Evaporation from soils and control of the salt accumulation

土壤中的溶解盐在蒸发过程中随土壤水分运动而向上运移，在潜在蒸发量超过降水量的条件下，在蒸发面处积累。由于蒸发速率随土壤表面干层的形成而减小，因此，用干层厚度来预测蒸发速率的减小对于预测和控制盐分积累是必要的，证实了蒸发发生在干层底部（湿层之间的边界）和蒸发速率由通过干层的蒸汽扩散，通过测量土壤中的温度分布，蒸发速率，土壤含水量和相对湿度剖面，在调查样地与土壤关东壤土。本文提出了一个蒸发模型，该模型中蒸发速率与大气层和干层底部的水汽密度差成正比，比例常数由空气中的边界层阻力和土壤中水汽扩散的干层阻力的串联电阻决定。在此基础上，对巴基斯坦费萨拉巴德严重积盐和土壤退化的农田进行了实地考察。我还检查和评估了巴基斯坦农民或研究人员的实际手段。并根据对土壤-植物-大气系统中水分运动的认识，提出了解决问题的对策。

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.