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Three glasshouse trials investigated N 2 fixation in white clover following inoculation with rhizobia from caucasian clover. We grew white clover in agar, vermiculite/perlite and soils low in available-N and with no detectable rhizobia. Media were subsequently treated with inoculum containing rhizobia effective on either (i) caucasian clover, (ii) white clover, or (iii) mixtures of the two. The percentage of ineffective nodules on white clover increased as the proportion of rhizobia from caucasian clover in the inoculant mix increased. However, the percentages of ineffective nodules on white clover were less than the proportion of ineffective rhizobia in the inoculant, indicating that the ineffective rhizobia were less competitive in nodule formation. Foliage yield and symbiotic N 2 fixation in white clover were not significantly affected when ineffective rhizobia from caucasian clover made up 67% or less of the inoculant. A03019; Online publication date 26 February 2004 Received 3 April 2003; accepted 15 August 2003However, when ineffective rhizobia made up a high proportion of the inoculant mix (>92%), both foliage yield and N 2 fixation were significantly reduced compared with plants inoculated with only white clover rhizobia. Extrapolation of the present glasshouse results to the field is difficult and further field trials are required to determine if rhizobia from caucasian clover have any effect on symbiotic N 2 fixation of white clover in pastoral situations.

Caucasian clover (Trifolium ambiguum) is being commercially released for use in New Zealand agriculture. Seed must be inoculated at sowing, as caucasian clover forms a nitrogen-fixing symbiosis only with specific rhizobia that are not native to New Zealand. These rhizobia have the potentially undesirable property of readily forming nodules on white clover that do not fix nitrogen. Caucasian clover inoculant strains available for use in New Zealand were found to be genetically unstable in the laboratory, and must be frequently monitored for their symbiotic properties. A strain of caucasian clover rhizobia that gives better establishment and growth of caucasian clover under oversowing conditions was identified. This strain maintained a higher level of viability under stress conditions in the laboratory and showed enhanced survival on seed in the environment. Growth of caucasian clover results in large populations of caucasian clover rhizobia in the soil. These formed nodules on white clover in the same field environment, although white clover rhizobia dominated nodule formation. Nevertheless it is possible that present caucasian clover inoculants may over time reduce nitrogen fixation and hence the production and persistence of white clover. Further research is required to develop a caucasian clover strain that does not form ineffective nodules on white clover. Keywords: caucasian clover, inoculation, nodulation, rhizobia, Trifolium ambiguum, Trifolium repens, white clover

Caucasian clover (Trifolium ambiguum M. Bieb.) is an alternative legume for areas where white clover (T. repens L.) growth is limited. However, slow establishment has been a problem when caucasian clover has been oversown. Results from two tussock grassland sites have demonstrated the importance of the initial establishment of caucasian clover. Caucasian clover dry matter production after 6 years was still related to original seedling establishment. This result was obtained in ungrazed swards, conditions likely to maximise the ability of caucasian clover to spread by rhizomes and natural reseeding. The results indicate that caucasian clover may make little contribution to legume yield in these environments for at least 6 years unless satisfactory numbers of plants are established initially. Maintenance fertiliser application, in early years at least, appears similar to that required by white clover. Yields of caucasian clover swards in the 6th year when maintenance fertiliser had been applied were 3-7 times those when fertiliser had been applied only at sowing. The paper also provides possible explanations for establishment failures that have already occurred, and provides information on correct management techniques to maximise establishment of oversown caucasian clover. Keywords: caucasian clover, establishment, fertiliser, hill country, inoculation, nodulation, oversowing, pasture, Trifolium ambiguum

The establishment from seed of 8 perennial legumes was investigated in 3 trials in drought-prone regions. Two trials, in central Hawke's Bay, aimed to determine the extent of establishment of 6 test species (Astragalus cicer, Coronilla varia, Dorycnium hirsutum, Dorycnium pentaphyllum, Lotus corniculatus, Lotus tenuis) and 2 standard species (Medicago sativa, Trifolium repens). The third trial, in Central Otago, aimed to identify the most effective strain of Rhizobium loti for nodulating D. hirsutum in the field. In Hawke's Bay, establishment of all species was satisfactory. Seedling emergence ranged from 0.2% (T. repens) to 25% (A. cicer, C. varia, D. hirsutum), but emergence levels for all species varied between trials. Herbage yields of A. cicer (4 t DM/ha), C. varia (3 t DM/ha) and L. tenuis (3.7 t DM/ha) were relatively high, and they could have potential as forages. Inoculation of seed of D. hirsutum with R. loti strain ICC211 resulted in 60% of seedlings being nodulated, compared with 25% where strain ICC224 was used. Foliage weights of all plants inoculated with strain ICC211 (154 mg) were higher than those inoculated with strain ICC224 (52 mg). Strain ICC211 is recommended for inoculating D. hirsutum. Keywords: dryland legumes, nodulation, plant establishment, revegetation