【作者】 陈丽湘；

【导师】 刘伟；

【作者基本信息】 华中科技大学 ， 工程热物理， 2009， 博士

【摘要】 土壤次生盐渍化过程是一种严重的土地退化现象,在世界各地普遍发生,尤其在干旱半干旱地区尤为明显,对粮食生产有极为严重的影响,甚而会影响到人类的生存和发展,因此长期以来引起世界各国的广泛关注。本文将多孔介质的热质传输理论应引入传统农业工程领域,对传统的农业土壤次生盐渍化过程进行研究。土壤作为一种典型的多孔介质,人们对其进行了长期的研究和探索,并取得了大量的研究成果。将多孔介质的研究成果引入对土壤次生盐渍化过程的研究,无疑为这一传统的研究领域开辟了新的研究思路,从而为问题的解决提供了新的可能。本文从多孔介质的研究视角,对土壤次生盐渍化过程进行了实验研究,对地下水位、蒸发量等环境因素对土壤水盐运动规律进行了定量测量和研究。研究了植被和根系的影响。并在多孔介质“七场-相变”模型基础上对土壤中水热盐耦合过程进行了数学建模和数值模拟。实验在环境风洞中进行,研究了环境因子,尤其是地下水位条件对于盐分运移过程的影响。研究结果表明,地下水临界深度(CDG)对于盐分的运移过程有十分重要而明显的作用。CDG是环境因子,如气温,湿度,风速,和土质,甚至植被等因素综合作用的结果。本文中通过实验手段进行了测量。通过对土壤次生盐渍化地区进行CDG的取样测量,取得的大量基础数据可以为农业灌溉等实践活动提供科学的指导,从而减少甚至避免土壤次生盐渍化过程的发生,对于世界粮食安全和人类的生存具有重大意义。基于对土壤次生盐渍化机理的认识,对典型的土壤表面“盐结皮”的形成要素分析和研究,并在实验条件下模拟了“盐结皮”现象,对“盐斑”的形成和消失进行了观察和研究,实验结果符合预期,证明我们对土壤次生盐渍化机理的认识在一定程度上是正确的。“七场-相变”模型从连续介质力学的观点,采用局部体积平均法,建立了描述湿分分层土壤中热湿迁移的数学模型,分析了湿分分层土壤中水、热、气的迁移机理;并在恒定环境条件下进行了稳态与非稳态的数值计算,得到了湿分分层土壤中的温度场、湿度场以及内部蒸发量场,分析了土壤内部热湿迁移规律。在此研究基础上,通过对土壤溶质运移过程的分析,建立了描述盐分运移方程,与“七场-相变-扩散模型”一起,构成土壤次生盐渍化过程的数学模型。并对盐分上升过程进行了初步的模拟,在趋势上表现出很好的一致性,为对其进行更为精确的模拟提供了良好的研究基础。在上述研究的基础上,本文总结了土壤次生盐渍化的发生机理,即环境气象因子(温度、湿度、风速),地下水位及其矿化度,植被和根系等。并提出了防止土壤次生盐渍化的根本原则,即“切断”水盐上升的通道,具体措施如地膜覆盖、产生表面干土层、降低地下水位(不大水漫灌)、改变土壤性质等都是防止土壤次生盐渍化过程的有效途径,提出了“坡地”种植模式的盐渍化防治理念。更多还原

【Abstract】 Soil Secondary Salinization (SSS) is a hazadous phenomenon widely happening around the world, especially in arid and semi-arid regions. It has been studied all the time. In the present thesis, the theory of the flow and heat and mass transfer in porous media is applied to the traditional agricultural field. It may produce new solution to the old problem. In the study of SSS, combination of both mathematical simulation and experimental research is an effective way. In the present thesis, experimental researches were conducted to study the influence of environmental factors such as ground water, evaporation rate. The experiments with plants were also conducted. The mathematical model was established based on the porous media model of "seven field-phase change" and some simulation results were got and analyzed.Based on theoretical analysis of soil solute transfer, the mathematical model of describing simultaneous heat, moisture and gas migration in porous media, and mathematical model of solute transfer in soil was developed using the volume-averaging method. Mathematical simulation was conducted to investigate soil secondary salinization owing to different watertable at environmental conditions, which might be applicable for agricultural practice. In this paper, the dynamic characteristics of soil salt migration and its influence factors are analyzed. Basing on the theories of solute transport and heat and mass transfer in porous media and taking the temperature effect into account, the model of moisture, heat and salt transport, which involved root water extraction, absorption-desorption, is established. By use of numerical method, the transient distributions of salt, temperature and moisture in soil, which might be useful to provide necessary information for preventing and curing soil salinization, are obtained and the influences of soil properties on salt migration are also analyzed.A series of experiments were designed and conducted in a closed-loop wind tunnel to study solute transport in porous media of soil. In such situation, Critical Depth of Ground watertable (CDG) acts an important role. Both mathematical simulation and experimental results indicate that moisture/solute transfer in the process of soil secondary salinization under different conditions of ground watertable exhibits different patterns as well. The influence of plant and its roots were also studied. Moreover, the comparisons of solute transfer between in cropped soil-bed and in bare soil-bed are also conducted.Based on the theoretical analysis and experimental result and mathematical simulation results, the quite typical phenomenon of "salt crusting" was simulated and observed in laboratory, which have not been reported in literature before.Based on present research work, the mechanism of soil secondary salinization was analysed to be the combination effect of temperature, humidity, wind speed, ground watertable , plant and its roots, etc. A new general principle of preventing soil secondary salinization was proposed as to "cut" the connecting channel between the saline groundwaer and the soil surface or root zone under vegetated condition. A new method of soil secondary salinization prevention was proposed as to be "slanted land" plantation pattern.The present work is financially supported by the National Natural Science Foundation of China (No.50376015).更多还原