Productivity of grazed perennial ryegrass dairy pastures from different ecotypes under nitrogen and irrigation treatments

Abstract

A two‐year experiment (1996–1998) was conducted at Hamilton, New Zealand, to compare the productivity of perennial ryegrasses from different ecotypes, under rotational grazing by dairy cows. ‘Ellett’ ryegrass, representing the Mangere ecotype, a major source of parent material for current perennial ryegrass cultivars, was compared with ‘Grasslands Ruanui’ representing an older Hawke's Bay ecotype. Nitrogen (N) fertiliser and irrigation were subplot and sub‐subplot treatments, respectively. Total herbage accumulation over two years was 13% greater for ‘Ellett’ ryegrass than for ‘Grasslands Ruanui’, with higher herbage production occurring mainly in spring and summer. ‘Ellett’ ryegrass had a consistently higher tiller weight and lower tiller density than ‘Grasslands Ruanui’. Tiller density response to N was much greater for ‘Grasslands Ruanui’ (+8698 tillers m‐2) than for ‘Ellett’ (+969 tillers m‐2) over the second year (spring 1997 to autumn 1998). Both ryegrass cultivars showed increased herbage accumulation and tiller weight when treated with N. Cultivar herbage accumulation was increased on average by 30% over the whole trial in response to N, but by only 19% in summer in response to irrigation. ‘Ellett’ ryegrass showed more pulling than did ‘Grasslands Ruanui’ during grazings over summer and autumn, especially when treated with N, but this had only minor effects on yield. Data on the reproductive behaviour of perennial ryegrass cultivars and tillering responses to N applied in spring‐summer, could provide useful selection criteria for persistence under intensive dairying. Ryegrass cultivars with different morphologies and tillering responses to N may require different grazing managements to optimise their performance. Pulling losses in summer are likely to be greater for cultivars with large upright tillers and when N fertiliser is applied.