Mountainous meadow chernozem-like soils of high mountains in the North Caucasus region

Original and literature data on the soil-forming conditions and the morphology, physicochemical properties, and bulk chemical and mineralogical composition of mountainous meadow chernozem-like soils of the North Caucasus region indicate that these soils are developed from the coarse-textured pebbly colluvium of calcareous bedrock under the impact of humus accumulation and clay formation. The intensity of these processes is directly related to the activity of soil biota. Suggestions aimed at improving the classification of high-mountain soils are discussed.     

Biological activity of alpine mountain-meadow soils in the Teberda Reserve

The intensity of the actual and potential CO₂ emissions, nitrogen fixation, denitrification, and methane production were determined by gas chromatography in alpine mountain-meadow soils under different types of phytocenoses at the Teberda State Reserve. The main factors that control the intensity of these processes in the mountain-meadow soils are moisture and accumulation of biophilous elements related to the position of the soils on the biogeochemical catena. The CO₂ emission and intensity of the nitrogen fixation in the soils under Geranium-Hedysarum meadows that occupy transit-accumulative positions were 2–3 times higher that these parameters in the soils under the alpine heathlands and Festuca meadows. The soils under the carpet-like alpine meadows, accumulating moisture and mineral nitrogen, were characterized by the highest intensity of denitrification and methane production.     

Specific features of soil formation in the taiga zone of Western Siberia

Specific features of soil formation in the taiga zone of Western Siberia are considered. The polygenetic nature of podzolic and gley-podzolic soils in the middle taiga zone, soddy-podzolic and soddy gley soils in the southern taiga zone, and meadow soils in the subtaiga zone is related to the pre-Holocene transformation of the lithogenic matrix upon activation of denudation and accumulation processes and the complicated Holocene evolution of these soils. A soil profile can be subdivided into separate layers according to the geomorphic features of the cryogenesis, the indices of interruption of soil formation, and the differences in the composition of the organic matter in the relict and modern humus horizons.     

Assessment of the mineralogical status of silicate components in chernozems

An approach to assess the mineralogical status of chernozems is discussed. It is based on ten characteristics of the main groups of minerals composing the silicate part of the soil and allows us to give a comprehensive assessment of the mineralogical status of chernozems and its transformation under the impact of pedogenetic processes. The obtained data may be used for determining the soil genesis; improving soil classification; and solving various applied problems, including the assessment of the adverse effect of irrigation of chernozems on the state of their minerals, the irrigation-induced degradation of smectites and illite formation, illite formation upon the nonexchangeable fixation of potassium from fertilizers, etc. The principles of this approach may also be applied to other soils with due consideration for their mineralogical composition.     

Transformations of layered silicates in soils of the boreal and subboreal zones: Literature review

The transformation mechanisms of layered silicates during the formation of vermiculite (vermiculitization), smectite (smectization), illite-like minerals (illitization), and soil chlorites (chloritization) have been considered. The mechanism of olivization has also been discussed. The manifestation features of these processes in different soils and horizons have been analyzed. It has been shown that the rate, direction, and depth of the transformations depend on the climatic conditions; the mineral composition; the acid-base, redox, and hydrological conditions; and the soil solution’s composition. The amount of the accumulated solid-phase products of the transformations depends on the rate of the given transformation stage and (or) the rate ratio between the given and the next transformation stages.     

Influence of drying of the samples on the transformation of nitrogen and carbon compounds in mountain-meadow alpine soils

The drying of samples of mountain-meadow soils characterized by their permanently high moisture under natural conditions fundamentally changes the concentrations of the labile nitrogen and carbon compounds, as well as the patterns of their microbial transformation. When the soil samples are dried, a four- to fivefold increase in the content of the extractable organic nitrogen compounds, carbon compounds, and inorganic nitrogen compounds is observed, while the content of nitrogen and carbon of the microbial biomass decreases by two-three times. The rewetting of the dried soil launches the process of the replenishment of the nitrogen and carbon reserves in the microbial biomass. However, even after two weeks of incubation, their values were 1.5–2 times lower than the initial values typical of the natural soil. The restoration of the microbial community in the samples of the previously dried soils occurs in the absence of a deficiency of labile organic compounds and is accompanied by their active mineralization and the low uptake of ammonium nitrogen by the microorganisms.     

Mineralogical and geo-chemical characterization of a diapiric formation in the North of Spain

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.     

土壤胡敏酸与富里酸热力学稳定性及其驱动因素初步研究

从过程考虑,腐殖质的形成和转化主要是微生物主导的生物化学过程,但就其始态和终态的能量水平变化而言,是热力学稳定性问题。在土壤中,影响腐殖质的形成转化的因素很多,如黏粒含量和类型,植被和微生物状况,土壤湿度、温度和空气组成,土壤溶液的化学组成、浓度、酸度和氧化还原状况等。但从热力学角度,为了计算反应平衡常数(logKR)和吉普斯生成自由能(ΔGfθ),如果将温度设为25℃,我们可以将土壤条件诸多因素简化为水活度([H2O])、氧分压(PO2)和二氧化碳分压(PCO2)这3个参数。之所以简化为这3个参数,因为任何有机成分均是由含有这3种元素的物质形成的,最终又均可以分解为含有这3种元素的H2O和CO2。本文按照上述新思路,以黑土为例探讨了胡敏酸(HA)、富里酸(FA)形成转化的驱动因素和热力学稳定性的研究方法,用元素组成-土壤条件参数法计算HA、FA的logKR和ΔGfθ及热力学稳定性范围。同时通过土壤添加有机物料的模拟培养实验研究了氧气和二氧化碳等单因素对HA和FA数量积累的影响。结果表明,黑土HA和FA的元素组成分子式分别为nC21H21O9N和nC24H33O17N。FA在缺氧、多水和高浓度二氧化碳条件下较稳定;HA则相反。培养实验中,高二氧化碳和低氧气浓度处理使FA与HA的相对比例增加。这一研究方法和结果将有助于解释和推测土壤腐殖质组成的空间变异规律,指导土壤肥力、土壤固碳的调控实践。     

Prospects and problems of using the methods of geochemistry of stable carbon isotopes in soil studies

A review of world investigations into the geochemistry of stable isotopes—a new area for soil science—is presented. Studies of the behavior of stable isotopes in soils are being developed in two major directions: reconstruction of the environmental conditions and indication of the soil processes. Investigations into the reconstruction of the environmental conditions are based on the assumption that the isotopic composition of carbon in the soil humus is inherited from and reflects the isotopic composition of carbon in the corresponding vegetation (the source of soil humus). At the same time, studies into the indication of soil processes are based on the effects of fractionation of carbon isotopes in the course of transformation of carbon compounds. In this case, the isotopic composition of carbon in the soil humus should differ from that in the initial plant material. The analysis of available data suggests that the current state of research does not allow assessing the entire diversity of the effects of isotopic fractionation in soils. New data on the isotopic composition of carbon of soil organic matter and carbonates are being actively accumulated at present. However, it is obvious that the effect of isotopic fractionation should be taken into account in the paleoenvironmental and paleoclimatic reconstructions.     

Impact of land use changes on soil carbon, nitrogen and phosphorus and water pollution in an arid region of northwest China

Abstract. Physical, chemical and environmental consequences of land use change from cultivated land to desert grassland and vice-versa were monitored in the middle reaches of the Heihe River basin, which is one of the largest inland basins of arid northwest China. Levels of N and P in soils and surface waters and soil organic carbon were measured. After the first 3–5 years of cultivation the N and P contents of various former grassland soils, including mountain-meadow and plains-meadow grasslands, decreased significantly. After some 13 years of cultivation, soil nutrient content in former mountain meadow grasslands gradually stabilized, whereas those of desertified grassland, where cultivation had simply been abandoned, showed a notable decrease. Under these latter conditions, soil N and P were lost at a rate of 276 kg ha⁻¹ and 360 kg ha⁻¹, respectively, over the 13-year period. The transformation of grassland into cultivated land and that of cultivated land into desert grassland resulted in organic carbon emissions of 1.68 Tg C and 0.55 Tg C, respectively, over 13 years. Land use changes in the arid inland region clearly have a significant influence on the soil organic carbon pool and carbon cycle. Falls in soil N and P led to 63% and 34% mean enrichment of N and P, respectively, in downstream waters, thus posing a future environmental problem for the arid region of northwest China.     

Mountainous meadow-steppe soils in high mountains of the Eastern Caucasus region

The results of comprehensive investigations into the soil-forming conditions, morphology, substantive composition, physicochemical properties, bulk elemental composition, and mineralogy of mountainous meadow-steppe soils of the Eastern Caucasus region are discussed. The analysis of the obtained and published data has shown that the formation of these soils takes place in a relatively arid high-mountain environment from the coarse-textured eluvium of noncalcareous rocks. Two major pedogenetic processes with the participation of soil biota—humus accumulation and argillization—are responsible for their origin. Suggestions for improving the classification of mountainous meadow-steppe soils are given.     

An assessment of anthropogenic soil transformation of the arkhangelskoe museum estate based on the example of studying inclusions

The natural soil cover of a territory is transformed during the formation of landscape architecture objects. Natural soils are replaced by anthropogenically transformed soils and soil-like bodies. Due to technological features, either only surface horizons of natural soils or an entire range of horizons within a significant profile can be replaced. To determine the extent of transformation, the composition of inclusions of anthropogenically transformed and anthropogenic soils of the museum-estate Arkhangelskoe was studied. The study results were used to assess the extent of soil contamination and to determine the features of the composition of anthropogenic inclusions. A practical proposal on research on the coarse fraction inclusions of the soil was made.     

Soil physical properties related to soil structure

The aim of this paper is to clarify the effect of soil aggregation on soil physical and chemical properties of structured soils both on a bulk soil scale, for single aggregates, as well as for homogenized material. Aggregate formation and aggregate strength depend on swelling and shrinkage processes and on biological activity and kinds of organic exudates as well as on the intensity, number and time of swelling and drying events. Such aggregates are, most of all, more dense than the aggregated bulk soil. The intra-aggregate pore distribution consists not only of finer pores but these are also more tortuous. Thus, water fluxes in aggregated soils are mostly multidimensional and the corresponding water fluxes in the intra-aggregate pore system are much smaller. Furthermore, ion transport by mass flow as well as by diffusion are delayed, whereby the length of the flow path in such tortuous finer pores further retards chemical exchange processes. The chemical composition of the percolating soil solution differs even more from that of the corresponding homogenized material the stronger and denser the aggregates are.

The rearrangement of particles by aggregate formation also induces an increased apparent thermal diffusivity as compared with the homogenized material. The aggregate formation also affects the aeration and the gaseous composition of the intra-aggregate pore space. Depending on the kind and intensity of aggregation, the intra-aggregate pores can be completely anoxic, while the inter-aggregate pores are already completely aerated. The higher the amount of dissolved organic carbon in the percolating soil solution, the more pronounced is the difference between the gaseous composition in the inter- and in the intra-aggregate pore system.

From the mechanical point of view, the strength single aggregates, determined as the angle of internal friction and cohesion, depends on the number of contact points or the forces, which can be transmitted at each single contact point. The more structured soils are, the higher the proportion of the effective stress on the total stress is, but even in single aggregates positive pore water pressure values can be revealed. Dynamic forces e.g. due to wheeling and/or slip processes can affect the pore system as well as the composition of the soil by: (1) a rearrangement of single aggregates in the existing inter-aggregate pore system resulting in an increased bulk density and a less aerated and less rootable soil volume, (2) a complete homogenization, i.e. aggregate deterioration due to shearing. Thus, the smaller texture dependent soil strength coincides with a more intensive soil compaction due to loading. (3) Aggregate deterioration due to shearing results in a complete homogenization, if excess soil water is available owing to kneading as soon as the octahedral shear stresses and the mean normal stresses exceed the stress state defined by the Mohr-Coulomb failure line. Consequently, normal shrinkage processes start again.

Thus, the rearrangement of particles and the formation of well defined single aggregates even at the same bulk density of the bulk soil both affect, to a great extent, various ecological parameters. Environmental aspects can also be correlated, or at least explained with the processes in soils, as a major compartment of terrestial ecosystems, if the physical and chemical properties of the structure elements and their composition in the bulk soil are understood.     

Seasonal dynamics of the mineral nitrogen forms in mountain-meadow alpine soils

The good agreement between the changes in the concentrations of ammonium and nitrate nitrogen, on the one hand, and the mineralization and nitrification activities, on the other hand, was shown in the annual dynamic cycle of the mobile mineral nitrogen concentrations, the net mineralization of its organic compounds, and the net nitrification in mountain-meadow soils of different ecosystems of the Teberda Reserve. The low nitrification activity in the mountain-meadow soils results in the predominance of ammonium nitrogen in its mineral forms during the entire vegetation period. The importance of the fall-winter-spring period, when the mineralization of organic nitrogen compounds proceeds actively and results in the accumulation of ammonium nitrate in the soil up to the beginning of the vegetation period, was emphasized. Due to the long duration of this period, its average contribution to the total annual mineralization is comparable to that of the vegetation period.     

Modifications of the mineralogical composition and surface properties of soils as related to steppe climate dynamics in historical time

This work presents the results of a study of changes in the soil mineral components and the related modifications of the chemical composition and surface properties of soils in the desert-steppe zone in the southern part of the Ergeni Upland. Burial mounds dating back to the Bronze epoch have been investigated. According to radiocarbon data, their ages are estimated at 5100 ± 50, 4410 ± 100, 4260 ± 120, 4120 ± 70, and 3960 ± 40 years. The substantial transformation of the clay minerals, the molar chemical coefficients, the magnetic mineralogy, and the surface properties of the soils permits us to assess the rates of the mineralogical transformations caused by the climate change during the time interval of less than <∼100 years. The ratio between the content of the mineral phases in the buried soils of different ages testifies to the primary importance of climatic factor in comparison with the total duration of weathering or the soil existence on the land surface prior to its burial, i.e., the soil age.     

Stages of development and palaeogeographical inheritance of the recent soils features in the center of the Russian plain

In the article an attempt was undertaken to make palaeogeographical analysis of the history of development of the present soils in the center of the Russian plain on the basis of the soils study in a series of sections, located in different microrelief elements of the cryogenic genesis in the Bryansk region. The analysis of the data on soil morphology, chemical and mechanical composition of soils, and peculiarities of microstructure made it possible to determine that the appearance of certain features in the soils structure was predetermined as far back as during the Late Pleistocene cryogenic period; i.e. before the beginning of the Holocene (up to 10 000 y. B.P.). The studied soils are considered as polygenetic formations. Six stages of their formation were singled out.     

ESP值和黏粒含量对土壤表面封闭作用的影响

降雨导致土壤表面结皮形成封闭是自然现象,它能降低土壤入渗,增加土表径流,导致土壤侵蚀。该文系统地研究了不同性质土壤表面的封闭作用过程,分别确定封闭过程中的物理机械作用和化学作用。试验采用了具有不同土壤交换性钠百分率(ESP)值(2、5、10、20)和黏粒含量(10％、20％、40％、60％)的4种土壤进行降雨模拟试验,通过土壤表面播撒磷石膏(PG)(2000 kg/hm²)和PG与聚丙烯酰胺(PAM)(PG 2000 kg/hm²+PAM 20 kg/hm²)混合物的处理,分别抑制了土壤的化学封闭和物理封闭,论述了ESP值和黏粒含量对土壤化学封闭和物理封闭作用的影响,结果表明：在高ESP值土壤中,化学封闭作用占土壤封闭的主导作用;低ESP值土壤中,土壤的物理封闭作用增大。当黏粒含量较低时,土壤物理封闭作用较低;当黏粒含量较大时,土壤物理封闭作用显著增大。     

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.     

Changes in soil properties at different levels of soil structural arrangement under the impact of irrigation

Processes taking place at different levels of the soil structural arrangement in irrigated and rainfed soils of the Lower Volga region are analyzed. Interactions between these processes and the dependence of their rates on the duration of irrigation are discussed. It is shown that irrigation-induced changes are more pronounced and proceed faster in soils of poorly drained landscapes in comparison with well-drained landscapes. Interaction of the processes taking place at different hierarchical levels of soil arrangement is observed. At the ionic-molecular level, migration and transformation of the composition of soil humus and soluble salts and various exchange reactions take place; at the level of elementary soil particles, the processes of disintegration, peptization, transformation, and the destruction of minerals; at the aggregate level, changes in the water stability of soil aggregates and the degree of soil micro- and macroaggregation; at the level of particular morphological elements, horizons, and pedons, reorganization of soil material (changes in the thickness and bulk density of soil horizons, synthesis and destruction of various neoformations, etc.); finally, at the level of the soil cover pattern, irrigation leads to a higher complexity of the soil cover; the degree of contrast in the soil cover pattern increases, and the soil development at different sites proceeds with different velocities.     

Polycyclic aromatic hydrocarbons in pyrogenic soils of swampy landscapes of the Meshchera lowland

The composition and distribution of polycyclic aromatic hydrocarbons (PAHs) were studied in organomineral and organic soils of the Meshchera National Park. It was found that the background oligotrophic peat soils unaffected by fires in central parts of the bogs are characterized by the increased PAH concentrations due to their high sorption capacity. The fires of 2007 and 2010 resulted in the transformation of the plant cover and soil morphology, the formation of new horizons, and the change in the PAHs content and composition. Significant burn-off of organic matter was found in oligotrophic-eutrophic soils and resulted in the decrease of PAHs content after fire. Only partial burn-off of organic horizons and intense formation of PAHs were recorded in the soil with initially great thickness of peat horizons. Pyrogenic accumulation of PAHs was identified in organomineral soils of the marginal parts of bogs and of forest sites.