森林火灾对土壤热导率影响的实验和模型研究

An understanding of soil thermal conductivity after a wildfire or controlled burn is important to land management and post-fire recovery efforts. Although soil thermal conductivity has been well studied for non-fire heated soils, comprehensive data that evaluate the long-term effect of extreme heating from a fire on the soil thermal conductivity are limited. The purpose of this study was to evaluate the long-term impact of fire on the effective thermal conductivity of soils by directly comparing fire-heated and no-fire control soils through a series of laboratory studies. The thermal conductivity was measured for ten soil samples from two sites within the Manitou Experimental Forest, Colorado, USA, for a range of water contents from saturation to the residual degree of saturation. The thermal conductivity measured was compared with independent estimates made using three empirical models from literature, including the Campbell et al.(1994), Cté and Konrad(2005), and Massman et al.(2008) models. Results demonstrate that for the test soils studied, the thermal conductivity of the fire-heated soils was slightly lower than that of the control soils for all observed water contents.Modeling results show that the Campbell et al.(1994) model gave the best agreement over the full range of water contents when proper fitting parameters were employed. Further studies are needed to evaluate the significance of including the influence of fire burn on the thermal properties of soils in modeling studies.     

A practical formula for quantifying the thermal conductivity of Tottori dune sand

Abstract

Sustainable agriculture needs appropriate management of water, chemicals and heat in soil. In this study, we focused on thermal conductivity, which is among the various soil physical properties that are crucial for the sustainable management of agricultural fields. To expand the Mochizuki model, which describes thermal conductivity as a function of water content and solution concentration, we considered the water content, solution concentration and temperature as independent variables. The thermal conductivity of Tottori dune sand was measured under conditions of various combinations of these three independent variables. We observed that the thermal conductivity increased linearly with increasing water content, 0.054–0.276 m³ m^?3, for fixed temperature and solution concentration, and varied linearly with solution concentration for fixed temperature and water content. These results are consistent with the Mochizuki model. Using the Mochizuki model, the experimental parameters, which are dependent variables of water content and solution concentration, are shown as functions of water content. From regression analyses of the relationships between the experimental parameters and temperature, we expanded the Mochizuki model into a new practical formula that quantifies the soil thermal conductivity as a function of water content, solution concentration and temperature.     

Effects of NaCl concentration on the thermal conductivity of sand and glass beads with moisture contents at levels below field capacity

Abstract

Soil thermal conductivity is a key factor governing its thermal regime. In the present study, we measured the thermal conductivity of Toyoura sand and glass beads using a heat probe method to clarify the effects of gravimetric water content (w) and NaCl concentration (C) and to evaluate the estimation effectiveness of four models (Mochizuki, de Vries, Noborio and Kasubuchi). The de Vries and Kasubuchi models predict the effect of w on soil thermal conductivity, whereas the Noborio model describes the effects of solute concentration and the Mochizuki model describes both parameters. With or without NaCl, the thermal conductivity of both samples increased with increasing w, and the increase could be grouped into three ranges based on w. The upper and lower limits of each water content range were constant, even at varying NaCl concentrations, but the width of the range differed among the three ranges and between the sand and glass bead samples. Although soil thermal conductivity has previously been reported to generally decrease with increasing C, the thermal conductivities of some glass beads increased in the present study, particularly at moisture contents close to field capacity. The change in thermal conductivity as a function of C was linear in all cases. This trend was similar to that of a non-swelling clay in a previous study. The Mochizuki model, which regressed measured thermal conductivity on C and w, predicted the thermal conductivity of sand as well as previous models, but the calculations were easier and the method offers more flexibility for soils with different textures.     

日光温室栽培基质有效导热系数预测模型

栽培基质为固流两相组成的多组分材料,其导热系数是日光温室热环境营造过程中重要的热参数之一,在温室地面热量的传输中起着重要的作用。为了预测日光温室生产中栽培基质的有效导热系数,以珍珠岩、蛭石、炉渣、河沙、椰糠、泥炭及腐熟牛粪与花生壳8种常用单一基质为研究对象,首先利用干燥与饱和状态下基质有效导热系数的测试结果,通过复合材料有效特性混合模型的反向计算,确定了8种单一基质的固相导热系数,得到珍珠岩、蛭石、炉渣、河沙、椰糠、泥炭及腐熟牛粪与花生壳的固相导热系数分别为0.058、0.139、0.252、0.817、0.148、0.518、0.262及0.066 W/(m·K);其次,利用复配基质有效导热系数的实测结果,通过复合材料有效特性混合模型的正向与反向计算,明确了组成固相的各组分呈并联关系排列,并确定了复配基质中固相导热系数与基质各组分体积比例的关联;进一步将复配基质在不同饱和度下的有效导热系数实测值与基于6种复合材料导热系数模型理论计算值进行比较。结果表明：并联模型适用于复配基质有效导热系数的理论计算,构建了日光温室栽培基质有效导热系数的预测模型。采用实际生产中常用的4种育苗和栽培基质在不同饱和度下的有效导热系数对所建模型进行检验,结果显示并联模型平均绝对误差为0.026 2%～0.137 4%,均方根误差为0.008 6～0.031 5 W/(m·K),模型决定系数R2为0.900 7～0.988 0,预测精度较高。基于并联模型构建的有效导热系数预测模型能够较为准确地计算日光温室栽培基质在不同饱和度下的有效导热系数。     

基于土壤物理基本参数的土壤导热率模型

土壤物理基本参数是影响土壤导热率的重要因素,为了获取土壤的颗粒组成、有机质含量与土壤导热率计算模型中参数之间的关系,该文分析了陕西省9个地区的土壤质地对土壤导热率的影响,对不同土壤导热率估算模型的准确性进行评价,并在C?té-Konrad模型和Lu-Ren模型的基础上,建立了基于土壤物理基本参数的改进模型,结果表明:改进的C?té-Konrad模型与改进的Lu-Ren模型可以用来拟合不同质地的土壤导热率,且具有较好的拟合精度,决定系数R2均在0.92以上,相对误差(relative error,Re)均低于9.6%;对于砂粒含量或粉粒含量较高的土壤导热率,改进的C?té-Konrad模型模拟结果的均方根误差(root-mean-square error,RMSE)≤0.1183、R2≥0.9259以及Re≤9.55%,均优于C?té-Konrad模型、Lu-Ren模型和改进Lu-Ren模型;对于砂粒和粉粒含量均较低的土壤导热率,改进Lu-Ren模型模拟结果的RMSE≤0.0815、R2≥0.9326,Re≤8.21%,均明显优于其他3种模型。两种改进的模型分别建立了模型参数与颗粒组成、有机质含量之间的关系,能够更加详细描述土壤物理基本参数与导热率之间的关系,并且针对不同的土壤质地,选取合适的改进模型能够更加准确地计算土壤导热率。     

原状土与扰动土导气率、导水率与含水率的关系

为分析土壤导气特性与土壤导水特性间的关系,该文通过研究陕西杨凌小麦试验田士样导水率和导气率随含水率的变化特征,比较原状土与扰动土导气和导水特征,分析相对导水率和相对导气率与饱和度的关系,结果发现导水率随含水率的增加而减小,且无论导水率还是导气率原状土都比扰动土大,证实土壤结构及孔隙特征对水和气的传输有巨大的影响,扰动土和原状土变化趋势虽然基本相同,但曲线不重合,说明扰动土和原状土的孔隙连接性和弯曲程度不尽相同.     

不同温度下的土壤热导率模拟

土壤热导率是研究陆地表层水热盐耦合运动的基本物理参数。由于水汽潜热传热在高温下的显著作用,高温下的土壤热导率显著高于常温值。该研究的目的是建立能够有效预测高温下土壤热导率的模型。在气体扩散定律的基础上,该文结合常温土壤热导率模型,提出了一个计算高温土壤热导率的新方法。并利用热脉冲技术实际测定了不同温度、不同含水率下的土壤热导率,对新模型进行了测试验证。结果表明,Cass等的水汽运移促进因子参数依赖于土壤质地,且存在较大的不确定性。经过对该参数修正后,建立的热导率模型均能够较好地模拟出高温下的土壤热导率。     

Apparent electrical conductivity integrated from layered soil profiles

Time domain reflectometry (TDR) trace analysis aims at extracting the water content profile along TDR probes. This can be done by applying a TDR forward solver inversely. Thus, TDR‐trace inversion is basically an optimization problem. As in any optimization procedure, it is worthwhile to include as much a priori information as possible about the problem to be solved. In this study, we discuss the feasibility to use the apparent electrical conductivity as constraint for the TDR inversion. The resistors‐in‐parallel circuit can be used to integrate a multislice soil model to obtain the apparent electrical conductivity. We apply additionally Archie's law to link the water content of a particular slice with its electrical conductivity. We compare the results from this approach with measured TDR traces and show that the problem is solved exactly. Finally, we address the thin‐layer issue because thin layers with a high permittivity contrast result in a delay of the run time of an electromagnetic pulse. We test numerically whether a similar behavior can be observed for a thin layered electrical conductivity profile. Our results show that the thickness of the soil layer with respect to electrical conductivity has no effect on the apparent electrical conductivity. We conclude that the apparent electrical conductivity is appropriate as boundary condition in TDR inversion as long as a procedure is known to convert the water content of a slice to its electrical conductivity     

土壤热参数确定方法比较与修正

土壤热参数是分析研究土壤热传递的基本参数,寻求确定热参数简单方法是研究的热点问题.该文利用自行研制的土壤热特性试验系统,测定了4种质地土壤热特性,计算了不同质地土壤在不同含水率、不同容重情况下的热扩散率,进一步推导出不同情况下的导热率,并与Campbell经验公式计算的导热率进行比较,发现计算值与实测值相差较大,并对Campbell经验公式进行修正,同时对修正经验公式进行分析、检验,并讨论此经验公式的适用范围.结果显示在体积含水率小于20%的时候,修正经验公式可以用于计算导热率.     

用土壤温度估算表层土壤导温率与热通量的研究

对比研究了6种用土壤湿度计算表层土壤导温率的方法结果表明，振幅法、相位法、反正切法、对数法虽需较少观测值，计算简单，但结果却不太稳定；谐波法计算过程虽较复杂，但导温度的估算值较稳定，是最可靠的方法之一。利用计算的土壤导温率估算近地表土壤热通量，结果与由温度积分法决定的土壤热通量值非常一致。     

Soil texture affects the conversion factor of electrical conductivity from 1:5 soil-water to saturated paste extracts

Electrical conductivity(EC) of soil-water extracts is commonly used to assess soil salinity. However, its conversion to the EC of saturated soil paste extracts(ECe), the standard measure of soil salinity, is currently required for practical applications. Although many regression models can be used to obtain ECe from the EC of soil-water extracts, the application of a site-specific model to different sites is not straightforward due to confounding soil factors such as soil texture. This study was...     

Effect of effective microorganism and gypsum amendments on nutrient leaching,pH, electrical conductivity,and Okra growth parameters under coastal saline soil

Nutrients losses through leaching are the main problem facing coastal saline soil. Effective microorganisms (EM) and Gypsum (G) at the application rate of 5%G and 10%G by weight were used as soil amendments. The pot experiment aimed to improve the leaching of nitrate (NO₃), ammonium (NH₄) and total nitrogen (TN) on the coastal saline soil. The EM+ 5%G treatment effectively reduced the content of NO₃ and NH₄ in the leachate by 86.59% and 68.18%, respectively. EM treatment reduced the leaching of NO₃ and NH₄ by 70.86% and 62.12% and EM+ 10%G reduced NO₃ and NH₄ by 11.80% and 50.76%, respectively. Moreover, the content of TN in leachate was reduced up to 13.23%, 5.80%, and 2.67% in response to EM, EM+ 5%G, and EM+ 10%G, respectively, compared to the control. These results indicate that EM combined with G as soil amendments can reduce leaching of nutrients and further support the regulation of a coastal saline soil pH and EC.     

多针热脉冲技术测定土壤热导率误差分析

土壤热导率是研究土壤热传输、水热耦合运移的基本物理参数。为了探知多针热脉冲技术的误差,该研究以能够准确测定热导率的单针法作为参比,在4种质地土壤上,对多针热脉冲技术在不同体积质量、含水率和气压条件下测定的热导率进行了分析。结果表明,多针热脉冲技术的热导率结果与单针法总体符合较好,其热导率测定值的平均误差为0.074 W/(m·K)。干土热导率随气压增大呈现对数增长,这是由于气体分子平均自由程下降的原因。多针热脉冲技术的测定误差主要出现在中等含水率区域,关键问题是加热针的温度升高偏大,促进了水汽潜热传输。另外,土壤与探针之间的热接触阻力、探针导致的土壤体积质量改变、温度梯度引起的液水流也影响测定结果的准确性。该研究可为农业水土工程中的土壤热导率模拟提供依据。     

采用新电导率指标分析土壤盐分变化规律

土壤电导率(Electrical conductivity,EC)是限制植物和微生物活性的阈值,影响到土壤养分和污染物的转化、存在状态及有效性[1],反映了在一定水分条件下土壤盐分的实际状况,且包含了土壤水分含量及离子组成等丰富信息[2]。在一定浓度范围内,土壤溶液含盐量与电导率呈正相关,溶解的盐类越多,溶液电导率就越大,故可根据溶液电导率的大小,间接地测量土壤含盐量[3-5]。     

Comparison of seven water retention functions used for modelling soil hydraulic conductivity due to film flow

The unsaturated soil hydraulic conductivity accounting for film flow is important for understanding soil hydrological and biological processes, especially in arid and semi‐arid regions. Recently, a theoretically based hydraulic conductivity model was developed to describe the hydraulic conductivity as a function of water content. We have used this model to compare seven soil water retention functions commonly used for predicting soil hydraulic conductivity due to film flow. A total of 30 soils, varying in basic properties, were selected from the Unsaturated Soil Hydraulic Database to evaluate the seven functions. The Webb method was applied to identify the critical soil matric potential (h _c) below which thin film flow controls water movement. Soil hydraulic conductivity measurements at matric potential below h _c were then used for curve fitting according to the seven functions. Slight differences were observed among the functions in predicting soil hydraulic conductivity due to film flow. Six of the seven functions in combination with the hydraulic conductivity model described the hydraulic conductivity due to film flow well, according to the terms of the coefficient of efficiency. The relatively poor performance of the one exception was due to the fact that the linear shape of the function made it less flexible at low matric potentials. In addition, the effect of textural class on its performance was substantial, showing a poorer fit for the sand soil compared with the loam and clay soils. These findings have important applications related to soil and water resources conservation especially in arid and semi‐arid regions.     

基于水分和原位电导率的西宁盆地盐渍土含盐量估算模型

为了探讨西宁盆地黄土状盐渍土导电特性与土体本身含水率和含盐量之间的关系,该文在土体洗盐试验基础上,测得了不同含水率和含盐量条件下黄土状盐渍土电导率,分析了土体电导率与含水率、含盐量之间的相互关系和作用机理;在此基础上,建立了土体电导率与含水率、含盐量之间的多元回归模型。结果表明,在土体含盐量一定条件下随着土体含水率增加土体电导率呈逐渐增大的变化趋势,且二者之间符合幂函数关系;土体含盐量愈高条件下土体含水率增加对电导率的影响则愈为显著。在土体含水率一定的条件下,土体电导率随着含盐量增加呈逐渐增大的变化趋势,且二者之间符合线性函数关系;当土体含水率相对较高时,含盐量增加对电导率的影响程度亦较为显著。对建立的区内黄土状盐渍土电导率与含水率、含盐量之间的多元回归模型(R2=0.995)进行验证,相对误差在10%之内,表明模型可有效确定含水率大于5%且小于25%(?5.52%)及含盐量为0.18%～2.18%条件下黄土状盐渍土的含盐量。研究成果对研究区及其周边地区黄土状盐渍土其盐渍化程度划分、工程地质特性评价,以及土体盐渍化等地质灾害现象的科学防治具有理论研究价值和工程指导意义。     

Effect of tillage treatments on soil thermal conductivity for some Jordanian clay loam and loam soils

Soil thermal conductivity determines how a soil warms or cools with exchange of energy by conduction, convection, and radiation. The ability to monitor soil thermal conductivity is an important tool in managing the soil temperature regime to affect seed germination and crop growth. In this study, the temperature-by-time data was obtained using a single probe device to determine the soil thermal conductivity. The device was used in the field in some Jordanian clay loam and loam soils to estimate their thermal conductivities under three different tillage treatments to a depth of 20 cm. Tillage treatments were: no-tillage, rotary tillage, and chisel tillage. For the same soil type, the results showed that rotary tillage decreased soil thermal conductivity more than chisel tillage, compared to no-tillage plots. For the clay loam, thermal conductivity ranged from 0.33 to 0.72 W m⁻¹ K⁻¹ in chisel plowed treatments, from 0.30 to 0.48 W m⁻¹ K⁻¹ in rotary plowed treatments, and from 0.45 to 0.78 W m⁻¹ K⁻¹ in no-till treatments. For the loam, thermal conductivity ranged from 0.40 to 0.75 W m⁻¹ K⁻¹ in chisel plowed treatments, from 0.34 to 0.57 W m⁻¹ K⁻¹ in rotary plowed treatments, and from 0.50 to 0.79 W m⁻¹ K⁻¹ in no-till treatments. The clay loam generally had lower thermal conductivity than loam in all similar tillage treatments. The thermal conductivity measured in this study for each tillage system, in each soil type, was compared with independent estimates based on standard procedures where soil properties are used to model thermal conductivity. The results of this study showed that thermal conductivity varied with soil texture and tillage treatment used and that differences between the modeled and measured thermal conductivities were very small.     

热融湖塘对青藏高原土壤饱和导水率的影响及因素分析

为研究多年冻土区热融湖塘对湖岸生态水文过程的影响,该文基于湖岸不同迹地植被发育、导水性及土壤理化性质的分析,并结合土壤转换函数(pedo-transfer functions,PTFs),对土壤导水性及其影响因素进行研究。结果表明:热融湖塘的形成使土壤环境发生了重要演变,其中湖岸死根区土壤饱和导水率相比于未影响区域(110.88 cm/d)增加了70.1%之多,而其在盐渍化区域相比于未影响区域减少了33.8%,同时土壤饱和导水率随着坡度的增加而增强;通过比较ROSETTA、CAMPBELL和VAUCLIN 3种土壤转换函数的预测能力,发现VAUCLIN模型更适合于模拟青藏高原高寒草甸土壤饱和导水率。热融湖塘影响迹地对土壤饱和导水率的变化,是植被盖度、有机质含量、颗粒组成等因素耦合影响作用的结果,运用土壤转换函数对其进行预测时,须综合考虑以上因子。对热融湖塘不同迹地土壤水力参数的研究可为区域土壤侵蚀,产流模式及水文过程的研究提供理论基础。