The establishment and yield of lucerne (Medicago sativa cv. Wairau) and the influence of cover crops, weeds, irrigation and lucerne seeding rate

Two field trials were conducted at Crop Research Division, D.S.I.R., Lincoln, in the 1971/72 and 1972/73 seasons to examine ways of reducing the cost of establishing lucerne and reducing the loss of production in the first year. Trial I examined the effect of a spring sown barley (cv Zephyr) cover crop at three seeding rates, 0, 56 and 112 kg/ha, on lucerne sown at the same time at three seeding rates, 2.9, 3.8 and 5.8 kg/ha with and without irrigation. The 1971/72 season was drier than normal but lucerne establishment was unaltered by a cover crop regardless of seeding rate or irrigation treatment. The overall establishment was high with 73% of viable seeds being present as plants after the first winter at a seeding rate of 2.9 kg/ha. Lucerne production at the harvest cut was reduced by barley sown at 56 kg/ha to 21% and 49% non-irrigated and irrigated respectively and remained depressed for two further cuts non-irrigated but yield was restored by the following cut irrigated. Irrigation increased the first season lucerne yield by 100% clear seeded and 194% with 56 kg/ha of barley and lucerne seeding rate had no effect on lucerne yield. Undersown lucerne at all seeding rates reduced barley grain yield by 20% at the low barley seeding rate but lucerne at the high seeding rate only reduced grain yield at the high barley seeding rate. Trial II examined the effect of a winter sown wheat (cv Arawa) and a spring sown barley (cv Research) on the establishment and early yield of lucerne sown in the spring at three seeding rates (2.25, 9.0, 35.0 kg/ha). The influence of cover crop competition was further examined by sowing the cover crops at three seeding rates (56, 112 and 224 kg/ha), and by simulated grazing of the wheat and the use of a herbicide on the barley and clear seeded lucerne. The 1972/73 season was drier than normal and although percentage lucerne establishment decreased as the lucerne seeding rate increased, no cover crop treatments effected lucerne establishment. Overall establishment was low with 36.5% of viable seed being present as plants after harvest at the 2.25 kg/ha seeding rate. Lucerne production at the harvest cut was low and was reduced markedly by cover crop treatments and height, root weight and root weight distribution data suggested that wheat had a greater effect than barley. No further cuts w.ere taken in the establishment season but cover crops continued to reduce lucerne yields in four cuts, in the following season. The use of spring sown cereal cover crops for lucerne establishment can be justified on the basis of providing a more profitable return, provided the establishment year production of clear seeded lucerne is low but cannot be justified on the basis of weed suppression. Lucerne seeding rates of 2.25 and 2.9 kg/ha produced stands with at least 30 plants/m² which was a density sufficient for maximum production.