SOME EFFECTS OF DROUGHT ON PERENNIAL RYEGRASS SWARDS

Abstract

Herbage production and tiller dynamics were measured in "Grasslands Nui" perennial ryegrass (Lolium perenne L.) swards for 3 months during summer, under conditions of either irrigation or water stress. Measurements continued through winter and early spring when both treatments were well supplied with water. At the end of the stress period tiller densities were 11000 and 4000 tillers/m* in the irrigated and the stressed plots respectively. Lack of moisture stopped tiller emergence but had little effect on the relative death rate of tillers formed before water stress. During the stress period, herbage production was greater in the irrigated than in the stressed plots, average accumulation rates of 68 and 21 kg DM/ ha/dav respectively being recorded. After re-watering, there was compensatory growth by the previously stressed swards resulting in a higher accumulation rate, the average accumulation rates were 24 and 15 kg DM/ha/dav for the previously stressed and irrigated plots respectively. The higher accumulation rate was due mainly to a greater rate of tillering in the previously stressed plots. Differences between treatments in herbage production and tillering were significant up to 3 months after rewatering. The results are discussed in relation to pasture management. Keywords: Nui, Perennial ryegrass, drought, tiller density, irrigation