干湿交替过程中土壤容重、水分特征曲线和热特性的动态变化特征
发布时间：2019-06-27 12:08
【摘要】：土壤作为一个复杂的三相体系,其结构呈现很强的时空变异特征。土壤结构及其稳定性直接影响土壤侵蚀、渗透、透气性以及机械强度等物理过程,可以通过容重、水分特征曲线和孔隙分布等物理指标来描述结构性质。干湿交替过程是影响土壤结构的因素之一,田间条件下土壤会经历周期性的干湿交替过程,影响土壤水分分布和水力学性质。利用传统方法测定土壤物理性质时,土壤样品会经历多次脱湿和吸湿过程。本研究利用时域反射技术(Time Domain Reflectometry,TDR)、热脉冲-TDR技术(thermo-TDR)和土壤基质吸力传感器,同时测定土壤含水量、热特性和基质吸力,实现了土壤容重、水分特征曲线以及热特性的连续定位观测。通过研究干湿交替过程中室内装填土柱(不同质地)和田间条件下裸土以及玉米田耕作层容重、水分特征曲线、孔隙分布以及热特性的变化规律,系统地探讨了干湿交替过程对土壤结构的影响。主要结论如下:第一,干湿交替过程对耕作层土壤容重的影响。干湿交替过程中,由于水分流动、水的吸附力和毛管力等相互作用,土壤颗粒会重新分布、组合,形成新的结构体系,并达到稳定状态。裸土耕作层共经历9次干湿交替过程。前四次干湿交替过程中,各层次容重快速增加,最大变化量出现在第四次干湿交替过程中,土壤第一次达到饱和状态。第四次干湿交替后,土壤容重达到稳定状态,各层次容重增加了约0.2 gcm-3。在快速增加阶段,5-10 cm和10-15 cm容重相近,但高于0-5 cm;随着干湿交替次数增加,容重随土层加深逐渐增加,并且层次间容重差异逐渐增大。翻耕和压实处理下玉米田耕作层土壤容重主要表现为:两种处理下0-5 cm容重逐渐增加,经过约40天干湿交替过程后,逐渐达到稳定;压实处理5-10和10-15 cm处容重基本保持稳定,而翻耕处理容重逐渐降低,40天后达到稳定。和裸土结果不同的是,干湿交替过程中玉米田耕作层容重逐渐趋于一致,层次间容重差异逐渐降低。本研究同时利用thermo-TDR技术和热导率方法计算了土壤容重动态变化。和环刀法测定结果相比,热导率法结果偏低,但能够较为准确地反映田间土壤容重的动态变化过程,均方根误差(RMSE)小于0.10 gcm-3,相对误差在10%以内。第二,干湿交替过程对裸土耕作层土壤水分特征曲线和孔隙分布的影响。耕作层容重随时间和深度逐渐增加,经过四次干湿交替后达到稳定。土壤水分特征曲线也表现出在相同基质吸力下含水量逐渐增加的趋势。在前三次干湿交替过程中,土壤含水量和饱和度低,干湿交替过程对各层次土壤水分特征曲线影响很小。第四次干湿交替过程中,土壤达到近饱和状态,同时水分特征曲线发生明显变化:相同基质吸力下含水量增加;在之后的干湿交替过程中不再发生明显变化。干湿交替过程对土壤持水性的影响主要表现在有效孔隙度降低和残余孔隙度的增加。第三,干湿交替过程对砂土、壤土和粉壤土三种不同质地土壤水分特征曲线和孔隙分布的影响。在五次干湿交替过程中,三种质地土壤均表现出:土壤饱和含水量θs降低、进气值增加;van Genuchten模型参数α降低而形状因子n逐渐增加;大于中值孔径孔隙的密度降低;和3cm结果相比,干湿交替过程对6 cm处水分特征曲线和孔隙分布的影响更大。在五次干湿交替过程中,壤土和粉壤土两个层次的残余含水量θr逐渐增加,而砂土 3 cm处θr不变,6 cm处θr随干湿交替逐渐降低。在孔隙分布方面,砂土和壤土的中值孔径密度逐渐增加,而粉壤土与之相反;砂土和粉壤土的中值孔径逐渐降低,壤土的基本保持不变;小于中值孔径孔隙的密度在砂土、壤土和粉壤土上分别表现为随干湿交替逐渐增加、降低和保持稳定。第四,干湿交替过程对砂土、壤土和粉壤土三种不同质地土壤热特性的影响。在五次干湿交替过程中,砂土和壤土容积热容量与含水量之间呈显著的线性关系,其斜率和截距分别和水的比热与容重有关。干湿交替过程中,砂土以及壤土 3 cm处斜率和截距基本保持稳定,壤土 6 cm处斜率逐渐降低,截距增加,表明干湿交替过程可能增加了容重以及吸附水含量,使得土壤水的比热值降低。粉壤土容积热容量随含水量的变化不再是直线关系,在0.15～0.20cm3cm-3范围内,随含水量降低容积热容量降低速率变慢。干湿交替过程对热导率的影响主要表现在砂土两个层次,以及壤土 6 cm处:含水量高于0.2 cm3 cm-3时在相同含水量下热导率增加。这种趋势在粉壤土上,以及壤土 3 cm处表现不明显。干湿交替过程对砂土和壤土热扩散率曲线的影响主要在高含水量范围:相同含水量下,热扩散率随干湿交替和深度逐渐增加,6 cm处的变化更明显。干湿交替过程中,当含水量相同时粉壤土热扩散率逐渐降低,并且6 cm处热扩散率低于3 cm处结果。土壤热特性,尤其是容积热容量对干湿交替过程中土壤孔隙结构的变化不敏感,不能很好地反映干湿交替过程中土壤孔隙的变化。本研究有利于进一步了解干湿交替过程对耕作层和不同质地土壤总孔隙度、孔隙分布以及水力学性质的影响,对研究土壤水、热、盐运移以及其他土壤物理过程具有很大的应用价值。
[Abstract]:As a complex three-phase system, the soil has strong spatial and temporal variation characteristics. The soil structure and its stability directly affect the physical processes such as soil erosion, penetration, air permeability and mechanical strength. The structure properties can be described by physical indexes such as volume weight, water characteristic curve and pore distribution. The wet and wet alternate process is one of the factors that affect the soil structure. Under the field condition, the soil will undergo a periodic wet and dry alternate process, which will affect the soil moisture distribution and the hydraulic properties. The soil samples are subjected to multiple dewetting and moisture absorption processes when the physical properties of the soil are measured by a conventional method. Time Domain Reflectometry (TDR), thermal pulse-TDR technology (thermo-TDR) and soil matrix suction sensor were used to measure the soil water content, thermal property and substrate suction, and the continuous positioning of soil bulk density, water characteristic curve and thermal characteristics was realized. The effect of the wet and wet alternate process on the soil structure was systematically studied by studying the variation of the volume weight, the water characteristic curve, the pore distribution and the thermal characteristics of the soil column (different texture) and the field condition in the dry and wet alternate process. The main conclusions are as follows: first, the effect of the alternation of wet and wet on the soil bulk density of the soil layer. In the course of wet and wet alternation, the soil particles can be re-distributed and combined to form a new structural system due to the interaction of the water flow, the adsorption force of water and the capillary force, and the stable state is achieved. A total of 9 dry and wet alternate processes were experienced in the bare soil. The first four times of dry and wet alternate process, the bulk density of each layer increased rapidly, the maximum variation appeared in the fourth wet and dry alternate process, the soil first reached the saturation state. After the fourth wet and dry alternation, the soil bulk density reached a steady state, and the bulk density of each layer increased by about 0.2 gcm-3. In the rapid increase stage, the bulk density of 5-10 cm and 10-15 cm is similar, but it is higher than 0-5 cm; with the increase of the number of alternation times of dry and wet, the volume weight increases with the depth of the soil layer, and the difference of the volume weight between the levels is gradually increasing. the soil bulk density of the corn field in the corn field under the ploughing and compaction treatment mainly comprises the following steps of: gradually increasing the volume weight of 0-5cm under the two treatments, and gradually achieving the stability after the dry and wet alternate processes of about 40 days; and the bulk density at the compaction treatment of 5-10 and 10-15 cm is basically stable, And the volume weight of the ploughing and treating process is gradually reduced, and stable after 40 days. The result of the bare soil is that the bulk density of the cropping layer of the corn field in the course of the alternation of dry and wet is gradually consistent, and the difference of the volume weight between the layers is gradually reduced. The dynamic change of soil bulk density was also calculated by thermo-TDR technique and thermal conductivity method. The mean square error (RMSE) is less than 0.10 gcm-3 and the relative error is within 10%. The effect of the second, wet and wet process on the soil moisture profile and pore distribution of the bare soil. The bulk density of the farming layer gradually increases with time and depth, and is stable after four times of wet and dry alternation. The soil moisture characteristic curve also shows the tendency of the water content to increase gradually under the same substrate suction force. In that course of the first three dry and wet alternation, the soil moisture content and the saturation are low, and the wet and dry alternation process has little influence on the soil moisture characteristic curve of each layer. In that course of the fourth wet and dry alternation, the soil reach a near saturation state, and the moisture characteristic curve is obviously change; the water content of the same substrate suction is increased; and no obvious change occurs in the subsequent wet and wet alternation process. The effect of the alternation of wet and wet on the water-holding capacity of the soil is mainly manifested in the decrease of the effective porosity and the increase of the residual porosity. The effects of the wet and wet alternate process on the soil moisture profile and pore distribution of three different textures of sandy soil, loam and silt loam. in that course of the five dry and wet alternation, the soil saturation water content is lower, the intake value is increased, the parameter value of the van genuchen model is reduced, and the shape factor n is gradually increase; the density of the pore with the median pore diameter is lower; and compared with the result of the 3 cm, The effect of the wet and wet alternate process on the water characteristic curve and pore distribution at 6 cm is greater. The residual water content of the two layers of the loam and the silt loam was gradually increased in the course of the five-time wet and wet alternation, while the velocity r of the soil at 3 cm of the sand was the same, and the velocity r of the soil at 6 cm decreased with the alternation of dry and wet. In the aspect of pore distribution, the median pore density of the sandy soil and the loam is gradually increased, while the silt loam is in the opposite direction; the median pore diameter of the sandy soil and the silt loam is gradually reduced, and the loam is basically kept unchanged; and the density of the pore with the median pore diameter is less than the density of the median pore pore, The loam and the silt loam are respectively shown to increase, decrease and remain stable with the alternation of dry and wet. The fourth, the effect of the wet and wet alternate process on the thermal characteristics of three different textures of sandy soil, loam and silt loam. There is a significant linear relationship between the heat capacity and the water content of the soil and the loam during the five-time wet-wet alternation, and the slope and intercept of the soil and the water are related to the specific heat and the volume weight of the water. In the course of wet and wet alternation, the slope and intercept of the sandy soil and the loam are basically stable, the slope of the loam is gradually reduced and the intercept is increased, indicating that the wet and wet alternate process can increase the volume weight and the adsorption water content, so that the specific heat value of the soil water is reduced. The volume heat capacity of the silt loam is no longer a linear relationship with the change of the water content, and the rate of heat capacity reduction with the water content decreases with the water content in the range of 0.15-0.20 cm3cm-3. The effect of the wet and wet alternate process on the thermal conductivity is mainly manifested in the two levels of the sand and 6 cm of the loam: the thermal conductivity is increased at the same water content when the water content is higher than 0.2 cm3 cm-3. This trend is not obvious on the silt loam and the 3 cm of the loam. The effect of the wet and wet alternate process on the thermal diffusivity of the sandy soil and the loam is mainly in the high water content range: under the same water content, the thermal diffusivity increases with the alternation and the depth of the dry and wet, and the change at 6 cm is more obvious. In the course of wet and wet alternation, when the water content is the same, the thermal diffusivity of the powder soil is gradually reduced, and the thermal diffusivity at 6 cm is lower than that of 3 cm. The soil thermal property, especially the volumetric heat capacity, is not sensitive to the change of soil pore structure in the course of wet and wet alternation, and can not reflect the change of soil pore in the course of wet and wet alternation. The study is beneficial to the further understanding of the effect of the wet and dry alternate process on the total porosity, pore distribution and the hydraulic properties of the soil, soil water, heat, salt and other soil physical processes.
【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：S152
本文编号：2506775
[Abstract]:As a complex three-phase system, the soil has strong spatial and temporal variation characteristics. The soil structure and its stability directly affect the physical processes such as soil erosion, penetration, air permeability and mechanical strength. The structure properties can be described by physical indexes such as volume weight, water characteristic curve and pore distribution. The wet and wet alternate process is one of the factors that affect the soil structure. Under the field condition, the soil will undergo a periodic wet and dry alternate process, which will affect the soil moisture distribution and the hydraulic properties. The soil samples are subjected to multiple dewetting and moisture absorption processes when the physical properties of the soil are measured by a conventional method. Time Domain Reflectometry (TDR), thermal pulse-TDR technology (thermo-TDR) and soil matrix suction sensor were used to measure the soil water content, thermal property and substrate suction, and the continuous positioning of soil bulk density, water characteristic curve and thermal characteristics was realized. The effect of the wet and wet alternate process on the soil structure was systematically studied by studying the variation of the volume weight, the water characteristic curve, the pore distribution and the thermal characteristics of the soil column (different texture) and the field condition in the dry and wet alternate process. The main conclusions are as follows: first, the effect of the alternation of wet and wet on the soil bulk density of the soil layer. In the course of wet and wet alternation, the soil particles can be re-distributed and combined to form a new structural system due to the interaction of the water flow, the adsorption force of water and the capillary force, and the stable state is achieved. A total of 9 dry and wet alternate processes were experienced in the bare soil. The first four times of dry and wet alternate process, the bulk density of each layer increased rapidly, the maximum variation appeared in the fourth wet and dry alternate process, the soil first reached the saturation state. After the fourth wet and dry alternation, the soil bulk density reached a steady state, and the bulk density of each layer increased by about 0.2 gcm-3. In the rapid increase stage, the bulk density of 5-10 cm and 10-15 cm is similar, but it is higher than 0-5 cm; with the increase of the number of alternation times of dry and wet, the volume weight increases with the depth of the soil layer, and the difference of the volume weight between the levels is gradually increasing. the soil bulk density of the corn field in the corn field under the ploughing and compaction treatment mainly comprises the following steps of: gradually increasing the volume weight of 0-5cm under the two treatments, and gradually achieving the stability after the dry and wet alternate processes of about 40 days; and the bulk density at the compaction treatment of 5-10 and 10-15 cm is basically stable, And the volume weight of the ploughing and treating process is gradually reduced, and stable after 40 days. The result of the bare soil is that the bulk density of the cropping layer of the corn field in the course of the alternation of dry and wet is gradually consistent, and the difference of the volume weight between the layers is gradually reduced. The dynamic change of soil bulk density was also calculated by thermo-TDR technique and thermal conductivity method. The mean square error (RMSE) is less than 0.10 gcm-3 and the relative error is within 10%. The effect of the second, wet and wet process on the soil moisture profile and pore distribution of the bare soil. The bulk density of the farming layer gradually increases with time and depth, and is stable after four times of wet and dry alternation. The soil moisture characteristic curve also shows the tendency of the water content to increase gradually under the same substrate suction force. In that course of the first three dry and wet alternation, the soil moisture content and the saturation are low, and the wet and dry alternation process has little influence on the soil moisture characteristic curve of each layer. In that course of the fourth wet and dry alternation, the soil reach a near saturation state, and the moisture characteristic curve is obviously change; the water content of the same substrate suction is increased; and no obvious change occurs in the subsequent wet and wet alternation process. The effect of the alternation of wet and wet on the water-holding capacity of the soil is mainly manifested in the decrease of the effective porosity and the increase of the residual porosity. The effects of the wet and wet alternate process on the soil moisture profile and pore distribution of three different textures of sandy soil, loam and silt loam. in that course of the five dry and wet alternation, the soil saturation water content is lower, the intake value is increased, the parameter value of the van genuchen model is reduced, and the shape factor n is gradually increase; the density of the pore with the median pore diameter is lower; and compared with the result of the 3 cm, The effect of the wet and wet alternate process on the water characteristic curve and pore distribution at 6 cm is greater. The residual water content of the two layers of the loam and the silt loam was gradually increased in the course of the five-time wet and wet alternation, while the velocity r of the soil at 3 cm of the sand was the same, and the velocity r of the soil at 6 cm decreased with the alternation of dry and wet. In the aspect of pore distribution, the median pore density of the sandy soil and the loam is gradually increased, while the silt loam is in the opposite direction; the median pore diameter of the sandy soil and the silt loam is gradually reduced, and the loam is basically kept unchanged; and the density of the pore with the median pore diameter is less than the density of the median pore pore, The loam and the silt loam are respectively shown to increase, decrease and remain stable with the alternation of dry and wet. The fourth, the effect of the wet and wet alternate process on the thermal characteristics of three different textures of sandy soil, loam and silt loam. There is a significant linear relationship between the heat capacity and the water content of the soil and the loam during the five-time wet-wet alternation, and the slope and intercept of the soil and the water are related to the specific heat and the volume weight of the water. In the course of wet and wet alternation, the slope and intercept of the sandy soil and the loam are basically stable, the slope of the loam is gradually reduced and the intercept is increased, indicating that the wet and wet alternate process can increase the volume weight and the adsorption water content, so that the specific heat value of the soil water is reduced. The volume heat capacity of the silt loam is no longer a linear relationship with the change of the water content, and the rate of heat capacity reduction with the water content decreases with the water content in the range of 0.15-0.20 cm3cm-3. The effect of the wet and wet alternate process on the thermal conductivity is mainly manifested in the two levels of the sand and 6 cm of the loam: the thermal conductivity is increased at the same water content when the water content is higher than 0.2 cm3 cm-3. This trend is not obvious on the silt loam and the 3 cm of the loam. The effect of the wet and wet alternate process on the thermal diffusivity of the sandy soil and the loam is mainly in the high water content range: under the same water content, the thermal diffusivity increases with the alternation and the depth of the dry and wet, and the change at 6 cm is more obvious. In the course of wet and wet alternation, when the water content is the same, the thermal diffusivity of the powder soil is gradually reduced, and the thermal diffusivity at 6 cm is lower than that of 3 cm. The soil thermal property, especially the volumetric heat capacity, is not sensitive to the change of soil pore structure in the course of wet and wet alternation, and can not reflect the change of soil pore in the course of wet and wet alternation. The study is beneficial to the further understanding of the effect of the wet and dry alternate process on the total porosity, pore distribution and the hydraulic properties of the soil, soil water, heat, salt and other soil physical processes.
【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：S152
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