土壤薄片中石英颗粒分布的分形特征

土壤中石英颗粒的粒度分布对揭示母质来源和模拟土壤结构等具有重要意义。本文根据石英的光学性质,利用数字图像处理技术提取土壤薄片中的石英颗粒信息,并应用分形维数来表征土壤薄片中石英颗粒的分布特征。采集免耕和翻耕处理下土壤样品并制作成土壤薄片,利用偏光显微镜和数字图像处理技术提取土壤薄片中石英颗粒,应用Sigma ScanPro5软件统计了石英颗粒的数量、大小和形状等信息,研究土壤薄片中石英颗粒的数量分形特征;并分析了其同石英颗粒数量、面积和平均半径等的关系。结果表明石英颗粒的数量分布具有明显的分形特征,分形维数在1.60～2.18之间,分形维数同薄片中石英颗粒的总面积和平均半径呈负相关。免耕处理下表层土壤石英颗粒的数量分形维数高于底层,而翻耕处理下则呈相反的趋势。免耕和翻耕措施下土壤薄片中石英颗粒的数量分形维数在0～5和10～15cm层次之间没有显著差异,但是在20～25cm层次,翻耕处理分形维数高于免耕处理,说明耕作措施会加速土壤矿物质的风化和破碎并改变石英颗粒在土壤剖面中的分布。     

土壤图像孔隙轮廓线分形特征及其应用

孔隙轮廓线分形维数是用来描述孔隙本身所具有的分形特征，它反映了土壤孔隙与固体颗粒接触界限的不规则性。该文采用数字图像处理技术研究了中国科学院封丘农业生态实验站内3种不同质地土壤样本图像的孔隙轮廓线分形特征。结果表明：土壤孔隙轮廓线分形特征与土壤质地之间存在着一定的相关关系，即土壤质地越细(黏粒含量越高)分形维数取值越大。同时，根据这3种土壤的孔隙轮廓线分形维数，结合不同分形方法分别预测了它们的水分特征曲线，并与实测的土壤水分特征曲线进行了比较。     

The relation between the moisture-release curve and the structure of soil

The limit to the precision with which moisture-release data may be related to soil structure is examined. Thin sections in two orthogonal planes were prepared from cores for which moisture release data and saturated conductivity measurements were also collected. Structural parameters are inferred indirectly through estimation of the mass fractal dimension from the moisture-release curve, and directly through measurement of the scaling properties of the pore space and solid matrix from the thin sections using image analysis. Theoretical results are presented which show that, in the absence of additional information, the interpretation of the moisture-release curve is ambiguous for several reasons. A power-law exponent is a consequence of either a fractal pore volume; a fractal solid volume; a fractal pore wall; or a non-fractal, self-similar pore wall, and one cannot infer from the measurement which is the case. Experimental results are presented which confirm that direct measurement of the fractal dimension of the solid matrix is a good predictor of the Brooks–Corey exponent for the soils studied here. Therefore, although a specific structural parameter characterizes the moisture-release curve, the latter cannot be used as a detailed measure of soil structure.     

用显微CT研究不同植被恢复模式的土壤团聚体微结构特征

为了更好了解不同植被恢复模式对土壤团聚体微结构的影响,该研究采用显微CT技术扫描3~5 mm土壤团聚体,获取了3.25μm分辨率的二维图像,并应用数字图像处理软件对团聚体孔隙结构进行三维重建,定量研究了黄土丘陵区不同植被恢复模式下(自然草地、人工灌木和坡耕地)土壤团聚体微结构特征。结果表明,两种植被恢复模式均显著提高了土壤有机碳含量和团聚体水稳性(P0.05),降低了土壤容重。与坡耕地处理相比,自然草地土壤团聚体总孔隙度、大孔隙度(100μm)、瘦长型孔隙度分别增加了20%、23%和24%,而分形维数和连通性指数欧拉特征值分别降低了2%和75%,且各指标二者间差异均显著(P0.05)。人工灌木土壤团聚体的上述各项孔隙参数均优于自然草地(较坡耕地分别增加了70%、88%和43%以及降低了4%和92%),且除欧拉特征值外,差异均显著(P0.05)。分形维数和连通性对土壤结构变化的响应相当敏感,可作为该地区植被恢复过程中土壤质量评价的指标,研究结果可为黄土高原土壤质量评价提供科学参考。     

The over-estimation of clay and the under-estimation of pores in soil thin sections

The amounts of clay visible in four thin sections from paleosol horizons (clay contents 9–32%) were measured by point counting. These sections were used as references for visual estimates, without point counting, of the amounts of clay in 14 further sections. The measurements and estimates were recorded on pore-free and gravel-free bases so they could be related to gravimetric analyses. Amounts of clay measured and estimated by area in these thin sections were between 1.6 and 3.1 times those determined gravimetrically. The reasons for these differences are discussed. Firstly, clay in soil thin sections contains much pore space beyond the resolution of the optical microscope and has an apparent density dependent on the amount of submicroscopic pore space. An edge effect also causes over-estimation of clay in soil thin sections and under-estimation of visible pore space. Components (clay, mineral grains, pores) are usually sloped at their borders with each other within the standard 25–30 μm (three-dimensional) thin sections. Clay, for instance, may overcap a pore at its border, hiding some pore space. The need for true two-dimensional images of soil pore patterns in image analysis is indicated. A nomogram has been constructed, using apparent density, to allow estimation of clay in thin sections of soils with any clay content. Coarse/fine ratios can be determined more accurately and estimates of clay can also be recalculated to provide illuvial to total clay ratios that are more meaningful. It is recommended that the micromorphological identification criterion for the argillic horizon be reassessed and that 4% illuvial to total clay in a soil thin section be adopted as the diagnostic cut-off.     

An evaluation of 2D-image analysis techniques for measuring soil microporosity

To compare soil porosity measurements, manual, semiautomatic and automatic 2D‐image analyses were performed on three sets of images of the same fields. The first and second image sets were obtained, by a fluorescence microscope, on the polished surfaces of soil blocks impregnated with a fluorescent resin and on the thin sections made from them, respectively. A scanning electron microscope in backscattered mode was used to acquire the third set of images on the thin sections. In the manual image analysis procedure, image segmentation was based on the best visual impression and carried out individually for each image with the UTHSCSA Image Tool software. For the semiautomatic method, the software μCTanalySIS was used; the images were segmented by double hysteresis, after interactive selection of the thresholding values. Automatic thresholding, based on an analysis of the image intensity histogram, was performed using the image analysis software Image‐Pro^® Plus. Average microporosity measurements were compared between image types and image analysis methods using marginal regression models for continuous outcomes. The mean area covered by pores was significantly different depending on the type of image and the method of image analysis. Results after the automatic procedure were significantly larger than after manual or semiautomatic thresholding. On the other hand, average porosities were larger for backscattered electron images than for fluorescent images, regardless of the image analysis procedure used. These results stress the need for standardization of image analysis protocols and warn of the dangers of comparing soil porosity measurements performed on different types of images.     

基于CT数字图像的土壤孔隙分形特征研究

通过CT扫描获得了河南封丘地区3种不同质地潮土样本的高精度图像,利用数字图像分析方法识别出土壤孔隙及其轮廓线,然后用计盒法确定了表征土壤孔隙形态不规则性的分形维数.在此基础上,通过不同形式的分形模型预测了土壤水分特征曲线.结果表明,河南封丘地区不同质地潮土的孔隙分形维数(包括面积和轮廓线分维)差异不明显;预测水分特征曲线时,针对不同质地的土壤选择适宜的分形模型才能得到较好的模拟结果.     

From fractal analysis along a line to fractals on the plane

Self-similar fractals are useful models for soil solid and pore sets. The scaling properties of these fractals along a line and across an area can be described by the fractal dimensions. One method, for estimating the soil areal fractal dimension from the solid and pore set distributions along the lines, was proposed and tested with real macro- and micromorphological data on three soils of Mexico. The soil areal fractal dimension (D_a) was compared with the soil mass fractal dimension (D_m) estimated by two-dimensional binary image analysis, separately for solids and pores. Both methods are based on the box-counting technique and are suitable for determining the soil ‘box' or ‘capacity' fractal dimension, that seems to be apt to estimate the alternative filling of an area by a fractal set of solids and pores. This paper examines the relations between the fractal dimensions obtained along a line, across an area and directly from the image. Analysis of D_a and D_m data seems to suggest that both soil genesis and management practice can contribute to areal fractal dimension dynamics. It was shown that fractal dimensions are useful parameters able to monitor tillage influence on soil properties and to estimate the degree of soil compaction.     

Effect of rain on the macroporosity at the soil surface

Rain falling on soil causes slaking, mechanical disruption of aggregates and compaction. Too few data exist to predict the changes likely to occur in particular soil, landscape and management conditions. Experiments with simulated rain were set up to study and to model mathematically the changes of the pore system within the surface layer of a soil when rain was applied on a field cropped with maize. Macroporosity, pore‐size and pore‐shape distributions, and the pore volume were measured by image analysis of thin sections and the fractal dimensions of the pore surface roughness were estimated. The general trends of changes in porosity indicated the presence of two different sets of processes at the surface (0–3 cm) and in the layer immediately underneath (3–6 cm). In both layers most of the variation in macroporosity was due to a loss of elongated porosity. A theoretical approach recently developed to link rain and erosion to sealing properties was extended to describing the effect of rain on the elongated porosity and the pore volume fractal dimension in these two layers. The resulting set of equations describe in detail the evolution of soil porosity near the soil surface. Our approach could be useful when modelling the effects of sealing processes in soil erosion.     

基于Menger海绵模型的煤矸石粉改良膨胀土微结构特征

为解决膨胀土对工程结构以及农业生态环境的危害，进行煤矸石粉改良膨胀土的试验研究。对煤矸石粉掺量为0、3%、6%、9%的膨胀土土样进行压汞试验，测得微观孔隙特征值；选取Menger海绵模型建立孔隙分分形模型，计算土体孔隙分形维数，探究土体孔隙分形维数与孔隙特征参数以及煤矸石粉掺量变化的关系。结果表明：随着煤矸石粉掺量增加，土中大孔隙所占的含量较素膨胀减少61.5%，孔隙类型从团粒间孔隙转化为颗粒间孔隙；煤矸石粉的掺入改变了土体的孔隙结构特征，煤矸石粉与膨胀土发生胶结反应，孔隙连通性降低，使得总孔隙体积、孔隙率、孔隙平均孔径、孔隙临界孔径等孔隙特征参数呈减小趋势；基于分形理论分析孔隙分形维数，分形维数随煤矸石粉掺量的增加而增加，且与孔隙特征参数呈显著相关性。孔隙分形维数反应了孔隙特征参数以及孔隙发育程度，为土的孔隙表征提供方法借鉴。     

土壤孔隙质量分数维D_m二元图像分析及其影响因素研究

本文简要介绍了利用土壤切片的二元图像分析了土壤孔隙结构的质量分数维Dm 的方法 ,并研究比较了四类土壤类型的Dm 及其影响因素。结果表明Dm 可以较好地定量描述土壤孔隙的空间分布特征 ,Dm 与土壤孔隙面积、孔隙孔径分布、土壤深度以及土壤质地之间均具有一定的联系     

The relation between silty soil structures and their mercury porosimetry curve counterparts: fractals and percolation

Mercury porosimetry data can be interpreted in terms of soil structure using ideas drawn from (i) network modelling and percolation theory and (ii) fractal geometry. We linked mercury intrusion to soil structure quantified by image analysis within a relevant common pore radius scale. We compared (i) three independent methods for computing fractal dimensions of the matrix and of the solid–pore interface, namely fitted square boxes method and pore chord distribution on scanning electron microscope images of soil thin sections, and mercury porosimetry, and (ii) two independent methods for characterizing pore connectivity (image analysis) and percolation process (pressure threshold from mercury porosimetry). The results from analyses of the pore size distribution by mercury porosimetry differed from those from the image analysis. Mercury intrusion is controlled by both the connectivity of the pore space network and locally by pore throats leading to larger pore bodies. By contrast, image analysis is unaffected by pore connectivity and measures pore bodies. On the other hand, the chord length method might not adequately capture the scaling properties of the solid–pore interface, whereas the mercury porosimetry data were also difficult to interpret in terms of fractal geometry because of the effects of pore connectivity. However, fractal dimension values of both the solid phase and the solid–pore interface increased as a function of clay content, whereas both percolation probability values and throat radius values at the mercury percolation threshold decreased. The results show the merit of applying both fractals and percolation theory for determining structural parameters relevant to mercury and water transport in soil.     

基于多尺度分形特征的ETM+影像耕地提取

耕地是重要的农业资源,如何利用经济可行的遥感技术快速准确地提取耕地已成为研究的热点和难点。以北京密云县为研究区,建立了基于多尺度分形特征的ETM+遥感影像提取耕地的方法：将计算表面分形维的双层地毯法用于计算每一个像元的上分形信号和下分形信号,并对上分形信号和下分形信号进行耕地特征分析;选用下分形信号的第3尺度和第4尺度做差值处理进一步增强耕地信息,利用简单的图像分割提取出密云县耕地信息的空间分布;基于ArcGIS的空间分析利用密云县同期的土地利用现状图进行耕地信息提取精度评价。结果表明,全县耕地总面积精度达到91.0%,全县耕地点位匹配精度达71.8%;耕地中的旱地提取精度较差,而耕地中的水浇地和菜地提取精度较高,点位匹配精度可以达到86.6%。该方法可快速有效地提取出耕地信息,也可供以后耕地信息的相关研究参考。     

The development of soil porosity in experimental sandy soils with clay admixtures as examined by quantimet 720 from besi and by other techniques

For this study thin sections have been prepared of natural and artificial sands mixed with 20% and 40% clay. These and other samples had already been examined using soil physical and soil mineralogical methods for loose samples. Initial thin section studies, with the help of the light microscope alone, have been enlarged upon in this investigation using backscattered electron scanning images and an image analyzer (Quantimet 720). This allowed quantitative information to be obtained on the development of different types of soil porosity patterns using various clay admixtures. Information was also obtained on the influence the form of mineral grains had on the shape of pores in the mixtures of sand and clay. It was also possible to obtain quantitative information on the amount of clays and larger mineral grains in the thin sections. Much of the present data cannot be obtained automatically but must be manually controlled by using the image editor of the Quantimet. This type of work, however, may provide basic data which can subsequently be used to help explain various processes which occur in soils.     

Micromorphometric and micromorphological investigations of a clay loam soil in viticulture under zero and conventional tillage

Porosity, pore size distribution and the orientation pattern of pores were measured on thin sections prepared from undisturbed soil samples by means of electro-optical image-analysis. Total porosity was significantly higher at all sampling times in conventionally tilled plots, but the proportion of pores ranging from 30 to 500 μm, which are considered the most important both in soil-water-plant relationships and in maintaining a good soil structure, was higher in no-tilled plots. Modifications of pore orientation pattern were also observed. Micromorphological observations revealed some differences between the two series of soil samples; the formation of surface soil crusts was strongly reduced in no-tilled plots.     

Three-dimensional analysis of a loamy-clay soil using pore and solid chord distributions

Examples of pore and solid chord distributions obtained for ideal porous media are presented, and the distributions of the porous and solid phases of a soil have been studied by pore and solid chord distributions. Serial sections, 100 μm apart, were cut in a soil core, impregnated with resin, and images were obtained of them. The 2D images from 160 sections were used to build a 3D reconstruction of the core. The initial 2D images, the 3D reconstructed medium and 2D computed images from the latter were studied. We found that the solid matrix of the particular soil is homogeneous and isotropic at the scale studied, and it could be characterized with a single 2D image. For pores ranging from 500 μm to 2 mm we also found similar pore chord distributions for the 2D images in the three orthogonal directions and the 3D medium. A single 2D image can be used to study these pores. For larger pores more than one 2D image is required, and we showed that eight 2D images are sufficient to describe these pores.     

Investigation into the fractal scaling of the structure and strength of soil aggregates

The hierarchical nature of soil structure is examined by measuring the physical properties of a range of aggregate sizes obtained using repetitive fracture. Fractals are used to assess the change with aggregate size of the specific volume, the proportion of pre-existing cracks which link to form the aggregate failure surface, and the aggregate failure stress. The pore size distribution, evaluated using mercury porosimetry and the application of the box counting algorithm to thin sections and thick sections, is also used to obtain a fractal dimension, D. Our results show that D depends upon the measurement approach for mass fractal scaling. This finding may limit the application of fractals to predict the scaling behaviour of soil physical properties.     

土壤和润湿研究中的分形现象

分形几何学的理论与方法已被用于土壤表面不规则性、旋耕土块轮廓及表面裂纹形状和分布、土壤值的空间分布及固体表面润湿性的研究中,利用分形维数定量探讨它们的规律性。本文综合评述了土壤表面、土块轮廓与裂纹、土壤值及润湿研究中的分形特性。     

Quantification of the effects of contrasting crops in the development of soil structure: an organic conversion

Soil structure can be greatly affected, and hence manipulated, by agricultural management practices, such as crop rotation. This study aims to illustrate how soil structure under a stockless organic system differed between contrasting crop types using quantified data derived from image analysis. Undisturbed soil samples were collected from five organic conversion strategies in the second year of conversion, during two contrasting seasons in 2001 and following one uniform crop (oats) grown on all the plots in 2004. The samples were impregnated and images of soil structure collected at selected depth intervals. The images were analysed for macroporosity, pore size distribution and pore‐perimeter fractal dimension. Significant differences were found between treatments in terms of overall macroporosity (%) and average pore size (mm²) in 2001. The red clover (Trifolium pratense) treatments had the highest soil macroporosity in 2001, but showed a dramatic drop in 2004 accompanied by a reduction in average pore size (mm²). Pore–perimeter fractal dimensions for four of the five crop treatments in 2001 did not show significant differences. However, there was a significant decrease in the fractal dimensions in 2004, indicating the presence of pores with less rough and irregular pore boundaries following a uniform cereal crop. Benefits to soil structure and porosity from clover were large and significant but were not lasting.     

Structure and self-similarity in silty and sandy soils: the fractal approach

Soil structure was studied using the concept of fractals and related to soil texture and aggregate properties such as surface charges and aggregate stability. The mass and porosity fractal dimensions (D_m and D_p) of silty and sandy soils were determined on in situ soils using a variety of soil sections (thin, very-thin and ultra-thin), by image analysis on a continuous scale from m to 10^?9 to 10^?1m. Surface fractal dimensions (D_s) of these soils were determined on < 2 mm air-dried samples using mercury porosimetry and the fractal cube generator model. The results suggest that soils are not pore fractals but mass and surface fractals with D_m= 1.1 D_s when the dimension of the embedding Euclidean space d is 3. The soil structures could possibly be described by fractal diffusion-limited aggregation with complex interconnected aggregates or by fractal cluster–cluster aggregation models. As a preliminary conclusion, the fractal approach appears to be a potentially useful tool for understanding the underlying mechanisms in the creation or destruction of soil structure.