Short‐time clay‐mineral evolution in a soil chronosequence in Oléron Island (France)

Major weathering sequences in soils are well established; however, knowledge on rates of mineral transformations remains unknown, because it is often difficult to date precisely soil processes. This work was carried out on soils developed on recent (< 188 y) sand dunes on the W coast of Oléron Island (France). The coast has been protected against marine and wind erosion by constructing five consecutives barriers close to the coastline since 1820 (1820, 1864, 1876, 1889, 1948) defining the maximum age of the soil parent material, as before the areas between the barriers were under water. Soils on the older dunes have low clay content (> 94% of sand) and exhibit a bleached E horizon that overlies a yellowish brown B horizon. The process responsible for their formation is podzolization promoted by the high permeability of the material and complexing organic matter produced by coniferous vegetation. Initial mineralogy of C horizons is homogenous and constituted of chlorite, illite, illite/smectite mixed‐layer minerals, and kaolinite, quartz, calcite (≈ 8% related to shell fragments), and feldspars. The initial clay‐mineral assemblage of the E horizons is dominated by illite (well‐crystallized WCI and poorly crystallized PCI) and chlorite. With progressive podzolization, poorly crystallized illite is first transformed to illite/smectite mixed‐layer minerals and in a further step into smectite. In addition, transformation of well‐crystallized illite leads to formation of ordered illite/smectite mixed‐layer minerals in the E horizons, which is not commonly described in soils. In the B horizons, illite/smectite mixed‐layer minerals are present with traces of smectite, as well as Al and Fe oxi‐hydroxides as revealed by DCB and oxalate chemical extractions. This chronosequence illustrates that over short distances and short time (< 188 y) intense mineral weathering and soil development occur. Major clay‐mineral changes occur between 132 and 188 y in agreement with development of the pine forest producing acidic litter.     

Reduction of structural iron in selected iron‐bearing minerals by soybean root exudates grown in an in vitro geoponic system

Research on the reduction of iron (Fe) by plant‐root exudates has been conducted using hydroponic solutions containing Fe salts or chelates. These solutions, however, fail to reflect the true soil environment because plants derive their majority requirement from the solid Fe(III) sources. An in vitro Geoponic system (IVGS) is developed to study the reduction of Fe‐bearing clay minerals, i.e., Upton and SWa‐1 (smectite), and Si‐containing amorphous Fe oxide by soybean‐root exudates. Surface sterilized soybean seeds, [Glycine max (L.) Men.] cv. Williams (marginally susceptible to Fe chlorosis), were germinated in presterilized glass culture tubes containing semi‐solid agar media (sucrose free) and Fe minerals. These tubes were placed in an incubator programmed for a white‐fluorescent light cycle for 16 h and temperature setting of 25±2°C. After 15 d of plant growth, the system was analyzed for Fe²⁺ and total Fe. The amount of structural Fe reduction was 0.012, 0.095 and 0.182 mmol/g for Upton, SWa‐1, and Si‐containing amorphous Fe oxide samples, respectively. The reduction of structural Fe in the Fe containing minerals was likely caused by phenolic root exudates which oxidized to diquinones.     

Bildung schlechtkristalliner bis amorpher Verwitterungsprodukte in stark bis extrem versauerten Waldböden

Formation of poorly crystallized weathering products in strongly to extremely acid forest soils Poorly crystallized weathering products, formed as a consequence of wide-spread extrem acidification and silicate weathering in forest soils, were examined using X-ray diffraction (XRD) and fluorescence (XRF), scanning electron microscopy (SEM, EDXRA) and chemical analyses. The investigations were carried out on five extremely acid forest soils (different Luvisols, a Gleyic Luvisol and a Luvic Podzol) derived from different parent materials (loess, sand loess, glacial sands/loam) in Northrhine Westfalia and Schleswig-Holstein. The results reveal an intense destruction of clay minerals and other silicates in the extremely acid topsoils leading to an accumulation of poorly crystallized to amorphous compounds. These weathering products occur predominantly as silicic coatings on the surface of soil aggregates or as small spherical precipitates on mineral surfaces. Besides Si they contain small amounts of Al and Fe.     

Differential weathering of granitic stocks and landscape effects in a Mediterranean climate,Southern Iberian Massif (Spain)

Mineralogical and structural features control the weathering processes and landform development of two different crystalline stocks in the Iberian Massif, Spain (the Santa Elena and Linares stocks). The Santa Elena stock shows irregular saprolite profiles and boulder landforms whereas the Linares stock develops broad and plain landscapes with uniform saprolites and less boulder forms. The Santa Elena stock is more closely jointed and fractured than the Linares body. The main secondary minerals are kaolinite, and illite; illite/smectite interstratification was only observed in deep samples from the Linares profile. The Linares profile is feldspar-enriched whereas in Santa Elena plagioclase is almost absent and clay mineral content, especially kaolinite, is higher. Feldspars show dissolution channels developed along cleavage planes filled by clay minerals. Biotite–kaolinite intergrowths have fanned-out textures of epitaxial disposition. Weathered materials are enriched in Al and H₂O and Fe, and depleted in Ca, Na, Mg, Ti, P. The Santa Elena weathered materials are richer in H₂O than those from Linares and have lower Si/Al ratios. Mineralogical and geochemical evidence indicate the Santa Elena materials are more intensely weathered. High fracturation and high Ca-richer plagioclase contents are key factors producing the pervasive Santa Elena stock weathering. Fluvial erosion removed the alteration products in incised tectonically controlled streams resulting in boulder accumulation.     

四种常规方法提取伊利石有效钾的机制比较

采用化学分析、X射线衍射、中红外光声光谱以及原子力显微镜的方法,比较了0.2 mol L~(-1)四苯硼钠法、1 mol L~(-1)沸硝酸法、2 mol L~(-1)冷硝酸法和2 mol L~(-1)热盐酸法浸提伊利石中有效钾的机制。结果表明,四苯硼钠法浸提时,伊利石中钾素释放量达到全钾量的59.5%,且基本均通过层间交换反应予以释放,结构离子铁、铝和硅释放量极低;采用三种酸溶液浸提时,其钾素释放量仅占全钾量的1.53%~2.46%,通过层间交换反应释放的钾量占释放量的比例为88.4%~94.0%。四苯硼钠浸提时伊利石层间距扩大,产生次生过渡矿物,并形成富硅表层,但在伊利石表面无溶蚀特征;三种酸溶液浸提时伊利石结构无改变,但其结晶度降低,且表面有明显的溶蚀特征。因此,土壤矿物层间钾是作物可利用有效钾的主要来源,三种酸溶液浸提方法一方面低估了有效钾容量,另一方面提取了一部分不能为植物所利用的结构态钾,不适宜于用来评价伊利石及土壤有效钾库容量。     

紫云英与化肥减施对土壤颗粒中黏粒矿物组成与转化的影响

为了探讨紫云英与不同比例化肥减施下,土壤纳米颗粒中黏粒矿物的组成与转化,以湖南省南县长期紫云英还田(MV)与100%、80%、60% 和40%(F100、F80、F60和F40)4个比例化肥配施的长期定位试验为对象,将土壤分为4个粒级(>2 000、2 000 ~ 450、450 ~ 100、100 ~ 25 nm)的颗粒,研究黏粒矿物在不同粒级颗粒中的分布特征和转化规律。结果表明,①土壤颗粒由>2 000 nm减小至100 ~ 25 nm,2 000 ~ 450和450 ~ 100 nm颗粒中伊利石的相对含量降低8% ~ 11%,100 ~ 25 nm颗粒中1.4 nm过渡矿物和蛭石极少甚至消失,游离铁和非晶质氧化铁的含量增加,在100~ 25 nm颗粒中最高。②紫云英与化肥减施下,化肥配施量80% 前后矿物的转化出现明显差异。化肥从100% 降至80%,高岭石的相对含量增加,增幅为14.1% ~ 51.2%,而伊利石的相对含量降低,降幅为3.6% ~ 11.7%;继续降低化肥配施量,高岭石的相对含量却降低,降幅为13.7% ~ 28.8%,而伊利石的相对含量增加,增幅为2.6% ~ 18.5%。③紫云英还田下随着化肥配施量的降低,游离铁的含量无明显变化规律,而非晶质铁的含量在所有粒径中均先显著提高后降低,在MV+F80处理100~ 25 nm颗粒中达到最高为9.45 g/kg。综上,紫云英配施减量化肥与土壤颗粒中高岭石、伊利石和非晶质铁转化有明显关系,以化肥减施20% 处理影响效果最显著。     

Dispersion and migration of fine particles in two palygorskite‐containing soils of the Jordan Valley

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.     

Decomposition of clay minerals in model experiments and in soils: Possible mechanisms, rates, and diagnostics (analysis of literature)

The analysis of model experiments on the dissolution of clay minerals showed that, beginning from a certain moment, this process reaches a steady state and proceeds at a constant rate. The minimum dissolution rate was observed in a neutral environment, where this value varied in the range from n × 10^?14-n × 10^?12 mol/(m² s). Under acidic and alkaline conditions, this value increased to n × 10^?12 or n × 10^?10 mol/(m²s) for most clay minerals. The first stage of the dissolution mechanism involved the formation of protonated (in an acidic environment) and deprotonated (in an alkaline environment) complexes, which destabilized and polarized metal-oxygen (or metal-hydroxyl) bonds in the crystal lattice. At the second stage, the rupture of Si-O and Al-O bonds and the release of these components into the solution occurred at a specific concentration of these complexes, and this stage largely controlled the dissolution rate of the mineral. The presence of organic ligands forming mononuclear polydentate complexes on the surface of the mineral particles at the same solution pH increased the dissolution rate of the minerals by several times and sometimes by an order of magnitude proportionally to the concentration of these complexes on the surface of the particles. It was found that the dissolution rates of kaolinite, illite, and smectite in the podzolic horizon of loamy podzolic soil calculated from the losses of clay minerals in the soil profile with consideration for the soil age exceeded the corresponding values obtained in model laboratory experiments at the same pH values by several orders of magnitude. The revealed differences could be related to the long-term functioning of biota in native soils and the existing uncertainties in the assessment of the active surface of mineral particles.     

南京地区水稻土中固定态铵与伊利石的相关性

本文以南京地区长城岗和泉水两个水稻土剖面为研究对象,在利用Silva-Bremner法测定土壤全样和3个粒级(黏粒、粉粒和细砂粒)的固定态铵含量、利用X-射线衍射仪测定矿物成分的基础上,讨论了固定态铵含量与粒级以及矿物种类的关系.结果认为,两个剖面在以下几个方面具有共性:①在黏粒、粉粒和细砂粒3个粒级中,黏粘粒含量与固定态铵含量的关系最为密切,相关系数分别为0.68和0.64;②在黏粒中的伊利石、高岭石和蒙脱石3种主要矿物中,伊利石含量与固定态铵含量相关性最好,相关系数分别为0.50和0.49;⑨对于全样来说,其中的伊利石含量与同定态铵含量呈极显著正相关,相关系数分别为0.68和0.66.这些数据充分说明,伊利石是南京地区水稻土中固定态铵赋存的最主要载体.     

Resistance of mineral soils to Fe(III) reduction

Gleying and enhancement of hydromorphism in wetland soils due to Fe(III) reduction entail a series of degradation processes. The resistance of wetlands to degradation can be calculated from the content of potentially reducible iron, Fe(III)_pr, which is found from the van Bodegom equation taking into account the contents of oxalate-soluble iron Fe_ox and dithionite-soluble iron Fe_dit in the soil. In addition, this makes it possible to distinguish relict and actual gleysols. The van Bodegom equation is applicable to soils from which the oxalate solution extracts only amorphous and poorly crystallized iron compounds, which are quickly reduced by Fe-reducing bacteria. These soils have a low proportion of Fe(II) (no more that 15% of the total iron), as well as an accumulative profile distribution of Fe_ox. The van Bodegom equation is unsuitable for calculating the Fe(III)_pr content in soils with a high proportion of Fe(II) and a nonaccumulative profile distribution of Fe_ox.     

Iron Mobilization and Mineralogical Alterations Induced by Iron-Deficient Cucumber Plants (Cucumis sativus L.) in a Calcareous Soil

Dicotyledons cope with ion (Fe) shortage by releasing low-molecular-weight organic compounds into the rhizosphere to mobilize Fe through reduction and complexation mechanisms. The effects induced by these root exudates on soil mineralogy and the connections between Fe mobilization and mineral weathering processes have not been completely clarified. In a batch experiment, we tested two different kinds of organic compounds commonly exuded by Fe-deficient plants, i.e., three organic acids (citrate, malate, and oxalate) and three flavonoids (rutin, quercetin, and genistein), alone or in combination, for their ability to mobilize Fe from a calcareous soil and modify its mineralogy. The effect of root exudates on soil mineralogy was assessed in vivo by cultivating Fe-deficient and Fe-sufficient cucumber plants (Cucumis sativus L.) in a RHIZOtest device. Mineralogical analyses were performed by X-ray powder diffraction. The batch experiment showed that citrate and, particularly, rutin (alone or combined with organic acids or genistein) promoted Fe mobilization from the soil. The combinations of rutin and organic acids modified the soil mineralogy by dissolving the amorphous fractions and promoting the formation of illite. These mineralogical alterations were significantly correlated with the amount of Fe mobilized from the soil. The RHIZOtest experiment revealed a drastic dissolution of amorphous components in the rhizosphere soil of Fe-deficient plants, possibly caused by the intense release of phenolics, amino acids, and organic acids, but without any formation of illite. Both batch and RHIZOtest experiments proved that exudates released by cucumber under Fe deficiency concurred to the rapid modification (on a day-scale) of the mineralogy of a calcareous soil.     

Reductive dissolution of crystalline and amorphous Fe(III) oxides by microorganisms in submerged soil

Summary Reduction of Fe(III) of amorphous and crystalline Fe(III) oxides to Fe(II) in flooded soils was studied using ⁵⁹Fe(OH)₃ and ⁵⁹Fe₂O₃. The results indicated that Fe(III) in the amorphous oxide was readily amenable to microbial reduction in anaerobic soil condition whereas Fe(III) in the crystalline oxide was not. Following soil submergence, the native as well as the applied crystalline Fe(III) oxides were rapidly converted into the amorphous form. The transformation of the crystalline oxides to the amorphous form appears to be a prerequisite for the reduction of Fe(III) of the oxide. This transformation, probably through hydration, is also mediated by microorganisms.     

Fibrous goethite in some soils from Japan and Scotland

Fibrous particles 20—50Å wide and several μm long have been found in the clay fractions from a number of Japanese and Scottish soils. The particles dissolved in buffered dithionite and hot acid oxalate (0.15 M) but were resistant to hot alkali (2% Na₂CO₃, 0.5 M NaOH) and acid (0.1 M HCl) treatments, suggesting a ferruginous and crystalline nature. The ferruginous nature was further indicated by energy-dispersive X-ray spectroscopy, which, at the same time, showed the presence of large quantities of Al and some Si. Electron diffraction analysis indicated goethite of low crystallinity as the most likely mineral. Incorporation of numbers of Al ions in the crystal lattice was inferred from the results of elemental analysis after chemical dissolution treatments.     

Heavy metal sorption on soil minerals affected by the siderophore desferrioxamine B: the role of Fe(III) (hydr)oxides and dissolved Fe(III)

Phytoextraction of heavy metals from polluted soils has often been found to be limited by the bioavailability of the pollutants. Inorganic or organic ligands are occasionally used as complexing agents to enhance the mobility of the heavy metals. However, the opposite effect is also possible. We studied the influence of the hydroxamate siderophore desferrioxamine B (DFOB) on the sorption of Cu, Zn and Cd to clay minerals, with the emphasis on the role of dissolved Fe(III) and Fe(III) minerals. Depending on the surface charge of the minerals and on pH, sorption of heavy metals can be either enhanced or diminished. We show here that this effect of DFOB disappears if dissolved Fe(III) is added to suspensions of clay minerals in excess to DFOB. We found that the solid Fe(III) phases ferrihydrite and goethite did not impede the effect of DFOB on the sorption of heavy metal, however. Between pH 4 and 10, DFOB completely prevented Cu sorption on ferrihydrite. A strong mobilizing effect was also observed for Zn, but not for Cd. In presence of goethite, concentrations of dissolved Cu, Zn and Cd were enhanced only above approximately pH 5, 7 and 8, respectively. Below these pH values the binding of these metals to goethite was even stronger with than without DFOB. In the absence of heavy metals, DFOB‐promoted dissolution of ferrihydrite was much faster than that of goethite due to the larger surface area of ferrihydrite. In the alkaline pH range, where sorption of DFOB on the surfaces of the iron oxides was greater, dissolution of both minerals was reduced.     

Silicon dynamics in the rhizosphere: Connections with iron mobilization

Silicon (Si) is a beneficial element for plants as it increases their resistance to several biotic and abiotic stresses. In the rhizosphere, root exudates, especially when released by nutritionally stressed plants, promote the mineral weathering and, consequently, influence Si biogeochemistry. This study aims at evaluating the mineralogical alterations in the rhizosphere of Fe‐deficient or Fe‐sufficient barley plants grown either in a natural or in an artificial calcareous soil, focusing on the dynamics of both Fe and Si. After 6 d of soil–plant contact, X‐ray diffraction (XRD) analysis of rhizosphere soil samples of Fe‐deficient plants revealed, for both natural and artificial soil, a decrease of amorphous phases and an increase of smectite compared to the unplanted soil. Root exudates released by Fe‐deficient plants were most likely the main responsible for the weathering of the amorphous phases by a ligand controlled dissolution mechanism. When the soil–plant contact was prolonged up to 12 d, plants overcame Fe nutritional stress and their effect on soil mineralogy completely changed, as proved by the considerable increase of amorphous and decrease of smectite. Smectite decrease might evidence the effort of plant to mobilize Si and micronutrients other than Fe from the soil through the exudation of organic ligands. When the artificial soil was treated with Fe‐sufficient barley plants, the mineral weathering trend appeared reversed compared to the experiments with Fe‐deficient plants. Plant nutritional status regulates the root exudation pattern and, consequently, drives mineral weathering processes in the rhizosphere. Barley has shown to be able to mobilize Si from smectite, yet depending on its Fe supply and proving the strict connection between Si and Fe dynamics in the rhizosphere.     

Speciation and sorption structure of diphenylarsinic acid in soil clay mineral fractions using sequential extraction and EXAFS spectroscopy

Purpose

The mobility of arsenic (As) in soils is fundamentally affected by the clay mineral fraction and its composition. Diphenylarsinic acid (DPAA) is an organoarsenic contaminant derived from chemical warfare agents. Understanding how DPAA interacts with soil clay mineral fractions will enhance understanding of the mobility and transformation of DPAA in the soil-water environment. The objective of this study was to investigate the speciation and sorption structure of DPAA in the clay mineral fractions.

Materials and methods

Twelve soils were collected from nine Chinese cities which known as chemical weapons burial sites and artificially contaminated with DPAA. A sequential extraction procedure (SEP) was employed to elucidate the speciation of DPAA in the clay mineral fractions of soils. Pearson’s correlation analysis was used to derive the relationship between DPAA sorption and the selected physicochemical properties of the clay mineral fractions. Extended X-ray absorption fine structure (EXAFS) L_III-edge As was measured using the beamline BL14W1 at Shanghai Synchrotron Radiation Facility (SSRF) to identify the coordination environment of DPAA in clay mineral fractions.

Results and discussion

The SEP results showed that DPAA predominantly existed as specifically fraction (18.3–52.8%). A considerable amount of DPAA was also released from non-specifically fraction (8.2–46.7%) and the dissolution of amorphous, poorly crystalline, and well-crystallized Fe/Al (hydr)oxides (20.1–46.2%). A combination of Pearson’s correlation analysis and SEP study demonstrated that amorphous and poorly crystalline Fe (hydr)oxides contributed most to DPAA sorption in the clay mineral fractions of soils. The EXAFS results further demonstrated that DPAA formed inner-sphere complexes on Fe (hydr)oxides, with As-Fe distances of 3.18–3.25 Å. It is likely that the steric hindrance caused by phenyl substitution and hence the instability of DPAA/Fe complexes explain why a substantial amount of DPAA presented as weakly bound forms.

Conclusions

DPAA in clay mineral fractions predominantly existed as specifically, amorphous, poorly crystalline, and crystallized Fe/Al (hydr)oxides associated fractions. Amorphous/poorly crystalline Fe rather than total Fe contributed more to DPAA sorption and DPAA formed inner-sphere complexes on Fe (hydr)oxides.

     

皖南第四纪红土伊利石结晶度值与风化强度的关系

对安徽宣城市宣州和郎溪两地第四纪红土黏土矿物组合和伊利石结晶度进行研究,探讨其对第四纪红土形成环境的指示意义。结果表明,两地第四纪红土黏土矿物的组合基本相似:剖面上部末次冰期下蜀黄土层(黄棕色土层)黏土矿物主要为伊利石、高岭石和2∶1型的蛭石;均质红土和网纹红土以伊利石和高岭石为主,无蛭石;网纹层下部出现伊利石-蒙脱石混层矿物。根据伊利石的X射线衍射(XRD)峰,获得伊利石结晶度(Illite crystallinity,IC)值,可以反映伊利石结晶程度。两地第四纪红土同类层次的IC值较接近。宣州和郎溪剖面黄棕色土的IC值平均为0.463,均质红土为0.599,网纹红土为0.726。全剖面样品IC值与风化强度指标呈显著负相关,充分说明红土IC值可有效地反映红土的风化强度。第四纪红土剖面从黄棕色土→均质红土→网纹红土,IC值升高,伊利石结晶变差,反映了红土风化强度增加,形成的气候环境更加湿热。     

黄河三角洲不同土地利用类型土壤微观结构特征

黄河三角洲不同土地利用类型盐碱土微观结构的研究,对认识该地区盐碱土的工程性质和对滨海盐碱地治理具有重要意义。该研究结合粒度分析(particle size distribution,PSD)、X射线衍射(X-ray diffraction,XRD)、压汞(mercury intrusion porosimetry,MIP)和扫描电镜(scanning electron microscopy,SEM)方法,对3种不同土地利用类型盐碱土的微观结构进行定量分析,旨在揭示其微观特性,为黄河三角洲盐碱地治理提供微观理论依据。结果表明:不同土地利用类型下的土壤黏粒含量表现大小依次为农田、滩地、草地,而土壤孔隙度大小依次为草地、滩地、农田;农田、草地与滩地盐碱土矿物成分中,石英、方解石和钠长石等原生矿物占绝对优势,仅含少量黏土矿物,且农田黏土矿物含量远大于草地与滩地;草地与滩地盐碱土孔隙特征类似,两者在0.1≤孔隙直径<10μm范围内小孔隙与微孔隙占有绝对优势,而农田盐碱土以孔隙直径在<2μm范围内的微孔隙与超微孔隙为主。农田盐碱土由致密片状、扁平状结构与微裂隙构成,骨架颗粒间由黏土矿物胶结;草地盐碱土由紧密镶嵌的块状颗粒和架空孔隙构成,骨架颗粒间无胶结;滩地盐碱土由紧密堆积的粒状颗粒和粒间孔隙构成,骨架颗粒间无胶结。研究成果可提高对黄河三角洲不同土地利用类型盐碱土微观结构的认识,为滨海盐碱地的治理、利用和开发提供了微观尺度上的依据。     

Spatial distribution of clay minerals in agrochernozems of erosional and denudational plains in the Stavropol region

The distribution pattern of the fine fractions (<1.0 and 1?C5 ??m) and the mineralogical composition of the agrochernozems formed on the erosional-denudational plains of the Stavropol region have been studied. Erosion and denudation caused the redistribution of the fine material within the catena with its maximal accumulation on the lowermost part of the slope. The same processes favored the formation of surface deposits slightly differing in the composition of the principal mineral phases, i.e., complex disordered mixedlayered micas-smectites with varying combinations of micaceous and smectite layers in crystallites and di- and trioctahedral hydromicas. Imperfect kaolinite and magnesium-ferric chlorite are accompanying minerals. An increase in the amount of mixed-layered minerals with smectite layer is observed down the profile. In addition to the mentioned minerals, the individual smectite and clinoptilolite, which are components of Tertiary deposits, are identified in the lower parts of the agrochernozem profiles. The fine-silt fractions consist of (in decreasing order) di- and tri-octahedral micas, quartz, feldspars, plagioclase, and an admixture of phyllosilicates (kaolinite, chlorite, and mixed-layered chlorite-smectites). The maximal amount of the fine fraction, as well as the maximal amount of mica in it, is registered in the soils in the lower part of the slope. The phyllosilicates are decomposed in this fraction in the upper horizons. The seven-year-long application of mineral fertilizers intensified the peptization of the soil mass in the arable horizons, which increased the content of clay particles in them. A more contrasting distribution of the mixed-layered formations in the profiles, a considerable decrease in their reflection intensities, an increase in the structural disorder of the minerals, and a certain increase in the content of the fine-dispersed quartz are observed.     

中国土壤胶体研究 Ⅵ.西藏高原几种主要土壤的粘土矿物组成和演变

西藏高原突起于我国西南,绝大部分地面的海拔高度在4000米以上,为世界上最高的大高原。它大致在第三纪开始形成,后来曾受第四纪冰川的深刻作用,高山顶部至今仍是冰川的活动场所^[1,2]。高原为昆仑山、唐古拉山、喜马拉雅山和横断山等大山脉所盘踞。