Pasture yield responses and nitrogen leaching losses from rolling downland grazed by sheep in the South Island of New Zealand

ABSTRACT

A sheep grazing trial on rolling downland in East Otago was conducted from 2004 to 2007 to measure the effect of increasing rates of nitrogen (N) fertiliser on pasture yield and N leaching losses. For fertiliser rates ranging from 100 to 500 kg N/ha/yr, the efficiency of response averaged 20 kg DM/kg N and increased up to 300 kg N/ha/yr. Pasture yield averaged 12,680 kg DM/ha/yr in the control plots and peaked at 21,000 kg DM/ha/yr at 300 kg N/ha/yr. Clover content was significantly depressed by N use, declining from approximately 15% for the control to 2% when 200 kg N/ha/yr or more was applied. Leaching losses of 8–30 kg N/ha/yr at 100 and 200 kg N/ha/yr measured using mini-lysimeters were only slightly more than the control but increased up to 116 kg N/ha/yr at 500 kg N/ha/yr. The results from this site suggested that up to 100–200 kg N/ha/yr can be applied to produce more pasture on rolling downland grazed by sheep with only a small increase in N leaching losses.

KEYWORDS:

• Grazing
• hill country
• leaching
• nitrogen
• pasture yield
• rolling downland
• sheep

Acknowledgements

The authors wish to thank the Fertiliser Association of New Zealand and the MAF Sustainable Farming Fund for their financial support. Also Dennis Enright for his technical assistance and Invermay farm staff for managing the stock.

Disclosure statement

No potential conflict of interest was reported by the author(s).