia ranged from 0.2 × 103 to 260 × 103 seed−1 Over the 9 sites, seedling nodulation progressively increased from 5% up to 66% as the number of rhizobia seed−1 increased. Seedling establishment at the end of the first year was directly related to nodulation. These results have important practical implications in improving the establishment of this legume, as the number of rhizobia required to maximize nodulation is higher than that obtained by inoculation at the recommended rate.