干濕交替過(guò)程中土壤容重、水分特征曲線和熱特性的動(dòng)態(tài)變化特征
發(fā)布時(shí)間：2019-06-27 12:08
【摘要】：土壤作為一個(gè)復(fù)雜的三相體系,其結(jié)構(gòu)呈現(xiàn)很強(qiáng)的時(shí)空變異特征。土壤結(jié)構(gòu)及其穩(wěn)定性直接影響土壤侵蝕、滲透、透氣性以及機(jī)械強(qiáng)度等物理過(guò)程,可以通過(guò)容重、水分特征曲線和孔隙分布等物理指標(biāo)來(lái)描述結(jié)構(gòu)性質(zhì)。干濕交替過(guò)程是影響土壤結(jié)構(gòu)的因素之一,田間條件下土壤會(huì)經(jīng)歷周期性的干濕交替過(guò)程,影響土壤水分分布和水力學(xué)性質(zhì)。利用傳統(tǒng)方法測(cè)定土壤物理性質(zhì)時(shí),土壤樣品會(huì)經(jīng)歷多次脫濕和吸濕過(guò)程。本研究利用時(shí)域反射技術(shù)(Time Domain Reflectometry,TDR)、熱脈沖-TDR技術(shù)(thermo-TDR)和土壤基質(zhì)吸力傳感器,同時(shí)測(cè)定土壤含水量、熱特性和基質(zhì)吸力,實(shí)現(xiàn)了土壤容重、水分特征曲線以及熱特性的連續(xù)定位觀測(cè)。通過(guò)研究干濕交替過(guò)程中室內(nèi)裝填土柱(不同質(zhì)地)和田間條件下裸土以及玉米田耕作層容重、水分特征曲線、孔隙分布以及熱特性的變化規(guī)律,系統(tǒng)地探討了干濕交替過(guò)程對(duì)土壤結(jié)構(gòu)的影響。主要結(jié)論如下:第一,干濕交替過(guò)程對(duì)耕作層土壤容重的影響。干濕交替過(guò)程中,由于水分流動(dòng)、水的吸附力和毛管力等相互作用,土壤顆粒會(huì)重新分布、組合,形成新的結(jié)構(gòu)體系,并達(dá)到穩(wěn)定狀態(tài)。裸土耕作層共經(jīng)歷9次干濕交替過(guò)程。前四次干濕交替過(guò)程中,各層次容重快速增加,最大變化量出現(xiàn)在第四次干濕交替過(guò)程中,土壤第一次達(dá)到飽和狀態(tài)。第四次干濕交替后,土壤容重達(dá)到穩(wěn)定狀態(tài),各層次容重增加了約0.2 gcm-3。在快速增加階段,5-10 cm和10-15 cm容重相近,但高于0-5 cm;隨著干濕交替次數(shù)增加,容重隨土層加深逐漸增加,并且層次間容重差異逐漸增大。翻耕和壓實(shí)處理下玉米田耕作層土壤容重主要表現(xiàn)為:兩種處理下0-5 cm容重逐漸增加,經(jīng)過(guò)約40天干濕交替過(guò)程后,逐漸達(dá)到穩(wěn)定;壓實(shí)處理5-10和10-15 cm處容重基本保持穩(wěn)定,而翻耕處理容重逐漸降低,40天后達(dá)到穩(wěn)定。和裸土結(jié)果不同的是,干濕交替過(guò)程中玉米田耕作層容重逐漸趨于一致,層次間容重差異逐漸降低。本研究同時(shí)利用thermo-TDR技術(shù)和熱導(dǎo)率方法計(jì)算了土壤容重動(dòng)態(tài)變化。和環(huán)刀法測(cè)定結(jié)果相比,熱導(dǎo)率法結(jié)果偏低,但能夠較為準(zhǔn)確地反映田間土壤容重的動(dòng)態(tài)變化過(guò)程,均方根誤差(RMSE)小于0.10 gcm-3,相對(duì)誤差在10%以內(nèi)。第二,干濕交替過(guò)程對(duì)裸土耕作層土壤水分特征曲線和孔隙分布的影響。耕作層容重隨時(shí)間和深度逐漸增加,經(jīng)過(guò)四次干濕交替后達(dá)到穩(wěn)定。土壤水分特征曲線也表現(xiàn)出在相同基質(zhì)吸力下含水量逐漸增加的趨勢(shì)。在前三次干濕交替過(guò)程中,土壤含水量和飽和度低,干濕交替過(guò)程對(duì)各層次土壤水分特征曲線影響很小。第四次干濕交替過(guò)程中,土壤達(dá)到近飽和狀態(tài),同時(shí)水分特征曲線發(fā)生明顯變化:相同基質(zhì)吸力下含水量增加;在之后的干濕交替過(guò)程中不再發(fā)生明顯變化。干濕交替過(guò)程對(duì)土壤持水性的影響主要表現(xiàn)在有效孔隙度降低和殘余孔隙度的增加。第三,干濕交替過(guò)程對(duì)砂土、壤土和粉壤土三種不同質(zhì)地土壤水分特征曲線和孔隙分布的影響。在五次干濕交替過(guò)程中,三種質(zhì)地土壤均表現(xiàn)出:土壤飽和含水量θs降低、進(jìn)氣值增加;van Genuchten模型參數(shù)α降低而形狀因子n逐漸增加;大于中值孔徑孔隙的密度降低;和3cm結(jié)果相比,干濕交替過(guò)程對(duì)6 cm處水分特征曲線和孔隙分布的影響更大。在五次干濕交替過(guò)程中,壤土和粉壤土兩個(gè)層次的殘余含水量θr逐漸增加,而砂土 3 cm處θr不變,6 cm處θr隨干濕交替逐漸降低。在孔隙分布方面,砂土和壤土的中值孔徑密度逐漸增加,而粉壤土與之相反;砂土和粉壤土的中值孔徑逐漸降低,壤土的基本保持不變;小于中值孔徑孔隙的密度在砂土、壤土和粉壤土上分別表現(xiàn)為隨干濕交替逐漸增加、降低和保持穩(wěn)定。第四,干濕交替過(guò)程對(duì)砂土、壤土和粉壤土三種不同質(zhì)地土壤熱特性的影響。在五次干濕交替過(guò)程中,砂土和壤土容積熱容量與含水量之間呈顯著的線性關(guān)系,其斜率和截距分別和水的比熱與容重有關(guān)。干濕交替過(guò)程中,砂土以及壤土 3 cm處斜率和截距基本保持穩(wěn)定,壤土 6 cm處斜率逐漸降低,截距增加,表明干濕交替過(guò)程可能增加了容重以及吸附水含量,使得土壤水的比熱值降低。粉壤土容積熱容量隨含水量的變化不再是直線關(guān)系,在0.15～0.20cm3cm-3范圍內(nèi),隨含水量降低容積熱容量降低速率變慢。干濕交替過(guò)程對(duì)熱導(dǎo)率的影響主要表現(xiàn)在砂土兩個(gè)層次,以及壤土 6 cm處:含水量高于0.2 cm3 cm-3時(shí)在相同含水量下熱導(dǎo)率增加。這種趨勢(shì)在粉壤土上,以及壤土 3 cm處表現(xiàn)不明顯。干濕交替過(guò)程對(duì)砂土和壤土熱擴(kuò)散率曲線的影響主要在高含水量范圍:相同含水量下,熱擴(kuò)散率隨干濕交替和深度逐漸增加,6 cm處的變化更明顯。干濕交替過(guò)程中,當(dāng)含水量相同時(shí)粉壤土熱擴(kuò)散率逐漸降低,并且6 cm處熱擴(kuò)散率低于3 cm處結(jié)果。土壤熱特性,尤其是容積熱容量對(duì)干濕交替過(guò)程中土壤孔隙結(jié)構(gòu)的變化不敏感,不能很好地反映干濕交替過(guò)程中土壤孔隙的變化。本研究有利于進(jìn)一步了解干濕交替過(guò)程對(duì)耕作層和不同質(zhì)地土壤總孔隙度、孔隙分布以及水力學(xué)性質(zhì)的影響,對(duì)研究土壤水、熱、鹽運(yùn)移以及其他土壤物理過(guò)程具有很大的應(yīng)用價(jià)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.
【學(xué)位授予單位】：中國(guó)農(nóng)業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：S152
本文編號(hào)：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.
【學(xué)位授予單位】：中國(guó)農(nóng)業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：S152
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