【作者】 高金芳；

【导师】 李毅；

【作者基本信息】 西北农林科技大学 ， 农业水土工程， 2010， 硕士

【摘要】 近年来由于盐碱地开发和改良以及土壤次生盐碱化防治的必要性和紧迫性,使得对西北干旱—半干旱地区覆膜条件下土壤水、盐、热耦合迁移规律的研究受到重视。目前国内外对覆膜开孔条件下的土壤物质迁移过程还研究较少。本论文结合国家自然科学基金课题,以室内试验为主、理论分析为辅,采用土柱加热室内试验系统,研究覆膜开孔率对入渗和蒸发条件下土壤水、盐、热耦合迁移的影响及作用机制,所得主要结论如下:(1)砂土毛管水上升速度和地下水补给速率均与时间呈明显的幂函数关系,二者之间可近似为线性关系,且斜率表示土壤在此期间含水量变化量。(2)在不同覆膜开孔条件下,毛管水补给对蒸发产生影响,不同开孔率的累积蒸发量随着时间逐渐增加,采用Rose经验公式对累积蒸发量和时间以及相对开孔率进行拟合,得到幂函数关系;单位膜孔面积蒸发量随开孔率的增加而减小,因此覆膜开孔抑制蒸发速率。土壤剖面温度呈现出上大下小的趋势,土体上部温差梯度较大,越深温差梯度越小,30cm以下土温增幅相对于30cm以上都不大,因此可将30cm定义为温度变化的影响深度,土层温度T与深度Z之间存在幂函数关系。不同开孔率时的温度变化趋势相同,在一定深度土体温度不随深度变化;覆膜开孔率越小,土壤剖面的温度相对越大,全覆膜时的土温最高。(3)不同高度土体的单位深度累积蒸发量与时间变化符合裸土蒸发的Gardner理论关系,单位深度累积蒸发量与时间和土体总高度存在二元线性函数关系,土体高度和开孔率与单位膜孔面积单位深度累积蒸发量的乘幂关系;土柱高度越小单位深度含盐量和盐分浓度变化幅度越大,覆膜开孔限制土壤水分蒸发速度进而影响土体盐分表聚,因此可以通过控制覆膜开孔率达到改良盐渍土的目的。(4)土壤水分含量影响蒸发时土壤供水能力,根据蒸发系数可推算已知土壤含水率下、不同覆膜开孔率条件下任意时刻的累积蒸发量变化,单位膜孔面积累积蒸发量(ER)随开孔率增大而急剧减小,不同含水率的ER与开孔率可用幂函数表示;含水率越大,不同覆膜开孔率土体的土表积盐量越多,不同含水率土体的盐分浓度剖面分布规律一致,不同开孔条件下不同含水率土体剖面盐分浓度与垂直位置之间可用幂函数表示。(5)土壤质地是影响蒸发的因素之一,在稳定蒸发条件下土表的水吸力较大时,砂土导水率小于塿土的,随着夹层层位的变化,水分运动由被加速到被抑制的转折点为砂土与塿土的导水率相对大小发生变化之时,不同夹层层位裸土的累积蒸发量的变化趋势保持一致,夹层层位越浅对土体累积蒸发量的抑制作用较明显;覆膜开孔条件下,累积蒸发量、相对累积蒸发量、单位膜孔面积的累积蒸发量与开孔率及夹层层位均存在定量函数关系。(6)蒸发过程中,塿土层中的含水量明显大于上下砂土层的含水量,而塿土层以下砂土的含水量变化不大,塿土层以上的砂土含水量则随层位的不同发生明显变化,这与毛管水上升阶段的情况相似;土壤剖面温度增加是因干燥层的形成所致,而干燥层的形成使水分蒸发强度明显减小,较高的夹层层位对于土壤剖面温度的分布影响较大,不同开孔率时的温度变化趋势相同。覆膜开孔率越小,土壤剖面的温度越大,由此可见,覆膜能够有效地增加土体温度。更多还原

【Abstract】 Owing to the neccecity and emergency of reclamation of salinized soils and prevention of secondary salinization in recent years, study on the coupled movement of soil water, soil salt and soil heat under plastic mulch in arid and semi-arid areas had been paid attention to. Rsearch on soil mass transfer process under plastic mulch has been conducted limitedly in the world. This work was supported by National Natural Science Fundation. We combined laboratory tests with theoretical analysis, used laboratory soil column test systems to study the effect of plastic film hole ratios on the movement of soil water, soik salt and soil heat during soil water infiltration and evaporation process to analyze the mechanism. The main results are as follows:(1) Power functions were both found for relationship between capillary water rise velocity with time, and between capillary water supply rate with time. There was linear function relationship between the capillary water rise velocity and the capillary water supply rate for uniform soil.(2) The supply of capillary water impacted evaporation at different plastic film hole ratios, the cumulative evaporation of different open hole ratios increased with time gradually, there was power relationship between cumulative evaporation and time as well as relative open hole ratios with Rose empirical formula. Unit film hole area of evaporation decreased when open hole ratios increased, so did the rate of evaporation at different plastic film hole ratios. Soil temperature on soil surface was large and was small when soi depths increased, the upper soil temperature gradient was large, the deeper of soil depth, the smaller of the temperature gradients, soil temperature at depths depper than 30cm varied not so obviously, so 30cm can be defined as influence depth for soil temperature changes. There were power functions between soil temperatures and soil depths.(3) The variations between cumulative evaporation at unit depth and evaporation time fit Gardner’s theory for all the soil column heights, there were 2-variable linear functions between cumulative evaporation at unit depth, evaporation time and total soil height. There was power relationship between cumulative evaporation at unit depth by unit film hole area and total soil height as well as open hole ratios. The smaller the total soil height, the larger the variation ranges of soil salt content at unit depth and soil salt concentration. Plastic mulch with open holes restrained soil water evaporation rates and also affected accumulation of soil salt on soil surface, it was effective to decrease soil salt accumulation on soil surface by decreasing open-hole ratios of plastic.(4) The initial soil water contents affected soil water supply capacity. During soil evaporation, the cumulative evaporation changes at any time at different film hole ratios were calculated according to evaporation coefficients at known initial soil water contents, cumulative evaporation per unit hole area film(ER)decreased rapidly when the open hole ratios increased, the function of ER and the open hole ratios of different soil moisture were established; the greater of the soil moistures the greater of the salt concentrations on surface under perforated plastic mulch. The salt concentration distributions in the profiles were similar at different initial soil moisture, there were power functions between soil salt concentration at different initial soil moistures and vertical positions under perforated plastic mulch.(5) Soil texture affected soil evaporation. Hhydraulic conductivity of sandy soil were smaller than loam when soil water suction was large under the stability evaporation, when the loamy soil layer position changeed, the changing point of soil water movement was accelerated or was restrained when the relative size of soil hydraulic conductivity changed for sandy and loamy soils. The trends of cumulative evaporation were similarly for bare soils at different loamy soil layer positions, it was clear that the restrain effects of soil layer on cumulative evaporation were more obvious when layer position were closer to soil surface. There were quantititative functions between cumulative evaporation, relative cumulative evaporation, unit film hole area of evaporation and open hole ratios for different loamy soil layer positions.(6) The soil water contents in the loamy soil layers were higher significantly than the upper and lower sand layers during evaporation, and soil water content of sand changed less than loamy soil, soil water content in the sand soil layers on the top of loamy soil changed significantly, which was similar with situations of capillary water rise process; increase of soil temperature was caused by the formation of dry layer, and it significantly reduced intensity of soil water evaporation. The higher of the layer positions, the greater of its impacts on the distributions of soil temperature. The trend of temperature changed and was similar under different open hole ratios. The smaller the open hole ratios, the larger the soil temperature in the profiles, which showed that plastic mulch can increase the soil temperature effectively.更多还原