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

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.