Heat Flow in the Soil
- - - ______- loam
_ c - - - - - _ _ _ _ _ - - -
clay
organic
-
-
0.0
0.1 0.2 0.3 0.4 0.5 0.6
0.7 0.8
Volume Fraction of Water
FIGURE 8.4. Thermal difisivities of soils from Figs. 8.2 and 8.3.
Example 8.3. Compare the diurnal damping depths for moist organic
soil with dry and wet loam soil.
Solution. From Fig. 8.4 the difisivities appear to be around 0.14, 0.2,
and 0.4 mm2/s for the organic, dry loam, and wet loam respectively. Using
Eq. (8.81,
J
2 x 0.2 x 10-6 $
Ddry loam =
= 0.074 m = 7.4 cm
7.3 x 10-5 S-1
D w e t loam =
= 0.105 m = 10.5 cm.
7.3 x 10-5 S-I
If the same diurnal temperature variation were applied to the surface of
each profile, it would penetrate about twice as deep into the wet mineral
soil as it would the organic soil.
Example 8.4. At what depth would soil temperature be measured if you
wanted to find the mean annual temperature to within l o C?
Solution. From Ch. 2 we know that the range of annual temperature
variation is 20 to 30" C, so A(0) is 10 to 15' C. We want the variation to