Use of Italian ryegrass on seasonal dairy farms in northern New Zealand .1. Feed production and persistence

Four field plot experiments were conducted to determine the effects different methods of establishment, nitrogen (N) fertiliser applications, and sowing time, had on the growth of Italian ryegrass (Lolium multiflorum Lam. cv. Concord), particularly in late winter/early spring when feed shortages occur on seasonal dairy farms. Data were collected on the seasonal herbage accumulation and persistence of autumn-sown Concord ryegrass, and its chemical composition and digestibility. An insecticide treatment was applied to examine possible damage by insects such as Argentine stem weevil (Listronotus bonariensis (Kuschel)) at various sowing dates. These experiments provided background data for a large-scale farmlet trial measuring milk production responses, following the introduction of Concord ryegrass. Compared with existing unrenovated pasture (EP), Concord ryegrass drilled into plots after spraying existing pasture with herbicide (DD), accumulated, on average over consecutive years, twice as much extra dry matter (DM) in late winter/early spring (0.8 t DM/ha) as did those that were undersown (US, 0.4 t DM/ha). Responses to winter-applied N fertiliser were small. Initial density of Concord ryegrass was nearly twice as high in DD as in US plots (1182 vs 632 plants/m(2)); 64 and 51% of plants, respectively, were lost following the first grazing. Regardless of treatment, losses of Concord plants were high during the first summer and only 2% of the established population (20 plants/m(2)) remained in the second winter. Drilling in February as opposed to March produced an extra 1-2.5 t DM/ha, and insecticide treatment increased herbage accumulation by 30% in the first regrowth period after drilling, although the risk of damage from Argentine stem weevil appeared to be low. The chemical composition and digestibility of Concord ryegrass were generally similar to perennial ryegrass, and adequate for lactating dairy cows. It was concluded that removal of existing pasture provided the best winter/spring growth from Concord ryegrass, and the persistence of Concord over summer was poor.