The nature of alkalinity in virgin and anthropogenically modified solonetzes of northern Kalmykia

The alkalinity of virgin solonetzes and its changes under the impact of 50-year-long afforestation and agricultural loads were investigated. It was found that the maximum alkalinity in both virgin and anthropogenically modified solonetzes is typical of the gypsum-free carbonate horizons containing exchangeable sodium. In these horizons of the virgin (B2, BCca) and anthropogenically modified (BMK, BCca) solonetzes, sodium carbonates (Na₂CO₃ and NaHCO₃) are present because of the in situ ion exchange reaction between sodium in the exchange complex and calcium of calcium carbonates in the solution (the Gedroits reaction). The boundaries of the occurrence of soda in the soil profile are controlled by calcium compounds: the upper boundary of soda formation is specified by the presence of calcium carbonates, whereas the lower boundary is specified by the appearance of calcium sulfates (gypsum). In other horizons, including the solonetzic (B1) horizon, in which calcium carbonates are absent, soda is not formed, and the soil pH and carbonate alkalinity are controlled by the carbonate-calcium equilibria.     

Alkalinity of virgin solonetzes in northern Kalmykia (the Arshan-Zel’men Experimental Station)

The alkalinity of virgin solonetzes of the Ergeni Upland, Ergeni Plain, and Sarpinsk Lowland has been studied. These soils are characterized by the neutral salinization and the high alkalinity of the solonetzic and subsolonetzic horizons. The analysis of the soil water extracts demonstrated that the highest alkalinity is typical of the subsolonetzic horizons containing calcium carbonates (the B2 and BCca horizons). In the solonetzic horizons without CaCO₃, the alkalinity is lower despite the high exchangeable sodium percentage (up to 42%). The alkalinity of the solonetzic and subsolonetzic horizons may be conditioned by two processes: (a) the hydrolysis of the exchange complex (EC) containing sodium (EC-Na + H₂O ↔ EC-H + Na⁺ + OH⁻) and (b) the reaction of the ion exchange with the substitution of calcium for sodium in the exchange complex (EC-2Na + CaCO₃ ↔ EC-Ca + 2Na⁺ + CO₃²⁻). Calculations performed on the basis of the thermodynamic equations of the physicochemical equilibria according to the LIBRA program indicate that soda is absent in the solonetzic horizons, whose alkalinity is related to the carbonatecalcium equilibria. The high alkalinity of the calcareous subsolonetzic horizons is related to the presence of soda in combination with CaCO₃. The formation of soda in these horizons is due to the reaction of ion exchange described by Gedroits.     

Gypsic pedofeatures and elementary pedogenetic processes of their formation

Elementary pedogenetic processes forming gypsic pedofeatures in gypsiferous soils are discussed. Several groups of such processes are distinguished: (1) weathering of gypsum-bearing rocks; (2) gypsum formation associated with weathering of sulfuric (pyritic) rocks; (3) precipitation of gypsum owing to the inflow of soil solutions saturated with Ca and SO₄ and their evaporative concentration; (4) gypsum formation owing to exchange reactions in soils between calcium in the exchange complex and sodium sulfate solutions; (5) gypsum formation upon interaction of calcium carbonates with sodium sulfate water resulting in the loss of CaCO₃ and gypsum accumulation (decalcification process); (6) colluvial and alluvial redeposition of gypsum in the landscape with its accumulation in the subordinate positions, where gypsiferous soils are formed; and (7) eolian deposition of gypsum on the soil surface with the formation of gypsum-bearing horizons. The micromorphological specificity of the gypsic pedofeatures reflects the processes of their destruction and/or accumulation in the soil profiles. It is shown that gypsum accumulation in soils is a pedogeochemical process that manifests itself in different natural zones upon the presence of gypsum sources.     

The origin of sulfate salts in soils developed on Maikop clays in the North Caucasus region (According to data of the isotope composition of sulfur)

The ratio of ³²S/³⁴S stable isotopes was determined for soils developed on the Maikop clay sediments in the North Caucasus region in order to study the salt geochemistry in the soils. The soil sulfates were proved to be polygenetic. Three groups (generations) of sulfates of different geneses were distinguished according to their isotopic composition (³⁴S). In the underlying deposits and, partially, in the salt-bearing horizons of the soils, secondary sulfates originated from the oxidation of sulfides contained in the marine clay predominate. In the soil profiles, the sulfates inherited from the parent material (marine clay) are mixed with sulfates arriving with the atmospheric precipitation. The portion of the latter reaches about 30% of the total amount of sulfates in the soils. The salt (gypsum)-bearing horizons were formed in the course of the eluvial-illuvial redistribution of salts to the depth of seasonal wetting. The mobilization of sulfate salts from the underlying deposits and their transport to the upper parts of the soil profile with ascending water flows in the course of evaporation from the soil surface did not play a significant role in the accumulation of sulfates in the studied soils.     

Soil properties that affect sulphate adsorption by palexerults in western and central Spain

Abstract

The beneficial action of gypsum in suppressing aluminum (Al) toxicity in Bt horizons of Ultisols is related to the self‐liming effect of the adsorption of sulphate (SO₄ ^2‐) ion. The relationship between SO₄ ^2‐ adsorption by gypsum‐amended soils and some components and properties of 38 surface and subsurface horizons from seven Palexerults in western and central Spain was analyzed. The highest correlations of maximal SO₄ ^2‐ adsorption as determined from langmuir isotherms were with clay, free iron oxyhydroxides (Fe_dcb), and exchangeable Al contents, and pH. Liming reduces SO₄ ²’ ion adsorption; consequently, the joint application of limestone and gypsum to the surface of these soils results in increased availability of gypsum for the subsurface horizons.     

Thermal properties of typical chernozems in Kursk Oblast

Thermal diffusivity and heat capacity of virgin and plowed heavy loamy typical chernozems of Kursk oblast were studied. Thermal diffusivity was determined in the course of step-by-step drying of the initially capillary-saturated samples to the air-dry state. Specific heat capacity was determined for absolutely dry samples. Volumetric heat capacity was calculated according to the de Vries equation. Thermal diffusivity varied within the ranges of (1.15–3.46) × 10^–7 m²/s in the Ap horizon, (1.14–3.35) × 10^–7 m²/s in the А1 horizon, (1.49–3.70) × 10^–7 m²/s in the АВ horizon, (1.49–3.91) × 10^–7 m²/s in the В1 horizon, and (1.60–3.80) × 10^–7 m²/s in the Вса horizon. The thermal diffusivity vs. water content dependencies had distinct maximums and were flattened in the range of low water contents. The maximums were most pronounced for the mineral B1 and Bca horizons; for the A1 and Ap horizons, the curves were rather S-shaped. Volumetric heat capacity of the air-dry soils varied from 0.96 J/(cm³ K) in the A1 horizon to 1.31 J/(cm³ K) in the Bca horizon; in the state of capillary saturation, it varied from 2.79 J/(cm³ K) in the А1 horizon to 3.28 J/(cm³ K) in the Вса horizon. Thermal properties of topsoil horizons were higher in the plowed chernozem compared with the virgin chernozem, which is explained by an increase in the bulk density and a decrease in the organic matter content in the plowed soil.     

Field application of industrial by-products as Al toxicity amendments: chemical and mineralogical implications

Lime, gypsum and various gypsum‐like by‐products have long been applied to soil surfaces as ameliorants of soil acidity and aluminium and manganese toxicity. We examined changes in chemical and mineralogical properties at two different depths in two acid soils one year after the application of gypsum, phosphogypsum + dolomitic residue, red gypsum + dolomitic residue, sugar foam, and sugar foam + mined gypsum. All treatments were found to increase the proportion of Ca²⁺ and decrease those of Al³⁺ and Mn²⁺ in the exchange complex of the surface and subsurface horizons, thus reducing its effective Al and Mn saturation. However, the mined gypsum treatment resulted in losses of Mg²⁺ from the Ap horizon of the soils, and the sugar foam treatment was not so effective with the AB horizons as the other treatments. The combined application of both gypsum‐like by‐products and the dolomitic residue proved the most effective choice with a view to reducing the effective Al and Mn saturation of the exchange complex in the Ap and AB horizons. In addition, both treatments reduced Mg²⁺ losses at both depths. Finally, all treatments resulted in the formation and retention on mineral and organic surfaces of a large fraction of the Al³⁺ released by exchange with Ca²⁺ as Al polymers. This is quite consistent with the observed changes in the CuCl₂‐, oxalate‐ and DTPA‐extractable Al contents as well as by SEM and EDS analyses. Based on these results, the use of the appropriate mixtures of these by‐products is an effective alternative to that of mined gypsum and lime to alleviate soil acidity and reduce toxic concentrations of Al³⁺ and Mn²⁺ in agricultural acid soils.     

Ionic balance in the interaction of meadow-chestnut soils with saline groundwater under model experimental conditions

The effect of ascending migration of medium and highly saline sodium-sulfate groundwaters on the salinization of nonsaline meadow-chestnut soils was simulated and quantified in model column experiments over 10 months. Sodium from saline water accumulated in the soil as similar amounts of water-soluble and exchangeable compounds in lower soil horizons. Calcium accumulation as CaCl@2 in the topsoil and as gypsum throughout the profile was accompanied by substitution of Na for exchangeable Ca. Magnesium and chlorine mainly accumulated as soluble salts in the topsoil, and sulfate ions accumulated as gypsum through the profile and as soluble salts in the lower part of the column.     

Contribution of separate solid-phase components to the formation of the cation exchange capacity in the main genetic horizons of meadow-chestnut soils

Different types of cation exchange capacity (CEC) and related chemical properties were determined in the main genetic horizons of meadow-chestnut soils in the mesodepressions at the Dzhanybek Research Station of the Institute of Forestry of the Russian Academy of Sciences. In the A horizon, the CEC is mainly due to the organic matter from the clay and coarse fractions, which provides 36% of the soil CEC, and to labile silicates and other clay minerals of the clay fraction. In the Bt horizon, the CEC is mainly provided by the labile minerals of the clay fraction and organic matter of the clay and coarse fractions. The standard soil CEC was found to be significantly higher than the sum of the exchangeable cations in the A horizon and slightly lower than the sum of the exchangeable cations in the Bt and Bca2 horizons. This difference can be related to the fact that the NH₄⁺ ion, which is selectively adsorbed by clay minerals, is used as a displacing cation during the determination of the exchangeable bases, while the Ba²⁺ ion, which is more selectively adsorbed by organic matter, is used during the determination of the standard CEC. In all the genetic horizons, the experimentally determined value of the standard CEC almost coincides with the CEC value obtained by summing the standard CECs of the different particle-size fractions with account for their contents; hence, this parameter is additive in nature.     

Penetration resistance of gypsiferous horizons

To assess the importance and the possible causes of penetration resistance of horizons with gypsum, 20 horizons in seven irrigated profiles were studied. Gypsum contents ranged from 0 to 900 g kg^?1. Penetrometer tests were performed on undisturbed soil cores by means of a needle penetrometer at different matric potentials. The increase of penetration resistance on drying was caused by changes in the effective stress of the soils, calculated from their soil water characteristic curves. Multiple regression tests showed that besides water content and bulk density, gypsum content was positively correlated with penetration resistance. It seems that in the soils studied the increase of penetration resistance caused by gypsum is due to the growth of gypsum crystals in pre-existing pores, which reduces the volume of regular and continuous voids necessary for root growth.     

Morphometric profiles of pore space in loamy soils of the forest and steppe zones of European Russia

A computer-based image analysis of vertically oriented thin sections was applied to study changes in the shape and orientation of fine soil macropores (d = 0.2−2.0 mm) in the profiles of soddy-podzolic soils and typical (migrational-mycelial) chernozems. Generalization of the obtained morphometric data was based on the theory of mereology, a scientific discipline studying the structure (part-whole relationships) of classified objects. As a first approximation, generalized data characterized archetypes of morphometric porespace profiles of the studied soils. The archetype of the pore-space profile of the soddy-podzolic soil consists of four components (meronyms) corresponding to the humus-accumulative, eluvial, textural (clay-illuvial), and transitional to the parent material (BC) horizons. Sharp boundaries between the upper horizons specify sharp changes in the studied meronomic indices of the shape and orientation of soil pores. The pore-space profile of the migrational-mycelial chernozem consists of two major components: specific pores in the granular dark-humus (AU) horizon and complex pore space of the BCA and BCca horizons that are poorly differentiated with respect to the shape and orientation of their fine macropores despite clear genetic differences between these horizons. Pore-space patterns in the lower (transitional to the parent material) horizons of the studied soils are characterized by the high degree of similarity (>75%). Pore-space patterns in the upper horizons of the studied soils are different; the level of their similarity does not exceed 24–41.5%. The results obtained in this study hold promise in the use of morphometric characteristics of the pore space in separate genetic soil horizons as meronyms composing archetypes of the pore-space profiles of different soils. Such archetypes may be used for diagnostic purposes as reference pore-space profiles of the particular types of soils.     

Dynamics of Sodium in Saline and Sodic Soils

Abstract

Soil salinization and sodication affect large areas of agricultural land in the world. Amelioration of these soils to make them suitable for agricultural production depends on understanding sodium dynamics and chemical interactions governing nutrient availability. Three locations in eastern Croatia were characterized to the 5‐m depth. The two solonetz‐solonchak soils were alkaline, whereas the solonetz soil had near‐neutral A/E horizon and alkaline deeper horizons. Electrical conductivity of the saturated extract (ECe) was greater than 4 dS m^?1 in the top horizons in the solonetz‐solonchak soils. The solonetz soil had 2.8–4.7 dS m^?1 in shallow A/E, CG, and G horizons and up to 6.3 dS m^?1 below 1.5 m. Highly alkalinized sodic horizons (exchangeable sodium percentage, ESP >20) had 24–47% Ca²⁺ and 27–33% Mg²⁺ on the cation exchange complex. Sodium adsorption ratio (SAR) was high (18–26) in the P horizon and even more so in Bt,na horizon (35–36) of solonetz‐solonchak soils. A strong negative exponential relationship existed between soluble Ca²⁺ and SAR (SAR increased greatly when Ca²⁺ dropped to around 3 mg dm^?3). An increase in pH to greater than 8.4 resulted in an exponential increase in SAR. Leaching of Na⁺ with successive volumes of water was similarly effective for the P and Bt,na horizons in the solonetz‐solonchak soils, but SAR remained greater than 15 even after six successive cycles of leaching. In conclusion, extensive amelioration of tested soils with gypsum and leaching will be required to overcome poor physical and chemical characteristics caused by various degrees of alkalization and sodication to bring these soils into production.     

Exchange-induced dissolution of gypsum and the reclamation of sodic soils

A study was undertaken to define the dissolution kinetics of gypsum in the presence of ion exchange resins and to study sodic soil reclamation in laboratory soil columns.
Gypsum pellets were prepared at 1.5 MPa pressure and the time course of their dissolution followed by measuring the electrical conductivity of the solution. Dissolution experiments were carried out in distilled water with and without Na- and Cl-saturated exchange resins or a combination of the two. The results indicate that in the presence of resin the reaction is first order as calcium and/or sulphate are removed from solution by the resin driving the reaction to completion. In water alone the reaction follows second-order kinetics and depends on the rate of mixing as the reaction is transport controlled.
The effect of gypsum placement (uniformly mixed with the entire soil, mixed with the top third of the soil, applied to the soil surface or applied as a saturated gypsum solution) on the efficiency of exchangeable sodium removal, leaching of soluble salts and soil hydraulic conductivity was studied. In addition, the effect of various flow rates on reclamation efficiency was investigated.
The amount of leachate required for reclamation was found to be dependent on gypsum placement, tending to decrease in the order mixed < top third mixed < saturated gypsum solution < gypsum surface application < water. Soil hydraulic conductivity was much higher in the mixed gypsum column than in the gypsum applied on the surface; a result of the higher effective gypsum solubility. Sodic soil electrical conductivity in the presence of solid-phase gypsum is linearly related to the total amount of exchangeable sodium expressed in mol dm⁻³.     

The use of gypsum for preventing soil sodification: effect of gypsum particle size and location in the profile

Laboratory studies were conducted on a mixture of surface soils from the Nile Delta (Egypt). Twenty-two soil columns, initially saturated both with respect to their water-holding capacity and to their base exchange capacity with calcium, contained 0.0, 0.25, 0.5, 1.0 and 2.0 per cent solid gypsum in the total weight of the solid material in the column. Three particle sizes of gypsum (>0.5, 0.5–1 and 1–2 mm) were mixed either with the top layer or with the whole soil column. The result of leaching these columns with saline water (36 meq 1^?1 NaCl+4 meq 1^?1 CaCl₂) at 0.1 cm h^?1 was compared with a mathematical model based on thermodynamic equilibria. The three different particle sizes gave the same experimental results. Applying a given amount of gypsum to the surface soil was more effective in reducing the exchangeable sodium percentage (ESP) than mixing the same quantity through the soil. The mathematical model adequately predicted the changes in the soil column.     

Gypsum applications to aggregated saline—sodic clay topsoils

Gypsum application was highly efficient as a treatment for reducing amounts of exchangeable sodium and inhibiting clay dispersion in highly structured saline-sodic clay topsoils. Phosphogypsum, applied to the surfaces of aggregates in soil columns treated with simulated rainfall, was dissolved efficiently by frequent intermittent ‘rainfall’. The calcium released by dissolution displaced sodium on the exchange complex within soil aggregates ranging from 7.5 mm to 45 mm in diameter. Of the applied calcium, 64–74% was transferred to ion exchange sites; however, almost one-third of this adsorbed calcium displaced exchangeable magnesium. Comparison of three gypsum treatments, phosphogypsum, rock gypsum, and a saturated gypsum solution (representing a top dressing of highly soluble gypsum), showed that the effectiveness of calcium uptake on the exchange complex followed the order: rock gypsum < saturated solution < phosphogypsum, but differences were small. Application of phosphogypsum caused a 90% reduction in the total amount of dispersed clay released in column leachates, and decreased the maximum clay concentration in the effluents by at least 80%, when compared to soils leached without gypsum treatment.     

SW—Soil and Water: Improvement of Whitish Oasis Soil, Part 1: Field Experiments with a Four-stage Subsoil Mixing Plough

A prototype four-stage subsoil mixing plough was designed in Japan and built in China for the improvement of whitish oasis soil. The machine was transported to two places in China for field tests where the whitish oasis soil is found. This paper presents the trash mixing rate into mixed layer of Bca and C horizons, the inverting rate of the Bca and C horizons and the draught of the plough in the whitish oasis soil.The results show that the rolling resistance of the tracked vehicle (T802), on which the plough was mounted, was about 8 kN and the draught of the first plough body which tilled the Ap horizon was about 4 kN with a working depth of 200 mm and a working width of 500 mm. The draught of the second plough body, which tilled the surface of the Ap horizon, was about 2 kN with a working depth of 50 mm. The draught of the third plough body increased steeply with greater working depths. The draughts were about 8, 14 and 24 kN, respectively, for working depths of 117, 239 and 300 mm. The draught of the fourth plough body also increased steeply with greater working depth. The draughts were about 7, 14 and 18 kN, respectively, for working depths of 117, 178 and 239 mm. When the whitish oasis soil was disturbed by the plough bodies, it was observed that the whitish oasis soil was very hard but comparatively brittle and easily broken up. This property explains the smaller draught requirements in the whitish oasis soil despite a greater soil strength. The values of the soil-inverting rate ranged between 0·45 and 0·6, and the average value was 0·5. Perfect inversion of the Bca and C horizons was not possible, but good mixing was achieved by the plough. The average trash mixing rate in Inner Mongolia was 0·85, and that in North of River was 0·95. These data show that even in Inner Mongolia where the trash material is long, a fairly uniform trash mixing was possible.     

Influence of Lime and Gypsum on Growth and Yield of Upland Rice and Changes in Soil Chemical Properties

Upland rice is an important crop in the cropping systems of South America, including Brazil. Two greenhouse experiments were conducted to determine influence of lime and gypsum on yield and yield components of upland rice and changes in the chemical properties of an Oxisol. The lime rates used were 0, 0.71, 1.42, 2.14, 2.85, and 4.28 g kg^?1 soil. The gypsum rates were 0, 0.28, 0.57, 1.14, 1.71, and 2.28 g kg^?1. Lime as well as gypsum significantly increased plant height, straw and grain yield, and panicle density in a quadratic fashion. Adequate lime and gypsum rates for maximum grain yield were 1.11 g kg^?1 and 1.13 g kg^?1, respectively. Plant height, straw yield, and panicle density were positively related to grain yield. Lime as well as gypsum application significantly changed extractable calcium (Ca), magnesium (Mg), hydrogen (H)+aluminum (Al), base saturation, and effective cation exchange capacity. In addition, liming also significantly increased pH, extractable phosphorus (P) and potassium (K), calcium saturation, magnesium saturation, and potassium saturation. Optimum acidity indices for the grain yield of upland rice were pH 6.0, Ca 1.7 cmol_c kg^?1, base saturation 60%, and calcium saturation 47%. In addition, upland rice can tolerate 42% of acidity saturation.     

Transformations des carbonates dans une sequence de sols developpees sur marnes dans Le Bassin Aquitain,France

Soils of a toposequence formed chiefly in Tertiary marls in the south-eastern part of the “Bassin Aquitain” have been studied by field and micromorphological methods. Profiles were examined in detail in the field and oriented samples taken of horizons for observations of micromorphology. From the upper to the lower part of the toposequence, the four profiles also form a chronosequence, viz., a recent calcareous brown soil (sol brun calcaire), an old calcic brown soil (sol brun calcique), a still older leached brown soil (sol brun lessivé) and a hydromorphic leached soil (sol lessivé hydromorphe).The profile distribution and forms of calcite can be related to the morphology, ages and parent materials of the soils. Calcite is found as relics in the upper horizons of the calcareous brown soil and in the form of accumulations in the Bca and Cca horizons of the calcareous brown soil, the calcic brown soil and the leached brown soil. Where accumulations are limited, calcite forms pseudomycelia associated with roots, first as calcitans in tabular pores or craze planes and second as coalescing pseudomycelia. Finally, the calcite invades the S-matrix by epigenesis and results in crumbly masses. These masses have the shapes of the structural voids originally present in the parent materials. The common voids in the marl are vertical craze planes, the widths of which differ with the moisture regime of a soil. In the sandstones, the craze planes are horizontal and very small. The distribution of the calcitans and the presence of the crumbly masses indicate that the processes of accumulation of calcite are in part biodependent, i.e., related to root distribution, and in part lithodependent, i.e., related to structure of the parent rock.Finally, the presence in the calcareous brown soil of calcite as relics in the upper horizons and as successions of cutans from outsides to insides of pores (calcitan, argillan, calcitan) in the Bca horizon shows that the profile has a polycyclic origin.     

Postpyrogenic Polycyclic Soils in the Forests of Yakutia and Transbaikal region

Periodical forest fires are typical natural events under the environmental and climatic conditions of central and southern Yakutia and Transbaikal region of Russia. Strong surface fires activate exogenous geomorphological processes. As a result, soils with polycyclic profiles are developed in the trans-accumulative landscape positions. These soils are specified by the presence of two–three buried humus horizons with abundant charcoal under the modern humus horizon. This indicates that these soils have been subjected to two–three cycles of zonal pedogenesis during their development. The buried pyrogenic humus horizons accumulate are enriched in humus; nitrogen; total and oxalate-extractable iron; exchangeable bases (Са⁺² and Mg⁺²); and the fractions of coarse silt, physical clay (<0.01 mm), and clay (<0.001 mm) particles in comparison with the neighboring mineral horizons of the soil profile. The humus of buried pyrogenic horizons is characterized by the increased content of humic acids, particularly, those bound with mobile sesquioxides (HA-1) and calcium (HA-2) and by certain changes in the type of humus.     

Efficiency of Phosphogypsum and Mined Gypsum in Reclamation and Productivity of Rice–Wheat Cropping System in Sodic Soil

In this study, efficacies of mined gypsum and phosphogypsum (PG), when applied at equivalent doses, were compared for sodic soil reclamation and productivity of rice–wheat system. Application of PG, followed by karnal grass as first crop, resulted in the greatest reduction of soil pH and exchangeable sodium percentage (ESP) followed by PG applied at 10 Mg ha^?1 alone. Application of PG at 10 Mg ha^?1 resulted in greater yields of both rice and wheat than other treatments. Ditheylenetriaminepentaacetic acid (DTPA)–extractable micronutrients of PG-treated soil were greater than in mined gypsum–treated soil. A greater portion of applied P entered the calcium (Ca)–phosphorus (P) fraction in PG-treated soil, which also resulted in more soluble P than the mined gypsum–treated soil. Phosphogypsum effected greater increase in aggregation, soil organic carbon, microbial biomass carbon, and aggregate associated carbon and decrease in zeta potential, leading to increased hydraulic conductivity and moisture retention capacity in soil over mined gypsum–treated soil.