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An irrigated 'Grasslands Nui' perennial ryegrass (Latium perenne L.) sward was mown during reproductive growth and subsequent vegetative summer growth using 6 cutting treatments. The treatments included combinations of stages of interruption of reproductive development and regrowth intervals. Tagged ryegrass tillers were used to measure tillering, tiller longevity, and tiller weight at different ages. Periods of rapid tillering in spring before culm elongation started, and after interruption of reproductive growth were observed. Interruption of reproductive development at inflorescence emergence increased tillering in the second period compared with other treatments. Later interruption of reproductive development reduced the number of pre-flowering tillers surviving into summer. Longevity of tillers tagged at the start of the experiment was greatest with early interruption of reproductive growth followed by infrequent cutting. Youngest tillers were smallest, and new tillers took 60-100 days after appearance to reach the same weight as old, established tillers tagged at the start of the experiment. There was evidence that the growth rate of established tillers declined with time. Herbage accumulation was greater with mowing at 95% light interception than

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.

The application of three multivariate analysis techniques (canonical discriminant analysis (CDA), principal component analysis (PCA), and canonical correlation analysis (CCA)) for evaluation of pasture botanical composition data is illustrated and discussed. CDA and PCA were used to describe differences in pasture botanical composition for different microsites within a pasture near Palmerston North, New Zealand. CCA could not be validly applied to this data set because a sampling strategy inappropriate for CCA had been used to collect the data. However, CCA is conceptually ideal for determining association between two groups of variables and CCA was used for a second data set from the Hawkes Bay region to establish association between differences in pasture botanical composition and differences in environmental variables. CCA identified a A94010Received 24 February 1994; accepted 28 July 1994 transition from white clover (Trifolium repens L.) to subterranean clover {Trifolium subterraneum L.) presence associated with decreasing rainfall, and a similar transition from ryegrass presence to browntop presence associated with altitude. There are practical difficulties in obtaining a suitable data set for canonical correlation, but with attention to sampling strategy a more precise definition of effect of environmental factors on pasture botanical composition would be expected.

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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