SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...

http://www.magim.com) are used to parameterize the model HYDRUS-1D.
Conversely, modeling results are compared with in situ soil water and
temperature measurements to verify the model parameterization. The objectives
of this study are: (i) to quantify the grazing effects on water and heat fluxes by a
Richards’ based hydraulic model, and (ii) to identify water use mechanisms in a
typical Inner Mongolia grassland ecosystem.
Study Site Descriptions
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MATERIALS AND METHODS
Experimental Site and Measurements
This study was performed on long-term experimental sites of the Inner
Mongolia Grassland Ecosystem Research Station (IMGERS; 43 o 37′50′′N,
116 o 42′18′′E) situated in the Xilin River catchment (3650 km 2 ). The vegetation is
characterized by the perennial rhizome grass Leymus chinensis and bunch
grass Stipa grandis, respectively. Soils are classified as Mollisols according to
USDA (1999). In the last two decades, annual mean air temperature was 0.7°C
and precipitation was 343 mm, of which more than 85% fell during the growing
period. Although rainfall season occurs during the vegetation period, plant water
uptake is limited because of strong seasonal and inter-annual rainfall
fluctuations (Chen and Wang, 2000).
Four sites with different grazing intensities were investigated. Two sites
were ungrazed since 1979 (UG 79, 24 ha) and 1999 (UG 99, 35 ha). The other
two sites were grazed: one was grazed only during winter time with 0.5 sheep
units (ewe and lamb) ha -1 yr -1 (WG, 40 ha) and the other was heavily grazed with
2 sheep units ha -1 yr -1 (HG, 100 ha) during the whole year. Before fencing, all
sites were moderately grazed.
Field and Laboratory Measurements
Soil moisture and temperature were measured at 30-min intervals using
horizontally inserted Theta-probes (Type ML2x, Delta-T Devices, Cambridge, UK)
and Platinum ground temperature probes (Pt-100), respectively. Theta-probes
were calibrated soil specific and installed in three depths at 5, 20, and 40 cm.
Soil temperature was measured in five depths at 2, 8, 20, 40, and 100 cm. At