SOME EFFECTS OF SPRING DEFOLIATION AND DROUGHT ON PERENNIAL RYEGRASS SWARDS

Abstract

An automatic rain-out shelter and an oscillating sprinkler irrigator were used to give contrasting wet and dry soil moisture regimes during summer in ryegrass swards, which had been differentially mown (7.5 ems vs 2.5 ems) during spring to create differences in tiller density. Swards with a higher tiller density before drought had a higher tiller density after drought. Although there was no effect of spring defoliation on summer production, there was a trend for pastures with a higher tiller density to recover more quickly after drought. The effect of water stress was to reduce herbage yield to only 8% of that of irrigated treatments. This was attributed to reductions in tiller density and rates of leaf extension and -~rnrn---r=,.+.n.ce. Water stresa- also increased the kiieis of lamina soluble sugars. Rewatering after moisture stress resulted in compensatory growth which partly offset the yield loss incurred during stress. Keywords: Spring grazing management, dryland, water stress, perennial ryegrass, sward dynamics, lamina soluble sugars.