Genesis of gypsum enriched soils in north-west Isfahan,Iran

Most of gypsum-enriched soils in Isfahan and neighboring provinces occur on alluvial fans, dissected flood plains (old dissected alluvium)and piedmont plains. Herein we investigate the processes of formation and alteration of gypsic horizons and their pedofeatures. We described and sampled representative pedons on a transect from the mountain to the piedmont plain. In the study area, different gypsic pedofeatures have various kinds of internal lenticular cryslalitic fabrics. Micromorphologic observations confirmed that gypsic horizons have an evolutionary sequence across the different geomorphic surfaces from the upper fan to the piedmont plain. In primary stages (upper fan), gypsum crystals occur individually in the soil groundmass or as clusters in voids with idiotopic or xenotopic fabrics. Eventually, they form internal coatings or infillings and pendants (in middle and lower fans). In the more developed horizons (dissected flood plains or plateaus), the fibrous gypsum crystals are banded and perpendicularly distributed with reference to the gravels and soil surface. These loosely compacted fibers constitute the bulk of the soil materials, leaving non-gypsic particles as islands between crystals. In these pedofeatures, perpendicularly oriented fibrous crystals, with their lateral inter-connections give rise to a continuous three-dimensional firm structure.The fabric of these lenticular gypsum crystals is xenotopic or hyp-idiotopic. In the piedmont plain, the idiotopic crystals have no preferred orientation and have random distribution. Internal fabric of these pedofeatures is porphyrotopic. This study indicates that, physical environment plays a great role in formation of different gypsic pedofeatures.     

Determination of gypsum and cation exchange capacity in arid soils by a resin method

A simple and direct method for the quantitative determination and removal of gypsum in gypsiferous soil samples was developed. This procedure incorporates a combination of Na- and Cl-resins to aid in the dissolution of the gypsum. The primary effect of the exchange resins is to buffer the composition of the solution and thereby keep the rate of gypsum dissolution high. The dissolved calcium and sulfate exchange with the sodium and chloride on the resins, resulting in a solution containing primarily Na and Cl. The electrical conductivity of the supernatant is directly related to the amount of gypsum dissolved. This method was used on samples of artificially prepared mixtures and naturally gypsiferous soils. Compared with results obtained by other methods, the resin method gave identical results, while requiring much less time and fewer calculations. The resin method was also used to remove gypsum from gypsiferous soil samples prior to CEC determinations to see if the presence of gypsum effects the CEC as determined by the Bower method. No significant effect was noted for soil samples containing less than 20% gypsum.     

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.     

Micromorphology and classification of Argids and associated gypsiferous Aridisols from central Iran

Gypsiferous Aridisols occupy the largest area within the Iranian Aridisols. Information on the genesis and classification of these soils is rather limited. Objectives of this research were to study the micromorphology of the gypsic, argillic, and calcic horizons, to understand the mode of formation of gypsic horizon in three different landscapes, and to test the criteria of the most recently revised Soil Taxonomy and FAO classification system in selected gypsiferous Aridisols occurring in central Iran. A total of 15 representative pedons occurring on three different landscapes (colluvial fans, plateaus, and alluvial plain) were studied. Evidence of illuviation in the colluvial soils is provided by the increase in the clay content and the fine to total clay ratio in the subsoil and by the well-developed, but considerably disrupted, clay coatings observed in thin sections. In addition to pendants, gypsum occurs as microscopic-sized particles, such as single and radiating fibrous shaped particles, random lenticular and granular crystals, along channels and planar voids with no apparent orientation to the associated surface. Gypsum also occurs as relatively larger interlocking plates. The horizon sequence, together with their chemical and micromorphological properties, reveals that gypsum accumulated in different landscapes has different modes of formation. The coexistence of argillic, calcic, and gypsic horizons in colluvial soils is a peculiar combination, suggesting a multistage pedogenesis in this landscape. Paleo-argillic horizons were likely developed under a moister environment than today. This study has also shown that the most recently revised version of the American Soil Taxonomy and FAO soil classification can reasonably well classify these soils. However, there is still a need to modify the criteria of both classification systems at the lower levels, particularly for the classification of the soils that are polygenetic.     

Evaluating the land use potential of gypsiferous soils from field pedogenic characteristics

Abstract. Although gypsiferous soils cover approximately 100 million ha in the world, it is only in the past two decades that their pedogenic and agronomic properties have been better understood and their classification improved. There is still no method to assess adequately their production potential.
This paper focuses on gypsum accumulation forms as diagnostic criteria for a rapid soil suitability appraisal in the field. Pseudomycelia, gypsum spots, powdery coatings and other localized in situ precipitations usually indicate soils with less than 15% gypsum. Depending on their intensity and depth of occurrence in the root zone, they define a soil environment which is suitable for semi-sensitive and semi-tolerant crops. Continuous gypsum accumulations characterize soils or horizons with high (e.g. more than 25%) gypsum contents, and these can be used only for tolerant crops.
The land use potential of gypsiferous soils is primarily determined by: (a) the depth of the impermeable layer, (b)the gypsum content within the root zone, and (c) the crop tolerance level. A method is proposed to assess the land suitability of gypsiferous soils on the basis of these criteria.     

Soils and landscapes of the Kzyladyr karst field in the Southern Urals

The specificity of soil and landscape conditions in the area of the Kzyladyr karst field in the western folding zone of the Southern Urals is discussed. Unique karst landscapes and soils developing from hard gypsum rocks, gypsiferous weathered mantles, and gypsiferous saline rocks are characterized. These soils strongly differ from the background soils on silicate rocks in their morphology and physicochemical properties. At present, the territory under study is subjected to considerable anthropogenic loads and requires special protection measures. It is suggested that it should be included in the system of specially protected territories. The relic, rare, and unique soils of the karst field should be included in the Red Data soil book.     

Biogenic and chemogenic calcium accumulations in Mollisols developed from loess in Argentina pampas

The morphology of pedogenic calcium accumulations, their distribution in the soil profile, and the mechanisms of their formation in Mollisols of Argentina pampas were studied in the southeast of the Buenos Aires province. The chemogenic collomorphic calcareous films and tubes and the biogenic (cyanobacterial) gypsum framboidal structures (spherulites) were detected with the use of electron microscopy. Two mechanisms of the formation of framboidal gypsum were identified: (a) the formation of crystalline gypsum crusts around less soluble minerals (calcite) by spherical colonies of cyanobacteria and (b) the inheritance of the spherical shape of gypsum pedofeatures from the framboidal pyrite concretions accumulated in marine deposits and subjected to decomposition by sulfate-reducing bacteria. It is probable that the cyanobacterial gypsum accumulations are only formed in the studied soils during the dry season and are dissolved during the wet season.     

Use of langbeinite to reclaim sodic and saline sodic soils

Abstract

Langbeinite is a soluble potassium‐magnesium sulfate mineral (K₂SO₄2MgSO₄) found as an evaporite in many regions of the world. Langbeinite was used as a reclaiming material in a fine textured (clay loam) saline sodic soil (Grabe Series). This amendment can be dissolved and directly into the irrigation water, displacing sodium (Na) quickly with minimal water use. This amendment was superior over gypsum as a reclaiming material for a saline sodic soil in batch, column, and greenhouse studies. Langbeinite required 50% less irrigation water than gypsum to displace and leach exchangeable Na from soils. Langbeinite improved the infiltration rates of saline sodic soils, but not as effectively as gypsum. Significant increases in germination percent dry matter production mass of lima bean (Phaseolus lunatus L.) plants were observed when using langbeinite over the gypsum soil amendment.     

A rapid method to determine cation exchange capacity and exchangeable bases in calcareous,gypsiferous, saline and sodic soils

Summary

A simple, single‐step extraction with LiEDTA for the estimation of CEC and exchangeable bases in soils has been developed. Multivalent cations are stripped from the soil adsorption sites by the strongly chelating agent EDTA, and are replaced by Li. In soils without CaCO₃ or water soluble salts, exchangeable divalent cations (Ca, Mg) are chelated by EDTA and exchangeable monovalent cations (Na, K) are replaced in a single extraction step using 0.25–2.5 g of soil and 10.0 ml of extractant.

In calcareous soils the CEC can be determined in the same way, but for the extraction of exchangeable Ca and Mg, another separate extraction is needed because dissolution of calcite by EDTA is unavoidable. This extraction is done with as much NaEDTA as needed to extract only exchangeable Ca and Mg in a 1:2 (m/V) soil/alkaline‐50% (V/V) aethanolic solution to minimize dissolution of calcite.

In gypsiferous soils gypsum is transformed into insoluble BaSO₄ and soluble CaEDTA by LiBaEDTA thus avoiding interference of Ca from dissolution of gypsum, which renders the traditional methods for determining CEC unsuitable for such soils. To determine exchangeable Ca and Mg, Na₄EDTA is used as for calcareous soils.

In saline/sodic soils replacement of Na by Li is incomplete but the Na/Li‐ratio at the complex after extraction is proportional to the molar Na/Li‐ratio in the extracts, so that the CEC and original exchangeable sodium (ESP) content can be calculated. Additional analysis of Cl and, if necessary, SO₄ in the extracts of saline soils can be used to correct for the effect of dissolution of the salts on the sum of exchangeable cations.

This new method is as convenient as the recently developed AgTU (silverthiourea), but is better suitable for calcareous and gypsiferous soils.     

Temporal changes in the microfabrics of virgin and reclaimed solonetzes at the Dzhanybek Research Station

In the past three decades, a trend of an increase in the climatic humidity has been observed in the southeast of European Russia; it has been accompanied by the rising groundwater level. The study of solonetzes at the Dzhanybek Research Station in the north of the Caspian Lowland indicates that the recent climate changes are reflected in the soil microfabric. A comparative examination of thin sections prepared from the soil samples taken in 1982 and in 2002 from the same points characterizing virgin and reclaimed solonetzes has shown the following changes in the soil microfabric: (a) an increase in the amount and diversity of the mesofauna excrements, (b) the accumulation of fine plant detritus at various stages of decomposition, (c) an increase in the content of the dispersed and flocculated brown-colored microforms of humus and charcoal particles in the surface horizons, and (d) the formation of hydrogenic gypsum in the middle and lower soil horizons. The character of changes in the microfabric of virgin solonchakous solonetzes attests to the enhancement of the eluviation of the silty-clayey-humus substances, solodization, and gleyzation. In the reclaimed solonetzes, the artificially turbated horizons have been subjected to desalination, and the gypsiferous and calcareous pedofeatures inherited from the previous stages of soil formation have been destroyed.     

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.     

Amendment of drilling fluid-affected soils with calcium salts

Land disposal of waste drilling fluid is an environmental concern because of the high salt content and the presence of potential toxic elements. A water-based drilling fluid was tested in a laboratory column study to determine the feasibility of leaching excessive salt without mobilizing chromium (Cr). The drilling fluid-affected two Alfisols with similar mineralogy, acidity, and texture were treated with gypsum (CaSO₄ · 2H₂O), calcium carbonate (CaCO₃), or calcium phosphate (CaHPO₄) (0 to 2% of weight). The electrical conductivity (EC) increased and the sodium adsorption ratio (SAR) decreased with increasing Ca-salt concentration. The pH did not vary significantly with the changes in the concentrations of gypsum and calcium phosphate. The pH of the mixtures increased in proportion to the concentration of added calcium carbonate. The hydraulic conductivity increased and the mobility of the soil particles decreased with increasing Ca-salt concentration. The Cr mobility decreased by gypsum and CaCO₃ treatments but it increased by calcium phosphate treatment. The soil with a higher content of organic matter and cation exchange capacity (CEC) showed a higher hydraulic conductivity and lower Cr mobility than the other soils at the same levels of the treatment. The results of this study suggest that the amendment of drilling fluid-affected soils with CaCO₃ and gypsum can enhance the leaching of excessive salt and reduce the Cr mobility. Among loamy soil, those with a higher CEC and organic matter content are more suitable for land disposal of drilling fluid.     

Halochemical processes upon washing of calcareous gypsiferous solonchaks

Data on changes in the contents of carbonates, gypsum, and soluble salts upon washing of gypsiferous solonchaks were obtained in laboratory and field experiments. Chemical methods and micromorphological study of thin sections were applied. Stages of the halochemical changes upon the soil washing were identified. It was found that the soil washing results in the formation of secondary magnesium sulfate and pseudomorphic substitution of calcite for gypsum.     

Some physical and chemical characteristics of the Batinah soils

Abstract

More than 50% of the irrigated soils in the Sultanate of Oman is in the coastal plains of the Batinah area. Intensive agriculture and groundwater depletion have led to seawater intrusion and soil salinization. As a prerequisite to combat this problem, basic studies on some soil properties were done and are presented. The textural classification ranged from sand and loamy sand to fine‐textured silt loams, and the soil moisture characteristics (0.1–15 bars) revealed field capacities (0.3 bar) and permanent wilting point (15 bars) ranges of 40 to 2%, respectively. The soils are generally calcareous with about 40% calcium carbonate (CaCO₃), but low in gypsum [calcium sulfate (CaSO₄) content]. The EC_1:5 values disclosed the extent of salinization with increasing values of up to 16 dS/m towards the coastal areas of the fine‐textured soils. This was coupled with high sodium (Na) adsorption ratios of up to 30 indicating saline‐sodic conditions.     

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.     

天山荒漠景观内蒸发地球化学垒的研究

天山荒漠景观内的蒸发地球化学垒可分为碳酸盐蒸发垒、石膏蒸发垒和易溶盐蒸发垒。这些蒸发垒沿天山山脉呈带状分布 ,自天山山脉至两侧盆地依次分布碳酸盐蒸发垒、石膏蒸发垒和易溶盐蒸发垒。土壤中碳酸盐的积聚导致Mn、Ti、Fe、V、Sc、Cu、Co和B等元素含量的降低。石膏的富集常伴随着土壤中B和Sr含量的增加。随易溶盐的大量积累 ,元素B的聚集非常明显 ,而Mn、Fe、Ti、V、K、Ba、Li、F和Zn等元素含量则明显降低。蒸发地球化学垒对元素的生物有效性也有较明显的影响。碳酸盐的积累明显减低了Fe、Cu、B等元素的生物有效性 ,F元素在碳酸盐蒸发垒内CO2 -3 和HCO-3 含量较高的土壤中生物有效性较高。在易溶盐蒸发垒内元素B有较强的生物有效性     

Hydraulic conductivity of calcareous soils as affected by salinity and sodicity. II. effect of gypsum application and flow rate of leaching solution

Abstract

Saline‐sodic irrigation water, coupled with low annual rainfall and high evapotranspiration in the arid and semi‐arid regions have resulted in accumulation of soluble salts in the soil solution and of cations (especially sodium ions) on exchange sites, which can alter the structure and, consequently, affect the soil hydraulic conductivity (HC). Among the different factors, the amount of gypsum applied and the flow rate of leaching solution are major factors influencing the HC of the soil in the presence of saline sodic solutions. The study was initiated to improve the understanding of swelling and dispersion processes (as two major mechanisms responsible for reduction in HC) in response to saline‐sodic conditions, in particular, the role of gypsum application and the flow rate of leaching solutions. The study was conducted in a series of two leaching experiments. In the first set, different rates of gypsum (i.e., 0, 10, 20, and 30 tons ha^‐1) were mixed with 4 soil samples and leached with a saline‐sodic solution of concentration of 100 meq (NaCl+CaCl₂)L^‐1 with sodium adsorption ratio (SAR) 20 and the base flow rate (BFR) of 15 mL min^‐1. In the second set of experiments, the same soils treated with the same gypsum level and the same leaching solutions as in the first set, but leached with the BFR of 5 mL min^‐1 instead of the BFR of 15 mL min^‐1. In general, the gypsum application modified the suppressing effect of salinity and sodicity on the HC values of the tested soils, and the effects were more pronounced for higher rates of gypsum applied. However, increase in the BFR from 5 to 15 mL min^‐1, significantly masked this recovering effect of gypsum application, and the effect was reflected in both swelling and dispersion processes.     

SANDSTONE-DERIVED SOILS OF A CATENA AT IPERU, NIGERIA

Chemical and mineralogical properties of five soil profiles of a catena in Iperu, Western State of Nigeria, are reported. The pH values of the subsoils are extremely acid. Acidity decreases with improved drainage in the subsoils (pH 4.0–5.8). The cation exchange capacity (C.E.C.) of the soils range from 3.0 to 16.2 me/100g of soil. The silt: silt+clay ratio, calcium: magnesium ratio and Fe₂O₃:Al₂O₃ ratio are used as weathering indices. The low values of the silt: silt + clay index indicate that the soils must have undergone advanced weathering. The magnitude of the Ca: Mg ratio indicates that more calcium than magnesium is available in the soils. The values for sodium and potassium are extremely low. More iron than aluminium was extracted from the soils by the dithionite-citrate method. Kaolinite is the most abundant clay mineral. Halloysite, interstratified clay materials, vermiculite, quartz, and mica are present in considerable amounts. The silt fraction in which quartz is the most abundant mineral, also contain some kaolinite and mica.     

青藏高原石膏寒漠土的发生特点

寒漠土分布于我国青藏高原西北部的高寒荒漠带,它是在冰冻过程制约下形成的荒漠土壤,具有颗粒粗、粉粒和铁在表层(亚表层)聚积、有机质积累少等发生特征。石膏寒漠土除有上述特征外,还有石膏强烈聚积,因此,它通常有三个基本发生层:(1)孔状结皮层,厚度1-4厘米,多孔、呈片状或鳞片状;(2)铁质化紧实层,位于结皮层之下,厚度3-5厘米,游离铁,活性铁和粘粒含量高于上下土层,块状结构;(3)石膏层,厚度10-20厘米,石膏含量12-25%,最高达40%,结晶形态良好。根据寒漠土中具有典型的石膏层这一发生特征,拟划分出石膏寒漠土亚类。