Abstract :
[en] The soil water retention curve (SWRC) is a unique relationship between water content and soil water potential.
SWRC in near saturation gives the dimension of soil macroporosity which plays an important role in water
translocation into soil. Thus, the accurate measurement of SWRC is crucial. The aim of this study is to compare
SWRC obtained through two different methods: X-ray computed microtomography (X-ray CT) and evaporation
method by HYPROP device. Three different depths (0–10, 25–30 and 45–60 cm) are considered for soil
sampling. The results showed significant differences in SWRC between the techniques. The SWRC from X-ray CT
showed more volumetric water content at 25–30 cm (0.044) and 45–60 cm (0.024) than evaporation at
saturation (0 kPa) in cases where the macroporosity was higher. Macropores may have connections with
neighbouring pores of smaller sizes. Hence we assume that these pores can be observed through X-ray CT but
cannot be evaluated by evaporation. As macropores with narrow opening do not evaporate at very low tension.
These pores therefore got empty at relatively higher tension. Consequently, SWRC near saturation appeared
rather flatter with the evaporation method where the X-ray CT presented deviation. Accordingly, interpretation
of macro pores from SWRC through evaporation method would give comparatively smaller volume of
macropores than they really are. Pore morphology and other hydraulic functions of soil, for example, mean
connection surface of pores, hydraulic conductivity, and the efficiency of water conducting macropores also
support the X-ray CT findings.
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