3.2 Water

Question 1

How much water does a vine generally need in cool climates? In warm climates?

Answer 1

• Cool Climates: Minimum of 500 mm of rainfall per year

- Warm Climates: Minimum of 750 mm of rainfall per year

Question 2

For what 5 purposes does a vine need water?

Answer 2

1. Turgidity (so that it doesn’t wilt)
2. Photosynthesis
3. Regulating its temperature
4. Solvent for nutrients in the soil
5. Medium in which all of the vine’s biochemical and physiological mechanisms take place

Question 3

What is transpiration?

Answer 3

• 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.

Question 4

If a vine has sufficient water, what do the stomata do?

Answer 4

• 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.

Question 5

Describe how water stress occurs. If a vine doesn’t have sufficient water, what do the stomata do?

Answer 5

• Stomata partially close
• Can help conserve water-
• Reduces or even stops photosynthesis due to lack of carbon dioxide entering the leaves.

Question 6

What can water stress lead to for the vine?

Answer 6

• Stunted growth
• Ripening slowed
• Leaf loss (extreme)
• Vine death (extreme)

Question 7

Name 4 winemaking regions where the lack of rainfall in the growing season is a large issue.

How is it combatted?

Answer 7

• Argentina, California, South Africa and Australia

- Irrigation

Question 8

If water is too easily available into late spring and early summer, what can happen to the vine?

Answer 8

• 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

Question 9

When is mild water stress beneficial? Why?

Answer 9

• Just before véraison

- It inhibits further vegetative growth

Question 10

Name 4 reasons why excessive shading of the grape bunches can be harmful.

Answer 10

• Reduced formation of anthocyanins, tannins and aroma compounds
• Less tannin polymerisation
• Higher levels of methoxypyrazines
• Poor ventilation (fungal disease risk)

Question 11

Late in the ripening period, why can excessive water be harmful?

Answer 11

• Dilution of sugars in the grapes

- Grape splitting (encourages botrytis)

Question 12

Late in the ripening period, why can excessive water be harmful?

Answer 12

• Dilution of sugars in the grapes

- Grape splitting (encourages botrytis)

Question 13

Why can a water deficit late in ripening be harmful?

Answer 13

• Grape shrivel

- Grapes may not reach the desired level of ripeness.

Question 14

Why can damp soils be harmful?

Answer 14

• Often cold, especially early in the growing season

- Can delay budburst (shorter growing season)

Question 15

Why can warm soils be beneficial?

Answer 15

• Promote budburst

- Encourage root growth

Question 16

How can proximity to water effect fungal disease? Name 3 regions where this occurs beneficially.

Answer 16

• Increases the level of humidity in the vineyard
  1. Sauternes
  2. Tokaj
  3. Mosel

Question 17

What can be used in areas where there is not sufficient rainfall to meet the vine’s needs? What does this depend on?

Answer 17

Irrigation (depending on legislation, availability of irrigation water and other factors)

Question 18

What is the natural source of water for the vine? What vineyard factors moderate water?

Answer 18

Rainfall

- Moderated by the water-holding capacity and depth of the soil

Question 19

What causes rainfall?

Answer 19

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

Question 20

Describe how rain shadows happen.

Answer 20

• 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’).

Question 21

Give an example of the rain shadow effect.

Answer 21

• 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

Question 22

What does the amount of water in the soil available to the vine depend on?

Answer 22

• 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

Question 23

What type of soil has good water retention? Give an example.

Answer 23

• Clay

- albariza in Jerez, Spain

Question 24

What type of soil has good drainage? Give an example.

Answer 24

• Gravel

- Hawkes Bay in New Zealand

Question 25

What is the downside of soil that drains too easily?

Answer 25

• Extremely free draining could mean that irrigation is necessary

Question 26

What is the downside of soils that retain a lot of water? What is this called?

Answer 26

• Water-logged soils (usually as a result of poor drainage)
• Reduce the amount of oxygen available to the roots
• Slows growth
• Eventually kills the vine

Question 27

How does topography influence water availability?

Answer 27

• There will be greater surface run-off in vineyards on slopes.
• This can mean there is less penetration of water into the soil and therefore less water available to vine roots

Question 28

Is water run-off on slopes advantageous or disadvantageous?

Answer 28

• Can be both
• Advantageous: in regions with high rainfall
• Disadvantageous: surface run-off causes erosion of the soil and leaching of nutrients

Question 29

What is the evapotranspiration rate?

Answer 29

• Evapotranspiration rate is the amount of transpiration from the vine, combined with the evaporation of water from the soil surface.
• The rate at which water is no longer available, either because it has been taken up by the vine or because it has been lost to the atmosphere (e.g. evaporation from the soil surface).

Question 30

What factors lead to a higher evapotranspiration rate? Name 2 regions that experience this.

Answer 30

• Hot
• Dry
• Windy weather

(e.g. Mendoza, Patagonia)

Question 31

Why do vines in hot, dry, windy conditions need more water than vines in cool and humid conditions?

Answer 31

The rate of evapotranspiration is higher.