Effect of a salt crust on evaporation from a bare saline soil
Effect of a salt crust on evaporation from a bare saline soil
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DOI：
10.2136/vzj2005.0144
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发表时间：
2006-11-01
影响因子：
2.8
通讯作者：
Nakane, Kazurou
中科院分区：
文献类型：
--
作者：
Fujimaki, Haruyuki;Shimano, Takahiro;Nakane, Kazurou
土壤表面蒸发是干旱和半干旱地区灌溉土壤盐碱化的主要原因。为了优化盐渍条件下的灌溉制度，必须能够准确地预测土壤中的溶质运移和蒸发速率。我们在恒定的气象条件下进行了实验室柱实验，但辐射是自动调节的，使土壤的温度与空气的温度保持相同。初始土壤溶液浓度和从5.2 cm长的柱子底部流入的水的浓度设定为3000g m(-3)。对土壤和溶质的三种组合进行了蒸发实验。虽然通过保持底部的低吸力来保持土壤表面的湿润，但蒸发率随着时间的推移而显著下降。这一下降不能仅用渗透势的下降来解释，而是由于在地表附近形成了盐壳。因此，对蒸发的体积转移方程进行了修改，以包括盐壳引起的水蒸气扩散的阻力。从实验和理论上评价了盐壳阻力与积盐量的关系。在我们的数值分析中，我们使用了独立估计的土壤水力和溶质运移参数。结果表明，对流扩散方程(CDE)往往高估了蒸发土壤表面附近的后向扩散，从而显著延缓了土壤表面盐分的积累，降低了土壤蒸发速率。由于CDE使用费克定律的类比来描述机械弥散，因此弥散项高估了溶质向下的输送相对于向上的对流输送。
Evaporation from the soil surface is a major cause of the salinization of irrigated soils in arid and semiarid regions. To optimize irrigation scheduling under saline conditions, it is essential to be able to accurately predict solute transport in soils and the evaporation rate. We conducted laboratory column experiments under constant meteorological conditions, except for radiation, which was automatically regulated such that the temperature of the soil remained the same as that of the air. The concentration of the initial soil solution and that of the inflowing water from the bottom of the 5.2-cm-long column were set at 3000 g m(-3). The evaporation experiments were performed with three combinations of soil and solute. Although the soil surface was kept wet by maintaining a low suction at the bottom, the evaporation rate was found to decrease considerably with time. This decrease could not be explained by a decrease in osmotic potential alone, but rather was due also to the formation of a salt crust near the surface. The bulk transfer equation for evaporation was therefore modified to include a resistance to water vapor diffusion caused by the salt crust. The dependence of the salt crust resistance on the amount of accumulated salt was evaluated experimentally and theoretically. In our numerical analysis, we used independently estimated soil hydraulic and solute transport parameters. Results show that the convection-dispersion equation (CDE) tends to overestimate backward diffusion near an evaporating soil surface, thus significantly delaying salt accumulation at the soil surface and decreasing the evaporation rate. Since the CDE uses an analogy of Fick's law to describe mechanical dispersion, the dispersion term overestimated the downward transport of solutes against upward convective transport.