An experimental study on behaviors of water and chemicals in a non-uniform soil layer and its mechanism under evaporation

In arid and semi-arid areas，evaporation and salinization becomes quite important phenomena which must be to clarified。In this study，Akadama-soil layers with a dual pore structure(macro-pores and micro-pores)were focused on as a non-uniform soil，and evaporation experiments using the layers moistened by distilled water and enriched NaCl solution were undertaken in a temperature and humidity controlled room at 25℃and 20%.To examine effects of a solar radiation，water-table and turbulent surface wind to evaporation，in some cases，such conditions were applied to the layer。Through the evaporation experiments，the following are clarified.1.Micro-pores play a role of transmission route of underlying soil-water to an evaporation zone，and it causes evaporation rate higher.2.Turbulence of applied surface wind to the exposed surface penetrates easily into soil through macro-pores，and it affects vapor transfer in the soil layer significantly。Therefore，in the vapor transfer in the soil layer，not only molecular diffusion but also turbulent one caused by the surface wind must be taken account3.The heating on the upper surface leads a characteristic vapor density profile in the soil with a peak at which the evaporation zone is located。Water vapor created by evaporation is transported in the upper and lower directions。The downward moving vapor condenses in a deep location，therefore soil-water is carried to a deep zone via evaporation，vapor transfer and condensation process.4.Enrichment of soil-water appears in an upper zone of the soil layer，where the concentrations of Na+and Cl start to increase abruptly with decreasing depth.This location is more or less consistent with the upper end of drying front.The concentrations below that depth，as a result，become lower than initial ones·this may be due to absorption and ion exchange on the soil-particles。

In arid and semi-arid areas, evaporation and salinization becomes quite important phenomena which must be to clarified. In this study, Akadama-soil layers with a dual pore structure (macro-pores and micro-pores) were focused on as a non-uniform soil, and evaporation experiments using the layers moistened by distilled water and enriched NaCl solution were undertaken in a temperature and humidity controlled room at 25℃ and 20%. To examine effects of a solar radiation, water-table and turbulent surface wind to evaporation, in some cases, such conditions were applied to the layer. Through the evaporation experiments, the following are clarified.1.Micro-pores play a role of transmission route of underlying soil-water to an evaporation zone, and it causes evaporation rate higher.2.Turbulence of applied surface wind to the exposed surface penetrates easily into soil through macro-pores, and it affects vapor transfer in the soil layer significantly. Therefore, in the vapor transfer in the soil layer, not only molecular diffusion but also turbulent one caused by the surface wind must be taken account3.The heating on the upper surface leads a characteristic vapor density profile in the soil with a peak at which the evaporation zone is located. Water vapor created by evaporation is transported in the upper and lower directions. The downward moving vapor condenses in a deep location, therefore soil-water is carried to a deep zone via evaporation, vapor transfer and condensation process.4.Enrichment of soil-water appears in an upper zone of the soil layer, where the concentrations of Na+ and Cl start to increase abruptly with decreasing depth. This location is more or less consistent with the upper end of drying front. The concentrations below that depth, as a result, become lower than initial ones・this may be due to absorption and ion exchange on the soil-particles.