Water as a Limiting Factor Part 1

Question 1

First three important principle of water requirements?

Answer 1

1. Know the symptoms on the vine of water stress
2. Know the physiological stages when a lack of water will affect the size and quality of the crop
3. Know the depth and size of the root system

Question 2

Last two important principles of water requirements?

Answer 2

4. Know the soil in order to know what the storage capacity of the soil is for water
5. Know how much water to apply

Question 3

3 indicators of plant water stress:

Answer 3

1. Leaf water potential (pressure machine)
2. Leaf stomatal conductance
3. Soil water potential

Question 4

What does stomatal conductance describe?

Answer 4

It describes gas diffusion through plant stomata.
- Plants regulate stomatal aperture in response to environmental conditions

Question 5

Do stomata control leaf water loss?

Answer 5

When we look at the the transpiration flux vs stomatal aperature we can see that on windy days there is a higher transpirational flux at lower aperatures.

Question 6

Why do we have slow transpiration under still air?

Answer 6

Because the boundary layer is higher

Question 7

Boundary layer conductance relies on three things:

Answer 7

1. Wind speed
2. Leaf size
3. Diffusing gas

Question 8

What can we see when we look at a graph showing mid-day leaf water potential (bars) vs. Stomatal Conductance?

Answer 8

Here we can see that there is a positive linear relationship, in that when there is more negative leaf water potential, we have less stomatal conductance

Question 9

What does soil water potential define when looking at water stress?

Answer 9

Defines the supply part of the supply/demand function of water stress

Question 10

When looking at the graph showing when to irrigate we can see that…

Answer 10

Silt and Loam have the highest amount of available water

Question 11

What are the 6 critical physiological stages for water stress?

Answer 11

1. Prior to bud break in dry regions without winter rainfall (Dormant phase)
2. Bud Break before flowering
3. Flowering a fruitset up to pea size
4. Pear size to berry softening
5. Ripening (berry softening to harvest)
6. After Harvest

Question 12

The bleeding phase is positively affected by

Answer 12

a good content of water in the soil

Question 13

Bleeding is a very important stage for two reasons:

Answer 13

1. If we see a drop of water coming out from the pruning cut that means that there is a continuous water transport from the soil to that point
2. If we have a good bleeding phase, we also have a good transport of auxins to the buds that stimulate bud burst.

Question 14

What can we see from the graph showing days of bloom vs. Yield loss?

Answer 14

We can see that with very early water stress we can have a hugely negative impact on yield. The earlier the stress, the more limitations on final yield

Question 15

2 Practical methods for evaluating soil moisture and 3 tools

Answer 15

1. Dig a soil pit
2. Feel the soil

Tools:
1. Tensiometers (Water potential)
2. Resistance blocks (water content)
3. Neutron probe (water content)

Question 16

The relationship between soil water potential and volumetric water contentdepends on…

Rate of water infiltration depends on…

Answer 16

1. Soil type
2. Soil type and volume of water applied

Question 17

3 different indicators for when to irrigate. Which is the best?

Answer 17

1. Visual symptoms
2. Vine water status (the best)
3. Weather conditions

Question 18

What is ET?

Answer 18

Evapotranspiration

Question 19

Two important considerations for deficit irrigation

Answer 19

1. Applied water is less than ET
2. Water stress is when photosynthesis is down and transpiration is down

Question 20

The purpose of a regulated deficit irrigation is triple:

Answer 20

1. Save water.
2. Preserve yield because I’m not really going into a severe stress.
3. Diminish the competition between vegetative structure and bunches, I would increase the quality.

Question 21

What is the main philosophy of RDI?

Answer 21

Regulated Deficit Irrigation philosophy is that we never want the vineyard working at the maximum transpiration level, we want to keep our vineyard in a condition of saving water without having big limitations.

Question 22

What is RDI? (3)

Answer 22

1. Again Regulated Deficit Irrigation.
2. Maintain vine water status within prescribed range of water stress (e.g., -0.5 to -1.0 MPa) for a defined part of the growing season.
3. Water stress needs to be removed after this period by irrigating >100%ETc.

Question 23

What is PRD? (3)

Answer 23

1. Alternately irrigating two spatially separate parts of the rootzone
2. Each cycle 5 to 14 days, depending on the site and weather
3. Deep sandy loam

Question 24

True or false: RDI is a evolution of PRD

Answer 24

False PRD is an evolution of RDI

Question 25

What is the main point of utilizing RDI or PRD, why would intentionally induce a water stress?

Answer 25

We would do this in order to control vigor, increase berry quality and increase water use efficiency. We do this via reducing vegetative growth

Question 26

Is more stress better?

Answer 26

Too much water stress and when it is too late, can be incredibly detrimental

Question 27

Plant water status affects berry size in which way, what are two ways that we can irrigate and how could they affect berry weight or size?

Answer 27

1. Irrigate less before veraison to limit berry size
2. Irrigate more after veraison to prevent weight loss

Question 28

Discuss the difference between red and white grapes and how RDI and PRD can be used in respect to the different grapes (2)

Answer 28

1. Deficit irrigation/nutrition useful for most red grapes
2. RDI less suited for white grapes than is PRD

Question 29

The more severe is the water stress, the faster is the ________, the faster is the _________ into the cluster, affecting an higher pH, to low acidity and so on.

Answer 29

1. senescence
2. recycling of K

Question 30

Too little water before budbreak = (2)

Answer 30

delayed budbreak and stunted shoot growth.

Question 31

No bleeding =
Normal bleeding =

Answer 31

1. Bad budbreak
2. Good budbreak

Question 32

Too much water stress after veraison = (3)

Answer 32

• Berry dehydration
• Decrease in yield
• Sunburn

Question 33

Too much water stress after veraison = (2)

Answer 33

Yelow leaves
Early defoliation

Question 34

Yelow leaves and Early defoliation =

Answer 34

Recycled leaf K+ = undesirable increase in berry k+, increased juice pH

Question 35

Which one is doing better?
Sangio on left, Montepulciano on right?

Answer 35

Sangio on the left

Question 36

What is the function of ABA?

Answer 36

We know that ABA is the regulator of stomatal closure, it’s produced at the root level, it’s transported by xylem up to the leaves

Question 37

______occurs when the soil moisture is well above field capacity and water drives gases out of the soil pores so that there is insufficient oxygen for proper root function.

Answer 37

Waterlogging

Question 38

Depending on the severity of waterlogging this condition is termed?

Answer 38

hypoxia or anoxia

Question 39

Which vine rupestris or riparia is better suited to water logging?

Answer 39

Riparia is better suited