SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...

Chapter 6 Modeling of Coupled Water and Heat Transfer in Freezing and Thawing Soil
duration of ground freezing (in average about 140 to 150 days), which decreases
with increasing soil depth (Table 1).
Amplitude ( o C)
Soil temperature ( o C)
15
12
9
6
3
0
30
20
10
0
-10
-20
2 cm
UG 99 WG
9-Sep 19-Oct 28-Nov 7-Jan 16-Feb 28-Mar 7-May 16-Jun 26-Jul
9-Sep 19-Oct28-Nov 7-Jan 16-Feb28-Mar 7-May 16-Jun 26-Jul
Time (days)
Fig. 6.3. Soil temperature and amplitude in topsoil (2 cm) as a function of grazing
intensity (UG 99 and WG) from August 2005 to July 2006.
Furthermore, soil temperature and amplitude are affected by grazing
intensity, which is exemplarily shown for the ungrazed site UG 99 and the winter
grazed site WG at the topsoil (2 cm) (Fig. 3). Compared with UG 99, WG has a
higher temperature in summer but a lower value in winter, indicating that soil
thermal properties are not only seasonal specific but also treatment-dependent.
We observe that the monthly mean of soil temperature decreases in winter and
increases in summer with increasing grazing intensity (Table 1). It can be
ascribed to the differences in insulating effect of vegetation cover. The dense
vegetation at the ungrazed sites (Gao, 2007) protects soil from receiving strong
radiation in summer and from releasing energy quickly in winter. Consequently,
the temperature amplitude happened higher in the grazed sites than the
ungrazed sites (Fig. 3), indicating that grazing decreases the thermal diffusivity
by increasing thermal conductivity in the soil surface.
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