Irrigation in viticulture
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. 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. 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.
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.