Transcript Water & Transpiration or Water, water everywhere and all

Water & Transpiration
or
Water, water everywhere and all the boards did shrink.
Water, water everywhere and not a drop to drink.
J.G. Mexal
A/H 100
Soil Properties
Water Holding Capacity
• Water Holding Capacity (WHC): amount a water
held by a soil; a function of texture.
• Field Capacity (FC): amount of water held against
the force of gravity after irrigation.
• Permanent Wilting Point (PWP): amount a water at
which the plant wilts permanently. (Does not hold
well for trees & shrubs)
• Available Water Content (AWC): FC - PWP =
AWC
• Maximum Allowable Depletion (MAD): ~50%
AWC
Water & Transpiration
Important Definitions
• Field Capacity
~0.03 MPa
– amount of water held against the force of
gravity; usually measured 24 h after irrigation
• Permanent Wilting Point
~1.5 MPa
– amount of water resulting in wilting from
which plant will not recover; developed for
agronomic crops
Water & Transpiration
Colligative Properties of Water
• Conversions
MPa =
mega Pascal
1000 kPa
10 bar
1000 g/cm2
~ 1 atm (14.7 lb/in2)
~760 mm Hg
Water & Transpiration
Relative Humidity Comparison
R.H.
(%)
0
Water Potential
(Ψ = MPa)
0
Maximum pore size filled
with water (μm)
n.a.
99.999
- 0.001
300
99.990
- 0.010
30
99.930
- 0.100
3
99.270
- 1.000
0.3
92.700
- 10.000
0.03
50.000
- 50.000
0.003
20.000
-222.000
--
Soil Properties
Soil-Water Path
Irrigation Scheduling-nonstressed
Available Water (in/ft)
MAD (%)
2.4
70
2
60
1.6
1.2
50
AWC
PAW
MAD
40
30
0.8
20
0.4
10
0
0
Sand
Sandy loam
Loam
Soil Type
Clay loam
Clay
Soil Properties
Water Holding Capacity
Texture
Sand
Sandy Loam
Loam
Clay
Peat
F.C.
P.W.P.
A.W.C.
mm water / 300 mm soil
40
3
37
55
3
52
55
5
50
65
2
53
120
30
90
Water Holding Capacity
F.C.
P.W.P.
Water & Transpiration
Factors Influencing Transpiration
• RoT Water moves from Hi to Lo Concentration
• Water moves through the Soil-PlantAtmosphere-Continuum in response to this
concentration gradient.
Water & Transpiration
Factors Influencing Transpiration
•
•
•
•
•
•
•
Plant species
R.H.
Stomata (number, size, and aperture)
Leaf morphology
Wind
Temperature (air & soil)
Soil moisture availability
Water & Transpiration
Factors Influencing Transpiration
• Component
–
–
–
–
–
–
–
–
Soil
Root System
Xylem
Leaf Mesophyll
Substomatal Cavity
Stomata
Boundary layer
Atmosphere
• Water Potential (MPa)
–
–
–
–
–
–
–
–
> -0.1
~ -0.3
~ -0.7
~ -1.2
~ -2.0
< -2.0
< -3.0
< -10.0
Water & Transpiration
Factors Influencing Transpiration/Soil Water
Time (days)
Soil 
Plant 
Wilting 
Field Capacity 
Soil  at soil-root
interface
Water & Transpiration
Factors Influencing Transpiration
 ~ -2.0 MPa
 ~ -1.2 MPa
 < -3.0 MPa
Water & Transpiration
Factors Influencing Transpiration/Soil Temp
Collards
Watermelon
Cotton
Water & Transpiration
Factors Influencing Transpiration
Stomata Frequency & Location
Species
Corn
Frequency (no./mm2)
Lower
Upper
108
98
Area
(% of leaf)
0.7
Sunflower
175
120
1.1
Onion
175
175
2.0
Cottonwood
226
187
3.0
Oak
340
0
?
Water & Transpiration
Water Potential vs. Ps and Growth
Corn Ps
Sunflower
Corn Growth
Water & Transpiration
Factors Influencing Transpiration/ Wind
Wind Speed = 10 cm/sec
= 22 mph
Wind Speed = 0.5 cm/sec
= 1 mph
Irrigation Requirements/Harris et al. 1999
June
December
Water & Transpiration
Water Use Efficiency (WUE)
• Species
–
–
–
–
Alfalfa C3
Cotton C3
Corn C4
Sorghum C4
• g H2O/g D.W.
–
–
–
–
864
538
366
365
Things to Know
•
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•
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•
•
•
•
•
Colligative properties
•
Hydrologic cycle
•
Irrigation
•
Solvent
•
Solute
•
Field Capacity
•
Permanent Wilting Point
•
Water Use Efficiency
Potential Evapotranspiration
Transpiration
Turgor
Wilting
MAD
RH
AWC
Water Potential
Xeriscaping