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1.
Hydroxy-aluminous vermiculites have been identified in samples of soils and weathering products from the Armorican Massif of France by a combination of mineralogic, microanalytic and thermodynamic techniques.The hydroxy-aluminous vermiculites behave originally as intergrades between vermiculites sensu stricto and chlorites. The interlayered aluminum responsible for the intergrade behaviour cannot be removed by means of ammonia oxalate but can be by sodium citrate. After such a treatment the mineral loses its intergrade behaviour and acquires the behaviour of sensu stricto vermiculite. The extracting solution contains 12 mg of aluminum per gramme of clay in the studied sample.Further evidence on the nature of the aluminous vermiculites follows from microanalysis in situ. Such in situ quantitative microanalysis makes it possible to establish the structural formulae of minerals. This technique has been applied to weathering products of micas. The data obtained indicate that these weathering products are vermiculites and that one part of the aluminum must be in interlayer positions.The thermodynamic study of equilibrium between waters and aluminous vermiculites needs to be set in a multidimensional space Rn. In such space the chemical composition of a water is represented by one point. Waters in equilibrium with a given mineral are situated in a (n ? 1) dimension hyperplan. For a given population of waters and minerals a program can calculate water-hyperplan distances. The use of this program shows that one part of the examined waters is compatible with the equilibrium with aluminous vermiculites.  相似文献   

2.
Abstract

The effect of sesquioxides on the mechanisms of chemical reactions that govern the transformation between exchangeable potassium (Kex) and non‐exchangeable K (Knex) was studied on acid tropical soils from Colombia: Caribia with predominantly 2∶1 clay minerals and High Terrace with predominantly 1∶1 clay minerals and sesquioxides. Illite and vermiculite are the main clay minerals in Caribia followed by kaolinite, gibbsite, and plagioclase, and kaolinite is the major clay mineral in High Terrace followed by hydroxyl‐Al interlayered vermiculite, quartz, and pyrophyllite. The soils have 1.8 and 0.5% of K2O, respectively. They were used either untreated or prepared by adding AlCl3 and NaOH, which produced aluminum hydroxide. The soils were percolated continuously with 10 mM NH4OAc at pH 7.0 and 10 mM CaCl2 at pH 5.8 for 120 h at 6 mL h?1 to examine the release of Kex and Knex. In the untreated soils, NH4 + and Ca2+ released the same amounts of Kex from Caribia, whereas NH4 + released about twice as much Kex as Ca2+ from High Terrace. This study proposes that the small ionic size of NH4 + (0.54 nm) enables it to enter more easily into the K sites at the broken edges of the kaolinite where Ca2+ (0.96 nm) cannot have access. As expected for a soil dominated by 2∶1 clay minerals, Ca2+ caused Knex to be released from Caribia with no release by NH4 +. No Knex was released by either ion from High Terrace. After treatment with aluminum hydroxide, K release from the exchangeable fraction was reduced in Caribia due to the blocking of the exchange sites but release of Knex was not affected. The treatment increased the amount of Kex released from the High Terrace soil and the release of Knex remained negligible although with Ca2+ the distinction between Kex and Knex was unclear. The increase in Kex was attributed to the initially acidic conditions produced by adding AlCl3 which may have dissolved interlayered aluminum hydroxide from the vermiculite present, thus exposing trapped K as exchangeable K. The subsequent precipitation of aluminum hydroxide when NaOH was added did not interfere with the release of this K, and so was probably formed mostly on the surface of the dominant kaolinite. Measurement of availability of K by standard methods using NH4 salts could result in overestimates in High Terrace and this may be a more general shortcoming of the methods in kaolinitic soils.  相似文献   

3.
Purpose

Several interactions between Al and the solid phase of soil influence Al buffering in soil solution. This work evaluated soils cultivated with Pinus taeda L. to determine Al forms in organic and mineral horizons using various extraction methods and to relate acidity with clay mineralogy.

Materials and methods

Organic and mineral horizons of 10 soil profiles (up to 2.1 m deep) in southern Brazil were sampled. Organic horizons were separated into fresh, aged, and fermented/humified litter. The following Al extraction methods were utilized: 0.5 mol L?1 pH 2.8 CuCl2–Al complexed in organic matter; 1.0 mol L?1 KCl–exchangeable Al; water–Al soluble in soil solution; HF concentrated?+?HNO3 concentrated?+?H2O2 30% (v/v)–total Al. Six sequential extractions were carried out to isolate different forms of amorphous minerals that can buffer Al on soil solution: 0.05 and 0.1 mol L?1 sodium pyrophosphate; 0.1 and 0.2 mol L?1 ammonium oxalate; 0.25 and 0.5 mol L?1 NaOH. Samples of clay were also analyzed by XRD.

Results and discussion

There was a clear effect of litter age on increasing total Al concentration. In the aged litter and fermented and/or humified litter, levels of total Al were 1.4 to 3.8 and 1.5 to 7.8 times greater than in fresh litter, respectively. The CuCl2 method had higher Al extraction capacity than the KCl method for litter. The lowest Al–pyrophosphate values were observed in the Oxisol, which also had a predominance of gibbsite and the lowest levels of Al–KCl and Al–CuCl2. There was an inverse relationship between degree of soil weathering and soluble and exchangeable Al in soils. Available Al increased with higher Si proportion in minerals of the clay fraction (2:1?>?1:1?>?0:1).

Conclusions

The worst scenario was soils with the combination of high soluble and exchangeable Al levels and high concentrations of amorphous forms of Al minerals. The best predictors of Al accumulation in the youngest litter horizon were extractions of amorphous minerals with pyrophosphate and NaOH. These extractors are normally used to predict the level of Al buffering in soils. Organic matter had less influence on Al dynamics in soils.

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4.
A weathering sequence with soils developing on volcanic, trachy-basaltic parent materials with ages ranging from 100–115,000 years in the Etna region served as the basis to analyse and calculate the accumulation and stabilisation mechanisms of soil organic matter (SOM), the transformation of pedogenic Fe and Al, the formation and transformation of clay minerals, the weathering indices and, by means of mass-balance calculations, net losses of the main elements. Although the soils were influenced by ash depositions during their development and the soil on the oldest lava flow developed to a great extent under a different climate, leaching of elements and mineral formation and transformation could still be measured. Leaching of major base cations coupled with a corresponding passive enrichment of Al or Fe was a main weathering mechanism and was especially pronounced in the early stages of soil formation due to mineral or glass weathering. With time, the weathering indexes (such as the (K + Ca)/Ti ratio) tend to an asymptotic value: chemical and mineralogical changes between 15,000 and 115,000 years in the A and B horizons were small. In contrast to this, the accumulation of newly formed ITM (imogolite type materials) and ferrihydrite showed a rather linear behaviour with time. Weathering consisted of the dissolution of primary minerals such as plagioclase, pyroxenes or olivine, the breakdown of volcanic glass and the formation of secondary minerals such as ITM and ferrihydrite. The main mineral transformations were volcanic glass ? imogolite ? kaolinite (clay fraction). In the most weathered horizons a very small amount of 2:1 clay minerals could be found that were probably liberated from the inner part of volcanic glass debris. The rate of formation and transformation of 2:1 clay minerals in the investigated soils was very low; no major changes could be observed even after 115,000 years of soil evolution. This can be explained by the addition of ash and the too low precipitation rates. In general, soil erosion played a subordinate role, except possibly for the oldest soils (115,000 years). The youngest soils with an age < 2000 years had the highest accumulation rate of organic C (about 3.0 g C/m2/year). After about 15,000 years, the accumulation rate of organic C in the soils tended to zero. Soil organic carbon reached an asymptotic value with abundances close to 20 kg/m2 after about 20,000 years. In general, the preservation and stabilisation of SOM were due to poorly crystalline Al- and Fe-phases (pyrophosphate-extractable), kaolinite and the clay content. These parameters correlated well with the organic C. Imogolite-type material did not contribute significantly to the stabilisation of soil organic matter.  相似文献   

5.
The OAh and Ah horizons of acid brown and podzolic forest soils are reported to fix more radiocaesium than the mineral B horizons beneath them. We determined the respective influence of organic matter and clay minerals on the magnitude of Cs+ retention in a strongly acid brown forest soil in Belgium. The soil contained mica throughout the profile. Vermiculite was identified in the OAh and Ah horizons, and hydroxy interlayered vermiculite (HIV) in the Bw horizon. The OAh and Ah clay fraction retained much more Cs+ than the Bw horizon. The extraction of Al interlayers by Na-citrate resulted in a marked increase in Cs+ fixation in the Bw clays as well as the collapse of the vermiculitic layers after K+ saturation. Organic matter had a strong but indirect effect on Cs+ fixation. In the Bw horizon, acid weathering of layer silicates releases free Al and produces HIV minerals in which Al polymers block the access of radiocaesium onto Cs+-specific sites. In OAh and Ah horizons, free Al is complexed by organic acids. Consequently, the interlayer specific sites remain accessible for Cs+ fixation.  相似文献   

6.
This paper is a review of some advances in the studies on 1.4-nm intergrade mineral of soils in subtropical China. 1)1.4-nm intergrade mineral occurs ubiquitously in soils of subtropical China. The 1.4-nm mineral in red soil and yellow soil is mainly 1.4-nm intergrade mineral, and in acidic yellow-brown soil (pH < 5.5) is vermiculite alone or 1.4-nm intergrade mineral together with vermiculite. The distribution and the content of 1.4-nm intergrade mineral in the mountain soils are more widespread and higher than those of the corresponding soils in horizontal zone. 2) The interlayer material of 1.4-nm intergrade mineral in these soils appears to be hydroxy-A1 polymers instead of hydroxy-Fe, proto-imogolite or kaolin-like material. There is a significant positive correlation between A1 amount extracted from the soil with sodium citrate after DCB extraction and pH value of the citrate solution after the extraction. The citrate can also extract a certain amount of silicon from the soil, but the silicon may not come from interlayer of 1.4-nm intergrade mineral. 3) It was seldom studied that either vermiculite or smectite did the natural 1.4-nm intergrade mineral come from in soil, or it was commonly thought to come from vermiculite. A recent report has revealed that it can come from smectite. There are some different behaviors between the 1.4-nm intergrade mineral derived from vermiculite and that from smectite. For example, they exert different influences on the formation of gibbsite. The 1.4-nm intergrade mineral derived from smectite may promote the formation of gibbsite in the yellow soil. 4) The type of 1.4-nm minerals in soils. i.e., vermiculite or 1.4-nm intergrade mineral, may be significant to soil properties, such as soil acidity, exchangeable Al, electric charge amount and specific surface area. Therefore, the management for the soil in which 1.4-nm mineral is mainly 1.4-nm intergrade mineral or vermiculite should be dealt with differently.  相似文献   

7.
Pig slurry in quantities of 200, 400, 500, 600, 800, and 1000 m3 ha-1 year-1 was added to two calcareous soils, which differed in concentration and type of clay minerals. The soils were cultivated with two successive crops of pepper and tomatoes grown in containers. A control was given no slurry. The soils were analysed after harvesting for exchangeable K+. Differences in exchangeable K+ were studied in relation to the concentration and type of clay minerals. The soil with the higher clay content and of the illite type retained K in the exchangeable form to a much greater extent than the soil with the low clay content. In the soil with the lower clay content, of the interstratified illitic — montmorillonite type, very little K was incorporated into the exchange complex. The exchange capacity being low, the amount of K added had little effect on the level of exchangeable K+.  相似文献   

8.
We have selected seven profiles located in a diapiric formation in the North of Spain. The profiles have been analyzed for the mineralogy and the chemical composition of original materials, soils developed above them and clay fractions. Three soils formed on basic rock of volcanic origin (ophite) and rich in alterable minerals, three others formed on clay marl and one soil formed on gypsiferous marl. Plagioclases, pyroxenes, vermiculites, and biotites are the main minerals found in the soil samples and ophitic rocks. Biotite, smectite, chlorite and interstratified chlorite–vermiculite make up the predominant mineralogical association in the clay fraction of the soils. Calcite, biotite and on top of all chlorite are the main minerals in the marls and the soils developed on them, with gypsum predominant in the gypsiferous marl. The mineralogy of its clay fraction is comprised mainly of chlorite and biotite. The variations in content of Al2O3, TiO2 and Na2O in the ophites are considered to be associated with the differences in the evolution of the pyroxenes. The variability of the chemical composition of the Keuper sediments and the soils is attributed more to the chaotic disposition of the Triassic materials in the formation of the diapir than to intense chemical weathering. The low concentrations of silica, iron, and aluminum extractable with ammonium oxalate indicate the low proportion of non-crystalline products. Fundamentally, it is the semiarid conditions in the study zone, together with the processes of extrusion and hydrothermal activity affecting the formation of the diapir, that are responsible for the genesis of the minerals.  相似文献   

9.
Different types of cation exchange capacity (CEC) and related chemical properties were determined in the main genetic horizons of meadow-chestnut soils in the mesodepressions at the Dzhanybek Research Station of the Institute of Forestry of the Russian Academy of Sciences. In the A horizon, the CEC is mainly due to the organic matter from the clay and coarse fractions, which provides 36% of the soil CEC, and to labile silicates and other clay minerals of the clay fraction. In the Bt horizon, the CEC is mainly provided by the labile minerals of the clay fraction and organic matter of the clay and coarse fractions. The standard soil CEC was found to be significantly higher than the sum of the exchangeable cations in the A horizon and slightly lower than the sum of the exchangeable cations in the Bt and Bca2 horizons. This difference can be related to the fact that the NH4+ ion, which is selectively adsorbed by clay minerals, is used as a displacing cation during the determination of the exchangeable bases, while the Ba2+ ion, which is more selectively adsorbed by organic matter, is used during the determination of the standard CEC. In all the genetic horizons, the experimentally determined value of the standard CEC almost coincides with the CEC value obtained by summing the standard CECs of the different particle-size fractions with account for their contents; hence, this parameter is additive in nature.  相似文献   

10.
对重庆地区水稻土胶膜及基质土壤中某些元素含量情况及相互之间的关系进行了研究。结果表明:胶膜的pH值、有机质含量均明显高于基质土壤,且有机质含量差异极显著(P<0.01);胶膜中全氮、全磷含量高于其基质土壤且差异均达到极显著水平(P<0.01),全钾在胶膜与基质土壤中含量无明显变化,胶膜中铜、锌含量总体上高于其基质土壤,二者间锌含量差异达到显著水平(P<0.05);供试胶膜中全铁含量极显著高于基质土壤(P<0.01),全锰含量无一致性规律,胶膜中全锰含量总体上较基质土壤高,但二者差异不显著(P>0.05);供试胶膜中全磷与全铁含量显著相关(r=0.606*,n=12),具有较好的伴生关系,胶膜中铜与铁、锰含量均极显著相关(r铜铁=0.792**,r铜锰=0.737**;n=12),但铜与锰伴生关系较好,而锌与铁的伴生关系较好。  相似文献   

11.
The study assessed accessory minerals and metals in Tanzanian vermiculites with respect to their potential suitability for agricultural applications. Mineral and chemical analyses were involved. Pot experiments were also conducted to assess plant uptake of metals from soil with vermiculites. Fibrous sepiolite and amphiboles were minerals of health concern found in some samples. The sepiolite fibers had aspect ratios similar to those of asbestos minerals, which cause respiratory disorders and lung cancer when inhaled and thus pose a potential health risk to animals and humans. The amphibole fibers were thicker than 10 μm and are unlikely to be inhaled. Chromium (Cr) and nickel (Ni) concentrations in some samples were greater than the limits permitted in agricultural soils, but the elements are not highly plant available and do not inhibit the uptake of essential macronutrients. Heating vermiculites at 400–600 °C enhanced extractability of Cr and Ni and should preferably be avoided.  相似文献   

12.
Purpose

Clay minerals significantly affect the physical, chemical, and biological processes of soils. They undergo spontaneous modification and transformation depending to the climatic conditions. Information concerning the compositions and transformation of clay minerals in nanoparticle colloids (NPs) (25–100 nm) is severely lacking. Studying clay mineral transformation is important approach to understand soil formation. This study was conducted to determine the transformation sequence of clay minerals in several zonal soil NPs.

Materials and methods

Four soils (Haplustalf, Alf-1; Hapludalf, Alf-2; Hapludults, Ult-1 and Ult-2) were collected from B horizons developed under three different climatic zones of China. Alf-1 (36° 05′ N and 117° 24′ E) was located under a warm temperate zone and Alf-2 (30° 38′ N and 115° 26′ E), Ult-1 (29° 13′ N and 113° 46′ E), and Ult-2 (19° 27′ N and 109° 17′ E) under a subtropical zone. The clay particles (<?2000 nm) (CPs) and nanoparticles (25–100 nm) (NPs) of tested soils were separated. The element composition of CPs and NPs was identified by microwave digestion method. The mineralogy and chemical bonding of clay minerals were studied by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR).

Results and discussion

With decreasing latitude, NPs and CPs showed that the molar ratio of SiO2 to Al2O3 trends to diminish, indicating the phenomenon of desilication and allitization in the tested soils. XRD analysis revealed that the main clay mineral of Alf-1 NPs was illite, followed by vermiculite, kaolinite, and kaolinite interstratified minerals (KIMs). The clay minerals of Alf-2, Ult-1, and Ult-2 NPs were dominated by kaolinite (and KIMs), followed by illite, with a little content of hydroxyl-interlayered vermiculite (HIV) in Ult-1 NPs and trace content of gibbsite in Ult-2 NPs. With decreasing latitude, vermiculite and HIV decreased in NPs. When compared to CPs, smectite as well as illite-vermiculite mix-layer mineral (I-V) and illite-HIV mix-layer mineral (I-HIV) were not detected in NPs. The analysis of d060 region by XRD showed that with decreasing latitude, the main clay minerals in NPs were dioctahedral minerals (e.g., illite or kaolinite). These clay minerals resulted from the transformation of trioctahedral minerals in CPs. The disappearance of 2:1 swelling minerals and trioctahedral minerals showed that the NPs were more susceptible to weathering than CPs.

Conclusions

With decreasing latitude, the transformation of clay minerals followed the sequence of illite?→?HIV?→?kaolinite?→?gibbsite in tested NPs.

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13.
Radiocaesium fixation in soils is reported to occur on frayed edge sites of micaceous minerals. The weathering of mica in acid soils may therefore influence the Cs+ fixation process and thereby the mobility of the radiopollutant. We produced a laboratory weathering model biotite → trioctahedral vermiculite → oxidized vermiculite → hydroxy interlayered vermiculite (HIV) and quantified the Cs+ fixation of each mineral both in a fixed K+–Ca2+ background and in acid conditions. The transformation process was achieved through K depletion by Na-tetraphenylboron, oxidation with Br2 and Al-intercalation using NaOH and AlCl3. In a constant K+–Ca2+ background, vermiculite fixed 92–95% of the initial 137Cs+ contamination while biotite and HIV fixed only 18–33%. In acid conditions, the interlayer occupancy by either potassium (biotite) or hydroxy-Al groups (HIV) strongly limited Cs+ fixation to 1–4% of the initial 137Cs+ contamination. Cs+ fixation occurred on vermiculitic sites associated with micaceous wedge zones. Though both oxidized and trioctahedral vermiculites fixed similar Cs+ amounts in a constant K+–Ca2+ background (92–95%), the oxidized vermiculite retained much more radiocaesium in acid conditions (78–84% against 54–59%), because of its dioctahedral character.  相似文献   

14.
Availability of applied potassium (K) as a fertilizer to plants is influenced by soil mineralogy, environmental factors, and rates of K application. The objective of this research was to study the effects of clay minerals and K application on K supply characteristics of calcareous soils in Iran. Surface and subsurface horizons of six sites with different ranges of clay content and exchangeable K were selected. The soils were treated with potassium chloride (KCl) solution with different K concentrations. Four wet–dry cycles were sequentially applied. Illites, vermiculites, and chlorites were present in all soils. Smectites were present in larger amounts in one soil. The increase in soluble and exchangeable K was expressed by linear equations in which the slops influenced by the dominant clay minerals. Potassium fixation was much higher in soils with more illites and vermiculites. Results revealed that different forms of K were affected by the dominant clay minerals but were independent from the rate of applied K.  相似文献   

15.
Experiments were conducted with two typical paddy soils from China and a vermiculite to study the influence of iron oxides on the fixation and release of ammonium. Removing iron oxides, especially amorphous iron oxides, from the soils favoured the release of non-exchangeable NH4-N and stimulated the fixation of NH4-N in the presence of added (NH4)2SO4. Addition of artificial goethite and hematite to the original soils or to the soils free of iron oxides reduced the fixation of NH4+-ions. This effect was also observed with vermiculite. We conclude that the coating of clay minerals with iron oxides has an impact on the diffusion of NH4+-ions into and out of the interlayers of the clay minerals. The reduction and dissolution of iron oxides induced by low redox potential (Eh) after flooding of paddy soils is assumed to be an important mechanism controlling NH4+-fixation in paddy fields.  相似文献   

16.
The role of the mineralogy of the clay fraction and the physicochemical properties of alluvial soils in the floodplain of the Iput River and its tributary the Buldynka River (in the region of the settlement of Starye Bobovichi in Bryansk oblast) in the distribution and immobilization of radioactive isotope 137Cs from the atmospheric fallout after the Chernobyl accident was studied. The soils had a sandy texture; a significant variation in the content of amorphous iron oxides (0.1–0.77%) and labile manganese (11.2–193 mg/kg), the cation exchange capacity (6.1–54.2 meq/100 g soil), and the base saturation (29–100%) was common; an appreciable content of X-ray amorphous mineral substances in the clay fraction (<1 μm) enriched with organic carbon (7.7–13.1%); the predominance of trioctahedral hydromicas (Me=50%) in the clay fraction; and the presence of fine-disperse quartz and lepidocrocite. The specific activity of the 137Cs in the clay fraction of the moderately and strongly contaminated layers increased with the increasing portion of smectite formations and (or) hydromicas. On the whole, the presence of the clay fraction favored a decrease in the 137Cs mobility (the correlation between its content and that of exchangeable cesium was r=?0.608, n=17). However, the portion of exchangeable radiocesium (extracted with 1 M CH3COONH4, 1:10) had a tendency toward an increase with increasing content of hydromicas in the clay fraction. Thus, the minerals of this group were a potential source of exchangeable 137Cs in the soils. The significant role of amorphous and mobile iron forms in the immobilization and migration of radiocesium in the secondary contaminated horizons of the alluvial soils was revealed.  相似文献   

17.
Weathering of soil minerals under forest seems to depend on the species present. To study the influence of tree species we placed unweathered vermiculites in the soil and assessed the impact in terms of saturation index of earth‐alkaline cations and cation exchange capacity in 64 forest stands, dominated by different species and growing side by side at 20 sites on acidic soils. The vermiculites were of two types, one with a large charge and the other with a small charge. Minerals were maintained in the soil for 1 and 3 years. The minerals placed in the topsoil and in soils with low buffering capacity were more acidified and weathered than those deeper in the soil and in less acid conditions. The vermiculites were transformed into hydroxylated interlayered vermiculites, and the formation of hydroxides in the interlayer space decreased the vermiculites' cation exchange capacities. The high‐charge vermiculite had a greater affinity for aluminium than the low‐charge variety. The effect of tree species was significant but small compared with factors such as soil type, depth and duration of incubation. Nevertheless, we can rank the acidifying and weathering caused by the trees in the following order: Picea abies, Abies alba > Pinus sylvestris, Pseudotsuga menziesii > Quercus spp., Fagus sylvatica. This in situ experimental approach enabled us to study potential trends in pedogenesis in few years.  相似文献   

18.
The permeability of glacial till soils having mainly montmorillonite in the clay fraction was negligible when the exchangeable sodium percentage (ESP) exceeded 15 to 20. Relatively higher permeability values were obtained in soils containing gypsum, but water transmission through such soils was negligible above ESP of 30 to 35. The relative decrease in permeability with increase in exchangeable sodium depends not only on the ESP and electrolyte concentration in the soil solution but is affected by the types of clay minerals.  相似文献   

19.
The transformation of hydroxy-interlayered vermiculite (HIV) to vermiculite in humid temperate soils may involve the gradual alteration of illitic minerals. However, it is difficult to detect such minor and progressive changes using conventional methods. We measured the amount of the frayed edge site (i.e. the weathering front of illitic minerals) in soil clays using Radiocaesium Interception Potential (RIP) methodology, and elucidated the effect of hydroxy-Al polymers on the frayed edge site that may be occluded within HIV structures in the acidic soils of southwestern Japan. X-ray diffraction patterns showed the progressive transformation of HIV to vermiculite, or further, to smectite in soil clays located in upper horizons and therefore subjected to more intensive podzolization. In this process, the amount of hydroxy-Al polymers (represented by hot-citrate Al) gradually decreased, while the vermiculitic charges increased (represented by Cs-fixing capacity). However, the amount of the frayed edge site (represented by the RIP) firstly increased but then reversed and decreased in the upper layers of podzolic soils. After hot-citrate extraction to remove the hydroxy-Al polymers from HIV, the amount of the frayed edge site increased in HIV-dominated clays, whereas there was a negligible increase in vermiculitic- or smectitic-clays, thus indicating the blockage effect of hydroxy-Al polymers on the frayed edge site. The sequential increase followed by the decrease that we documented in the amount of the frayed edge site along with the HIV-vermiculite-smectite transformation, suggested that the weathering front of illitic minerals was exposed as the HIV layers lose hydroxy-Al polymers. Thereafter, the charges in the exposed frayed edge site might decline under the very acidic conditions of the upper layers of podzolic soils.  相似文献   

20.
Soil erosion has serious off-site impacts caused by increased mobilization of sediment and delivery to water bodies causing siltation and pollution. To evaluate factors influencing soil erodibility at a proposed dam site, 21 soil samples collected were characterized. The soils were analyzed for soil organic carbon (SOC), exchangeable bases, exchangeable acidity, pH, electrical conductivities, mean weight diameter and soil particles’ size distribution. Cation exchange capacity, exchangeable sodium percentage, sodium adsorption ratio, dispersion ratio (DR), clay flocculation index (CFI), clay dispersion ratio (CDR) and Ca:Mg ratio were then calculated. Soil erodibility (K-factor) estimates were determined using SOC content and surface soil properties. Soil loss rates by splashing were determined under rainfall simulations at 360?mmh?1 rainfall intensity. Soil loss was correlated to the measured chemical and physical soil properties. There were variations in soil form properties and erodibility indices showing influence on soil loss. The average soil erodibility and SOC values were 0.0734?t?MJ?1?mm?1 and 0.81%, respectively. SOC decreased with depth and soil loss increased with a decrease in SOC content. SOC significantly influenced soil loss, CDR, CFI and DR (P??1. Addition of organic matter stabilize the soils against erosion.  相似文献   

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