Subterranean clover to increase the legume content of pastures in spring

Traditional ryegrass/white clover pastures frequently have less than the optimum 50% legume content for animal production, particularly in early spring when white clover growth rates are low. Three experiments were used to investigate ways to increase the legume content of pastures in early spring. Experiments 1 & 2 investigated the potential for over-drilling subterranean clover in autumn into established ryegrass-based pastures to increase dry matter yields and legume content in early spring. Dry matter yields in Experiment 1 were 310 kg DM/ha greater in ‘Woogenellup’ pastures than controls, although these yields were depressed by higher than average rainfall and slug and grass grub damage. Total clover content in ‘Woogenellup’ reached 13.6% by early October, compared with 8.18% in the control. Experiment 2 at Invernia, a commercial dairy farm in North Otago, aimed to introduce subterranean clover under normal management of a dairy farm. Dry matter yields were not increased, but clover content was higher in ‘Woogenellup’ (21.7%) and ‘Antas’ (17.1%) than ‘Denmark’ (9.22%) and the control (5.95%). Subterranean clover was over-drilled into a second paddock, with no experimental design. In there, the subterranean clover content of pasture reached 25% in some areas, however it did not grow where white clover made up >25% of the pasture in spring. ‘Woogenellup’ showed greater production than ‘Denmark’ at both experiments, and ‘Antas’ was more productive in the higher pH soils of Experiment 2. The maximum subterranean clover yield measured in Experiments 1 & 2 was 320 kg DM/ha. Over-drilling subterranean clover was estimated to be profitable if yields could reach 500-1000 kg DM/ha. Experiment 3 applied gibberellic acid (GA) to pure subterranean clover swards to increase spring dry matter yields. However, dry matter yields were not increased by GA at any stage in the experiment. Plant height did increase 44 days after GA application. In mixed pastures, this may lead to increased light interception of subterranean clover, and represents an area for further work. Large leaved cultivars produced more dry matter than small leaved cultivars, which was consistent with results at Experiments 1 & 2. Dry matter yields of 3.5-4 t DM/ha in ‘Narrikup’, ‘Woogenellup’ and ‘Antas’ were recorded in early October. The concept of over-drilling subterranean clover into dairy pastures to increase early spring dry matter yields and production was successful, but not at levels that would support a financial return. The concept requires further work, which could include using balansa clover, which survives in the wet conditions that depressed subterranean clover growth in Experiments 1 & 2.