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SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...

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Chapter 5 Modeling Grazing Effects on Coupled Water and Heat Fluxes in Inner Mongolia Grassland<br />

the ungrazed sites, the grazed sites generally have lower soil water storage. In<br />

August, the driest soil conditions occur at HG, where water contents approach<br />

the permanent wilting point due to both strong evaporation losses and low water<br />

storage in the subsoil. In contrast to this, rainfall water can percolate into deeper<br />

soil layers (>40 cm) in the two ungrazed sites. At the topsoil (e.g., 20 cm), UG 79<br />

is drier than UG 99 probably due to higher water withdrawal at the more<br />

productive site UG 79.<br />

Soil temperature shows typical changes with diurnal weather condition (Fig.<br />

2). With increasing soil depth, soil temperature decreases, indicating energy<br />

transfer from the topsoil to the subsoil during the growing period. With increasing<br />

grazing intensity, soil temperature is higher, especially in the topsoil. In general,<br />

soils seem to warm up or cool down quicker in the grazed sites than the<br />

ungrazed sites. However, compared to the other sites, the soil in HG seems to<br />

buffer the abrupt drop in temperature as early autumn snow occurred on 7<br />

September, which might relate to the higher soil temperature and the lower heat<br />

conductivity of the drier soil at HG.<br />

a<br />

b<br />

Soil depth (cm)<br />

c<br />

d<br />

-20<br />

-40<br />

-20<br />

-40<br />

0<br />

-20<br />

-40<br />

0<br />

-20<br />

-40<br />

0<br />

0<br />

0<br />

20-May 9-Jun 29-Jun 19-Jul 8-Aug 28-Aug 17-Sep<br />

Time (days)<br />

0.25<br />

0.21<br />

0.17<br />

0.15<br />

0.13<br />

0.11<br />

0.09<br />

0.07<br />

0.05<br />

Soil moisture (cm 3 cm -3 )<br />

a<br />

b<br />

Soil depth (cm)<br />

c<br />

d<br />

-20<br />

-40<br />

0<br />

0<br />

0<br />

-20<br />

-40<br />

0<br />

-20<br />

-40<br />

0<br />

-20<br />

-40<br />

20-May 9-Jun 29-Jun 19-Jul 8-Aug 28-Aug 17-Sep<br />

Time (days)<br />

Fig. 5.2. Contour plots of soil moisture (left side) and soil temperature (right side) for the<br />

four grazing intensities from May to Sept. 2006 (a is UG 79, b is UG 99, c is WG, and d is<br />

HG).<br />

Model Calibration and Validation<br />

25<br />

22<br />

19<br />

16<br />

13<br />

10<br />

7<br />

4<br />

1<br />

Soil temperature ( 0 C)<br />

97

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