Geoscience Reference
In-Depth Information
50
Figure 6.2
The time
variation in subsurface soil
temperature beneath a sandy
loam soil with bare surface
measured for three days at
depths of 2.5 cm (full line), 15
cm (broken line), and 30 cm
(dotted line). (Redrawn from
Monteith and Unsworth,
1990, after Deacon, 1969,
published with permission.)
40
30
20
24
06
12
18
24
06 12
Local time (hr)
18
24
06
12
18
24
Table 6.1
Mass density and thermal properties of soils, air, and water.
Thermal
conductivity
k
s
(W m
−1
K
−1
)
Thermal
diffusivity
Mass density
r
s
c
s
(J kg
−1
K
−1
× 10
3
)
Specific heat
Heat capacity
C
s
(J m
−3
K
−1
× 10
6
)
a
s
(m
2
s
−1
× 10
−6
)
Material
Condition
(kg m
−3
× 10
3
)
Sandy Soil
(40%
porosity)
Dry
Saturated
1.60
2.00
0.80
1.48
1.28
2.98
0.30
2.20
0.24
0.74
Clay Soil
(40%
porosity)
Dry
Saturated
1.60
2.00
0.89
1.55
1.42
3.10
0.25
1.58
0.18
0.51
Clay Soil
(80%
porosity)
Dry
Saturated
0.30
1.10
1.92
3.65
0.58
4.02
0.06
0.50
0.10
0.12
Air
20°C, still
0.0012
1.00
0.0012
0.026
21.5
Water
20°C, still
1.00
4.19
4.19
0.58
0.14
thermal properties of air are profoundly different to those of the water which
replaces it. Values of the soil properties discussed below are given in Table 6.1,
together with those for air and water for purposes of comparison.
Density of soil,
r
s
The local density of soil in kg m
−3
is the mass of unit volume of soil. As just
mentioned, the density of soil changes greatly with the moisture content of the soil
