Evaporation from soils and control of the salt accumulation

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Dissolved salt in soil move upward with soil water movement during evaporation and accumulates at the evaporating surface under the condition where potential evaporation exceeds the amount of precipitation. As the evaporation rate decreases with formation of dry layer at the soil surface, predicting the decreased evaporation rate with a thickness of the dry layer is necessary for prediction and control of the salt accumulation.It has confirmed that evaporation occurs at the bottom of dry layer (the boundary between wet layer) and the evaporation rate is determined by vapor diffusion through the dry layer, by measuring temperature profiles in soil, evaporation rate, water content and relative humidity profile in soil, at a investigation plot with the soil of Kanto Loam. I came up with a model of evaporation in which evaporation rate is proportional to the vapor density difference between at the atmosphere and at the bottom of the dry layer, and also the proportionality constant is determined by the series resistance of the boundary layer resistance in air and dry layer resistance for vapor diffusion in soil. The calculated evaporation rates agree well with the observed evaporation ratesGetting these knowledge, I explored fields in Faisalabad, Pakistan where salt accumulation and soil degradation was serious. I also examined and evaluate the actual means that farmers or researcher in Pakistan did. I proposed counter measures for the problems, depending on the knowledge on water movement in soil-plant-atmosphere system.