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52 p r a c t i c a l w i n e r y & v i n e ya r d M a r c H 2 0 1 4 g r a p e g r o w i n g improvement in fruit and wine quality (and, hence, monetary value). When comparing irrigation strategies and water use across a single vineyard or vineyards in close proximity to each other for any given year, the effective rainfall component can be excluded. W U E p a n d W U E v c a n t h e n b e expressed as tonnes per ML and $ per ML respectively. when does the Vine require water? Minimizing the risk of crop loss when insufficient water is available requires an understanding of the vine's water require- ments duri ng t he g rowi ng season. Improvements in irrigation efficiency can be achieved by avoiding waste (over-irri- gation) and by ensuring sufficient water is applied during key growth periods (avoiding under-irrigation when the risk of yield reduction is high). The amount of water required during different stages of the growing season will depend on: • climatic conditions, • variety/rootstock combinations, • soil type and depth, • crop load. Table I provides guidelines on vine water requirements to ensure that pro- ductivity and fruit quality are not com- promised for the current and subsequent growing seasons. The effect of water stress on vine growth and berry development will depend on the timing and severity of water deficit during the growing season. P. Iland et al. provided guidelines for qualitatively assessing shoots, berries Table I. A guide to vine water requirements for key phenological growth periods Growth period Vine water requirements Budburst to flowering This period is cri cal for root growth and establishing canopy size and poten al yield. However, irriga ons that are applied too early will be wasted and not used by the vine. In many warm/cool regions, winter/ spring rainfall ensures an adequate supply of water for all or most of this period, and irriga on is not required. Under water-limi ng/drought condi ons, irriga on may need to be applied. Water stress during this period may result in reduced shoot growth and leaf size. Flowering to fruit set Flowering and fruit set are sensi ve to water stress as cell division is a cri cal development stage. It is a period when shoot growth is rapid. Irriga on should be applied prior to flowering if soil water levels are low. Fruit set to véraison The amount of water required depends on soil water content and the desired fruit quality. Irriga on techniques such as regulated deficit irriga on (RDI) and par al rootzone drying (PRD) can be implemented to impose water stress to control shoot growth and berry size, both of which can have posi ve effects on fruit quality. Véraison to harvest Poor leaf func on is likely to delay the accumula on of sugar and adversely affect the development and balance of flavor components in berries. Once berries have reached full maturity, water deficits are less harmful, so irriga on volumes can be reduced. Severe water deficits should be avoided in order to maintain leaf health and func on. Post-harvest Vines need to accumulate sufficient carbohydrate reserves for the next season before going into dormancy. If water is available, irriga on is likely to benefit vines by ensuring that condi ons are suitable for root growth and leaf func on.