Agronomic evaluation of Trifolium ambiguum M. Bieb : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Agricultural Science in the University of Canterbury [Lincoln College]

Caucasian clover (T. ambiguum M. Bieb.) was studied to assess its suitability in revegetation programmes on eroded mountain areas. One hexaploid and two diploid strains of T. ambiguum were compared with Grasslands Huia white clover in controlled environments, field and fertilized conditions. In New Zealand alpine climate, Summit, a diploid strain of T. ambiguum bred for high altitudes grew more slowly than white clover in the seedling year. Similar results were obtained during a winter at Lincoln with inoculated plants. However, the hexaploid C.P.I. (10803) T. ambiguum was clearly more productive closely approaching the growth rate of white clover at moderate temperatures. Two controlled environment studies were carried out at different temperatures but at constant light intensity of 20,000, lux, 16 hours photo-period and 85% relative humidity. The range of temperatures chosen simulated those experienced by plants in early summer at high, middle and low altitudes in Canterbury, New Zealand. In the first experiment plants of T. ambiguum cv. Summit yielded significantly more dry matter at low temperature (10°C day / 3°C night) than did T. repens cv. Huia. However at higher temperatures Huia was superior to cv. Summit. A later controlled environment experiment including three strains of T. ambiguum. Initially the hexaploid C.P.I. (10803) grew more rapidly than the other two diploid strains C.P.I. (2771) and summit and Huia white clover. But in terms of the relative growth rates of shoots, roots, increase in leaf area and net assimilation rates of shoots calculated over a period of four weeks seedling growth, Huia was superior to the three strains of T. ambiguum at all temperatures tested. Between T. ambiguum strains, though, there were some differences. It was concluded that few differences were significant over the complete range of temperatures used. Net carbon dioxide exchange was assessed by infra red gas analysis for Summit (2n) and hexaploid C.P.I. (10803) T. ambguum and Huia T. repens. The net photosynthesis of the hexaploid C.P.I. (10803), the high altitude diploid, Summit and Huia was low at 10°C and l5°C but increased dramatically at 20°C. The respiration rate rose with increasing temperatures in accord with expectations, but in cv. Summit, which had relatively high respiration rates at 5°C and 10°C there was a lower rate at 15°C compared with the other two strains. The hardened plants of C.P.I. (10803), C.P.I. (2771), Summit and Huia withstood freezing temperatures -10°C, while the unhardened plants were killed completely at -12°C. In the soil nutrient factorial pot trial, a significant linear response to added phosphate was exhibited by cv. Summit grown on subsoil of the alpine Spenser soil set. Responses to low levels of added phosphate and lime were measured in nodulation, nitrogen fixation and phosphorus uptake. Lime had no effect on the host plant growth but improved nodulation. The results were discussed in relation to other work on perennial herbacious legumes. An assessment has been made of the suitability of T. ambiguum for use in programmes for revegetation of eroded greywacke, argillite and schist mountains in New Zealand. Recommendations were made for future ecological, physiological and genecological research on this very interesting polyploid species