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The influence of controlled water inputs on grape quality in regions of Australia with hot Mediterranean climates
- Possingham, John V.
- Acta horticulturae 2002 no.582 pp. 101-107
- anthocyanins, canopy, clay, color, deficit irrigation, drying, emitters (equipment), flowering, fruit quality, fruit set, horticultural crops, irrigation requirement, irrigation water, leaves, odors, rain, rhizosphere, root systems, root zone drying, roots, salinity, shoots, soil water, solar radiation, soluble solids, spring, stomata, vines, viticulture, wine grapes, winemaking, Australia, Mediterranean region
- Management, trellis and pruning systems that increase the ratio of leaves to fruit and the exposure of leaves and fruit to sunlight are inputs that that are well known to contribute to the improvement of grape quality when combined with moderate cropping levels. However two irrigation systems regulated deficit irrigation (RDI) and partial root zone drying (PRD) are now available in the regions of Australia with warm dry summers typical of Mediterranean countries which are able to modify the vegetative and reproductive growth of grapevines and significantly improve the quality of grapes for wine making. Initial experiments involving the application of RDI to grapevines began in the late 1980s and involve reducing vine water inputs during the early stages of bunch development after flowering and fruit set are complete. RDI can reduce both bunch and berry size, and increase soluble solids, colour and aroma. When applied properly RDI improves fruit quality but has the potential to significantly decrease yield. It is effective in regions with limited spring rain where soil moisture tensions in the vine root zone reach and can be maintained in the range 200-400 kPa for heavy (clay) soils and 50-80 kPa for sands. RDI may contribute to salinity problems where soils and irrigation waters are high in salt. PRD is a novel irrigation technique of great potential importance to Australian viticulture and is applicable to a range of other horticultual crops. In PRD, water is given to half the vine root system for a 10 to14 day period using appropriately placed drippers and at the end of this period the other half of the root system is irrigated using an independently supplied dripper line. At any one time only about half of the roots of the vine receive water which significantly reduces the overall requirement for irrigation water. PRD reduces both vine vigour and canopy density, and improves the quality of red varieties by raising the levels of berry anthocyanins through better bunch exposure.. It does not markedly reduce yield. The PRD effect is not an hydraulic one, but is due to chemical signals translocated from the dry roots which induce only partial closing of stomata and reduce both shoot and leaf growth..