A novel experimental approach to determine soil hydraulic material propertiesfor the dry and very dry range is presented.Evaporation from the surface of a soil column is controlled by a constant flux of preconditioned air and theresulting vapour flux is measured by infrared absorption spectroscopy. The dataare inverted under the assumptions that (i) the simultaneous movement of waterin the liquid and vapour is represented by Richards' equation with an effectivehydraulic conductivity and that (ii) the coupling between the soil and thewell-mixed atmosphere can be modelled by a boundary layer with a constanttransfer resistance. The optimised model fits the data exceptionally well.Remaining deviations during the initial phase of an experiment are thought to bewell-understood and are attributed to the onset of the heat flow through thecolumn which compensates the latent heat of evaporation.
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