Lecture 33 Lecture on Soil Physics, part 1
• Soil Properties
–
–
–
–
soil texture and classes
heat capacity, conductivity and thermal diffusivity
moisture conductivity
porosity
it and
d diffusion
diff i
• Theory, Heat Transfer
– Heat transfer, Fourier’s equation
• Observations
Ob
ti
– Temperature profiles
• Daily patterns, Phase lags and Amplitudes of soil temperature
• Seasonal Patterns
• Soil Heat Flux
– Daily patterns
– Seasonal Patterns
ESPM 129 Biometeorology
Ode to Soil
“Darkle, darkle, little grain,
I wonder how you entertain
A thousand creatures microscopic.
Grains like you from pole to tropic
Support land life upon this planet
I marvel at you, crumb of granite! “
Dr. Francis Hole, Soil Scientist (1913-2002)
ESPM 129 Biometeorology
Soil Profile
ESPM 129 Biometeorology
Soil Components
• Clay
– < 0.002 mm
– Crystal lattices, Si, Al, O, OH
• Silt
– 0.05 to 0.002 mm
• Sand
– 2 to 0.05
0 05 mm
• Gravel
– > 2 mm
ESPM 129 Biometeorology
Soil Texture Triangle
g
ESPM 129 Biometeorology
Porosity,
y, P,, is a function of the volumes of air,, va, water,, vw and solid,, vs
va  v w
P
va  v w  v s
It is also a function of the soil bulk density, b
b
P  1
s
Mass of soil per unit volume
ms vs  s

b 
vt
vt
ESPM 129 Biometeorology
Soil Physical Properties
Soil type
Bulk density, kg m-3
Porosity, percent
Peat
0.65-1.1
60-80
Ideal soil
1310
50-60
Clay
1220
45-55
Silt
1280
40-50
Medium to coarse sand
1530
35-40
Uniform sand
1650
30-40
Fi to
Fine
t medium
di
sandd
1850
30 35
30-35
Gravel
1870
30-40
After Tyndall et al.. 1999
ESPM 129 Biometeorology
Soil Moisture
b
mw vw  w
w


l
ms
vs  s
Mass ratio, Mass of water to mass of solid
ESPM 129 Biometeorology
Volumetric water content
vw
b
 w
w
vt
Note: We need to know the Bulk Density!!!
ESPM 129 Biometeorology
Fourier Soil Heat Budget Equation:
Time rate of Change in Soil Temperature Is a function of the Flux Divergences
of Soil Heat Flux, G
T
G
 sCs

t
z
T
Gk
z
s, soil density
Cs, specific heat of soil
k, thermal conductivity
ESPM 129 Biometeorology
Fourier Heat Transfer Eq
T

T
 s Cs
  (k
)
t
z z
T
2T
 2
t
z
Thermal Diffusivity
k

 s Cs
ESPM 129 Biometeorology
Soil Heat Capacity is a Weighted function of the Mineral
Organic and Water components
 sCs   m  mCm   o  o Co   w  wCw
Approximation of Campbell
Cs 
2400000 b
 4180000
2.65
ESPM 129 Biometeorology
Soil Heat Capacity
3000000
clay
Cp, heat capa
C
acity, J kg
-1
K
-1
3500000
sand
2500000
loam
silt clay
litter
2000000
1500000
1000000
500000
0
0.0
0.1
0.2
0.3
Soil Moisture content
Which Material is the Best and Worst Store of Heat?
ESPM 129 Biometeorology
0.4
Soil Thermal Properties
material
t i l
D it (M
Density
(Mg m-33)
Specific
S
ifi Heat
H t (J g-11
K-1)
Thermall
Th
conductivity (W m1 K-1)
Soil minerals
2.65
0.87
2.5
Granite
2.64
0.82
3.0
Quartz
2.66
0.80
8.8
g
matter
Organic
1.30
1.92
0.25
Water
1.00
4.18
0.56
Ice
0 92
0.92
21
2.1
2 22
2.22
air
0.0011875
1.01
0.024
Campbell and Norman, 1998
ESPM 129 Biometeorology
Thermal Conductivity is a function of soil texture and moisture
Thermal C
Conductivity
y ( W m-1 K-1)
1.50
clay
sand
loam
1.25
silt clay
litter
1.00
0.75
0.50
0.25
0.00
0.0
0.1
0.2
0.3
0.4
volumetric water content
ESPM 129 Biometeorology
0.5
0.6
Soil Temperature Profiles
ponderosa pine
0.0
-0.1
01
de
epth (m)
-0.2
-0.3
-0.4
1 am
9 am
12 pm
430 pm
-0.5
-0.6
06
-0.7
5
10
15
20
25
30
35
40
o
Soil Temperature ( C)
Where do we place the Wine Cellar?
ESPM 129 Biometeorology
T ( z, t )  T  A(0) exp(  z / D) sin( (t  t0 )  z / D)
Temperate Deciduous Forest
D180 1997
D180,
24
2 cm
4 cm
8 cm
23
Soil Temperatture (C)
16 cm
32 cm
22
21
20
19
0
4
8
12
16
20
24
Time (hours)
Damping Depth
D
2

 is angular frequency (radians per second)
 is period of fluctuation
ESPM 129 Biometeorology
Summer, Dry CA Grassland
Day 204, 2001, Vaira Grassland
40
So
oil Temperaturre
35
2 cm
4 cm
8 cm
16 cm
32 cm
30
25
20
15
10
0
5
10
15
Time (hours)
ESPM 129 Biometeorology
20
Temperate Deciduous Forest
D80, 1997, dormant
20
2 cm
4 cm
18
8 cm
So
oil Temperature (C)
16 cm
32 cm
16
14
12
10
8
0
4
8
12
16
Time (hours)
ESPM 129 Biometeorology
20
24
Less Ideal, Heterogeneous Site
young ponderosa pine
45
Soil Temperrature
40
2 cm
4 cm
8 cm
16 cm
32 cm
35
30
25
20
15
10
5
0
500
1000
1500
Time
ESPM 129 Biometeorology
2000
L z  z OP
 M
2 N ln( A / A Q

2
1
1
ESPM 129 Biometeorology
2
2
Amplitude Method
3.0
Vaira grassland, 2002
Verhoef method
2 to 16 cm
-1
therma
al diffusivity (W m K )
2.5
-1
L z  z OP
 M
2 N ln( A / A Q

2.0
1.5
2
1
1
10
1.0
0.5
0.0
0.0
0.1
0.2
0.3
0.4
3
0.5
-3
volumetric soil moisture @ 10 cm (cm cm )
ESPM 129 Biometeorology
2
2
Annual Course in Soil Temperature
Air temperature, daily average
Soil temperature, daily average
T
Temperature
30
20
10
0
-10
10
0
50
100
150
200
250
Day
ESPM 129 Biometeorology
300
350
Mean Soil Temperature Scales with Mean Air Temperature
FLUXNET Database
18
16
b[0] 0.6243257655
b[1] 0.9216133206
r ² 0.9342107631
Tso
oil: annual (C))
14
12
10
8
6
4
2
2
4
6
8
10
12
14
Tair:annual (C)
ESPM 129 Biometeorology
16
18
Wheat
150
125
G modelled
d (W m-2)
100
75
50
25
0
-25
-50
-75
0
400
800
1200
1600
2000
Time (hours)
ESPM 129 Biometeorology
2400
30
D id
Deciduous
Forest
F
-2
Soil Heat Flux Density, G (W
Wm )
25
20
15
10
5
0
-5
0
400
800
1200
1600
Time (hours)
ESPM 129 Biometeorology
2000
2400
30
Temperate Deciduous Forest
--2
Soil Heat Flux Dens
sity, G (W m )
20
10
0
-10
-20
-30
0
50
100
150
200
250
D
Day
ESPM 129 Biometeorology
300
350
Summary Points
•
•
•
•
•
Soils consist of a mixture of silt, sand and clay and organic matter.
Together these components affect the soil’s
Together,
soil s texture,
texture water holding
capacity and heat capacity and conductivity.
Sand has the highest heat capacity and conductivity and
litter/organic matter the lowest, when dry. Heat capacity and
conductivity
d ti it off allll soils
il iincrease iin a non-linear
li
manner with
ith soilil
moisture.
The amplitude of the temporal course of temperature (daily/annual)
gg ((relative to air temperature)
p
)
decreases and becomes more lagged
with soil depth.
Soil heat flux averaged over the course of a day or year is close to
zero
There is a close correspondence between mean soil temperature
and mean annual air temperature.
ESPM 129 Biometeorology