The relationship between herbage mass and pasture accumulation rate in winter

Herbage mass of rotationally grazed paddocks was measured by pasture plate meter on Massey No. 4 Dairy Farm in the Manawatu and at Limestone Downs, a sheep and beef property near Port Waikato, in the North Island, New Zealand. Data were collated and pasture accumulation rates calculated. A quadratic regression model was fitted to both farm data sets to investigate the relationship between herbage mass and pasture accumulation rate for the May to August period over two years. Although the data sets contained a large amount of unexplained variation, the effect of herbage mass on pasture accumulation rate was found to be significant (P < 0.01). The estimate for herbage mass which maximised pasture accumulation rate was 2500 kg DM ha(-1) for No. 4 Dairy Farm. The optimum could not be estimated for Limestone Downs because of substantial data variability. Because the confidence interval for the dairy farm estimate of optimum is wide, it can not be concluded unequivocally that optimum herbage mass for New Zealand conditions is higher than the figure of 1250 kg DM ha(-1) identified in Britain. However, there is indication that management that results in higher post-grazing residuals will enable higher pasture accumulation rates on at least some New Zealand dairy farms. This question of optimum pasture cover should be the focus of further research on a range of New Zealand farm types.