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Irrigation in viticulture is the process of applying extra water in the cultivation of grapevines. It is considered both controversial and essential to wine production. In the physiology of the grapevine, the amount of available water affects photosynthesis and hence growth, as well as the development of grape berries. While climate and humidity play important roles, a typical grape vine needs 25-35 inches (635-890 millimeters) of water a year, occurring during the spring and summer months of the growing season, to avoid stress.〔T. Stevenson ''"The Sotheby's Wine Encyclopedia"'' p. 15 Dorling Kindersley 2005 ISBN 0-7566-1324-8〕 A vine that does not receive the necessary amount of water will have its growth altered in a number of ways; some effects of water stress (particularly, smaller berry size and somewhat higher sugar content) are considered desirable by wine grape growers. In many Old World wine regions, natural rainfall is considered the only source for water that will still allow the vineyard to maintain its ''terroir'' characteristics. The practice of irrigation is viewed by some critics as unduly manipulative with the potential for detrimental wine quality due to high yields that can be artificially increased with irrigation.〔J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition pp. 236-263, 361-362, 507-566, 635-641, 709-763 Oxford University Press 2006 ISBN 0-19-860990-6〕 It has been historically banned by the European Union's wine laws, though in recent years individual countries (such as Spain) have been loosening their regulations and France's wine governing body, the ''Institut National des Appellations d'Origine'' (INAO), has also been reviewing the issue.〔R. Joseph & J. Payne ''"(Yves Benard: The new broom at the INAO )"'' Meininger's Wine Business International, August 24, 2007〕 In very dry climates that receive little rainfall, irrigation is considered essential to any viticultural prospects. Many New World wine regions such as Australia and California regularly practice irrigation in areas that couldn't otherwise support viticulture. Advances and research in these wine regions (as well as some Old World wine regions such as Israel), have shown that potential wine quality could increase in areas where irrigation is kept to a minimum and managed. The main principle behind this is controlled water stress, where the vine receives sufficient water during the budding and flowering period, but irrigation is then scaled back during the ripening period so that the vine then responds by funneling more of its limited resources into developing the grape clusters instead of excess foliage. If the vine receives too much water stress, then photosynthesis and other important processes such as nutrient storage could be impacted with the vine essentially shutting down. The availability of irrigation means that if drought conditions emerge, sufficient water can be provided for the plant so that the balance between water stress and development is kept to optimal levels.〔 ==History== The practice of irrigation has a long history in wine production. Archaeologists describe it as one of the oldest practices in viticulture, with irrigation canals discovered near vineyard sites in Armenia and Egypt dating back more than 2600 years.〔 Irrigation was already widely practiced for other agricultural crops since around 5000 BC.〔Think Quest Library ''"(What is Irrigation? )"'' Accessed: January 10, 2010〕 It is possible that the knowledge of irrigation helped viticulture spread from these areas to other regions, due to the potential for the grapevine to grow in soils too infertile to support other food crops. A somewhat robust plant, the grapevine's largest need is for sufficient sunshine, and it is able to flourish with minimum needs of water and nutrients. In areas where its water needs are unfulfilled, the availability of irrigation meant that viticulture could still be supported.〔 In the 20th century, the expanding wine industries of California, Australia and Israel were greatly enhanced by advances in irrigation. With the development of more cost efficient and less labor-intensive ways of watering the vines, vast tracts of very sunny but dry lands were able to be converted into wine-growing regions. The ability to control the precise amount of water each vine received, allowed producers in these New World wine regions to develop styles of wines that could be fairly consistent each year regardless of normal vintage variation. This created a stark contrast to the Old World wine regions of Europe where vintage variation, including rainfall, had a pronounced effect on the potential wine style each year. Continuing research explored the way that controlled (or supplemental) irrigation could be used to increase potential wine quality by influencing how the grapevine responds to its environment and funnels resources into developing the sugars, acids and phenolic compounds that contribute to a wine's quality. This research lead to the development of ways to measure the amount of water retention in the soil, so that individual irrigation regimes could be plotted for each vineyard that maximized the benefits of water management.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Irrigation in viticulture」の詳細全文を読む スポンサード リンク
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