Forage and sheep production from oats, rape and vetch sown in autumn with or without nitrogen fertilizer

Abstract

Oats (Avena sativa cv. Acacia), vetch (Vicia dasycarpa cv, Lana) and rape (Brassica napus cv. Rangi) were sown with or without 67 kg ha-1 nitrogen (N) in the autumns of 1969 and 1970 at Armidale, N.S.W. In both years the crops were rotationally grazed by sheep in late winter and spring at two fixed stocking rates (experiment 1). When grazing began in both years oat dry matter (DM) availability was approximately double that of vetch and rape. Oats remained highly productive in successive grazing periods whereas the recovery of vetch after the first grazing was slow. At the high stocking rates employed the rape crops were overgrazed and failed to regrow. Fertilizer N increased oat yields by more than 50 per cent and N content by 20 to 40 per cent, but neither vetch nor rape responded significantly. Minimum nitrogen contents of oats, rape and vetch were respectively 1.3, 2.7 and 4.0 per cent. Digestible organic matter content of the three forages exceeded 74 per cent throughout the experiment. Daily rates of liveweight gain per sheep were not significantly different on the three crops in the first grazing period. Daily gain per sheep responded significantly to fertilizer N only on oats in the second period in 1970 (P < 0.05). The total liveweight gain ha-1 pooled over all periods was much greater on oats than on vetch or rape. Clean wool per day tended to be higher on vetch than on the other crops but total wool production per hectare was greatest from oats in both years because of the longer period of grazing it provided. In a supplementary experiment (experiment 2) in 1969 the crops were grazed at an initially uniform stocking pressure (1 sheep per 10 kg dry matter available). Sheep grazing vetch gained 146 g head-1 day-1 which was faster than sheep on oats (92 g head-1 day-1) or rape (66 g head-1 day-1) (P < 0.05). The general effect of N fertilizer was to increase daily gain and almost double the mean gain per hectare.