Nitrogen fertiliser application rates and nitrogen leaching in intensively managed sheep grazed hill country pastures in New Zealand

Effects of rates of nitrogen (N) fertiliser application on mineral N leaching from grazed New Zealand hill country were investigated. Paddocks of 12-25 degrees slope received annual N inputs of 0, 100, 200, 300, 400, 500 or 750 kg N ha(-1) and were rotationally grazed by non-lactating ewes, stocking rate being increased to utilise extra pasture production generated from N application. Mineral N leaching was measured using in situ minilysimeters (150 mm diameter and 300 mm depth) with leachate collected at monthly intervals or after each accumulation of 100 mm rain. Average annual net herbage accumulation ranged from 11 to 16 t dry matter ha(-1) for the N treatments. Total mineral N leaching increased linearly with fertiliser N application rate. Potential increases in N leaching for commonly used fertiliser N regimes were estimated to be 11% (for 20 kg N ha(-1)) to 29% (for 50 kg N ha(-1) application rate).