3.2 Water Flashcards
How much water does a vine generally need in cool climates? In warm climates?
- Cool Climates: Minimum of 500 mm of rainfall per year
- Warm Climates: Minimum of 750 mm of rainfall per year
For what 5 purposes does a vine need water?
- Turgidity (so that it doesn’t wilt)
- Photosynthesis
- Regulating its temperature
- Solvent for nutrients in the soil
- Medium in which all of the vine’s biochemical and physiological mechanisms take place
What is transpiration?
- Water vapour diffuses out of the stomata (tiny pores) on the underside of vine leaves.
- The loss of water from the cells in the leaf causes water to be pulled upwards from the soil, through the roots and the above-ground parts of the vine.
If a vine has sufficient water, what do the stomata do?
- Stomata stay open all day.
- Open stomata allow the free exchange of water vapour out of the vine, and also let carbon dioxide and oxygen diffuse in and out of the leaves.
Describe how water stress occurs. If a vine doesn’t have sufficient water, what do the stomata do?
- Stomata partially close
- Can help conserve water-
- Reduces or even stops photosynthesis due to lack of carbon dioxide entering the leaves.
What can water stress lead to for the vine?
- Stunted growth
- Ripening slowed
- Leaf loss (extreme)
- Vine death (extreme)
Name 4 winemaking regions where the lack of rainfall in the growing season is a large issue.
How is it combatted?
- Argentina, California, South Africa and Australia
- Irrigation
If water is too easily available into late spring and early summer, what can happen to the vine?
- Vegetative growth (growth of shoots and leaves) is promoted and prolonged into the period of grape ripening, which acts as a competitive source for the vine’s sugars, delaying and compromising ripening
- Excessive shading of the grape bunches
When is mild water stress beneficial? Why?
- Just before véraison
- It inhibits further vegetative growth
Name 4 reasons why excessive shading of the grape bunches can be harmful.
- Reduced formation of anthocyanins, tannins and aroma compounds
- Less tannin polymerisation
- Higher levels of methoxypyrazines
- Poor ventilation (fungal disease risk)
Late in the ripening period, why can excessive water be harmful?
- Dilution of sugars in the grapes
- Grape splitting (encourages botrytis)
Late in the ripening period, why can excessive water be harmful?
- Dilution of sugars in the grapes
- Grape splitting (encourages botrytis)
Why can a water deficit late in ripening be harmful?
- Grape shrivel
- Grapes may not reach the desired level of ripeness.
Why can damp soils be harmful?
- Often cold, especially early in the growing season
- Can delay budburst (shorter growing season)
Why can warm soils be beneficial?
- Promote budburst
- Encourage root growth
How can proximity to water effect fungal disease? Name 3 regions where this occurs beneficially.
- Increases the level of humidity in the vineyard
1. Sauternes
2. Tokaj
3. Mosel
What can be used in areas where there is not sufficient rainfall to meet the vine’s needs? What does this depend on?
Irrigation (depending on legislation, availability of irrigation water and other factors)
What is the natural source of water for the vine? What vineyard factors moderate water?
Rainfall
- Moderated by the water-holding capacity and depth of the soil
What causes rainfall?
Rainfall is caused by water vapour condensing and precipitating
- Warm temperatures cause moisture from the land to evaporate and rise
- As the warm moist air rises in the atmosphere, it cools and condenses into clouds and eventually rain
Describe how rain shadows happen.
- Mountain ranges force winds of warm moist air upwards over high altitudes.
- This causes the water vapour to cool, condense and precipitate.
- This can mean that the regions on one side of the mountain experience greater rainfall, whereas regions on the other side are sheltered from the rain-bearing winds and often have very dry conditions (these regions are located in a ‘rain shadow’).
Give an example of the rain shadow effect.
- On the west of the Cascade Mountains the AVA of Puget Sound is cooler and much wetter than the warmer, drier AVAs to the east of the mountains, for example Columbia Valley.
- Puget Sound - can dry farm (apply no irrigation)
- Columbia Valley - requires irrigation
What does the amount of water in the soil available to the vine depend on?
- How easily the water drains
- The water-holding properties of the soil (a function of the soil’s texture and organic matter content)
- The soil depth
What type of soil has good water retention? Give an example.
- Clay
- albariza in Jerez, Spain
What type of soil has good drainage? Give an example.
- Gravel
- Hawkes Bay in New Zealand
