Effects of timing of water stress on yield and berry size.

Past irrigation research in Marlborough showed that reducing irrigation on grapes by up to 60% would not have any impact on yield, but that the timing of the irrigation might be important for maintenance of yields. A research trial was set up with Sauvignon blanc grapes planted in containers; periods of water stress were applied for three weeks at different times of the growing season. During the three years of the trial the post-flowering (PO-F) period was consistently most sensitive to water stress. At harvest time, the crop yields for the PO-F water-stressed vines were 55%, 72% and 90% of control yields for the three consecutive years, and the bunch weights were 59%, 84% and 95%. Berry weights for the PO-F water-stressed vines were 87%, 96% and 73% of the control values, although the second-year difference was not significant. In two years out of three, there was a trend for PO-F and pre-veraison (PR-V) water-stressed vines to have the lowest berry soluble solids contents ( degrees Brix), indicating a delay in maturity. We suggest that to use irrigation sustainably, it is safe to reduce water applications for most of the season, but that immediately after flowering, any water stress should be avoided. During the period leading up to veraison, some mild water stress can be applied.

Waste stream utilisation for sustainable viticulture.

Field trials were established at four vineyards in January 1999 to evaluate the effects of four mulch mixtures on different soil and plant parameters. Mulches were made from wine industry and other commercially available plant and animal wastes. Soil, grape petioles, grape leaves and grape juice were analysed over three seasons. The mulches applied released considerable quantities of nutrients, which were available for use by the grapevines. Generally, the type of mulch used had little impact on the parameters that were measured and the greatest differences occurred between non-mulched and mulch treatments. Soil pH showed an increase at three of the four sites after application of mulch. Soil phosphorus increased moderately at one site and substantially at the other three sites in the first year and soil potassium levels increased dramatically at all sites in the first year. After the application of mulches in 1999 the petiole nitrate levels increased dramatically at all sites, however there were no differences in the second year. In the third year petiole nitrate levels were again high indicating that the differences between years was probably largely attributable to differences in rainfall received among the three seasons. Petiole potassium levels also increased after the application of mulch, however the increase was nowhere near as large as the increase in soil potassium. The use of mulch increased leaf nitrogen and potassium levels but not phosphorus levels. The use of mulch did increase juice potassium, however there was greater seasonal and site variation than variation due to the effect of mulch.