A study of some factors affecting the growth of grasses introduced into hill pastures on sunny aspects in North Canterbury

Grass and legume seedlings were planted to form legume and legume-grass swards on north-facing hill slopes at two sites in North Canterbury. At Hunua “College Glutinosa” lucerne and "Grasslands Nui" perennial ryegrass or "Grasslands K1950" cocksfoot were planted into dominantly danthonia (Notodanthonia spp.) and blue wheat grass (Agropyron scabrum) vegetation. At Coopers Creek, where the resident sward was dominantly browntop (Agrostis tenuis) and sweet vernal (Anthoxanthum odoratum), "Grasslands Huia" white clover was also planted. Four harvests were taken at both sites over the 1975-76 season and one further harvest in the spring of 1976 at Hunua. Plots treated with herbicide before planting showed better plant survival and better herbage production in most harvests. Nitrogen fertiliser improved introduced and resident grass yields over the late autumn, winter and spring; drought restricted their production in other seasons. Nitrogen increased the cool season suppression of introduced grasses by resident vegetation competition. Introduction of grasses did not improve annual herbage yields of legume swards, although at Hunua lucerne-cocksfoot mixtures did give the best cool season yields in the second year. At Hunua, average annual yield of lucerne was 9,150 kg D.M./ha and average annual total yield was 12,890 kg/ha. Cocksfoot was the better surviving grass. At Coopers Creek, white clover did not persist well, its average annual yield was 3,460 kg D.M./ha and average annual total yield was 7,020 kg/ha. Cocks foot survived better than ryegrass, but ryegrass was the more productive over the cool season. Over the cooler months, when moisture supply was not restricting introduced and resident grass growth, the suppressive effect of resident grasses on introduced grass growth was mainly a nitrogen effect. The resident grasses were strongly competitive for nitrogen when it was in limited supply. With increased nitrogen in the second year at Hunua, introduced grasses became more competitive and productive