Microstructure of genetic horizons in automorphic soils of the Timan Ridge

Data are presented on the physicochemical composition and specific macro-, meso- and micro-morphological features of automorphic soils formed on silty loams in the northern and middle taiga subzones of the Timan Ridge. These soils have a texture-differentiated profile and are well aggregated, which is manifested at all levels of structural organization of the soil mass. The morphological structure of the middle soil horizons is characterized by the presence of specific nongleyed cryometamorphic horizon CRM. Its formation is due to the development of long-term seasonal cryogenic processes in relatively deep (up to 40 cm) light and medium loam deposits under conditions of the northern and middle taiga subzones. The processes of cryometamorphism, combined with Al-Fe-humus and textural differentiation, result in the formation of podzolic, iron-illuvial, cryometamorphic, and textural horizons (O-E-BF-CRM-BT). The textural horizons have a set of micromorphological features indicating that recent clay illuviation is a weak process.     

Automorphic soils of the central and southern Timan Ridge

Automorphic loamy soils developing from different parent materials in the central and southern parts of the Timan Ridge are described. Pale-podzolic soil and iron-illuvial texture-differentiated svetlozems are developed from silty covering loams underlain by moraine deposits. Podzolic, iron-illuvial, cryometamorphic, and clay-illuvial horizons are distinguished in the svetlozems; soils with such a complex morphology have been described in the taiga zone of European Russia for the first time. Humus-iron-illuvial podzols are developed from acidic slates. Raw-humus rzhavozems (iron-metamorphic soils) are developed from substrates with the high content of pebbles of mafic rocks. Such soils are typical of the middle taiga zone of Central Siberia and the south of Far East. In the northwestern part of European Russia, these soils occupy small areas.     

Rheological Properties of Automorphic and Semihydromorphic Cryometamorphic Northern Taiga Soils in Northeastern European Russia (Komi Republic)

Soil pastes at the water content corresponding to the maximum swelling of samples from different genetic horizons of cryometamorphic soils―surface-gleyic iron-illuvial svetlozem (Folic Albic Stagnosol) and peaty and peat humus-impregnated gleyic svetlozems (Histic Gleyic Stagnosols)―have been studied with an MCR-302 modular rheometer (Anton Paar, Austria). It has been found that the strongest interparticle bonds are formed in the horizons of cryometamorphic soils characterized by high contents of humic substances and organomineral Al–Fe–humus compounds. These are horizons of podzol microprofile (Eg and BHF) in iron-illuvial svetlozem and a humus-impregnated horizon (ELhi,g) in peaty and peat svetlozems. Organomineral Al–Fe–humus compounds, as well as the seasonal freezing of soils, determine the elastic-brittle character of interparticle interactions. The contents of clay fractions, exchangeable bases, and organic and organomineral substances impart viscoelastic properties to these contacts. An enhancement of elastic-brittle properties of soil is observed under the impact of gleying and freezing. The threefold decrease of the structural interaction parameter (∫Z) when going from automorphic to semihydromorphic conditions indicates a decrease in the resistance of peaty and peat svetlozems to mechanical loads under increasing hydromorphism compared to iron-illuvial svetlozems.     

Factors of the development of taiga and tundra soils with differentiation of Fe and Al oxides in the profile

Statistical data on the bulk contents of iron and aluminum oxides in iron-depleted and iron-enriched horizons of a wide range of taiga and tundra soils were compared. It was found that the soils could be arranged into the following sequence characterized by an increase in the relative contribution of iron oxides and a decrease in the relative contribution of aluminum oxides to the differentiation of sesquioxides in the soil profiles: sandy podzols—soddy-podzolic soils—loamy micropodzols and iron-illuvial svetlozems—cryogenic ferruginated gleyzems. It was concluded that the bleaching of eluvial horizons and the depletion of sesquioxides from them, as well as the accumulation of sesquioxides in the illuvial horizons, are controlled by different processes in different soils. In sandy podzols, the differentiation of sesquioxides is due to the Al-Fe-humus podzolization; in loamy micropodzols and iron-illuvial svetlozems, due to the redox-Al-Fe-humus podzolization; in podzolic and soddy-podzolic soils, due to the selective podzolization and lessivage; and, in cryogenic ferruginated gleyzems, due to the reduction-oxidation processes.     

Soils of the northern part of the Subpolar Urals: Morphology, physicochemical properties, and carbon and nitrogen pools

The morphology and physicochemical properties of mountain-tundra and mountain-forest soils of the Subpolar Urals are analyzed. Gleyic humus-illuvial podburs, in combination with humus-illuvial podburs and raw-humus gleyzems, predominate in the mountain-tundra zone; permafrost-affected gleyzems and peat gleyzems with a shallow (30–50 cm) permafrost table are developed on colluvial fans at the foots-lopes. Iron-illuvial podzols, iron-illuvial svetlozems, eluviated burozems, texture-differentiated podzolic soils with a microprofile of a podzol, and gleyed peat-podzolic soils occur in the mountain-forest zone. The organic carbon and nitrogen pools in the soils considerably vary depending on the soil type and local landscape conditions. The organic carbon pool stored in the upper 50 cm of the soil profile varies from 7.7 to 39.3 kg/m² in the mountain-tundra soils and from 6.5 to 11.8 kg/m² in the mountain-forest soils. The corresponding values for the nitrogen pool are 0.4–2.4 and 0.4–0.8 kg/m², respectively.     

Radiometric Study of Soil Profiles in the Infrared Band

The applicability of radiometric survey of soil profiles in the infrared range for the analysis of soil physical properties was studied. Radiometric data were obtained for different dates of the growing season for a number of soil profiles. The specificity of temperature profiles of texture-differentiated soils (Luvisols and Retisols) as related to weather conditions of the growing season was examined. The correlation analysis showed a close relationship between the air and surface soil temperatures and between the radiometric and thermodynamic soil temperatures in the upper 10 cm. In the studied profiles, the gradient of radiometric temperatures reached 0.5–0.8°C/cm in the humus horizons and sharply decreased at the depth of more than 15–20 cm. The gradient analysis of radiometric images made it possible to outline the boundaries of soil horizons. For the texture-differentiated soils, the most distinct boundaries were established between the gray-humus AY horizon and the underlying eluvial EL horizon in podzolic soils and between the AY horizon and the underlying humus-eluvial AEL horizon in gray soils.     

Cryometamorphic gleyzems in the taiga of Western Siberia: Chemical and mineralogical properties,ecology, and genesis

Earlier studies showed considerable differences in the properties of automorphic loamy soils developing under middle-taiga vegetation in Western Siberia and on the Russian Plain. It was found that the soils without clear features of textural differentiation are common in Western Siberia. In particular, they are represented by cryometamorphic gleyzems. In this study, we analyze the properties of a cryometamorphic gleyzem in the Vakh area (the Khanty-Mansi Autonomous Okrug). The distribution pattern of clay minerals in the soil profile is analyzed in relation to the specific features of the soil hydrothermic regime. In the upper mineral horizons, the clay fraction is enriched in minerals of the group of soil chlorites and somewhat depleted of labile phyllosilicates. In the cryometamorphic horizon and in the underlying permafrost, the degree of crystallization of the clay minerals somewhat decreases. An even distribution pattern of aluminum oxide in the soil profile is explained by the increased content of Al in the clay fraction from the upper horizons combined with the loss of Al from the coarse fractions (as judged from data on the bulk elemental composition of clay-free samples). These features can be explained by the specificity of the hydrothermic regime of the cryometamorphic gleyzems with late thawing of the soil profile and frequent phase transitions of soil water in the upper humus and middle-profile cryometamorphic horizons.     

Characteristics of brown forest soils developed on the paleozoic shale in northern Kyoto with special reference to their pedogenetic process

Abstract

Morphological and chemical properties of brown forest soils and podzolic soils developed on paleozoic shale under beech and/or cryptomeria have been studied with special reference to the eluviation-illuviation characteristics of Fe and Al.

Mobilization of Al was observed even in brown forest soils and its pattern was similar to that in podzolic soils. Its intensity was higher in the brown forest soils developed on the ridge under cryptomeria than in those on the slope under beech. Hence, podzolization is considered to be one of the genetic processes involved in the brown forest soils in question.

Furthermore, the value of (Fep+Alp)/clay that is employed to define a podzolic B or spodic horizon indicated the presence of a podzolic B horizon even in the brown forest soils studied, while no spodic horizon was found even in the podzolic soils with a clearly recognizable albic horizon. Moreover, the examination of the degree of podzolization showed that the brown forest soils almost corresponded to Ochreous brown earths.     

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.     

Clay minerals in chernozem-like soils of mesodepressions in the northern forest-steppe of European Russia

In the northern forest-steppe of European Russia, under the conditions of surface waterlogging (freshwater) and a stagnant-percolative regime, gleyic podzolic chernozem-like soils with thick light-colored eluvial horizons are formed. These horizons are close or similar to the podzolic horizons of bog-podzolic soils in many properties of their solid phase. They are bleached in color and characterized by the removal of Ca, Mg, Fe, Al, and Mn and the relative accumulation of quartz SiO₂. These soils differ from leached chernozems in their acid reaction and very low CEC, the presence of Fe-Mn concretions and coatings, and the significant decrease in the clay content in the A2 horizon as compared to the parent rock. The soils studied differ significantly from loamy podzolic and bog-podzolic soils by the composition of the clay minerals in the A2 horizons: (1) no essential loss of smectite minerals from this horizon was found as compared to the rest of the solum, (2) pedogenic chlorites (HIV and HIS) are absent, and (3) the distinct accumulation of illites is observed as compared to the subsoil and parent material, probably, due to the process of illitization.     

Anisotropy of the properties of some anthropogenically transformed soils of podzolic type

It is shown that the horizons and profiles of anthropogenically transformed soils of podzolic type—light typical agrozems, typical texture-differentiated soils developed from glaciolacustrine loamy sands and clays and from noncalcareous mantle loams, agrosoddy deeply podzolic soils developed from noncalcareous mantle loams, and agrosoddy shallow-podzolic soils developed from noncalcareous mantle loams and from calcareous loams underlain by ancient glaciolacustrine loams and clays—are characterized by some anisotropy of most of their properties. The highest anisotropy is typical of the field water content, bulk density, and total porosity. The coefficients of anisotropy (gradients) calculated for the separate horizons as the ratios between the values of the properties measured in the horizontal and vertical directions (k = P_horiz/P_vertic) of these properties are much higher than those of other soil properties. The coefficient of anisotropy of the soil profile (K) is suggested as the coefficient of correlation between the values of a given property determined in the horizontal and vertical soil sections. For the considered properties, K varies from 0.4 to 0.6. For other soils properties, such as the solid phase density, the electrical resistance determined in a laboratory and in the field, and the organic carbon content, the coefficients of anisotropy are close to 1.0. The clay content has an intermediate anisotropy. The values of anisotropy and its direction (gradient) should be taken into account upon the assessment of the soil physical properties and the processes controlling them; this is particularly important in the study of soil transformation. The revealed regularities of the soil anisotropy make it possible to suggest a new interpretation of the data on the distribution of water and energy in soil profiles.     

Roles of iron and clay in Genesis of acid soils under a humid,temperate climate

The occurence of acid brown soils, podzols and podzolic soils, and the intermediate types of ochreous brown and brown podzolic soils over arenaceous granite in Vosges was closely correlated with the contents of iron rather than with calcium plus magnesium in the parent materials. Acid brown soils were associated with high and podzols and podzolic soils with low contents of iron, the limiting value being near 5 percent. Additional investigations in beech forests of soils derived from a variety of acid rocks indicated that contents of iron and clay in the parent materials controlled the type of humification of litter. With higher contents of iron and clay, humification gave rise to mull. With lower contents, mor or moder was formed. The nature of humification was believed responsible for tilting pedogenesis toward brunification or toward podzolization. In brunification, the clay-iron-humus complexes that are formed tend to be immobile and promote formation of crumbly structure. The “active iron” occurs as films around clay particles and thus links them to humus. In podzolization, on the other hand, the complexes formed are of humus with iron or aluminum but without clay. These are mobile and are translocated downward in profiles to form spodic horizons. The organo-metal complexes in ochreous brown and brown podzolic soils are mobile to only a limited extent. The combined results of these investigations demonstrate that contents of iron and clay rather than calcium in parent materials determine the pathway of pedogenesis from acid rocks under humid, temperate climates.     

Pedogenic chlorites in podzolic soils with different intensities of hydromorphism: Origin,properties, and conditions of their formation

Minerals of the pedogenic chlorite group were studied in the clay fractions isolated from the mineral horizons of podzolic and gleyic peat-podzolic soils. In the AE and E horizons of the podzolic soil, pedogenic chlorites are thought to develop from vermiculite, whereas in the E horizon of the gleyic peat-podzolic soil, they can be formed from smectite minerals. For estimating the degree of chloritization (the degree of filling of the interlayer space of 2: 1 minerals with Al hydroxides), a numerical criterion was is proposed. The difference between the values of this criterion before and after the treatment of the preparations with NH₄F indicated that the degree of chloritization in the pedogenic chlorites decreases in the following sequence: the E horizon of the podzolic soil > the AE horizon of the podzolic soil > the E horizon of the gleyic peat-podzolic soil. Another numerical criterion was proposed to estimate the degree of polymerization of Al-hydroxy complexes in pedogenic chlorites. This criterion was based on the thermal stability of soil chlorites and represented the temperature at which an increase in the intensity of the 1.0-nm peak after heating the K-saturated preparations exceeds 50% of its initial value. According to this criterion, the degree of polymerization of the Al-hydroxy interlayers in pedogenic chlorites decreases in the following sequence: the E horizon of the podzolic soil > the E horizon of the gleyic peat-podzolic soil ≥ the AE horizon of the podzolic soil. The distinct interrelation between the soil properties and the degrees of chloritization and polymerization of the Al-hydroxy interlayers attests to the modern origin of the pedogenic chlorites.     

Mobile aluminum compounds in soils of the southern taiga (soils of the central forest reserve as an example)

The profile distributions of aluminum extracted by the Tamm and Bascomb reagents and of the exchangeable aluminum were studied in soils of automorphic, transitive, and accumulative positions in the landscapes of the southern taiga. In the mineral horizons of the gleyic peaty-podzolic soils developed on poorly drained flat surfaces and in the floodplain soils, the distribution of oxalate- and pyrophosphate-soluble aluminum has a strongly pronounced accumulative character. In the podzolic soils of the automorphic positions and slopes, an eluvial-illuvial distribution was characteristic with the maximal aluminum content in the podzolic horizons. The strong differentiation of the upper part of the profile in the automorphic podzolic soils in terms of the Al content in the Tamm and Bascomb extracts is mainly related to an increase of the pedogenic chlorite content upon the transition from the AE to the E horizon. In the podzolic horizons of these soils, aluminum can accumulate in the form of proto-imogolite structures. The exchangeable aluminum displays an accumulative type of distribution. On the basis of calculating the reserves of the different aluminum compounds, two main accumulative zones for the mobile compounds of this element were recorded in the soils of the landscapes studied: the E horizon in the automorphic podzolic soils, where Al accumulates as soil chlorite or, probably, as proto-imogolite, and the A1 horizon of the floodplain soils, where Al accumulates in aluminoorganic complexes.     

Solods of the Baraba Lowland and the Priobskoe Plateau: Their properties and genesis and the methods of their diagnostics

The properties, hydrological features, and genesis of the solods occurring in the Baraba Lowland and Priobskoe Plateau were studied. Methods for determining the hydromorphism degree are considered; the features of the similarity and differences between the solods and other soils with textural profile differentiation are shown. Depending on the reasons for the waterlogging, the solods should be divided into two groups: the solods of groundwater waterlogging and the solods of surface waterlogging. Criteria for their discrimination are suggested: the ratio between the contents of the clay fraction in the parent rock (or in the B2 horizon) and that in the A2 horizon, the changes in the pH values along the soil profiles, and the content of nonsilicate iron compounds. The solods studied are shown to be formed under the conditions of a stagnant-percolative regime and gleying. This circumstance is an obligatory and sufficient reason for the formation of the light-colored acid eluvial (A2) horizons. According to some basic properties of the soil solid phase (the acidity, the total chemical composition, and the clay pattern in the eluvial part), the gleyed solods are close or identical to the gleyed soddy-podzolic and gleyed chernozem-like podzolic soils. At the same time, the solods differ from the gleyed chernozem-like podzolic soils by their thicker A1 (or Ap) horizon and their higher humus content (5–7%).     

Transformation of properties of podzolic soils under development and cultivation in the middle taiga subzone (Komi Republic)

The results of long-term stationary studies on the properties of loamy soils under forest and plowland in the middle taiga subzone were summarized. Spatial and temporal changes in the morphology and physicochemical properties of agrosoddy-podzolic soils as compared to forest ones, the peculiar pedogenesis of the soils in automorphic positions and on the slopes, and the activation of gleying in these soils were discovered. The downward displacement of the eluvial horizon, the shift to a heavier texture of the arable layer due to the soil cultivation, the variation in the content of clay and silty particles in this layer depending on the duration and stability of the freezing periods, and the decrease in the removal of clay and most oxides in the developed soils were revealed. The removal of iron, aluminum, calcium, and magnesium oxides and the profile distribution of clay indicate the intensification of eluviation in the soils of mesodepressions. The long-term use of podzolic soils in agrocenoses resulted in the leveling of the humus reserves in the entire catena.     

Solods under conditions of excessive surface and ground moisture in Western Siberia: Properties,hydrology, and genesis

Depending on conditions of formation, solods should be differentiated into two groups: solods of ground overmoistening and solods of surface overmoistening. Criteria are offered to distinguish soils according to the ratio between the clay in the B2 horizon and that in the A2 horizon, as well as according to the changes in the soil pH. Formation of gley under conditions of stagnant to percolative water regime is a necessary and sufficient cause for light-colored acid eluvial horizons to form in their profile. In the main properties of the solid phase (acidity, total chemical composition, and distribution of silt), gley solods are identical to soddy-podzolic and chernozem-like podzolic gley soils.     

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.     

Variation in the acid-base parameters of automorphic loamy soils in the taiga and tundra zones of the Komi Republic

A database for the main genetic horizons of loamy automorphic soddy-podzolic, typical podzolic, gley-podzolic, and surface-gley tundra soils of the Komi Republic was developed on the basis of the available archive and literature data and unpublished results of the authors. The database included the following parameters: the pH_water and pH_KCl, the exchangeable and total acidity, and the degree of SEC saturation. All the parameters were characterized by normal distribution types. The variation coefficients V for the pH_water and pH_KCl were <10%. For the exchangeable and total acidities and the degree of SEC saturation, the V values varied among the soils and horizons in the range of 10–50%. The greatest differences in the acid-base properties of all the soils were revealed between the groups of organic horizons, the eluvial horizons, and the B horizon by the cluster analysis. Between the separate subtypes of podzolic soils, the maximum differences were observed in the organic and, to a lesser extent, eluvial horizons; the B horizons of the different soils in the taiga and tundra zones did not significantly differ in these terms. For the entire profiles, the highest similarity was found between the typical podzolic and gley-podzolic soils, which were more similar to the automorphic soils of the tundra zone than to soddy-podzolic soils.     

Genetic features of soils on sorted sand deposits of different origins in the Kola Peninsula

Differences in the chemical composition of soils developed from sorted sands of different origins are revealed. The iron-illuvial podzols on rich glaciofluvial and marine sands are characterized by well-pronounced Al-Fe-humus differentiation of the Si, Al, and Fe in the soil profile. These soils are relatively similar in their bulk elemental composition. The difference between them is seen in the degree of differentiation of the soil profiles; it is stronger in the soils developed from glaciofluvial deposits. This is particularly true with respect to the oxalate-soluble iron and aluminum hydroxides. The deposits derived from the red-colored Tersk sandstone and processed by the sea (in the coastal zone of the White Sea) have the poorest chemical composition. In the soils developed from them, the differentiation of oxalate-soluble compounds is slightly pronounced (for Fe) or completely absent (for Si and Al). These soils can be classified as podzolized ferruginous red-colored psammozems (within the order of poorly developed soils) with the following horizons: O-Ce-Cf-C. The Ce horizon has the features of podzolization, and the Cf horizon has some features attesting to the illuvial accumulation of Fe. The profile of these soils inherits a reddish tint from the parent material.