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)