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1.
Soil cracking is a well-known phenomenon, also seen in clay soils in the boreal climatic zone. This study was carried out to quantify soil shrinkage properties in six differently managed clay soils in Finland (Vertic Cambisols, 51% clay). Cylinder samples (100 cm3 ) were taken in spring from two depths (0–5 and 5–10 cm), then saturated with water and dried as a function of applied suction. The heights of the sample were measured after each drying step and the volume of soil was calculated assuming isotropic shrinkage. The volume loss by shrinkage at a suction of −50 kPa was 1.6–3.8% and the total shrinkage was 5.2–10.5% of the total soil volume, respectively. All shrinkage curves showed structural shrinkage which occurred in the matric potential range from saturation to around −6 kPa. The shrinkage curves were characterized by minor proportional and wide residual shrinkage zones. Eight of twelve sites showed a steeper shrinkage in the proportional shrinkage zone than the theoretical 1:1 line. Large slope values, up to 3.0, reflect the collapse of inter-aggregate pore space due to shrinkage pressure. The results indicate significant particle rearrangement and structural changes, e.g. structural collapse and changes in inter-aggregate pore space due to shrinkage pressure. Continuous water saturation and variable periods of freezing between spring and autumn are mostly responsible for soil weakness against increasing effective stress as soil dries. It is presumed that shrinkage behaviour will change substantially with increases in drying and wetting cycles. 相似文献
2.
Investigations on porosity and pedological features were carried out on thin sections of samples of a clay soil treated with a ferric conditioner. The effect of wetting-drying cycles was considered and also surface shrinkage was determined. Micromorphometric determinations of porosity, pore size distribution and number of pores per mm2 were carried out by a Leitz-Classimat apparatus. Pore shape and pedological features of ferric compounds were analysed by the point-count method. Surface shrinkage data show great differences between treated and control samples at the first wetting-drying cycle but similar values at the end of the experiment. The statistical processing of micromorphometric data shows significant differences between the control and treated soil material. Wetting-drying cycles influence the number of pores and porosity mainly in the treated soil samples. The pore size distribution is more homogeneously represented in all size classes within treated samples. Also the statistical processing of data of pore shapes and pedological features shows significant differences between control and treated soil samples. Only planar pores are not influenced by the treatment. The wetting-drying cycles affect neither the pore shape, except for planar pores, nor the different pedological features. 相似文献
3.
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
4.
水稻土的水理性质与土壤耕作的关系 总被引：1，自引：0，他引：1
最近的研究工作证明[10,13,18]生长与土壤物理环境有密切关系.一般水稻土有水、旱两作过程,土壤随着淹水、排水和落干的变化相应地发生膨胀、分散、凝聚和收缩.水稻土的物理环境不是固定不变的. 相似文献
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The evolution of clay soil porosity is currently demonstrated via the shrinkage curves in a large water content domain spreading from a shrinkage limit to a liquidity limit. In fact, the parallel between in situ profiles and the shrinkage curves in such a large water content range is difficult to obtain because of the lack of earth pressure in the laboratory tests and in situ limited water contents. The vertical distribution of porosity throughout a clay-rich marsh soil profile was studied in a grassland field with samples taken from the soil surface characterized by water contents near their shrinkage limit down to 2.00 m deep saturated sediments over their liquidity limit. The depth of the plasticity limit isolates a soil in a solid state characterized by a vertical prism-like structure from a plastic to pseudo-liquid state in depth. The porosity was calculated from the measurements of the density of intact samples by double weighing and image analysis of 100 cm2 polished sections. The initial structure of clay soil was maintained by impregnation based on water–acetone–resin exchange. An ultraviolet photo luminescent pigment added to the resin allowed the capture of images from which shrinkage cracks and microporosity of the clay matrix were easily separated. The distribution of porosity between the shrinkage crack mesoporosity and the clay matrix microporosity was evaluated after the mathematical decomposition of the grey level curves characteristic of each level. Vertical evolution of the porosity distribution from the soil surface in a solid state to the plastic and pseudo-liquid sediment in depth was presented on the shrinkage curve of the clay material. The measurements point out how the clay matrix microporosity and mesoporosity of shrinkage cracks are complementary and the role of the scale effect on the shrinkage curve. The analysis of images captured on an optical microscope under polarized and analyzed light and the SEM observation of freeze-dried samples demonstrated the isotropic arrangement of the clay particles in typical “honey-comb” architecture in the in situ plastic-to-liquid saturated domain. Eventually the distribution of porosity through the profile results from the evolution of the initial “honey-comb” microstructure of the sediment induced by the desiccation phenomenon. It is governed by the depth of plasticity limit of the clay material and by the depth of the water table. 相似文献
7.
The packing of elementary particles in soil largely determines the properties that depend on the textural soil pore space, but is studied little. The relations between packing and size and nature of soil particles were studied using fractions of clay, silt and sand, mixed when wet and then dried. Ternary mixtures (clay:silt:sand) were compared with binary mixtures (clay:silt, clay:sand). The pore space of the mixtures was studied using mercury porosimetry and scanning electron microscopy. In all the mixtures the textural pore space was divided into two compartments: (1) lacunar pores due to the presence of skeleton particles and to the shrinkage of the clay phase between these particles, and (2) the clay–fabric pores due to the packing of the clay. In the ternary mixtures, lacunar pores could be divided into two classes: (1) those due to sand particles within the clay–slit phase considered as a single phase, and (2) those due to silt particles within this same phase. For certain mixtures, lacunar pores, referred to as hidden lacunar pores, were not interconnected but were occluded. This occurred both for hidden pores caused by the presence of sand and occluded by the clay–slit phase, and for hidden pores caused by the presence of silt and occluded by the clay phase. The relations between these types of textural pores and the proportions of different size fractions in the mixtures provide guidelines for making optimum use of the particle-size characteristics of the soil to determine its properties. 相似文献
8.
The effect of three microbial dextrans of defined molecular weight, on shrinkage and porosity inside clods has been studied on two Italian clay soils, a Fluvisol and a Vertisol. Shrinkage was determined on dried soil samples using an electro-optical apparatus. The same apparatus was also used to measure porosity and pore size distribution inside the clods. For this purpose large thin sections were prepared from cracked soil samples after shrinkage measurements. Dextrans influenced shrinkage and the size distribution of clods and cracks in the two soils. The major effect was found in the Fluvisol where the arrangement of cracks was changed visibly. The dextrans caused a marked increase in total porosity in the Fluvisol but had only a small effect in the Vertisol. In both soils the pore size distribution was changed resulting in a greater number of larger pores in the dextran treated samples. 相似文献
9.
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。 相似文献
10.
氨化秸秆还田对土壤孔隙结构的影响 总被引：7，自引：0，他引：7
【目的】土壤孔隙性质是土壤结构性的反映,直接影响着土壤的肥力和水分有效性。定量研究氨化秸秆还田对土壤不同大小等级孔隙数量和孔隙分布的影响,可以为土壤培肥提供科学依据。【方法】采用室内试验方法,设置氨化秸秆加入量为土壤总质量的 0(CK)、 0.384%(S1)、 0.575%(S2)、 0.767%(S3)4个处理,室内培养。在培养0、60、120和180 d,取样测定土壤水分特征曲线(SWRC)数据,利用双指数土壤水分特征曲线模型(DE模型,Double-exponential water retention equation),分析氨化秸秆对土壤剩余孔隙、基质孔隙和结构孔隙的影响; 基于DE模型的微分函数,探究不同氨化秸秆处理对土壤孔隙分布的影响。【结果】不同处理的土壤水分特征曲线SWRC实测值和DE模型模拟值之间的均方根误差介于0.0036和0.0041 cm3/cm3之间,R2介于0.998和0.999之间,土壤含水量模拟值和实测值非常接近1 ∶1,表明DE模型可以准确反映添加氨化秸秆后土壤含水量随吸力的变化规律,较准确地估算土壤不同大小等级孔隙数量变化。培养120 d内,氨化秸秆对土壤剩余孔隙、基质孔隙和结构孔隙影响不显著; 培养180 d时,各处理土壤结构孔隙度表现出随着氨化秸秆添加量的增加而增加的趋势; 此时S3对土壤剩余孔隙影响不显著,显著减小了土壤的基质孔隙度(P0.05),极显著地增加了土壤的结构孔隙度(P 0.01)。在孔隙分布中,氨化秸秆促进了土壤已有孔隙向较大孔隙的发育,显著增加了土壤结构孔隙分布数量; 随着氨化秸秆添加量的增加,土壤结构孔隙的分布数量越大,且峰值出现的越早。氨化秸秆增加了土壤中有机质含量; 土壤结构孔隙和总孔隙均与有机质含量呈显著的正相关关系(P 0.05); 有机质可以黏结团聚土壤的矿物颗粒,有效地促进了土壤结构孔隙的发育; 氨化秸秆对土壤孔隙的影响随着时间的进行越来越明显。【结论】氨化秸秆增加了土壤中有机质含量,促进了土壤孔隙结构的发育,增加了土壤的结构孔隙度和总孔隙度,这对改良和培肥土壤、改善土壤耕性具有重要意义。 相似文献
11.
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
12.
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
13.
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. 相似文献
14.
The natural regeneration of soil structure following compaction was studied on a stagnogleyic paleoargillic brown earth (Albaquic Paleudalf) at Rothamsted Experimental Station. The compaction treatment was produced by wheelings, and the area between the wheelings was used as the control.The wheeled and unwheeled areas were sampled 4 times, in spring and after harvest in 1979 and 1980 The following techniques were used to monitor regeneration: measuring the profile of the soil surface in the field and laboratory measurements of air-filled pore space, water retention, shrinkage and clod density, micromorphometry and mercury intrusion.Compaction decreased the macroporosity (pores >60 μm diameter) by over a half. Pores <6 μm diameter were unaffected by compaction. Natural regeneration of porosity in the top 5 cm was achieved within 18 months, but the soil below remained compacted for longer. The regenerated structure consisted mainly of planar voids induced by physical processes unlike the unwheeled soil which was characterised by packing voids and biopores. 相似文献
15.
J. A. CURRIE 《European Journal of Soil Science》1983,34(2):217-232
Gas diffusion coefficients for hydrogen through air in packings of 1–2 mm crumbs from a clay loam (both under grass and under arable) and from a sandy loam were measured over a range of water contents as the soils were wetted. Diffusion coefficients decreased with increasing water content (decreasing air content) in three stages: in the first, to specific water contents of 0.08–0.10 gg1, decreases were small indicating the filling of pores less effective for diffusion; in the second, to crumb saturation, decreases were greater, and in the third, to complete saturation, decreases were greatest. Two of these stages are related to swelling: in the first, any slight swelling is contained within the crumb and there is loss to the gas of crumb pores only; in the second, the crumbs swell and there is simultaneous loss of crumb pore space and, more important, inter-crumb space; in the third, swelling is complete, so, as in nonswelling soil, there is loss of inter-crumb space only. Pore size and pore shape in the three soils, and pore distribution (intra-crumb structure) in the grassland clay loam, may also affect diffusion but to a lesser extent: these influences are discussed. On subsequent drying there was little evidence of hysteresis in diffusion with water content, and only a slight indication in the arable clay loam of decreases due to structural degradation during the measurements. 相似文献
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Ryszard Oleszczuk Klaus Bohne Jan Szatylowicz Tomasz Brandyk Tomasz Gnatowski 《植物养料与土壤学杂志》2003,166(2):220-224
The shrinkage of the peat soils that accompanies the soil moisture changes is an important feature of such soils and has strong influence on their physical attributes and soil water management. The relationships between soil moisture and volume are often described using shrinkage characteristic curves by relating void ratio (volume of voids per unit volume of solids) to moisture ratio (volume of water per volume of solids). For conversion of soil volume changes into cracks volume and subsidence, a dimensionless shrinkage geometry factor is used. The paper presents results of volumetric shrinkage behavior and the geometry factor at various loads in sedge and alder peat soils. The measurements were conducted on undisturbed soil samples without applying a load and with loads corresponding to field overburden. The shape of the shrinkage characteristics of such soils were completely different from those of clay soils. The application of loads did not significantly influence the shrinkage characteristics curve. The applied load strongly influenced on relationship between shrinkage geometry factor and the moisture ratio, showing higher values of subsidence and lower values of crack volume in comparison with unloaded conditions. 相似文献
18.
Helena Soinne Riikka Keskinen Mika Tähtikarhu Jukka Kuva Jari Hyväluoma 《European Journal of Soil Science》2023,74(5):e13424
Understanding of factors governing soil structural features is necessary for managing key processes affecting crop productivity and environmental impacts of agriculture, for example, soil water balance, aeration, and root penetration. Organic matter is known to act as a major binding agent in soil aggregation and thus constitutes a central pillar in soil structure formation. However, knowledge of the structural role of organic matter or carbon (OC) in soils highly rich in clay-sized particles (<0.002 mm) is limited. In this study, the effects of clay and OC contents on aggregate stability, water holding capacity, near-saturated hydraulic conductivity, total porosity, and pore size distribution were assessed in cultivated fields with high clay content located in private crop production farms in southern Finland. Significant positive correlations were found between OC content and proportion of water stable aggregates and specific pore sizes from the range of 30 μm up to 1 mm diameter determined by image analysis. Porosities on a smaller size range derived from water retention measurements likewise showed a positive correlation with OC in <0.2 μm sizes. On the range of 0.2–1 μm, a negative relationship was observed, which induced a negative effect of OC on soil plant available water reserves. In line with the positive correlation between OC and larger soil pores, free water, representing the amount of water that can be drained by gravity, exhibited a positive relationship with OC suggesting that OC content can enhance aeration of soils with high clay content. Compared to OC, clay content tended to have an adverse effect on soil structural properties. Clay correlated negatively with pores larger than 30 μm, free water content, and extrapolated field saturated hydraulic conductivity. Further, our imaging results showed how saturated hydraulic conductivity was controlled by pore morphology, and there was a power law relationship between the conductivity and critical pore diameter. in agreement with the percolation theory. Overall, the structural impacts and hydrological implications of OC and clay in heavy clay soils vary by pore size ranges and their emergent practical impacts are thus not straightforward. 相似文献
19.
Changes in the macro-pore structure of restored soil caused by compaction beneath heavy agricultural machinery: a morphometric study 总被引：2，自引：0，他引：2
B. Schäffer M. Stauber R. Müller & R. Schulin 《European Journal of Soil Science》2007,58(5):1062-1073
Compaction can seriously degrade soil in modern agriculture. Soil that has been temporarily removed and stored is particularly sensitive to compaction when restored, although little is known about the structural changes in such soils under mechanical loads. We investigated the structural changes in a restored soil that had been gently cultivated for several years and then was trafficked by a heavy combine harvester, analysing the macro‐pore structure by quantitative morphometry of three‐dimensional microcomputed tomography images. Increased trafficking caused decreases in both the porosity and connectivity of the macro‐pores. The fraction of spherical pores (and thus the convexity of the pore space) and the mean pore separation were increased. Trafficking had no clear effect on the orientation of pores. While the mean pore diameter tended to decrease, biopores were more stable than interaggregate pores originating from the packing of soil aggregates. This is relevant for the development of structural stability in restored soils, as the macro‐pores consist mainly of interaggregate pores initially, whereas biopores develop and increase in proportion only gradually over time. Quantitative morphometry provides valuable morphological indices for the objective assessment of the macro‐pore structure and changes induced by compaction. 相似文献
20.
Artificial soil blocks were made by mixing either ballotini or natural sand with a suspension of silt and clay (fines). The soil was allowed to dry, shrinkage was measured, and from thin sections, the type, area and size of voids in the horizontal plane were observed. As the fines content increased, from 0 to 25%, packing voids (spaces caused by a lack of sufficient small particles to fill voids between sand grains) decreased and were partly replaced by fissures (caused by shrinkage of fines leading to isolated cracks within blocks). From 25% to 50% fines, aggregate shrinkage increased rapidly resulting in the development of large inter-aggregate voids, but packing voids and fissures decreased. There was a transfer of porosity from within the block to the inter-aggregate spaces as the fines content increased. Blocks containing coarse sand-size particles had larger packing voids and fissures, a greater area of fissures, but similar shrinkage to blocks containing fine sand-size particles. 相似文献