Vertigenesis in soils of the central chernozemic region of Russia

On the basis of soil studies along routes and on key plots, 35 new areas of soils with definite features of vertigenesis have been identified in Belgorod and Voronezh oblasts and in the northern part of Volgograd oblast (in the Don River basin). Earlier, vertic soils were not noted for these areas. In the studied region, their portion in the soil cover is much less than 1%. All the delineated areas of vertic soils are confined to the outcrops of swelling clay materials of different origins (marine, lacustrine, glacial, and colluvial sediments) and ages (Quaternary or Tertiary) that may be found in four landscape positions: (1) in the deep closed depressions within vast flat watersheds; (2) in the bottoms of wide hollows on interfluvial slopes and, sometimes, on steeper slopes of local ravines; (3) in the hydromorphic solonetzic soil complexes, and (4) on step-like interfluvial surfaces with the outcrops of Tertiary clays. Within the studied areas, soils with different degrees of expression (six grades) of vertic properties are present. These soils belong to the type of dark vertic soils proper and to vertic subtypes of different soil types according to the Russian soil classification system; according to the WRB system, they belong to Vertisols proper and to reference soil units with a Vertic prefix in the groups of Chernozems, Phaeozems, and Solonetzes. Statistical data on the morphometric indices of the vertic properties (the depth and thickness of the soil horizons with slickensides, a wedge-shaped structure, and cracks filled with material from the upper horizons) and the depth and thickness of the Vertic horizon are analyzed.     

Characteristics of Clay Minerals in Podzols and Podzolic Soils

The clay minerals in Podzols and podzolic soils developed under coniferous forests in the Subarctic and Cool-temperate zones are characterized by the predominance of smectite and/or mica-smectite interstratified minerals in the eluvial horizons and chlorite-vermiculite intergrade in the illuvial horizons. A large amount of vermiculite is present in the eluvial horizons of some podzolic soils in the Cool-temperate zone. The illuvial horizons of these soils also contain free iron oxides such as goethite. Imogolite and allophane are present in the illuvial horizons of several soils derived from volcanic ashes. It is suggested that the critical bioclimate for the release of interlayered aluminum from the 2:1-type minerals lies between the Cool- and Warm-temperate zone. In the eluvial horizons of Podzols and podzolic soils, mica minerals and chlorite, as primary minerals, have been transformed to smectite through the pedogenic process. Based on previous studies on the structure and degradation of the dioctahedral mica minerals, it is considered that smectite is transformed from 1M-type mica minerals directly, and from 2M-type mica minerals via mica-smectite interstratifled minerals. The formation of a smectite lattice in the eluvial horizon should be a clay-mineralogical indicator of podzolization.     

Assessment of erosional disturbance of Vertisols in Israel by SAR values

An analysis of the spatial distribution of the sodium adsorption ratio (SAR) values in the upper subsurface horizons of Vertisols made it possible to estimate the degree of sheet erosion on the dissected coastal plain composed of the sodium-bearing montmorillonite clay in Israel. The depth of the appearance of slickensides in the profile of the Vertisols was used as an additional criterion of the disturbance of these soils by erosion. The approximate rates of erosional dissection of the local landscapes after the deposition of montmorillonite clay are discussed.     

Lessivage and its relation to the hydrological regime of soils

By the examples of four typical catenas in the East European Plain, the role of lessivage in the development of automorphic and hydromorphic loamy and clayey soils with light-colored acid eluvial horizons and with different degrees of gleyzation has been studied. It is found that characteristic features of lessivage are often observed in the soils without hydrological barriers hampering or preventing the vertical migration of soil water and mass transfer processes. The hydrological barriers may be represented by the shallow horizons of temporarily perched water, or by the ascending capillary fringe of the ground water, or by the water-saturated horizons, in which the volume of free pores does not exceed 2–4%. It is shown that light-colored acid eluvial horizons may be formed in the profiles of loamy and clayey soils without any signs of lessivage. The development of strongly gleyed soils (gleyed soddy-podzolic soils and pseudogley soils (Stagnosols)) is not related to colmatage (silting of their illuvial horizons through lessivage); it is conditioned by the actual hydrological regime of these soils. The role of lessivage, podzolization, and gleyzation in the development of clay-differentiated soils is discussed.     

Specific Features of Profile Distribution and Crystallochemistry of Phyllosilicates in Soils of the Cisbaikal Forest-Steppe

The mineralogical composition of agrogray, dark gray, and agro-dark gray soils (Luvic Greyzemic Retic Phaeozems); agro-dark gray residual-calcareous soils (Calcaric Cambic Phaeozems); clay-illuvial agrochernozems (Luvic Chernic Phaeozems); and agrochernozems with migrational–mycelial carbonates (Haplic Chernozems) developed in the forest-steppe of Central Siberia within the Irkutsk Depression has been studied. The clay (<1 μm) fraction separated from these soils consists of mixed-layer minerals with alternating layers of hydromica, smectite, vermiculite, and chlorite; the proportions between them change within the soil profiles. The clay fraction also contains hydromicas, kaolinite, chlorite, and some admixture of the fine-dispersed quartz. Each type of the soils is characterized by its own distribution pattern of clay material with specific alternation of layers in the mixed-layer formations. Mixed-layer minerals of the chlorite–vermiculite type predominate in the upper horizons of texture-differentiated soils. Down the soil profile, the content of mixed-layer mica–smectitic minerals increases. In the clay fraction of arable dark gray-humus soils with residual carbonates, the distribution of the clay fraction and major mineral phases in the soil profile is relatively even. An increased content of well-crystallized kaolinite is typical of these soils. The parent material of agrochernozems has a layered character: the upper horizons are generally depleted of clay, and the middle-profile and lower horizons are characterized by the considerable kaolinite content. In general, the clay material of soils of the Tulun–Irkutsk forest-steppe differs considerably from the clay material of foreststeppe soils developed from loesslike and mantle loams in the European part of Russia. In particular, this difference is seen in the proportions between major mineral phases and between biotitic and muscovitic components, as well as in the degree of crystallinity and behavior of kaolinite and chlorite.     

Diversity of clay minerals in soils of solonetzic complexes in the southeast of Western Siberia

Data on the mineralogical composition of clay in soils of solonetzic complexes of the Priobskoe Plateau and the Kulunda and Baraba lowlands have been generalized. The parent materials predominating in these regions have loamy and clayey textures and are characterized by the association of clay minerals represented by dioctahedral and trioctahedral mica–hydromica, chlorite, kaolinite, and a number of irregular interstratifications. They differ in the proportions between the major mineral phases and in the qualitative composition of the minerals. Mica–hydromica and chlorites with a small amount of smectitic phase predominate on the Priobskoe Plateau and in the Kulunda Lowland; in the Baraba Lowland, the portion of mica–smectite interstratifications is higher. An eluvial–illuvial distribution of clay fraction in solonetzes is accompanied by the acid–alkaline destruction and lessivage of clay minerals, including the smectitic phase in the superdispersed state. This results in the strong transformation of the mineralogical composition of the upper (suprasolonetzic) horizons and in the enrichment of the solonetzic horizons with the products of mineral destruction; superdispersed smectite; and undestroyed particles of hydromica, kaolinite, and chlorite from the suprasolonetzic horizons. A significant decrease in the content of smectitic phase in the surface solodic horizons of solonetzic complexes has different consequences in the studied regions. In the soils of the Priobskoe Plateau and Kulunda Lowland with a relatively low content (10–30%) of smectitic phase represented by chlorite–smectite interstratifications, this phase virtually disappears from the soils (there are only rare cases of its preservation). In the soils of the Baraba Lowland developed from the parent materials with the high content (30–50%) of smectitic phase represented by mica–smectite interstratifications, the similar decrease (by 10–20%) in the content of smectitic phase does not result in its complete disappearance. However, the smectitic phase acquires the superdispersed state and the capacity for migration.     

Clay materials in the soils of the Baraba Steppe and the Priobskoe Plateau

The composition and the regularities of the profile distribution of the clay minerals in the solods of the Baraba Steppe (ground moistening) and the Priobskoe Plateau (atmospheric moistening) were studied. The two profiles have the distinct eluvial-illuvial distribution of the clay fraction. The composition of the clay fraction in the eluvial layer is dominated by illite. The content of chlorite and labile minerals of the montmorillonite group increases downwards in the profile. The revealed regularities in the profile distribution of the clay fraction and some groups of clay minerals are explained by the joint influence of the mineral dissolution under the influence of the gleying and alkaline hydrolysis, as well as the processes of illitization and lessivage. The major differences in the content and distribution of the clay minerals between the solods and the podzolic soils are the following. The solods have a clear illuvial layer in the clay, while the majority of podzolic soil profiles have the eluvial distribution of the silty fraction. The solods in the eluvial part of the profile and sometimes in even the bottom layers have an unusually high content of the illite minerals in the clay fraction due to illitization. The podzolic layers of the solods do not contain soil chlorites common for the eluvial layers of the podzolic soils, which is due here to a less acidic medium that can not provide the proper conditions of aluminum mobilization and migration needed for the development of chloritization.     

MINERALOGY AND CHEMISTRY OF A TRANSVAAL BLACK CLAY TOPOSEQUENCE

Moralistic soils (vertic and non-vertic black clays) were sampled along a 200 m top sequence in the Transvaal Highveld, South Africa. The Milk wood soil on the upper part of the margalitic top sequence has an Al horizon which lacks both slickensides and self-mulching properties but has strong blocky structure, the others are all self-mulching (i.e. Vertisols). The Vertisols differ in some morphological properties such as the absence (Mngazi series) and presence (Arcadia series) of pedogenic calcite accumulation, both overlying decomposed dolerite, whereas the third member from a red-black centenary sequence is calcareous with a gleyed subsoil horizon. Chemical and XRD analysis suggest that the clays of the Vertisols comprise mainly a partly chloritized iron-rich smectite with Ie > Mg + Al in the octahedral layer (and interlayer positions), while in the upland Milkwood soil intergradient halloysitic clay occurs in addition to a more‘open’structured chloritized iron smectite. The mineralo-chemical results and the geomorphic data suggest that the genesis of these soils is controlled primarily by the internal soil water regime.     

The origin and early genesis of clay bands in youthful sandy soils along lake Michigan,U.S.A.

A beach ridge and dune complex with good radiocarbon control sampling the last 3500 radiocarbon years B.P. provides new insights on the early genesis of clay bands in sandy soils. Soil profiles were sampled by age groups, described in the field, and then subjected to laboratory analyses for particle-size distribution, pH, organic carbon, carbonate minerals, and extractable iron and manganese. This study suggests that small increases in pH, brought about by small increases in carbonate content within the soil profile, are responsible for flocculating small amounts of illuviated clay. This process, along with a transition to a greater hydraulic conductivity with soil depth due to coarser textures in any given profile, partly explains the existence and possible reason for the initiation of illuvial zones and eventually for clay-band horizons. A pronounced increase in the thickness of incipient clay-band horizons in soils older than 2300 years appears due to finer textures in the parent materials than are present in younger soils. Because of slightly reduced porosity and lower permeability, carbonates and a high pH are retained in both illuvial and eluvial horizons of some of these older soils. In addition, only in those profiles older than 2300 years do clay and iron oxide concentrations coincide and is there some suggestion of greater amounts of extractable manganese in horizons of minimum iron and clay. A pronounced segregation of clay-iron bands is not apparent at the study area but should occur in future years as additional amounts of iron and clay are deposited.     

Morphology,Radiocarbon Age,and Genesis of Vertisols of the Eisk Peninsula (the Kuban–Azov Lowland)

Data on the morphology and radiocarbon ages of humus of dark vertic quasigley nonsaline clayey soils with alternating bowl-shaped (Pellic Vertisols (Humic, Stagnic)) and diapiric (Haplic Vertisols (Stagnic, Protocalcic)) structures are discussed, and the genetic concept for these soils is suggested. The studied soils develop on loesslike medium clay in the bottom of a large closed depression on the Eisk Peninsula in the lowest western part of the Kuban–Azov Lowland. The lateral and vertical distribution of humus in the studied gilgai catena displays a lateral transition of a relatively short humus profile of the accumulative type with a maximum near the surface and with a sharp increase in ¹⁴C dates of humus in the deeper layers within the diapiric structure to the extremely deep humus profile with a maximum at the depth of 40–80 cm, with similar mean residence time of carbon within this maximum, and with a three times slower increase in ¹⁴C dates of humus down the profile within the bowl-shaped structure. The development of the gilgai soil combination is specified by the joint action of the lateral–upward squeezing of the material of the lower horizons from the nodes with an increased horizontal stress toward the zones a decreased horizontal stress, local erosional loss of soil material from the microhighs and its accumulation in the adjacent microlows, leaching of carbonates from the humus horizons in the microlows, and the vertical and lateral ascending capillary migration of the soil solutions with precipitation of calcium carbonates in the soils of microhighs.     

Mineralogical Composition of Particle-Size Fractions of Solonetzes from the North Crimean Lowland

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.     

Genesis,hydrology, and properties of soils in mesodepressions waterlogged by surface water in the northern Ryazan forest-steppe

On the interfluves and in small depressions of the Ryazan forest-steppe, under periodic stagnation of surface water, acid chernozem-like soils with a relatively thick humus horizon, podzolic horizons, and marble-colored gleyed B1 and B2 horizons are formed. The eluvial horizons of these soils contain Mn-Fe nodules, and dark humus coatings occur in the illuvial horizons. In the spring, the eluvial horizons of these soils are excessively moistened and gravitational water stagnates on the soil surface for 3–4 weeks. The formation of the acid light-colored eluvial horizons of the soils on leached rocks is related to gleying under the conditions of the stagnant-percolative regime. Their total thickness is 15–25 cm and more. According to the properties of their solid phase, these horizons are similar to the podzolic horizons of soddy-podzolic gleyed soils. These soils have not been represented in the classification systems of soils of the USSR and Russia. Based on the principles of the substantial-genetic classification, one of the authors of this article [9] referred this soil to gleyed podzolic chernozem-like soils, thus, considering it as an individual genetic soil type. The gleyed podzolic chernozem-like soils differ from the leached chernozems by their low productivity and difficulty of tillage. In humid and moderately moist years, the death of crops or a reduction in yield are probable because of the excess of moisture.     

Extractable Al and Si compounds in pale-podzolic soils of the Central Forest Reserve: Contents and distribution along the profile and by size fractions

The profile distributions of oxalate- and pyrophosphate-soluble Al compounds and oxalate-soluble Si compounds in the main horizons of pale-podzolic soils of the Central Forest Reserve and the fractions <1. 1–5, and >5 μm have been considered. In the clay-eluvial part of soil profile, the content of these compounds is differentiated by the eluvial–illuvial type with a clear accumulation in the EL horizon compared to the AEL horizon. This distribution is largely ensured by their differentiation in the clay and fine silt fractions, while an accumulative distribution of mobile Al compounds is observed in fractions >5 μm. The high correlation between the Al and Si contents in the Tamm extracts from the clay and fine silt fractions with the (Al_ox–Al_py)/Si_ox molar ratios, which are in the range of 1–3 in the EL horizon, confirms that mobile compounds are accumulated in these fractions in the form of amorphous aluminosilicates. In the AEL and EL horizons, an additional amount of Al can pass into the oxalate solution from the fine fractions due to the dissolution of Al hydroxide interlayers of soil chlorites. The eluvial–illuvial distribution of mobile Al and Si compounds typical for Al–Fe–humus podzols within the clay-illuvial part of profiles of the soils under study can be considered as an example of superimposed evolution.     

An experience in using the world reference base for soil resources for the soils of western Georgia

New and previously published data on the soils of western Georgia are generalized, and traditional soil names are correlated with the units of the World Reference Base for Soil Resources. It is argued that krasnozems (red ferrallitic soils) can be attributed to the group of Nitisols (the soils characterized by intense weathering (ferralization) and having shiny ped faces in the nitic horizon); yellow and yellow-brown soils (zheltozems), to the group of Luvisols (the soils with relatively high adsorption capacity in the eluvial horizons and with the horizon of the illuvial accumulation of clay); yellow-podzolic (zheltozem-podzolic) soils, to Alisols (slightly acid soils with the low adsorption capacity, poor aggregation of the upper horizons, low-activity (kaolinite) clay, and with the horizon of clay accumulation (argic horizon)); brown forest soils, to Cambisols (the soils with the cambic horizon characterized by some alteration of the lithogenic texture and structure into the pedogenic texture and structure); and mountainous forest-meadow and meadow soils, to Umbrisols (the soils with the dark-colored unsaturated umbric horizon).     

The origin of Vertisols and their relationship to Acid Sulfate Soils in the Senegal valley

In the Senegal valley, it is commonly considered that the Acid Sulfate Soils of the delta are fossil soils overlain by more recent sediments, and that the Vertisols, which abruptly overlie a thick sandy horizon, result from a change in the sedimentation mode of the river. However, we show that both soils belong to the same pedological system extending from the delta to the limit of the last marine transgression. This conclusion is based on (1) the study of soil profiles intermediate between Acid Sulfate Soils and Vertisols along a 100-m sequence in the delta, (2) the mineralogy of the clay fraction (<2 μm) in a 200-km transect along the river, and (3) the similarity of the sand size distribution across the textural discontinuity between the horizons. The following processes are involved in the pedological transformations: (1) development of acidity by oxidation of pyrite, (2) neutralization of acidity initially by the carbonate in shell beds, and later by the hydrolysis of easily weatherable silicate clays. The slightly alkaline river water precipitates kaolinite and later smectite at the contact between the strongly acidic and slightly alkaline environments. This results in the formation of a superficial vertic clay horizon surmounting a sandy horizon. Therefore, we emphasize that the soil morphology results from development and control of acidity and not from changes in past climates.     

Vertic processes and specificity of organic matter properties and distribution in Vertisols

Soil organic matter (SOM) was studied in relation to vertic processes (i.e., shrinking/swelling, cracking, vertical turbation, lateral shearing, gilgai formation) in Vertisols and vertic soils of the North Caucasus in Russia, and Texas and Louisiana in the USA. Their impact on SOM properties and distribution was analyzed according to various levels of soil organization, such as soil cover, profile, horizon, and aggregate structure using chemical methods, micromorphology, isotopic analyses, and physical fractionation. The greatest variations both in the distribution and properties of SOM were found in mature Vertisols at the level of soil cover including Ctot, organic carbon stocks, stable carbon isotopic composition, and SOM ¹⁴C-age, chemical composition. The distribution of SOM at the profile and horizon levels was related to the functioning of Vertisols during wet-dry cycles. The isotopic and chemical study of densi-granulometric fractions at the aggregate level reflected the minor role of vertic processes.     

PaleoVertisols of the northwest Caucasus: (Micro)morphological,physical, chemical,and isotopic constraints on early to late Pleistocene climate

Physical and chemical properties, macro‐ and micromorphology, clay mineralogy, and stable‐isotope compositions of paleosols within a pedostratigraphic column (PSC) of early to late Pleistocene age, interstratified paleosols, and loess (NW Caucasus, S Russia) were examined to better understand the evolution of the pedogenic environment over this time period, separating the effects of postpedogenic diagenesis. The column includes eight paleosols and six intercalated loessic horizons. Most of paleosols represent Vertisols or vertic intergrades. Vertic features increase in the middle of the PSC, where the paleosols are more clayey in texture and reddish in color. The morphology of carbonate nodules and soft masses, morphology‐ and depth(age)‐related changes in stable C and O isotope compositions, soil color, redoximorphic features, clay mineralogy, and illuviated clay indicate periods of wetter pedoenvironment in the past and suggest the Pleistocene paleosols are polygenetic and were formed with several wet/dry stages under a climate generally similar to the modern environment in the N Caucasus (mean annual temperature approx. 9°C–12°C). Interpretation of the time sequence of climate/environmental change requires careful separation of pedogenic mineral phases from phases altered by later diagenesis. The early Pleistocene period of paleosol formation appeared to be wetter or more humid, resulting in more significant development of vertic features. The terrestrial ecosystem remained dominated by C3 vegetation throughout the formation of the PSC, with four small periods of change towards a greater proportion of C4 plants or increased moisture stress.     

Spatial distribution of mineral components in microcombinations of agrogrey soils with the second humus horizon in the Vladimir opolie area

Mineralogical composition of silt and clay fractions (<1.1–5 and 5–10 µm) in heavy loamy agrogrey soils (Luvic Retic Phaeozems) considerably changes both in the vertical (along the soil profile) and horizontal (along soil microcatenas) directions. The eluvial–illuvial distribution pattern of the clay fraction in the podzolized agrogrey soils with the second humus horizon is replaced by the homogeneous distribution in the agrogrey soils with residual carbonates. The distribution of silt fractions in the soil profiles is relatively homogeneous. The clay (<1 µm) fraction of the parent material is represented by the poorly ordered micasmectite interstratifications minerals, the proportion between which changes in the soil profiles in dependence on the particular pedogenetic processes. Hydromicas represent the second important component of the clay fraction. They consist of di- and trioctahedral varieties, the proportion between which changes in the soil profiles. Kaolinite and iron–magnesium chlorite are present in smaller amounts. The second humus horizon is characterized by the lowest content of mica-smectite interstratifications minerals with the high content of smectitic layers and by the lowest content of the clay fraction. Silt fractions are composed of quartz, micas, potassium feldspars, and plagioclases.     

Organic matter in particle-size fractions from A and B horizons of a Haplic Alisol

The organic matter in soils may be stabilized by its interactions with minerals. We have studied such interactions in a Haplic Alisol under forest in which clay and organic matter have migrated from an eluvial A horizon to accumulate in an illuvial B horizon. We have tried to trace the fate of organic matter in these horizons (Ah and Bvt) by determining clay mineralogy, carbon and nitrogen content, hydrolysable amino acids, lignin signature by alkaline CuO oxidation and carbon species by ¹³C CPMAS NMR of bulk soils and particle‐size fractions. In both horizons, most of the organic matter was present in O–alkyl and methylene structures, each contributing one‐third to the bulk organic matter. In the Ah horizon the ratios of carbon‐to‐nitrogen, and yields for lignin and hydrolysable amino acids decreased as the particle‐size class decreased, but side‐chain oxidation of lignin compounds increased with decreasing particle size. In contrast to previous observations, the proportions of O–alkyl carbon increased as particle size decreased, constituting a major proportion of the organic carbon in the clay‐size fractions from both the Ah and Bvt horizons (≥ 38%), while proportions of methylene carbon decreased. Illite was the dominant mineral in the fraction ≤ 6 μm, whereas the mobile fine clay fraction (<0.2 μm) was rich in smectites – minerals with large surface areas. Our results support the hypothesis that potentially labile organic matter, such as O–alkyl carbon typically present in polysaccharides, may be stabilized against further degradation in organomineral complexes.     

滇桂地区变性土的发生特性和系统分类研究

本文研究了我国西南地区变性土的形成条件和发育程度，并结合世界主要分类系统进行了分类研究。结果表明，相对于地带性土壤而言，变性土风化成土作用较弱，发育程度较低，土壤中元素的淋溶迁移及相对富集程度也远低于地带性土壤。由于粘粒含量尤其是粘粒矿物组成的差异，变性土表现出极高的膨胀潜势。通过研究，本文还对我国土壤系统分类中变性土土钢、亚纲、土类等的划分标准和依据及变性土性土的确立等提出了见解。