Water as a Limiting Factor Part 1 Flashcards
First three important principle of water requirements?
- Know the symptoms on the vine of water stress
- Know the physiological stages when a lack of water will affect the size and quality of the crop
- Know the depth and size of the root system
Last two important principles of water requirements?
- Know the soil in order to know what the storage capacity of the soil is for water
- Know how much water to apply
3 indicators of plant water stress:
- Leaf water potential (pressure machine)
- Leaf stomatal conductance
- Soil water potential
What does stomatal conductance describe?
It describes gas diffusion through plant stomata.
- Plants regulate stomatal aperture in response to environmental conditions
Do stomata control leaf water loss?
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.
Why do we have slow transpiration under still air?
Because the boundary layer is higher
Boundary layer conductance relies on three things:
- Wind speed
- Leaf size
- Diffusing gas
What can we see when we look at a graph showing mid-day leaf water potential (bars) vs. Stomatal Conductance?
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
What does soil water potential define when looking at water stress?
Defines the supply part of the supply/demand function of water stress
When looking at the graph showing when to irrigate we can see that…
Silt and Loam have the highest amount of available water
What are the 6 critical physiological stages for water stress?
- Prior to bud break in dry regions without winter rainfall (Dormant phase)
- Bud Break before flowering
- Flowering a fruitset up to pea size
- Pear size to berry softening
- Ripening (berry softening to harvest)
- After Harvest
The bleeding phase is positively affected by
a good content of water in the soil
Bleeding is a very important stage for two reasons:
- 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
- If we have a good bleeding phase, we also have a good transport of auxins to the buds that stimulate bud burst.
What can we see from the graph showing days of bloom vs. Yield loss?
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
2 Practical methods for evaluating soil moisture and 3 tools
- Dig a soil pit
- Feel the soil
Tools:
1. Tensiometers (Water potential)
2. Resistance blocks (water content)
3. Neutron probe (water content)
The relationship between soil water potential and volumetric water contentdepends on…
Rate of water infiltration depends on…
- Soil type
- Soil type and volume of water applied
3 different indicators for when to irrigate. Which is the best?
- Visual symptoms
- Vine water status (the best)
- Weather conditions
What is ET?
Evapotranspiration
Two important considerations for deficit irrigation
- Applied water is less than ET
- Water stress is when photosynthesis is down and transpiration is down
The purpose of a regulated deficit irrigation is triple:
- Save water.
- Preserve yield because I’m not really going into a severe stress.
- Diminish the competition between vegetative structure and bunches, I would increase the quality.
What is the main philosophy of RDI?
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.
What is RDI? (3)
- Again Regulated Deficit Irrigation.
- 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.
- Water stress needs to be removed after this period by irrigating >100%ETc.
What is PRD? (3)
- Alternately irrigating two spatially separate parts of the rootzone
- Each cycle 5 to 14 days, depending on the site and weather
- Deep sandy loam
True or false: RDI is a evolution of PRD
False PRD is an evolution of RDI
What is the main point of utilizing RDI or PRD, why would intentionally induce a water stress?
We would do this in order to control vigor, increase berry quality and increase water use efficiency. We do this via reducing vegetative growth
Is more stress better?
Too much water stress and when it is too late, can be incredibly detrimental
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?
- Irrigate less before veraison to limit berry size
- Irrigate more after veraison to prevent weight loss
Discuss the difference between red and white grapes and how RDI and PRD can be used in respect to the different grapes (2)
- Deficit irrigation/nutrition useful for most red grapes
- RDI less suited for white grapes than is PRD
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.
- senescence
- recycling of K
Too little water before budbreak = (2)
delayed budbreak and stunted shoot growth.
No bleeding =
Normal bleeding =
- Bad budbreak
- Good budbreak
Too much water stress after veraison = (3)
- Berry dehydration
- Decrease in yield
- Sunburn
Too much water stress after veraison = (2)
Yelow leaves
Early defoliation
Yelow leaves and Early defoliation =
Recycled leaf K+ = undesirable increase in berry k+, increased juice pH
Which one is doing better?
Sangio on left, Montepulciano on right?
Sangio on the left
What is the function of ABA?
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
______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.
Waterlogging
Depending on the severity of waterlogging this condition is termed?
hypoxia or anoxia
Which vine rupestris or riparia is better suited to water logging?
Riparia is better suited
