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1.
ROTHAMSTED STUDIES OF SOIL STRUCTURE III 总被引：2，自引：0，他引：2
The response of three pairs of soils having contrasting management behaviour to changes in water content was investigated by measuring moisture characteristics, shrinkage, and pore size distributions by mercury porosimetry. Sample preparation for mercury porosimetry was by direct drying, or water replacement by methanol and liquid CO2 followed by evaporation above the critical temperature. In heavy textured horizons, water release on shrinkage between -0.05 and -15 bar matric potentials occurs when pores of 10–200 nm equivalent plate separation contract. Structure development is dependent on the stability and regeneration of pores in the size range 200 nm-30 μm during cycles of wetting and drying. Soils with little stable porosity in this size range show nearly normal shrinkage and have coarse structural units, whereas soils with stable or regenerating porosity depart more from normal shrinkage and structure in the profile tends towards a finer per unit. The application of mercury porosimetry shows promise for determining possible porosity limitations in soil profiles. 相似文献
2.
《Communications in Soil Science and Plant Analysis》2012,43(13-14):1643-1662
Abstract The retention of contaminants in soil and overburden is often estimated using a solid/liquid partition coefficient, Kd, which lumps all the processes into an empirical value. Determination of this value in unsaturated porous media requires the separation of the pore water from the solid phase. Soil pore‐water recovery and composition were investigated in three chemically and texturally different mineral soils and one organic soil. The removal of pore water was achieved through centrifugation at low (1000 to 2500 rpm) and ultra (10,000 to 20,000 rpm) speeds, ceramic plate extraction and immiscible displacement. Pore‐water recovery was highest using ceramic plate extraction and lowest with displacement. Pore‐water quality was not affected by centrifugation time. However, the pore‐water concentrations of F, Cl, NO3, Fe, and Na suggest that the effect of centrifuge speed on the element or ion of interest should be determined prior to extraction. Ceramic plates retained both cations and anions, and the immiscible displacent depressed the pH of the soil slurry affecting the pore‐water composition. Comparisons between distilled water extracts, standardized to field capacity moisture, and the centrifugate for a sand and an organic soil indicated that with low solid/liquid ratios, pore‐water concentrations are influenced by dissolution or desorption. Therefore, Kd values based on centrifuged pore water will be lower than those based on extraction/ desorption. 相似文献
3.
Soil pore networks have a complex geometry, which is challenging to model in three dimensions. We use a Boolean model of pore space that has proved useful in modelling gas diffusion in dry structures to investigate the distribution of water in this pore space and to quantify the effects on pore connectivity to the soil surface. We first show how total porosity in dry soil influences connectivity via the percolation threshold. Then we show that our model simulation of the ‘ink-bottle effect’ can account for much of the hysteresis of the soil water. The differences in distribution of water between wetting and drying result in maintaining greater connectivity of the air-filled pore space during drying than during wetting. Hysteresis is large at small total porosities and slowly declines as porosity increases. During wetting much pore space is blocked when more than 40% of the pore space is filled with water, although during drying all non-isolated air-filled pores are connected to the surface. Even when soil is allowed to wet to near saturation, there are rapid increases in pore connectivity during drying, which may explain, for example, rapid increases in production and emission of nitrous oxide in soils near saturation. 相似文献
4.
Y. Nagarajarao 《植物养料与土壤学杂志》1994,157(2):81-85
A method for the determination of pore size distribution in swell-shrink soils was described. Undisturbed core samples, saturated and drained at 1.5 MPa suction, were filled with a non-polar liquid (xylol), and its retention at suctions lower than 1.5 MPa was measured. Oven dry samples were analyzed in the same way. Derived pore size distributions were compared with those obtained by water desorption. Pore size distributions and their relative changes as a function of water content were related to some soil constituents and properties. Stability factor and sum of montmorillonite and vermiculite significantly influenced the pore size distribution by water release, A higher stability factor resulted in lower relative changes (ratios) in the pore size classes <10 μm and 0.2–10 μm when the samples were drained from saturation to 1.5 MPa suction, however, at extreme dryness, the relative changes were positively correlated to the sum of montmorillonite and vermiculite. 相似文献
5.
Management-induced structural dynamics in paddy soils of south east China simulated in microcosms 总被引：1，自引：0，他引：1
The puddling of paddy soils is the most common method of lowland rice cultivation in Asian countries and results in a complete distortion of the soil structure of the puddled layer and the formation of a distinct plough pan. In addition, the soil structure and the interrelated chemical and biological parameters in these soils are influenced by the alternating of flooding and drying stages. Since physical properties are basic features for the availability of water and nutrients characteristics such as soil structure and soil moisture have been recorded at the different stages of rice growth in detail. For a better understanding these results have been compared with micropedological investigations. For these purposes undisturbed microcosms filled with paddy soils of three different sites from south east China were taken and planted with rice in a climate chamber.Management-induced dynamics have been reflected very prominently as far as bulk density, pore size distribution and soil moisture of the puddled layer are concerned. The properties of the undisturbed plough pan did not change during all stages of the experiment. Most significant effects of soil puddling have been found in the soil with a clay content of more than 40%. Comparing the different sampling stages after puddling the soils with high clay contents have shown the greatest variety in pore size distribution.Micropedological investigations demonstrated the different texture-influenced aspects of pore size distribution and the arrangement of soil structure in the topsoil in detail. Micrographs verified the changes of microhabitats caused by soil structure dynamics. The structural alteration consequences different living-conditions of microorganisms and, therefore, population dynamics related to the management of paddy soils which has been reflected in this study. 相似文献
6.
In general, soils and their pore size systems are assumed to be rigid during the loss of water on drying. In reality, it is not the case for most soils, especially for soils with high quantities of clay or organic matter. As a result of shrinking, there are changes in the bulk density, the porosity, the pore size distribution, and the hydraulic properties of these soils. Currently, only a few methods enable the shrinkage behavior of soil samples to be determined while simultaneously quantifying the corresponding soil hydraulic properties. Either the methods need proprietary software for data processing, the equipment used is expensive or the calculation of the hydraulic properties is executed by inverse modelling. The aim of this study was to develop an alternative, simplified method for the simultaneous and automatic determination of the soil hydraulic properties, taking shrinkage into account. The HYPROP® evaporative device was combined with a circumference meter. A preliminary investigation found that the diameter of the cylindrical samples used for the HYPROP decreased linearly during evaporation from the bottom to the top. To sum up, recording the perimeter change in the middle position of the sample during drying‐out, together with the corresponding tension and water content, was sufficient to determine the hydraulic functions taking shrinkage into account. Measurements are presented for 6 samples which are different in texture and geological origin. The maximum shrinkage (19.5% by vol. between saturation and 5,000 hPa) was measured in the peat samples. The minimum shrinkage was quantified at 0.68% by vol. for the silty loam samples from Chile. The advantages of the method presented are: (1) the water retention curve and the hydraulic conductivity function can be determined simultaneously in the range between saturation and close to the wilting point, at a high resolution and taking into consideration shrinkage; (2) the method and device are simple and robust to use; (3) little time is required for measurement, between 3 and at most 10 d; (4) the functions are described over the whole tension range, using more than 100 user‐defined data points; (5) the evaluation of the volumetric soil water content measurement in shrinking soils is improved; and (6) common data models can be fitted to the hydraulic data as well as to the shrinkage data. 相似文献
7.
高矿化度土壤水分特征曲线及拟合模型适宜性 总被引：10，自引：5，他引：5
为分析高矿化度对土壤水分特征曲线的影响,以淡水及矿化度分别为30、100和250g/L的水样对土体进行饱水处理(简称TDS-F、TDS-30、TDS-100和TDS-250处理),测定脱湿过程的土壤水分特征曲线。结果显示,试验吸力变化过程中,各处理比水容量相近,局部存在差异:TDS-100及TDS-250处理土体对水分的吸持能力明显小于TDS-30及TDS-F处理。分析表明:TDS-30处理使土体中等孔隙体积变小、TDS-100处理使土体较小孔隙体积变小、TDS-250处理使土体较大孔隙体积变小,进而影响土壤水分特征曲线形态。利用RETC软件结合统计分析确定,TDS-F、TDS-30、TDS-100及TDS-250处理土壤水分特征曲线的最优拟合模型分别为:vanGenuchten-Mualem、Dual-porosity-Mualem、Lognormaldistribution-Mualem及Dual-porosity-Mualem模型;各处理最优模型的非饱和导水率模式均为Mualem模型;从机理上解释各拟合模型优劣还较为困难。研究结果为干旱区高矿化度土壤水、盐运移计算提供一定参考。 相似文献
8.
To characterize the fabric of a wet soil sample two sets of experiments were performed. In one, water retention and shrinkage curves were determined with samples stored at the field water content, and in the other, pore size distribution curves and microscopic observations were made as samples progressively dried. The experiments were performed with soil samples of different aggregate sizes to determine the contribution of each class of pores to porosity.
Data were analysed by comparing (i) the amount of water extracted from the sample, (ii) the air-filled porosity of the sample and (iii) the accumulated pore volume by mercury injection, each in relation to the equivalent pore radius. This gives information on the geometry of pores developed during the drying process. It has shown that micrometric cracks in dried soils are not artefacts but the result of a more severe drying never reached by the material in the field. 相似文献
Data were analysed by comparing (i) the amount of water extracted from the sample, (ii) the air-filled porosity of the sample and (iii) the accumulated pore volume by mercury injection, each in relation to the equivalent pore radius. This gives information on the geometry of pores developed during the drying process. It has shown that micrometric cracks in dried soils are not artefacts but the result of a more severe drying never reached by the material in the field. 相似文献
9.
WATER MOVEMENT IN DRY SOILS 总被引：2，自引：0，他引：2
D. A. ROSE 《European Journal of Soil Science》1971,22(4):490-507
hysteresis that occurs in the micro-hydrological characteristics of a soil (conductivity and diffusivity) as functions of water content and water potential between sorption and desorption is examined for three soils (sand, loam, and clay) and sepiolite. These materials, all aggregated, are sufficiently dry that both the vapour and liquid components of water movement are important. any water content or water potential the vapour conductivity is always bigger when wetting than when drying though differences may be small. There is hysteresis in water (vapour+liquid) conductivity as a function of water content when vapour flow but not liquid flow is dominant. Conversely, there is hysteresis in water conductivity as a function of water potential when liquid flow but not vapour flow is dominant. Both forms of this hysteresis are small. Hysteresis in diffusivity as a function of both water content and water potential exists, but is complicated. Variations caused by hysteresis, though real, are likely to be negligible in practice, swamped by effects caused by changes in the soil environment (e.g. temperature) or by changes in soil management (e.g. structure). 相似文献
10.
Effect of humic acids,sesquioxides and silica on the pore system of silt aggregates measured by water vapour desorption,mercury intrusion and microtomography 
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下载免费PDF全文 G. Jozefaciuk H. Czachor K. Lamorski M. Hajnos R. Swieboda W. Franus 《European Journal of Soil Science》2015,66(6):992-1001
Most of the information on soil aggregation and porosity comes from studies of natural soil in which the effects of the different constituents that form the structure overlap. The aim of this research was to study the effects of these constituents separately on well‐characterized artificial aggregates in order to understand them better. To do this, the pore system of model silt aggregates, amended with different amounts of humic acids, iron and aluminium hydroxides or colloidal silica, was investigated at three levels of magnification with water vapour desorption (nanometre sizes), mercury intrusion (micrometre sizes) and microtomography (tens of micrometres). Humic acid and aluminium hydroxide increased aggregate porosities measured by all methods. An increase in porosity with increasing additions of each constituent was indicated only by water desorption. We did not observe any well‐defined trends in the dynamics of average pore radii. The pore surface fractal dimension determined by mercury intrusion was negatively correlated with that measured by water desorption. The pore system in granular media comprises larger voids joined by narrower necks; therefore, we attempted to relate their sizes with a novel approach that combined microtomography with mercury intrusion and extrusion data. We observed a decrease in the size of pore necks that give access to voids of the same sizes with increasing additions of all constituents. With additions of humic acid this effect was the smallest. The mercury intrusion data showed the formation of separate concretions of iron hydroxides and silica in silt aggregates. 相似文献
11.
The role of rock fragments in crack and soil structure development: a laboratory experiment with a Vertisol 下载免费PDF全文
下载免费PDF全文 A large number of factors that influence soil surface cracking behaviour in swell‐shrink soils have been studied, but there are few studies on the influence of rock fragments on crack development. Effects of rock fragments have been investigated with reference to the soil pore system but they have mainly been studied indirectly through measurements of water flow and/or bulk density changes. A laboratory experiment was carried out with repacked soil samples that were prepared by adding rock fragments of three different sizes (2–4, 4–8 and 12–16 mm) to a Vertisol at two different rates (10 and 25% by volume). Soil image analysis procedures were applied in order to describe quantitatively the network of surface cracks and the pore system to a depth of 8 cm below the surface, which developed after wetting‐drying cycles. Mean values and standard deviations of surface crack or pore widths decreased with the increase in rock fragment content and the decrease in rock fragment size, while the density of the ‘skeleton’ of the crack and pore networks increased. Rock fragments also induced vertical homogenization of the soil structure. The number of rock fragments was a key factor in determining some crack network characteristics, inducing inverse variations in mean width and skeleton density of the crack or pore network. Overall results suggested that rock fragments acted as triggering points for crack and pore development in Vertisols. The findings of this work provide a contribution to the understanding of the mechanisms of crack network and soil structure development that are induced by stones in swell‐shrink soils. 相似文献
12.
The dynamics of pore space structure in different filled soil constructions during water infiltration and wetting–drying processes is studied. Model laboratory experiments in columns physically simulate water infiltration after penetration at a rate of 600 mm with free outflow from the lower end of the column followed by multiple drying of soil constructions composed by alternating layers of sand, peat, and A and В horizons of soddy-podzolic soil. In two- and three-dimensional tomographic images, changes in the pore space and the interpenetration of solid phase at the boundaries between individual horizons of soil constructions are analyzed. 相似文献
13.
Morphological determination of pore connectivity as a function of pore size using serial sections 总被引：9，自引：0，他引：9
H. J. VOGEL 《European Journal of Soil Science》1997,48(3):365-377
The geometry of pore space in soil is considered to be the key in understanding transport of water, gas and solute. However, a quantitative and explicit characterization, by means of a physical interpretation, is difficult because of the geometric complexity of soil structure. Pores larger than 40 μm within two soil horizons have been analysed morphologically on 3-dimensional digital representations of the pore space obtained by serial sections through impregnated specimens. The Euler-Poincaré characteristic has been determined as an index of connectivity in three dimensions. The pore connectivity is quantified as a function of the minimum pore diameter considered leading to a connectivity function of the pore space. Different pore size classes were distinguished using 3-dimensional erosion and dilation. The connectivity function turned out to differentiate between two soil materials. The pore space in an upper Ah horizon is intensely connected through pores between 40 and 100 μm, in contrast to the pore space in the AhBv beneath it. The morphological pore-size distributions were compared to the pore-size distribution obtained by water retention measurements. The discrepancy between these different methods corresponds to the expectation due to pore connectivity. 相似文献
14.
15.
Oxygen is a prerequisite for some and an inhibitor to other microbial functions in soils, hence the temporal and spatial distribution of oxygen within the soil matrix is crucial in soil biogeochemistry and soil biology. Various attempts have been made to model the anaerobic fraction of the soil volume as a function of structure, moisture content and oxygen consumption. Aggregate models are attractive but difficult to parameterize and not applicable to non-aggregated soils. Pore models are preferable for pragmatic reasons, but the existing versions appear to overestimate the anaerobic volume at intermediate soil moisture contents. A modified pore model is proposed, in which anaerobiosis is calculated from a range of air filled pore size classes, based on the soil water retention curve and the soil moisture content. In comparison with previous pore models which are based on the estimation of an average size of the air filled pores, the pore class model presented here appears to give more adequate estimates of anaerobic volumes, especially at intermediate moisture contents. The pore model is attractive for process modelling of anaerobic functions such as denitrification, since it can easily be parameterized by the water retention characteristics of a soil. 相似文献
16.
A. J. THOMASSON 《European Journal of Soil Science》1978,29(1):38-46
A classification of structural condition in surface soils is proposed, based on the volumes of two categories of pore size, termed air capacity (pores greater than 60 μm diameter) and available water (pores of 60 to 0.2 μm diameter. Relationships of pore volumes to particle size class, organic carbon content and soil water regime are examined. Soil structural conditions are mainly affected by water regime and organic carbon and, apart from the extremes of sandy or clayey textures, less influenced by particle size distribution. 相似文献
17.
Take home message Mucilage secreted by roots and EPS produced by microorganisms alter the physical properties of the soil solution and impact the water dynamics in the rhizosphere. The high viscosity of mucilage and EPS is responsible for the formation of thin filaments and interconnected thin lamellae that span throughout the soil matrix maintaining the continuity of the liquid phase across the pore space even during severe drying. The impact of these mechanisms on plant and microorganisms needs to be explored. 相似文献
18.
土壤斥水性影响土壤水分运动研究进展 总被引：4，自引：1，他引：3
土壤斥水性广泛存在于各类土壤,是影响植物生长、土壤水分运动以及土壤侵蚀等水土过程的重要因素。该文阐述了土壤斥水性的基本概念,介绍了几种常用的斥水性强度测定方法及适用范围。在此基础上,论文对土壤斥水性如何影响土壤水力性质以及水分运动特征等研究现状作了全面评述,重点讨论了近年来该领域的研究热点,如土壤斥水性影响下的指流观测和理论模拟以及斥水性土壤蒸发过程等。最后,提出了相关研究中亟待解决的若干关键科学问题,主要包括确定土壤斥水性影响指流现象和蒸发过程的物理机制的揭示;考虑土壤斥水性参数的土壤水分运动数学模型的构建;以及对新模型的求解及对数值解的理论分析。由于土壤斥水性对土壤水分运动有重要的关联效应,相关问题的深入研究对进一步认识土壤水分运动的内在物理机制具有重要理论意义,也将为掌握和有效利用土壤斥水性提供实践指导。 相似文献
19.
J.A. CURRIE 《European Journal of Soil Science》1979,30(3):441-452
Porosity and gas diffusion have been measured within dry crumbs sieved from the horizons of one soil from each of the Hanslope, Ragdale, Evesham, Denchworth, Flint and Salop series. Crumb porosities, ?c, ranged from 0.19 to 0.33, dimensionless gas diffusivities, Dc/D0, from 0.015 to 0.098, and the effectiveness of unit pore space for diffusion, given by αc= (Dc/D0)/?c, from 0.06 to 0.29. Values of ?c and Dc/D0 were used to calculate complexity factors kc for the crumb pores. The results are discussed in terms of soil texture, pore size, ease of soil management, and the frequency and intensity of wetting and drying of the soil in each horizon. None of the results suggests why the soils of the Ragdale, Denchworth and Salop series should be more difficult to manage than the others. 相似文献
20.
A comparative study of three methods of water removal prior to resin impregnation of two soils 总被引：1，自引：0，他引：1
C. P. MURPHY 《European Journal of Soil Science》1982,33(4):719-735
The water in replicate samples from sub-surface horizons of a clayey and a fine-silty soil was removed either by oven-drying, freeze-drying or by acetone-replacement prior to resin impregnation. Pore space photograms (pores >60 μm diam.) from thin sections were analysed on a Quantimet 720 image analysing computer following each drying technique. During oven- and freeze-drying the clayey soil contracted considerably and subsequently satisfactory impregnation of these samples was either difficult or impossible. This macro-shrinkage caused a decrease in number and lengths of most planar pores and a decrease in size and number of all intra-aggregate pores. The loss in pore space and continuity obviously affected resin impregnation. The clayey samples in which water was replaced by acetone, and all samples of the silty soil, however pretreated, showed no measurable macro-shrinkage and all impregnated well. Oven-drying the silty soil appears to increase the porosity, causing an increase in size of all pores. A mechanism for this apparent enlargement is proposed. It is evident that acetone-replacement of the soil water prior to resin impregnation is the best of the three methods used here and should be seriously considered when image analysis is to be carried out on resin-impregnated blocks from soils of similar or related textures. 相似文献