Solonetzic process in postagrogenic and postameliorative conditions of the Kamennaya Steppe area

The physicochemical conditions and morphological features of solonetzic process in soils of chernozemic solonetzic complexes were studied in the area of solonetzic experimental station no. 1 in the Kamennaya Steppe area in 55 years after a single application of ameliorative measures (earthening, gypsuming, and manuring) and cessation of the annual plowing. It was found that the modern soil-forming factors favor the development of soil processes inherent in native chernozems and solonetzes prior to their plowing and amelioration. They cause the restoration of the humus horizon in chernozems and the morphological differentiation of solonetzes after the cessation of plowing. Active postameliorative and postagrogenic restoration of solonetzic features is related to the preservation of the physicochemical conditions (the low concentration of salts and the presence of exchangeable sodium) in the soil profile. The humus horizon of chernozems applied over the surface of solonetzes is characterized by the appearance of solonetzic features under hydromorphic conditions.     

Morphological and chemical properties of the meadow-semidesert soil complexes of the Khaki playa (the Caspian Lowland) and the influence of the biogenic factor on them

The initial stage of the development of the complex soil cover pattern in the Caspian Lowland was studied. The obtained data made it possible to reveal the specific features of the morphological and chemical properties of the soils on terraces of the Khaki playa and the role of burrowing animals in the formation of the microtopography and complex soil cover patterns on the youngest surfaces. The soil cover of the studied area consists of three-component complexes: light-humus quasi-gley solonetzes on relatively flat background surfaces, zooturbated solonetzes on microhighs, and humus quasi-gley soils in microlows. The layered deposits of the Khaki playa terraces and the shallow depth of the saline groundwater are responsible for the specificity of the modern salinization of the studied solonetzes. The distribution of the salts in their profiles has a sawshaped patter, which is related to the nonuniform texture of the deposits. On the microhighs composed of the earth extracted from 5- to 7-year-old suslik burrows, specific zooturbated solonetzes are formed. The known age of these formations makes it possible to determine the rate of the desalinization of the gypsum- and salt-bearing material extracted onto the soil surface and the rate of the salt accumulation in the lower part of the solonetzic horizon and in the subsolonetzic horizons in comparison with the data on the solonetzes of the background flat surfaces. The specific features of the soils in the closed microlows suggest that these soils have a polygenetic origin. The features of the recent hydromorphism predetermine the specificity of their morphology.     

Ecological-hydrological and genetic features of the soils of the Tambov Plain

Specific features of the genesis of chernozem-like, solonetzic chernozem-like soils, and hydromorphic chernozem-like solonetzes were investigated on the southern Tambov Plain. Typical chernozems occupy well drained areas. The yield of cereals is limited by the amount of precipitation. On the flat surface of weakly drained watersheds, deeply gleyed chernozem-like soils are formed under the influence of bicarbonate-calcium ground water and water stagnation on the plow sole. In closed depressions with the 1.5- to 2.0-month long stagnation of surface water on the compact lower horizons, podzolized gleyic chernozem-like soils are formed. They have favorable physical properties, weak eluvial differentiation, and rather high acidity. In humid and moderately humid years, the cereals on these soils are waterlogged; in dry years, their yield increases by 20% as compared to that on the typical chernozem. In the low undrained areas of the watersheds, solonetzic chernozem-like soils and hydromorphic chernozem-like solonetzes are formed under the influence of bicarbonate-sodium water. Despite the unfavorable physical properties of the solonetzic horizons, their better supply with moisture determines the possibility to obtain stable high yields of cereals on the solonetzic chernozem-like soils. The productivity of the gleyic chernozem-like solonetzes is low irrespective of the humidity of the year.     

Salt regime of post-irrigated soils at the Kislovsk irrigation system

The study of post-irrigated and virgin soils at the Kislovsk irrigation system has shown that the salt regime of the post-irrigated soils is determined by the (1) depth and salinity of the groundwater, (2) the litho-logical structure of the soil and subsoil, (3) the local microtopography, (4) the presence or absence of a solonetzic horizon in the post-irrigated solonetzes, and (5) the portion of solonetzes in the soil cover. The post-irrigated soil complexes on the Privolzhsk sand ridge with a groundwater depth of more than 4 m do not undergo secondary salinization. At the groundwater depth of 2.0–2.6 m, post-irrigated meadow-chestnut soils remain nonsaline, chestnut soils and solonetzes with an artificially destroyed (due to deep tillage) solonetzic horizon undergo desalinization, and solonetzes with a preserved solonetzic horizon undergo salinization in the subsolonetzic layers. The post-irrigated soils of the Khvalyn undrained sea plain used for rainfed farming have become saline in the deep part of the profile, and their plow layers remain nonsaline.     

On the manifestation of solonetzic properties in soils of the steppe and dry steppe zones in the south of Ukraine

Solonetzic soils are widespread in the south of Ukraine; some of them are represented by low-sodium solonetzes whose diagnostics is complicated by the absence of correspondence between the low content of exchangeable sodium and the clearly pronounced features of the illuvial solonetzic horizon. The statistical treatment of available literature, personal materials, and the materials of soil surveys in the south of Ukraine demonstrated that the diagnostics of low-sodium solonetzes should be based on the assessment of the degree of illuviation in the soil profile. It was shown that the degree of correlation between the content of exchangeable sodium and the degree of illuviation of the soil profile varies in dependence on the size of the statistical sample and differs for the low-sodium and medium-sodium solonetzes. Two scales characterizing the degree of soil illuviation were developed for these soil groups. It is suggested that these scales should be applied during soil surveys in the areas with solonetzic soils.     

Distribution of exchangeable cations in a soil catena in the area of Baer mounds

The soil cover of the Baer mounds in Astrakhan oblast consists of brown solonetzes on the tops of the mounds, solonetzic brown and meadow brown soils on the slopes, and solonchaks at the footslopes. The exchangeable sodium percentage in the brown soils on the tops and slopes varies from 7 to 42%. However, the morphological features of the solonetzic process are weakly pronounced in these soils, except for some cementation of the soil mass and the poorly developed columnar structure in the B horizon. This is probably related to the coarse soil texture and the relatively low exchange capacity (<10 meq/100 g of soil). The portion of exchangeable sodium reaches 2–9%. A direct correlation between the sodium concentrations in the water extracts and in the soil exchange complex is clearly seen.     

Buried vertic paleosols of the North Caucasus in the third millennia BC

Paleosols buried under kurgans dating back to the Yamnaya, Catacomb, and Post-Catacomb cultural epochs of the Bronze Age (4600–3900 BP) on the territory of the Stavropol Upland (the North Caucasus) in the area occupied by vertic chernozems were studied. It was found that solonchakous and deeply solonchakous and solonetzic chestnut soils and solonetzes proper predominated in the study area during the Bronze Age. The solonetzic process was the leading pedogenetic process in the automorphic paleosols of the second half of the third millennium BC. The vertic features were weakly developed in the automorphic paleosols; they were better manifested in the paleosols developed on the floodplains. The paleosol data were used to reconstruct the environmental conditions in the region during the Bronze Age. The climatic conditions of that period were more arid and with less sharp contrasts between wet and dry seasons in comparison with the modern climate.     

Changes in the properties of solonetzic soil complexes in the dry steppe zone under anthropogenic impacts

Long-term studies of changes in the properties of solonetzic soil complexes of the dry steppe zone under anthropogenic impacts (deep plowing, surface leveling, irrigation, and post-irrigation use) have been performed on the Privolzhskaya sand ridge and the Khvalyn and Ergeni plains. The natural morphology of solonetzic soils was strongly disturbed during their deep ameliorative plowing. At present, the soil cover consists of solonetzic agrozems (Sodic Protosalic Cambisols (Loamic, Aric, Protocalcic)), textural (clay-illuvial) calcareous agrozems (Eutric Cambisols (Loamic, Aric, Protocalcic)), agrosolonetzes (Endocalcaric Luvisols (Loamic, Aric, Cutanic, Protosodic), agrochestnut soils (Eutric Cambisols (Siltic, Aric)), and meadowchestnut soils (Haplic Кastanozems). No features attesting to the restoration of the initial profile of solonetzes have been found. The dynamics of soluble salts and exchangeable sodium differ in the agrosolonetzes and solonetzic agrozems. A rise in pH values takes place in the middle part of the soil profiles on the Khvalyn and Ergeni plains.     

Soils and the soil cover of the arkaim reserve (Steppe Zone of the Trans-Ural Region)

Soils of the Arkaim Reserve in the area around a unique settlement-fortress of the Bronze Age in Chelyabinsk oblast have been studied. These soils are generally typical of the entire Trans-Ural Plateau. The soil properties are characterized in detail on the basis of factual data on 170 soil pits and four soil catenas. The soil cover of the reserve is specified into six geomorphic groups: (a) denudational surfaces of the low mountains, (b) accumulative-denudational surfaces of the low mountains, (c) denudational-accumulative plain surfaces, (d) lacustrine-alluvial plain surfaces, (e) floodplain surfaces, and (f) slopes and bottoms of the local ravines and hollows. Chernozems occupy about 50% of the reserve; solonetzes and saline soils, 32%; meadow chernozems, 7%; and forest soils, 1%. The soils of the reserve are relatively thin; they have a distinct tonguing of the humus horizon and are often saline and solonetzic. The latter properties are inherited from the parent materials and are preserved in the soils for a long time under the conditions of a dry continental climate. The genetic features of the soils differ in dependence on the composition and age of the parent materials. With respect to the thickness of the soil profiles and the reserves of soil humus, the soils can be arranged into the following lithogenic sequence: the soils developed from the eluvium of igneous rocks-redeposited kaolin clay-montmorillonite-hydromica nonsaline and saline loams and clays. The content of C_org in the upper 20 cm varies from 2.5 to 5.6%, and the reserves of C_org in the layers of 0?C0.5 and 0?C1.0 m reach 57?C265 and 234?C375 t/ha, respectively. The soils of pastures subjected to overgrazing occupy two-thirds of the reserve. Their humus content is 10?C16% higher in comparison with that in the analogous plowed soils. Another characteristic feature of the humus in the soils of the pastures is its enrichment in the labile fraction (28?C40% of C_org).     

Properties of solonetzes on terraces of salt lakes Bulukhta and Khaki in the Caspian Lowland

A comparative assessment of pedogenetic processes in solonetzes (Calcic Gypsic Salic Solonetzes (Siltic, Albic, Cutanic, Differentic)) developing on terraces of lake depressions within the Volga–Ural interfluve of the Caspian Lowland has been performed on the basis of data on their macro- and micromorphological features and chemical, physicochemical, and physical properties. The studied soils have number of common characteristics shaped by the humus-accumulative, solonetzic, eluvial–illuvial, calcification, and gypsification processes. However, it is shown that macro- and micromorphological indicators of solonetzic processes (the development of clay–humus coatings and the character of structural units in the solonetzic (B) horizon) do not always agree with the modern physicochemical conditions of the development of this process. This is explained by differences in the degree and chemistry of the soil salinization and the depth and salinity of the groundwater. Solonetzes developing on the second terrace of Playa Khaki are distinguished by the highest water content and maximum thickness of the horizons depleted of soluble salts. They are characterized by the well-pronounced humus-accumulative process leading to the development of the light-humus (AJ) horizon. In other solonetzes, the accumulation of humus is weaker, and their topsoil part can be diagnosed as the solonetzic-eluvial (SEL) horizon. Active solodic process and illuviation of organomineral substances with the development of thick coatings and infillings in the B horizon are also typical of solonetzes on the second terrace of Playa Khaki. Micromorphological data indicate that, at present, layered clayey coatings in these soils are subjected to destruction and in situ humification owing to the active penetration of plant roots into the coatings with their further biogenic processing by the soil microfauna. The process of gleyzation (as judged from the number of Fe–Mn concentrations) is most active in solonetzes developing on the first terrace of Playa Khaki. These soils are also characterized by the highest degree of salinization with participation of toxic salts. The maximum accumulation of gypsum is typical of the heavy-textured horizons.     

Changes in the properties of soils in a solonetz soil complex thirty years after reclamation

The long-term (30 year) dynamics of a solonetz soil complex composed of solonetzic light chestnut soils and chestnut solonetzes under standard conditions and with the application of agromeliorative measures are considered. When the standard zonal agricultural practice is used, the soils of the solonetzic complex have unfavorable agrophysical, chemical, and physicochemical properties and low productivity. After 30 years of the standard three-level tillage of the soils to a depth of 40–45 cm, the productivity of the biogeocenosis decreased. Thirty years after a single rotary-milling subsoil treatment of the 20- to 45-cm soil layer using a milling tool FS-1.3, there were no morphological features pointing to the restoration of the solonetzic process. The humus content in the 0-to 20-cm and 20-to 40-cm soil layers was 2.3 and 1.7%, respectively; the content of adsorbed Na⁺ in the 20-to 30-cm layer was 11.6% of the total exchange capacity, or 38% lower than its content in the reference soil. The additional yield reached 30–70% and more of that obtained with the standard agricultural technology used during the whole period under investigation. The method of systems biogeotechnology (systems bio-geo engineering) is proposed as a method for the preventive control of soil evolution and the maintenance of the stability and high productivity of the soil cover.     

Diagnosis of solonetzic process in virgin and agrogenically transformed soils of different regions

To diagnose solonetzic process in virgin and agrogenically transformed soils of solonetzic soil complexes in the chernozemic and chestnut soil zones of European Russia and Western Siberia, their swelling kinetics and physicochemical characteristics were been studied. It was shown that a simultaneous application of these two approaches is more efficient than their separate use. The degree of manifestation of solonetzic process in the studied soils was determined. Swelling curves of sodic reclaimed solonetzes of Lyubinsk district of Omsk oblast and of a virgin solonetz of the Baraba Lowland with a moderate content of adsorbed sodium proved to be similar to those described for the vertic soils with a low infiltration capacity in the North Caucasus.     

Saline-alkali soils of Russia

Diagnostics, methods of evaluation, and geography of saline-alkali (soda) soils are discussed. The saline-alkali soils include soils of different genetic types with the following chemical properties: the pH of the water suspensions equal to or higher than 8.5; the total alkalinity exceeding 1.4 meq/100 g of soil and the sum of water-soluble calcium and magnesium; and the presence of soluble “alkaline” salts in the soil profiles, the hydrolysis of which results in the alkaline reaction of the soils. The chemical properties of the saline-alkali soils are largely related to the presence of soda (Na₂CO₃, NaHCO₃) in the soils. According to their morphological properties, saline-alkali soils are divided into two groups: alkaline soils with an undiferentiated profile and without a morphologically pronounced solonetzic (natric) horizon, and alkaline soils with a pronounced natric horizon (solonetzes). Solonetzes, in turn, are divided into (a) alkaline solonetzes (with soda or with soda and neutral salts), (b) solonetzes salinized with neutral salts (saline soils) with increased alkalinity in the solonetzic and lower lying horizons, (c) saline solonetzes throughout the profile, and (d) leached solonetzes containing no soluble salts in the profile and almost no exchangeable sodium in the soil exchange complex (SEC) (“dead” solonetzes). The latter two groups of solonetzes cannot be ranked among the alkaline soils. The alkalinity of the saline-alkali soils under study is due to carbonate and bicarbonate ions (carbonate alkalinity), organic acid anions (organic alkalinity), and borate ions (borate alkalinity). The carbonate alkalinity is due to both soda (Na₂CO₃, NaHCO₃) and CaCO₃.     

Changes in the soils of solonetzic associations in 30 years after their reclamation with the use of moldboard plowing,deep tillage with a three-tier plow,and deep rotary tillage

Changes in the properties of solonetzic soil associations (chestnut solonetzic soils and chestnut solonetzes) in the dry steppe after their reclamation have been studied for 30 years. The reclamation included the deep three-tier plowing and the approach of rotary tillage. A single rotary tillage operation resulted in the formation of fine aggregates of equal sizes in the plow layer; any morphological features of the restoration of solonetzic pedogenesis are absent. The atmospheric moisture easily penetrates into the soil, and soluble salts are leached off to a great depth. In 30 years since the soil amelioration with the use of a PMS-70 rotary tiller, the humus content has increased up to 3.3% in the upper 20-cm-thick layer and up to 2.4% in the layer of 20–40 cm. The content of adsorbed Na⁺ in the 20- to 30-cm-thick layer has decreased to 10.6% of the cation exchange capacity (in comparison with 19.8% in the nonreclaimed soil). The spatial heterogeneity of the soil cover has decreased in comparison with that prior to the reclamation. During the entire observation period, crop yields gained from the fields reclaimed with the use of the rotary tiller have been by 25–60% higher in comparison with those on the fields with traditional treatments.     

Specific surface area and wetting heat of different soil types in European Russia

The surface properties (specific surface area and wetting heat) of the solid phase were estimated for the main soil types of European Russia: soddy-podzolic, alluvial, and gray forest soils; typical, leached, ordinary, and vertic chernozems; and soils of the solonetzic complex. It was found that the values of the specific surface area and wetting heat are indicative of particular features of the genetic horizon of each soil type. Changes in these soil properties under the effect of different anthropogenic impacts were studied. The bonding strength between the adsorbed water and the soil solid phase was characterized. It was shown that the water content at the potential of the first wetting film layer is close to the content of strongly bound water calculated from the wetting heat of the soils.     

Irrigation of steppe soils in the south of Russia: Problems and solutions (Analysis of Irrigation Practices in 1950–1990)

Experience in irrigation of chernozems in the steppe zone of Russia for a period from 1950 to 1990 is analyzed. By the end of this period and in the subsequent years, the areas under irrigation reduced considerably, and the soil productivity worsened. This was caused by the improper design of irrigation systems, on the one hand, and by the low tolerance of chernozems toward increased moistening upon irrigation, on the other hand. The analysis of the factors and regimes of soil formation under irrigation conditions shows that irrigation-induced changes in the soil hydrology also lead to changes in the soil physicochemical, biochemical, and other properties. In particular, changes in the composition of exchangeable cations lead to the development of solonetzic process. In many areas, irrigation of chernozems was accompanied by the appearance of solonetzic, vertic, saline, and eroded soils. The development of soil degradation processes is described. In general, the deterioration of irrigated chernozems was related to the absence of adequate experience in irrigation of steppe soils, unskilled personnel, improper regime of irrigation, and excessively high rates of watering. In some cases, the poor quality of irrigation water resulted in the development of soil salinization and alkalization. To improve the situation, the training of personnel is necessary; the strategy of continuous irrigation should be replaced by the strategy of supplementary irrigation in the critical periods of crop development.     

Zonal,provincial, lithological,and geomorphic features of soil salinization in the Southern federal okrug of Russia

The relationships between soil salinization and the zonal and provincial bioclimatic conditions, the lithological composition of the sediments, and the geomorphic features of the territory have been analyzed for the Southern federal okrug of Russia. It is shown that the lithological and geomorphic conditions (relief, salinity of parent materials, degree of drainage, and the depth of saline groundwater) play an important role in the distribution of salt-affected soils against the background of the more general regularities specified by the climate. The participation of salt-affected soils in the soil cover of the Southern federal okrug increases in the eastward direction from the forest-steppe zone to the semidesert zone in agreement with an increase in the aridity and continentality of the climate. The chemical composition of soil salts also changes: the sulfate and soda-sulfate types predominate in the forest-steppe zone; the sulfate type or the sulfate type with the participation of soda, in the steppe zone; the sulfate-chloride type, in the dry steppe zone; and the chloride type, in the semidesert zone. The lithological and geomorphic conditions within the particular zones and provinces affect the distribution pattern of the salt-affected soils and the degree and chemistry of the soil salinization. The areas of salt-affected soils were calculated with the use of a digital version of the Map of Salt-Affected Soils of Russia (1: 2.5 M scale) with due account for the participation of these soils in the soil cover of the particular delineations and the data on the depth of the upper boundary of the salt-bearing horizons, the degree and chemistry of the soil salinization, and the area of solonetzes and solonetzic soils.     

Comparison of two approaches for assessing solonetzic process in the virgin and human-transformed soils of the dry steppe zone

Two approaches to diagnose the development of secondary solonetzic process in the reclaimed solonetzes and solonetzic soils of the dry steppe zone were compared. For this purpose, the kinetics of swelling of crushed soil and the physicochemical characteristics of the soils were studied in the same samples. Both approaches gave similar results for the soils with the absence of the solonetzic process and for the soils in which this process was clearly manifested. To assess the risk of the development of the solonetzic process in the soils where its morphological manifestations are absent, the determination of the swelling kinetics and the calculation of the B index of the physicochemical conditions may be used.     

Quantitative characteristics of soil mesofauna in the semidesert solonetzic complex of the north Caspian region

The results of long-term quantitative assessments of the invertebrate populations inhabiting the soils of a clayey semidesert are analyzed. The dominant species in the different soils of a solonetzic soil complex are compared. The distribution patterns of the dominant groups of invertebrates in relation to the soil and vegetation complexity dictated by the clearly expressed microrelief are discussed. The changes in the populations of the soil invertebrates are considered against the background of changes in the precipitation during the growing season in different years. It is shown that the population density of the soil invertebrates varies within broad limits in all the soils of the complex. At the same time, it remains considerably lower in the solonchakous solonetzes of the microhighs in comparison with that in the soils of the slopes and microlows. The most contrasting differences in the species composition and the numbers of soil invertebrates are observed for the solonetzes of the microhighs and the meadow-chestnut soils of the microlows. This work was performed at the Dzhanybek Research Station of the Institute of Forestry of the Russian Academy of Sciences on the Volga-Ural interfluve (30 km to the north of Lake El’ton).