page_title: Irrigation in viticulture
section_title: Role of water in viticulture
hierarchical_section_title: Irrigation in viticulture / Role of water in viticulture
caption_attribution_description: Rain on a grapevine leaf in a vineyard.
context_page_description: 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 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 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.
context_section_description: The presence of water is essential for the survival of all plant life. In a grapevine, water acts as a universal solvent for many of the nutrients and minerals needed to carry out important physiological functions, and the vine receives these by absorbing the nutrient-containing water from the soil. In the absence of sufficient water in the soil, the root system of the vine may have difficulties absorbing these nutrients. Within the structure of the plant itself, water acts as a transport within the xylem to bring these nutrients to all ends of the plant. During the process of photosynthesis, water molecules combine with carbon derived from carbon dioxide to form glucose, which is the primary energy source of the vine, as well as oxygen as a by-product.
  In addition to its use in photosynthesis, a vine's water supply is also depleted by the processes of evaporation and transpiration. In evaporation, heat (aided by wind and sunlight) causes water in the soil to evaporate and escape as vapor molecules. This process is inversely related to humidity with evaporation taking place at faster rates in areas with low relative humidity. In transpiration, this evaporation of water occurs directly in the vine, as water is released from the plant through the stomata that are located on the undersides of the leaves. This loss of water from the leaves is one of the driving factors that results in water being drawn up from the roots, and it also helps the vine combat against the effects of heat stress which can severely damage the physiological functions of the vine (somewhat similar to how perspiration works with humans and animals). The presence of adequate water in the vines can help keep the internal temperature of the leaf only a few degrees above the temperature of the surrounding air. However, if water is severely lacking then that internal temperature could jump nearly 18 °F (10 °C) warmer than the surrounding air which leads the vine to develop heat stress. The dual effects of evaporation and transpiration are called evapotranspiration. A typical vineyard in a hot, dry climate can lose as much as 1,700 U.S. gallons (6,400 l; 1,400 imp gal) of water per vine through evapotranspiration during the growing season.
caption: Water is vital to many of the physiological processes of the grape vine, including photosynthesis.
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