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.     

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.     

MICROMORPHOLOGICAL QUANTIFICATION OF CLAY ILLUVIATION

Three concepts are introduced to describe the extent of clay illuviation phenomena quantitatively for pedogenic interpretations: (1) the degree of clay illuviation per thin section or (sub)horizon, subdivided into 5 classes, ranging from negligible (< 0.3 per cent by vol.) to very strong (> 7 per cent by vol.) clay illuviation; (2) the degree of reworking of the illuviated clay, subdivided into 3 classes, ranging from weak (< 30 per cent reworking) to strong (> 70 per cent); (3) the profile clay illuviation index: the sum of products of clay illuviation percentage per (sub)horizon and horizon thickness (in cm). The index ranges from very low (< 50 per cent cm) to very high (> 700 per cent cm). A distinction was made between the profile index based on the in situ illuviation features only and that based on all the illuviation features.     

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.     

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.     

Geochemical characterization of placic horizons in subtropical montane forest soils,northeastern Taiwan

Well‐developed placic horizons have been found in subalpine forest soils with large clay contents in Taiwan. We investigated their formation processes in five profiles in a subalpine ecosystem of northeastern Taiwan, using scanning electron microscopy (SEM), energy‐dispersive spectrometry (EDS), electron probe microanalysis (EPMA), differential X‐ray diffraction (DXRD) and chemical extractions. The placic horizons, ranging from 3‐ to 17‐mm thick, always occurred above argillic horizons with abrupt changes in pH and texture between the two horizons. When fully developed, the placic horizons were clearly differentiated between upper and lower sub‐horizons. EDS and chemical extractions revealed that the cementing materials in both were predominantly inorganic Fe oxides. However, contents of aluminosilicates and organically complexed Fe and Al were greater in the lower than in the upper placic sub‐horizon. Results of EPMA indicated that interstitial fine materials in the upper placic sub‐horizon were composed mainly of Fe oxides, whereas Fe oxides were codominant with illuvial clay in the lower sub‐horizon. These analyses identified the migration of Fe and clay as major formation processes in both sub‐horizons. We hypothesize that there is a pedogenic sequence that starts with clay illuviation, followed by podzolization. The resultant textural and permeability differentiation reinforces the tendency to profile episaturation that is already inherent from the heavy rainfall and clayey surface soils. Topsoil Fe is therefore reduced and mobilized, and then illuviated with clay and organically complexed Fe/Al to initiate the lower placic sub‐horizon. The poor permeability of this layer reinforces the moisture conditions in the surface soils, and the further reduction, illuviation and deposition of inorganic Fe to form the upper placic sub‐horizon.     

Clay illuviation in Red Mediterranean soils

Theories regarding pedogenesis in Red Mediterranean soils have undergone several stages of development. The concept of clay illuviation in these soils was not a part of early theories and it is not yet unanimously accepted as a leading soil forming process. A methodology is presented for studying the illuviation of clay in these soils emphasizing typology of textural features and fabrics. The problem of age determination is also addressed, through the use of radiometric dates and correlation with archaeological artifacts. Clay illuviation in Red Mediterranean soils under present day environmental conditions suggests that it occurs presently only on humid and sub-humid margins of the Mediterranean basin. Elsewhere illuvial clay accumulations are inherited from Interglacial periods. Red Mediterranean soils during glacial periods were eroded, colluviated, aggraded with aeolian dust, calcitic fraction of which was redistributed in form of calcitic features and eventually were affected by water logging. An example of water logging of Red Mediterranean soils (Mamora, Morocco) which took place during the last Glacial cycle, consists of yellow illuvial clays accompanied by a yellowing of the ground mass. During earlier cycles water logging resulted in whitish grey stains in which hydromorphic textural features were deposited.     

Clay illuviation and calcium carbonate accumulation along a precipitation gradient in Kansas

One of the significant features of loess-derived soils in Kansas is the occurrence of clay-rich subsurface horizons above a layer enriched with pedogenic carbonates. In order to examine the extent of clay increase and pedogenic carbonate enrichment in a precipitation gradient, ten soil profiles from three different precipitation regions were studied using micromorphological and mineralogical techniques. The precipitation gradient was divided into three groups: 400–550 mm, 550–750 mm, and 750–1100 mm regions. The objectives were to (1) understand the cause of clay orientation in clay-rich horizons (2) investigate the reasons for the clay increase, and (3) observe the interaction of clay and pedogenic carbonate accumulation features along a precipitation gradient in Kansas. Although clay films were identified in the field for soils in the 400–550 mm regions, illuvial clay films were not observed in thin section analysis. The clay accumulations mostly occurred as grain coatings. The rest of the clay accumulations observed were very thin, striated, and mostly associated with voids. The argillic horizons had a granostriated b-fabric, which indicates stress orientation of micromass caused by high shrink–swell activity. Thick and continuous illuvial coatings were observed in the buried horizons of paleosols. In the other two regions where precipitation exceeds 550 mm, illuvial clay coatings with strong orientation were observed along with thin and striated stress-oriented clay. Both types of clay orientations exceeded 1% of the cross-sectional area for the thin section. Although illuvial clay features and pedogenic carbonates were observed in all soils at approximately the same depth, complete obliteration of clay coatings was not observed in these horizons. In-situ weathering of biotite was one of the reasons for the clay increase in all soil profiles. In all soils studied, the clay increase and cause of clay orientation cannot be attributed to a single genetic process or event. Both illuviation and shrink–swell activity were involved in the orientation of clay. Although orientation of clay and pedogenic carbonates were observed in all soils at approximately the same depth, the decomposition of clay coatings was not observed in these horizons.     

Study of a toposequence for variability in micronutrients from the moist subhumid Siwalik agro-ecological subregion of Punjab

A toposequence from the moist subhumid Siwalik agro-ecological subregion ofPunjab was studied for available and total micronutrient variability. The toposequence showed the least developed soils with only an A–C horizon sequence on steep slopes and a well-developed profile with an argillic horizon on moderate slopes. The soils consist of a variety of minerals and thus belong to the mixed mineralogy class. There were higher levels of DTPA-extractable micronutrients in the surface horizon than in the subsurface horizon due to their association with organic matter through chelation and adsorption. The surface horizons have relatively lower total micronutrient contents than the subsoil horizons. Soils from moderate slopes and lower terraces showed higher total micronutrients contents in the middle horizons, suggesting some redistribution of the constituents due to the illuviation process of pedogenesis. DTPA-extractable and total micronutrients showed an irregular increasing trend from the steep slope to the lower terrace soils. The DTPA-extractable micronutrients showed relatively greater variability (8–107%) than the corresponding total micronutrient contents (2–34%), suggesting the relatively dynamic nature of the former. Variability in DTPA-extractable and total micronutrients within and among the different soils was caused by several processes involved in the differentiation ofmicronutrients. DTPA-extractable micronutrients show the influence of organic matter through the processes of chelation and adsorption, whereas total micronutrients varied due to differences in pedogenic processes of eluviation/ illuvial on different landscapes and textural variation.     

Dynamics of the dispersity of model soddy-podzolic soils in a long-term lysimetric experiment

Changes in the particle-size composition and specific surface area were considered for soddy-podzolic soils in large lysimeters of the Soil Research Station of Moscow State University, which simulated anthropogenically modified soils with different sequences of genetic horizons in a long-term (1961–2002) experiment. Changes were detected in the degree of dispersion of the soil horizons occurring under conditions inadequate for their genesis: a decrease in the clay content by 7% and in the external specific surface area from 28.9 to 7.4% in the illuvial horizon placed on the surface and the accumulation of colloidal mineral fractions in the Ap horizon buried at a depth of 80–100 cm. The degree of change depended on the occurrence depth of the buried horizons and increased with approaching the surface. The changes in the dispersity of the model soddypodzolic soils in the lysimetric experiment were primarily due to the translocation of the fine fractions with vertical water flows. The long-term experiment carried out under completely controlled conditions showed that, at the initial functioning stages of the soils with anthropogenically modified profiles, this process was well detectable and significant for the monitoring studies.     

A MATHEMATICAL MODEL FOR THE DIFFERENTIAL MOVEMENT OF TWO SOIL CONSTITUENTS INTO ILLUVIAL HORIZONS: APPLICATION TO CLAY RATIOS IN ARGILLIC HORIZONS

The effects of the migration of two soil constituents into illuvial horizons is described by a set of equations. Differential movement of clay fractions during illuviation causes changes in the fine to total clay ratios in A and B horizons. A mathematical model is used for the interpretation of clay fraction data in order to estimate the degree of profile development, the amounts of fine and total clay which have moved, and to determine the original composition of the parent material. No bulk density data of the soil horizons are necessary for the computation. The equations can be programmed on desk calculators. Comparison with measurements on Alfisols in temperate regions was found to be satisfactory.     

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.     

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.     

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.     

Textural differentiation in chronosequences from eastern australia,II. evidence from particle-size distributions

Data from particle-size analyses were used to determine the relative importance of the four mechanisms proposed to explain the development of strong textural contrast in the end members of four chronosequences. The mechanisms proposed were sedimentary layering, in-situ chemical weathering, clay illuviation and physical breakdown.Depth functions of fine clay: total clay ratios and detailed particle-size distributions at ø intervals from 0.6 μm to 2000 μm indicated that there had been a marked increase in fine clay in the B horizons of the older soils of each sequence, a result consistent with, but not proving, a clay illuviation hypothesis. Cumulative particle-size distribution indices showed that most profiles had texturally uniform parent materials. Changes in the ratio fine silt : total silt with depth were slight for all but one profile, indicating no significant contribution to the clay fraction by in-situ chemical weathering of the silt fraction.From changes in the depth functions of gravel with time, it was concluded that physical breakdown had occurred but that it had not been responsible for the development of the textural B horizon. The rate of disintegration was particularly high early in pedogenesis, preceding the development of texture-contrast. Breakdown contributed fines to the whole solum and was not generally any more intense in one horizon than another. Grain counts of rock fragments in the medium sand range lent support to this conclusion.Changes in the particle-size distribution of quartz from 0.2 μm to 2000 μm indicated that the contribution to the clay fraction from physical disintegration was only slight.     

Mobile iron, aluminium and carbon in sandy coastal podzols of Fraser Island, Australia: a quantitative analysis

In this paper podzols of free-draining sands in south-eastern Queensland are examined. The 14 profiles represent a chronosequence from young incipient podzols, to ancient ‘giant podzols’ of Pleistocene age, with a spodic horizon at a depth of 8–10 m. Carbon, Fe and Al were determined in pyrophosphate, and Fe, Al and Si in oxalate extracts. The resulting profile distributions were modelled by three expressions, fitted for each attribute, which accounted for surface accumulation, B horizon development and a phase (B/C horizon) of constant composition with depth. The parameters may be used to characterize soil profiles. They show that there is a tendency for the accumulation of carbon in the B horizon to be reflected by Fe and particularly A1 accumulation, which supports the proposition that carbon is directly associated with the transport of A1 and Fe. A feature of many of these soils is a deeply weathered surface with little tendency for commensurate development of an illuvial horizon. Rates of removal of Fe and Al from the A horizon were obtained by comparison of the depths of leaching with age estimates based on geomorphology, and they indicate a non-linear rate of increase in the thickness of the A horizon.     

巨尾桉工业原料林下植物多样性与土壤因子的关系

采用野外调查与室内分析相结合的方法,研究了巨尾桉工业原料林下植物多样性、土壤因子的变化特征以及二者之间的关系。结果表明,物种丰富度指数是草本层最高,而Simpson指数,Shannon—Wiener指数和均匀度指数是灌木层最高。巨尾桉林地土壤水分含量的变化规律为:母质层淀积层腐殖质层,有机质、水解氮、有效磷和速效钾含量的变化规律为:腐殖质层淀积层母质层。腐殖质层、淀积层和母质层的土壤水分含量、有机质含量与灌木层或草本层丰富度指数、多样性指数和均匀度指数无显著相关性;腐殖质层速效钾含量与草本层Simpson指数极显著相关;淀积层速效钾含量与灌木层Simpson指数极显著相关;水解氮与灌木层及草本层以Simpson指数为基础的均匀度指数,以Shannon—Wiener指数为基础的均匀度指数极显著相关;母质层土壤各因子含量与灌木层或草本层多样性指数无显著相关。研究结果为巨尾桉林的可持续经营管理提供理论基础和科学依据。     

The formation and evolution of colluvium on arable land in northern Luxembourg

The paper deals with colluvial deposits found in dry valley heads in a farmland area near the village of Berlé in northern Luxembourg. The colluvium, with a maximum depth of 1.50 m, overlies a truncated red and gray mottled IIBtb horizon of an older soil. The colluvium shows signs of groundmass illuviation in the form of matriargillans, matrans or agricutans, as this feature is variously called. These coarse grained cutans are also found in the buried IIBtb horizon, where they are superimposed upon illuviation ferriargillans. From a review of the literature it appears that matrans are generally considered to result from structural breakdown of the superficial soil horizons under human cultivation. That the colluvium was formed under cultivation is in agreement with its pollen content of practically only non-tree species associated with human occupation and cereals.The colluvium contains heavy minerals from a volcanic eruption in the Eifel which took place during the Upper-Pleniglacial or Late-Glacial of the Weichselian. Furthermore it is rich in charcoal fragments, presumably from charcoal burning after 1450 A.D. and/or from forest burning for agricultural purposes. The presence of pollen of Fagopyrum (buckwheat), which was introduced in the area around 1460 A.D., in the colluvium confirms a late-mediaeval and/or later time of formation of the colluvium.     

Unterscheidung der Subtypen Humus-, Eisenhumus- und Eisenpodsol

Differentiation of the subtypes humuspodzol, humus-iron podzol and iron podzol Humic podzols are characterized by a distinct Bh-horizon and deep humus illuviation (humic bands). They may be thus recognized by morphological features. Differentiation of humic podzols on layered sands, of humus-iron podzols and of iron podzols is only possible by quantitative analytical data. For that the ratio of pyrophosphate-extractable C/Fe is proposed: humic podzols (Bh) > 10, humus-iron podzols (Bhs) 3–10, iron podzols (Bs) < 3. For differentiation of soil varieties quantities of illuviated matter in the investigated illuvial subhorizons (Bh, Bhs, Bs) may be chosen.