Studies of the establishment of subterranean clover (Trifolium subterraneum L.) and the rate of breakdown of hardseededness

Abstract

The object of first experiment was undertaken to determine the best time of subterranean clover (Trifolium subterraneum) sowing in autumn. The effect of dates (6 February, 4 March, 27 March and 9 April) of sowing, irrigation or no irrigation and vegetation cover (high and low) on the emergence and establishment of subterranean clover, c.v. Mt.Barker, oversown into unimproved pasture was investigated on a Templeton silt loam soil at Lincoln College. With no irrigation, the best establishment of subterranean clover (74.5% and 81.5%) was obtained from 27 March and 9 April sowings in the presence of cover. Vegetation cover was vital for good emergence and establishment of sub clover under no irrigation. With irrigation, time of sowing and vegetation cover were not critical.

A second experiment was conducted to determine the rate of breakdown of sub clover hardseededness in the field on a steep sunny slope facing north west in North Canterbury hill country. This involved two herbicide treatments (with and without) and two insecticide treatments (with and without). The seed (c.v. Mt.Barker) used had a high level of hardseededness. Germination rate was 6% just after sowing in February but increased to a relatively low maximum of 24% by May. There was no significant differences in total percentage of germination between treatments.

Germination studies were also carried out in the growth cabinets using hand harvested seed stored in the laboratory or buried in the soil. The germination percentages at constant temperature of 15°C remained low at each different time of sampling of the seed and there was no differences between seeds from laboratory or buried in the soil. A study over five months showed that germination remained low at constant temperature of 15°C. However, the fluctuating temperature of 35°/15°C significantly (<0.01) increased the germination by about 45% as compared with the constant temperature at the end of five months period. It is clear that in the field, temperature fluctuations were insufficient to cause substantial breakdown of hardseededness, thus resulting in a relatively low field germination.

A further experiment was also conducted in 1986 to determine the total seed production, level of autumn germination and fate of natural seedlings of nine subterranean clover cultivars (Mt.Barker; Woogenellup; Trikkala; Nangeela; Seaton Park; Tallarook; Howard; Larisa; Clare) in the same hill site as Experiment two. Total seed production and total autumn germination were different between cultivars. The early flowering strain Howard produced the highest seed yield and the late flowering Larisa the least. The best autumn germination was obtained from midseason flowering strain Mt.Barker. Autumn germination of Nangeela and Trikkala were better in comparison to other six strains. When the seedlings were measured after grazing on 10 July, about 70% of the seedlings recorded before grazing were dead. This was probably because of hard grazing and trampling by sheep.