NITROGEN FERTILISER ON GRAZED HILL PASTURES

Abstract

The effect of N fertiliser on pasture yields and species composition, and spring stock carrying capacity was measured undergrazing at Ballantrae, the Grasslands Division hill country area. N fertiliser was applied as urea in early spring at rates up to 100 kg N/ha. Paddocks were set stocked with sheep with additional sheep being added to N fertilised paddocks to maintain similar herbage availabilities. N fertiliser increased pasture growth by an average of 7 kg DM/ kg N applied. Stock carrying capacities over spring ranged from 18 sheep/ ha without N, to 26 sheep/ ha with 100 kg N/ha. The major species composition effects of N was a reduction in clover yields and clover nitrogen fixation rates, in the spring, summer and autumn after the spring application. Clover growth and N fixation decreased most over summer when clover yields and nitrogen fixation were 41% and 52% lower respectively on hill slopes, at the highest rate of N fertiliser. Pasture yields were lower in autumn on pastures previously N fertilised.