An evaluation of the phosphate and temperature requirements of Trifolium ambiguum M. Bieb selections : a dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours in the University of Canterbury [Lincoln College]

Abstract

Trifolium ambiguum is a very diverse species containing three distinct chromosome races. It is a rhizomatous perennial species with a potentially wide range of adaptation. Two cultivars have been developed in Australia specifically for high altitude revegetation roles. Two more selections are about to be released with a higher productive capacity though still tolerant of low fertility acid soils, cold temperatures and drought conditions. One of these more productive selections, C.P.I. 10803 a hexaploid was grown in a glasshouse pot trial with T. repens cv Huia and Lotus pedunculatus cv Maku on a P deficient moderately acidic upland yellow-brown earth. Five phosphate treatments were applied - namely 0, 10, 20, 40 and 80 kg P/ha. Initially vigour of C.P.I. 10803 was good, mainly due to a large seed but after 71 days was inferior to both Maku and. Huia at all but Pₒ in both root and shoot yields. At Pₒ growth of all species was negligible. C.P.I. 10803 had a flat linear response curve to the maximum P rate. Maku was superior at all P rates but especially at 10 and 20 kg/ha P. Huia was intermediate. Much of the superiority of Maku was attributed to the ability to form large numbers of fully effective nodules especially at low P rates. Effective nodulation of T. ambiguum has proved difficult and although considerable work has been done by Hely (1957-72) it appears that this species remains inferior to domesticated legumes in terms of prompt formation of a large effective nodule mass. In a second pot trial in a controlled environment six T. ambiguum selections (i.e. cv Summit (2 N), C.P.I. 51139 (4 N), C.P.I. 51140 (4 N), C.P.I. 57353 (6 N), C.P.I. 50329 (6 N) and C.P.I. 10803 (6 N)) and T. repens cv Huia were grown at two temperature regimes - namely 20/10°C and 15/5°C day/night for 84 days. All T. ambiguum selections were inferior to T. repens cv Huia especially at 15/5°C where dormancy of T. ambiguum was marked. The 6 N selections were more productive (root and shoot D.M.) than the 4 N selections which only out produced cv Summit at 20/10°C day/ night. As a species T. ambiguum has a high root: shoot ratio which is responsive to stress conditions and may be used as an index of adaptability. Again the relatively poor performance of T. ambiguum is partly due to low levels of effective nodulation. The hexaploids had a higher effective nodule mass and were more productive than 2 N or 4 N selections. These results are discussed in relation to previous short term pot experiments (Paljor 1973) and suggestions for future research are made. The need for long term field experiments to fully assess the potential of this species as a pasture legume is stressed.