Autumn nitrogen effects on perrenial ryegrass (Lolium perenne L.) and cocksfoot (Dactylis glomerata L.) pastures in dryland Canterbury.

Abstract

This research examined the effects of autumn nitrogen application at five rates (0, 50, 100, 200 and 400 kg N/ha) on dry matter production and the nutritive value of cocksfoot and perennial ryegrass, and the subterranean clover content of these pastures. The experiment was run as two experiments overlain on a nine-year old cocksfoot pasture and a five-year old perennial ryegrass pasture from 28 February 2012 to 17 August 2012. Average yields increased with increasing N application rate for both cocksfoot and perennial ryegrass. Accumulated yields ranged from 0.8 t DM/ha (control) to 5.6 t DM/ha (400 kg N/ha) in cocksfoot, and 1.7 ± 0.25 t DM/ha (control and 50 kg N/ha) to 5.4 t DM/ha (400 kg N/ha) in perennial ryegrass. These increases were largely contributed to increases in leaf extension of up to 100% in cocksfoot and 108% in perennial ryegrass. Pasture ME was reduced to 10.4 MJ/kg DM in cocksfoot and 10.2 MJ/kg DM in perennial ryegrass as a result of mowing pastures in winter and removing stored sugars in the leaves. Water use efficiency was increased from 3.7 to 25.5 kg DM/ha/mm PET in cocksfoot and from 8.0 to 24.7 kg DM/ha/mm PET in perennial ryegrass with the addition of 400 kg N/ha. Frequent grazings in rotations of 21-28 days in autumn are required to maintain persistence and production of subterranean clover. In this dissertation the physiological basis for pasture responses was examined to offer practical guidelines of autumn nitrogen application to dryland farmers.