Measurements of Soil Water Content Using Time Domain Reflectometry Sensor and Water Vapor in Surface Soil at the Gobi Site in the Taklimakan Desert

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Measurements of soil water content, relative humidity of soil air, and soil temperature in surface soil at 0.01 m and 0.05 m depths were carried out at a gobi site near Qira in the southern part of the Taklimakan Desert, China from the end of March 2001 to April 2004. By calibrating Time Domain Reflectometry (TDR) sensors at the site, the applicability of TDR sensors for use in natural hyper-arid conditions was shown. In the wetting process, soil water infiltrated in the liquid phase, while the soil water was in the vapor phase during the drying process. As the first step of the drying process, the surface ground at both depths rapidly and thoroughly dried by evaporation due to the daytime soil temperature increase. As the second step, the soil water evaporated predominantly from the shallower depth. However, because of the supply of water vapor from deeper soil, saturated conditions continued at 0.01 m depth. As the third step, the surface ground gradually dried, repeated diurnal variations in humidity of soil air resulted from the decreased supply of water vapor from deeper soil. Once soil water was supplied in the soil at the gobi site, soil water and water vapor of soil air at 0.05 m depth were not easy to remove.
2005-12-26