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1.
G.R Mehuys  C.R De Kimpe 《Geoderma》1976,15(5):371-380
Saturated hydraulic conductivity (K) values were measured in the laboratory on two podzolic soils (Spodosols) with fragipans developed from till deposits in the Appalachian and Laurentian Highlands of Quebec. The main difference between these tills lies in their contrasting textures. Due to the presence of coarse fragments and to a brittle and compact horizon, usual methods of measuring K in the field could not be used. Instead, blocks of soil were carved out and encased in paraffin. The technique insures minimum disturbance of the samples and accommodates variations in sample size due to stones.Sainte-Agathe sandy loam (sandy, mixed, frigid Fragiorthod) had higher K values than Arago loam (fine-loamy, mixed, frigid Fragiorthod) throughout the profile. In both soils, K decreased with depth largely as a result of an increase in bulk density. At any given bulk density, however, K was always lower in Arago than in Sainte-Agathe soil. This was attributed to illuviation and reorganization of particles within pores and partings. In the Arago profile, rearrangement of clay-size particles created an important vesicular porosity, thus closing off a portion of the pore volume to water transmission. In the Sainte-Agathe profile, material ranging from fine silt to clay was deposited selectively according to size class. Accessibility of the pore volume to percolating water was thus maintained.A second eluvial horizon Aex (A'2x) is present in the Arago, but not in the Sainte-Agathe soil, just above the fragipan, probably as a result of the very abrupt increase in bulk density from the podzolic B horizon to the fragipan. Water accumulating at the top of the fragipan seeps laterally, enhancing the eluviated character of the Aex horizon. Hydraulic conductivity was higher in this horizon than in over- and underlying horizons, although bulk density was greater.  相似文献   

2.
In this first of three papers, the parent materials, morphology and field relationships of soils with fragipans, similar to those in north-eastern United States, are described and analyses of their chemical and physical properties are presented to support a periglacial stage of development. The soil materials have been affected by periglacial processes, including ice-wedge formation, the age of which has been established by reference to a buried paleosol. The fine earth bulk density of the fragipans is between 1.75 and 1.91 g cm−3 whereas the density of overlying Eb horizons is < 1.40 g cm−3. The formation of the compact lenticular structures and polygonal fissuring of fragipans is ascribed to the former presence of permafrost during the Loch Lomond Stadia1 11 000 to 10 000 years B.P. The polygonal fissures, after subsequent infilling with illuvial material, have determined the position of the greyish polygonal zones which have formed by the eluviation of Fe and Mn from fissure infill and fissure walls by redox processes. Clay migration from the Eb horizon into the fragipan is well marked. Clay and silt have also been locally removed from the upper parts of the greyish zones and redeposited towards their lower parts. Similar textural degradation has affected eluvial pockets in the upper fragipan. It is concluded that periglacial processes fully explain the genesis of macrostructural features but not the distinctive consistence of the fragipan.  相似文献   

3.
Pedogenetic processes following a permafrost stage of development in four argillic brown earths with fragipans (Glossic and Ochreptic Fragiudalfs) are investigated by soil microscopy, including SEM observations of unimpregnated soil material, and by determination of clay mineralogy. Micromorphology of the apparently massive fragipan confirms both the presence of subhorizontal fissures infilled with illuvial deposits separating dense lenticular structures formed by ice-lens growth, and former vertical fissures formed by dessication on freezing with subsequent widening by ice-vein development. The firmness and brittle failure of the fragipans are attributed to a closely-packed, well-graded matrix of skeleton grains bonded by clay bridges consisting of non-swelling illite and chlorite and to weak interconnection of macrovoids. Weak cementation is rejected as an explanation of fragipan consistence. Sequential stages of particle translocation have been critical to fragipan formation. High bulk density is attributed not only to irregular compression and contraction of the soil matrix under permafrost conditions but also to the infilling of voids by illuvial silt and clay. The full development of the fragipans has depended on Flandrian clay migration which has contributed to clay-bridge formation, void infilling and localized seasonal impedance of drainage resulting in eluviation of iron oxides, the development of grey polygonal patterning, and processes of degradation at the pan surface leading to glossic features.  相似文献   

4.
A Fragipan (Bx) is a soil horizon hard when dry and brittle when moist, that undergoes slaking upon water immersion, forming a barrier to roots and limiting land use. Brittleness and slaking depend on soil porosity and particle arrangement, but still no agreement exists on the inorganic components responsible for such arrangement. We hypothesized that the same kind of particle arrangement may originate from different soil components, ultimately depending on the lithology of parent material, and evaluated the soil and clay characteristics that best differentiate Bx from B horizons. Thirty-six samples were taken from Typic Fragiudalfs developed on the two sides of an alluvial fan characterized by different amounts of ultramafic materials. Discriminant Analysis evidenced that pedogenic Fe oxides were fundamental in discriminating Bx from B horizons on pure ultramafic parent material, while clay mineralogy was more important in soils with less ultramafic materials. In the first case, the association between clay minerals and self-assembling oxides systems may lead to brittleness, while in the second case the higher abundance of kaolinite may contribute to weak associations between pH-dependent sites and negatively charged surfaces. The only common feature to fragipans on both river sides was a higher degree of weathering.  相似文献   

5.
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   

6.
Three hard layers have formed in a Spodosol developed on aeolian coastal sands under the influence of litter from kauri (Agathis australis). A densipan in the albic horizon and a humus-pan in the spodic horizon slaked in water whereas a clay-pan in a buried soil only softened in 1 M HCl. Blocks sawn from these three pans showed a maximum of unconfined compressive strength in the humus-pan.Specimens made from remoulded pan materials with minimum compaction developed only a proportion of the original strength. Greater compaction enhanced the strength of all three materials. Raising the pH during remoulding caused a marked increase in strength, but above pH 10.5 all the pan materials lost strength when silicate was solubilised from surfaces of clay and quartz particles.Scanning electron micrographs showed that the densipan was a close-fit configuration of sand- and silt-sized quartz particles that attained a high density without cementation of particles. In the humus-pan organic matter bridged across a third of the surfaces of the quartz particles and prevented a close-fit configuration. The clay-pan below the spodic horizon had all its particles thickly coated with clay and humus and these were aggregated into an open-fit arrangement of lower density.According to Soil Taxonomy procedures, the Te Kopuru sand lies within the Aquod sub-group of Spodosols. In the absence of a non-slaking duripan it was the presence of a fragipan below the spodic horizon that directed the soil into being a Fragiaquod. It is the densipan in the albic horizon above the spodic horizon, however, that controls plant roots and cannot be ignored in soil classification. We suggest that a new great group, Densiaquod, be recognized for these soils.  相似文献   

7.
Flocculation tests and permeability measurements were carried out for silt and clay fractions separated from surface and subsurface horizons of four paddy soils. There was not much difference in the flocculating power between A1(OH)2.2C10.8 and CaSO4. Their flocculation value, 0.3 to 3 mM, was attained by adding the reagents at the rate of 0.24 to 2.4 mmol/100 g of the silt and clay. The flocculation with A1(OH)2.2C10.8 or CaSO4 did not affect the sediment volume of the silt and clay. This sediment volume was smaller for the surface than for the subsurface horizons of each soil, suggesting that soil organic matter and repetition of wetting and drying contribute to the stable aggregation of the silt and clay in the surface horizon. The permeability was higher for the silt and clay fractions separated from the surface horizon than that from the subsurface horizon, and the addition of 2.5 to 4.2 mmol of A1(OH)2.2C10.8 or CaSO4/100g of the silt and clay increased its permeability by 1.5 to 4 times. The effect of A1(OH)2.2C10.8 was more lasting than that of CaSO4 and was recognized even after 200 ml of water passed through 1 g of the silt and clay. The effect of the flocculating reagent on the permeability was more or less enhanced by air-drying the treated silt and clay.  相似文献   

8.
A comparison is made between the properties of permafrost and those of fragipans. The permafrost characteristics are summarized from published data on active permafrost and from personal observations on fossil permafrost. The study of the fragipans mainly concerns the silty sediments of Weichselian age which occur in Belgium and northern France.The distribution and the physical, macromorphological and micromorphological properties of fragipans can all satisfactorely be explained by the growth of segregated ice during permafrost aggradation. Particularly striking is the relationship of both permafrost and fragipans, to drainage conditions: the quantity of segregated ice is highest in moist or poorly drained soil and it is at such places that the best developed fragipans are observed.Certain arguments that can be stated against the hypothesis of fragipan genesis by permafrost are discussed: (1) the development of a platy structure by freeze-thaw or by wet-dry cycles, (2) the discontinuous distribution of the fragipan, (3) the development of the fragipan by pedogenetic weathering and migration processes. It is concluded that only the permafrost hypothesis can explain the complete set of properties of the fragipan.  相似文献   

9.
The influence of clay content and silt–clay fabric on aggregate stability was investigated. Two silt—clay fabrics were produced in the laboratory by mixing silt particles with a clay phase: (i) a loose packing of the silt particles with clay aggregates, and (ii) a close packing of the silt particles with the dispersed clay phase, the latter coating and bridging the silt particles. Porosity and pore size distribution were measured, and the silt—clay fabric was described using scanning electron microscopy. The aggregate stability was measured under three treatments corresponding to different wetting conditions and energy levels: fast wetting, mechanical breakdown and slow wetting. Our results show that aggregate stability is related to both clay content and silt—clay fabric. Comparison of fragment size distributions and their mean weight diameter amongst the three treatments enabled identification of mechanisms responsible for the variation of aggregate breakdown. The compression of trapped air was the predominant breakdown mechanism for both fast and slow wetting and was related mainly to porosity characteristics. For the mechanical breakdown, the degree of disintegration depended on the cohesion of the silt–clay fabric, which is related to the continuity of the solid phase.  相似文献   

10.
A Xeralf on feldspathic sandstone was sampled from a hillslope in the Mount Lofty Ranges in order to study its genesis and, in particular, the origin of the strong texture contrast. Micromorphological study demonstrated that the clay present in void argillans and papules in the B2 horizon accounted for only a small amount of the clay present. Elemental analysis of the whole soil (< 2 mm) and sand, silt and clay fractions showed that there had been considerable weathering of both quartz and microcline, which were the dominant minerals present. Kaolinite is the dominant clay mineral weathering product. Illite appears to be forming from vermiculite in the A horizon. Using zircon as an internal standard, it was shown that elemental losses of SiO2 and reductions in weight and volume were similar in A and B horizons. Losses of aluminium and potassium were greatest in the A horizon, least in the B3. There has been an absolute increase in the amount of iron. A possible source is iron from heavy mineral bands upslope. It was concluded from the similarity of the quartz particle-size distributions of the A2, B2 and B3 horizons that the intensity of weathering of quartz was the same in A and B horizons. In the case of feldspar (mostly microcline), there is a greater proportion of feldspar in the fine sand and silt fractions of the A2 horizon than in the B horizon. Weathering of feldspar is greatest in the A horizon. The texture profile is principally a function of greater lateral loss of clay from the A horizons compared to the B horizons.  相似文献   

11.
The aim of the study was to elucidate the spatial distribution of soil microorganisms and enyzme activities in a long‐term wastewater treated soil. Soil was sampled from a plough layer of the Ah horizon of a sandy Haplic Luvisol which was either (1) irrigated with municipal wastewater for almost 100 years, or (2) no more irrigated since 20 years, or (3) never received wastewater. The samples were fractionated by wet sieving to obtain seven size fractions of organic and mineral soil particles, and a separate silt+clay fraction. The individual soil samples contained between 1.2% (never irrigated) and 4.1% (long‐term irrigated) organic particles by weight, but these particles harboured up to 47.8% of the total soil carbon and 41.7% of nitrogen, and thus represented an important storage of energy and nutrient for microorganisms. In total, however, the highest C and N amounts were accumulated in the silt+clay fraction, whereas coarser mineral particles which dominanted by weight in the Haplic Luvisol were low in C and N. The highest numbers of bacteria, actinomycetes and fungi per gram of the individual soil fractions were found in organic particles of the long‐term irrigated soil. Less nutrient‐dependent oligotrophic bacteria were for the most part associated with the silt+clay fraction, irrespective of the soil treatment with wastewater. Similar to microbial counts, also the ATP content, as a measure of active microbial biomass, and the activities of β‐glucosidase, β‐acetylglucosaminidase, and proteinase were higher in the long‐term irrigated soil than in that which was never irrigated. In most cases slightly enhanced values of microbiological and biochemical parameters were still detectable 20 years after the wastewater irrigation was terminated. The values of the individual parameters decreased in all soil samples under testing in general gradually with decrease in size of the organic soil particles. In conclusion, the coarse soil organic particles > 5 mm and the silt+clay fraction < 0.05 mm represent the sites with the highest microbial inhabitance, ATP contents and enzyme activities in the Ah horizon of an Haplic Luvisol. Long‐term wastewater irrigation resulted in an increase of microbial counts, total biomass and soil enzyme activities.  相似文献   

12.
The micromorphology of eluvial and glossic areas with weak soi1, strength from the upper fragipan, and the upper parts of grey polygonal zones, in some argillic brown earths (Glossic Fragiudalfs) from north-east England shows unstable void walls stripped of clay with remnants of ferri-argillans, pale grey grainy clay coatings and darker grainy coatings. These occur alongside loose surface residues of skeleton grains and thin grey fine silt coatings of quartz and muscovite. SEM and EDAX studies of coating surfaces, and optical microscopy, SEM and EDXRA of very thin polished sections, show that some grainy clay coatings form as alteration rims of ferri-argillans through localized waterlogging, iron oxide loss and micro-erosion leading to micropitting and disoriented fabrics. The inclusion of coarse clay to fine silt-sized quartz, feldspar and muscovite in other grainy coatings suggests either alteration of impure ferri-argillans or accumulation of degradational products derived from elsewhere on void walls. This is more certainly the case for dark grainy coatings in layered compound illuviation coatings adjacent to glossic areas. These fragipans are degrading from the top downwards by processes which are partly a consequence of the effects that the fragipan has on water percolation and root penetration. The destabilization of void walls, the degradation of ferri-argillans and the remobilization of clay to form glossic features did not begin until seasonal waterlogging in parts of the upper pan was sufficient to mobilize iron.  相似文献   

13.
At about 1000 m above sea level in the Vallombrosa Forest, northern Apennines, Central Italy, a dense pan that meets the diagnostic criteria for fragipans is discontinuously distributed. The unusual slope-parallel “digitate” distribution of the pan suggests that it could have formed on water-saturated soil material that moved as earthflows. Actually, several soils in the Vallombrosa Forest have buried or truncated horizons, indicating episodes of mass movement and deposition. However, the fragipan under study shows a homogeneous morphology throughout, hence not providing clues about the occurrence of episodes that have contributed to the emplacement of the parent material. Also, the physical, chemical, and mineralogical analyses of the fragipan do not reveal discontinuities that help to resolve distinct episodes of deposition. Nevertheless, discontinuities in features such as the degree of alteration of biotite grains and the amount of plasma, seen through the micromorphological investigation at 50–60 cm of the current depth, suggest the occurrence of at least two depositional events. Radiocarbon dating of large-size pieces of charcoal collected at three depths within the fragipan yielded three ages that may reflect different times of accumulation of the parent material during the last glacial period. Post-depositional micromorphological features, such as relatively undamaged clay coatings and a weak platy structure, indicate pedogenesis with the absence of intense pedoturbation.  相似文献   

14.
Visible near-infrared (vis-NIR) and portable X-ray fluorescence (pXRF) spectrometers have been increasingly utilized for predicting soil properties worldwide. However, only a few studies have focused on splitting the predictive models by horizons to evaluate prediction performance and systematically compare prediction performance for A, B, and combined A+B horizons. Therefore, we investigated the performance of pXRF and vis-NIR spectra, as individual or combined, for predicting the clay, silt, sand, total carbon (TC), and pH of soils developed in loess, and compared their prediction performance for A, B, and A+B horizons. Soil samples (176 in A horizon and 172 in B horizon) were taken from Mollisols and Alfisols in 136 pedons in Wisconsin, USA and analyzed for clay, silt, sand, pH, and TC. The pXRF and vis-NIR spectrometers were used to measure the pXRF and vis-NIR soil spectra. Data were separated into calibration (n=244, 70%) and validation (n=104, 30%) datasets. The Savitzky-Golay filter was applied to preprocess the pXRF and vis-NIR spectra, and the first 10 principal components (PCs) were selected through principal component analysis (PCA). Five types of predictor, i.e., PCs from vis-NIR spectra, pXRF of beams at 0-40 and 0-10 keV (XRF40 and XRF10, respectively) spectra, combined XRF40 and XRF10 (XRF40+XRF10) spectra, and combined XRF40, XRF10, and vis-NIR (XRF40+XRF10+vis-NIR) spectra, were compared for predicting soil properties using a machine learning algorithm (Cubist model). A multiple linear regression (MLR) model was applied to predict clay, silt, sand, pH, and TC using pXRF elements. The results suggested that pXRF spectra had better prediction performance for clay, silt, and sand, whereas vis-NIR spectra produced better TC and pH predictions. The best prediction performance for sand (R2=0.97), silt (R2=0.95), and clay (R2=0.84) was achieved using vis-NIR+XRF40+XRF10 spectra in B horizon, whereas the best prediction performance for TC (R2=0.93) and pH (R2=0.79) was achieved using vis-NIR+XRF40+XRF10 spectra in A+B horizon. For all soil properties, the best MLR model had a lower prediction accuracy than the Cubist model. It was concluded that pXRF and vis-NIR spectra can be successfully applied for predicting clay, silt, sand, pH, and TC with high accuracy for soils developed in loess, and that spectral models should be developed for different horizons to achieve high prediction accuracy.  相似文献   

15.
Data on the mineralogical composition of clay (<1 μm), fine silt (1–5 μm), medium silt (5–10 μm), and coarser (>10 μm) fractions of meadow solonchakous solonetzes (Calcic Gypsic Salic Stagnic Solonetz (Albic, Siltic, Columnic, Cutanic, Differentic)) developing from loesslike loam and clay in the North Crimean Lowland are presented. Fractions >5 μm constitute nearly 50% of the soil mass and are characterized by the same mineralogical composition in the entire profile; they consist of quartz, plagioclases, potassium feldspars, and micas (biotite and muscovite). The eluvial-illuvial redistribution of clay in the course of solonetzic process is accompanied by changes in the portion of mixed-layer minerals and hydromicas in the upper part of the profile; a larger part of the smectitic phase is transformed into the superdisperse state. In the eluvial SEL horizon and in the illuvial BSN horizon, the clay fraction is impoverished in smectitic phase and enriched in trioctahedral hydromicas. Upon calculation of the content of clay minerals per bulk soil mass, the distribution of mixed-layer minerals is either eluvial, or eluvial-illuvial, whereas the distribution of hydromicas has an illuvial pattern without distinct eluvial minimum in the SEL horizons. The eluvial-illuvial distribution pattern of clay minerals in solonetzes of the North Crimean Lowland is compared with the distribution pattern of clay minerals in solonetzes of the West Siberian Lowland. Coefficients characterizing differentiation of solonetzes by the contents of particular mineral components are suggested.  相似文献   

16.
In the sandy soils of northeast Thailand, root development is generally limited to the topsoil (0–20 cm depth) but a simple slotting intervention (20–40 cm) significantly increased the root frequency in the slotted material (Eslot) compared with the undisturbed subsoil (E horizon). The aim of this study was to investigate the consequences of slotting on the soil structure by analysing at different scales the pore characteristics of the original soil profile and of the soil material inside the slot. These characteristics were studied using bulk density measurements, image analysis of thin sections and mercury porosimetry. Our results showed that the total porosity of the E horizon and Eslot material was similar when measured in 100 cm3 cylinders, but that the pore size distribution had been changed by slotting. The unaltered E horizon contained mainly small pores characterized by a narrow distribution related to close packing of the sand grains, associated with some biological macropores probably with poor continuity as they did not contain roots despite their size. On average, pores were larger in the Eslot material, with a broader distribution resulting from looser packing of the sand grains but with fewer biological macropores. Although slotting reduced the number of biological pores, the looser packing appeared to be more favourable to root development than the presence of macropores in the E horizon. Finally, the comparison of the porosity in the different horizons with the porosity of the Eslot material, indicated the significance of the closeness of the sand packing on root development.  相似文献   

17.
The estimation of pore size distribution from texture, organic matter content and bulk density Using regression analysis the dependence of the pore size distribution of soils on the compactness and percentage of organic matter, clay and silt was studied on 450 soil horizons. From the results nomograms for determination of the pore size distribution were constructed. The average deviation between pore size distribution as read from the nomograms compared and determined in the laboratory is ～ ± 3 Vol.-%.  相似文献   

18.
W. SZYMA&#SKI  M. SKIBA 《土壤圈》2013,23(4):445-454
Iron and manganese oxides are common components of soils. They frequently occur in nodules constituting important soil sorbents and play a crucial role in a number of chemical reactions in the soil environment. In addition, the oxides are very sensitive to environmental changes (moisture, pH, Eh) constituting important indicators of soil-forming processes and water movement in the landscape. The objectives of the study were: i) to examine the distribution and size of Fe-Mn nodules in Albeluvisols containing a fragipan horizon; ii) to determine the morphology and chemical composition of the nodules, and iii) to estimate the effect of the fragipan horizon on water movement within the soil profile. An investigation was carried out on five soil profiles containing a fragipan horizon and classified as Fragic Albeluvisols within the Carpathian Foothills in Poland. In the Albeluvisols studied, the maximum concentration of Fe-Mn nodules occurred in the horizon lying directly on the fragipan horizon. This suggests that the pan acts as a natural barrier restricting water infiltration and leads to the seasonal development of a perched water table promoting redox processes. The most common are coarse (1--0.5 mm) and medium (0.5--0.25 mm) irregular Fe-Mn nodules showing a gradual boundary and undifferentiated internal fabric. Eluvial horizons contained also larger amounts of round and dense nodules with a sharp boundary, suggesting frequent oxidation and reduction. The fragipan horizon contained mainly irregular and soft nodules, suggesting longer saturation with water during the year. Concentrations of trace elements (Cu, Zn) and P were higher within Fe-Mn nodules than in the surrounding soil materials, showing that iron and manganese oxides adsorbed and immobilised these elements.  相似文献   

19.
Periodical forest fires are typical natural events under the environmental and climatic conditions of central and southern Yakutia and Transbaikal region of Russia. Strong surface fires activate exogenous geomorphological processes. As a result, soils with polycyclic profiles are developed in the trans-accumulative landscape positions. These soils are specified by the presence of two–three buried humus horizons with abundant charcoal under the modern humus horizon. This indicates that these soils have been subjected to two–three cycles of zonal pedogenesis during their development. The buried pyrogenic humus horizons accumulate are enriched in humus; nitrogen; total and oxalate-extractable iron; exchangeable bases (Са+2 and Mg+2); and the fractions of coarse silt, physical clay (<0.01 mm), and clay (<0.001 mm) particles in comparison with the neighboring mineral horizons of the soil profile. The humus of buried pyrogenic horizons is characterized by the increased content of humic acids, particularly, those bound with mobile sesquioxides (HA-1) and calcium (HA-2) and by certain changes in the type of humus.  相似文献   

20.
Migration of different mineral particles within columns of soil‐sand mixtures containing 10 or 20 mass % of soil was investigated by establishing differences in the mineral suite between the ”︁bulk clay” and the ”︁mobile fine material” fractions. The ”︁bulk clay” fractions of all soils contained smectite, palygorskite, kaolinite, quartz, feldspar, and calcite. The soils were saturated with sodium by leaching with NaCl solution, and then leached with distilled water. Clay dispersion and particle migration occurred in the columns. Values of SAR (sodium adsorption ratio) of the effluent decreased with time due to carbonate dissolution. At a certain SAR value, the clays apparently formed aggregates, and as a consequence particle migration stopped in the column. In addition to clay‐sized particles (< 2 μm), very‐fine‐silt‐sized particles (2— 5 μm) were able to migrate in the soil‐sand mixtures, too, and to some extent fine‐silt‐sized particles (5—10 μm) as well. Average size of mobile particles decreases with increase of soil content in the soil‐sand mixtures. The mineralogical composition of the ”︁mobile fine material” changed during the experiment. At the beginning of the experiment, the ”︁mobile fine material” was enriched in the non‐phyllosilicates (especially in calcite, and in some cases in quartz, feldspar and dolomite) and contained low concentrations of phyllosilicates (smectite, palygorskite and kaolinite). At the end of the experiment, the proportion of non‐phyllosilicates decreased, and as a consequence, the proportion of phyllosilicates increased. Among the non‐phyllosilicates, calcite was the most mobile mineral. Among the phyllosilicates, palygorskite was preferentially mobilized in topsoil horizons. In subsoil horizons, on the other hand, kaolinite was preferentially mobilized. This difference was explained by the different nature of carbonates in the topsoil and subsoil horizons. Palygorskite is preferentially occluded within the soil carbonates of lacustrine origin over smectite and kaolinite. These carbonates are present mainly in the subsoil horizons. As a consequence, the presence of these carbonates in the subsoil horizons decreases the migration of mainly palygorskite.  相似文献   

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