Effects of nitrogen and irrigation on productivity of different ryegrass ecotypes when grazed by dairy cows

Abstract

The responses of two perennial ryegrass cultivars, Ellett and Grasslands Ruanui, to nitrogen fertiliser and irrigation, applied before and after flowering, were studied in a field experiment at the Dairying Research Corporation, Ruakura. The former was included as representative of the Mangere perennial ryegrass ecotype, and the latter as representative of older material. Data on herbage accumulation, tiller density and tiller weight were collected, before and after grazing by dairy cows, from September 1996. Nitrogen increased summer herbage accumulation and tiller density by 41% and 37%, respectively. Irrigation increased ryegrass yield by 21% in summer but effects on tiller density and weight were small and inconsistent. No significant effects of nitrogen fertiliser or irrigation treatments on herbage accumulation, tiller density, or tiller weight were observed in spring. Ellett swards produced 5390 kg DM/ha over the trial period, compared with 4450 kg DM/ ha for Grasslands Ruanui, although this difference was not statistically significant. However, Ellett had a larger mean tiller weight and a lower tiller density than Ruanui. The contrasting tiller size/ density characteristics of the two cultivars are quantified and discussed. Keywords: dairy cow grazing, Ellett ryegrass, Grasslands Ruanui ryegrass, herbage accumulation, irrigation, Lolium perenne,