Polyphasic origin of salinity in the Senegal delta and middle valley

Saline areas are a major obstacle to the development of sustainable irrigated agriculture in the Senegal valley. They have been attributed to the incorporation of marine salts in the sediments during the last marine transgression. However, this does not explain their geomorphological situation and geochemical features. They are distributed as strips about 100–200 m wide and several kilometers long, which are composed of two parallel substrips, one located in the depressions of former creek beds, and the other on higher ground on the southern bank. In these two substrips, the chemical composition of salinity and its distribution in the soil suggest that it arises from more than one source. Comparison of saline areas of the middle valley with present-day salt accumulation in the delta suggests a four-stage salinization process, which involves evaporation from a shallow water table, aeolian salt accumulation as clay dunes, deep transformation of shell beds into gypseous layers under temporary acid conditions induced by oxidation of pyrite under the mangrove vegetation, and secondary salinization by runoff. The four-stage model agrees with a regional salinity chemical database and the geomorphology of the saline areas. In the Senegal valley, the lower middle valley and the delta can therefore be regarded as a chronosequence, the recent salinity features occurring in the delta and the more developed ones upriver at the limit of the marine transgression.     

The origin of Vertisols and their relationship to Acid Sulfate Soils in the Senegal valley

In the Senegal valley, it is commonly considered that the Acid Sulfate Soils of the delta are fossil soils overlain by more recent sediments, and that the Vertisols, which abruptly overlie a thick sandy horizon, result from a change in the sedimentation mode of the river. However, we show that both soils belong to the same pedological system extending from the delta to the limit of the last marine transgression. This conclusion is based on (1) the study of soil profiles intermediate between Acid Sulfate Soils and Vertisols along a 100-m sequence in the delta, (2) the mineralogy of the clay fraction (<2 μm) in a 200-km transect along the river, and (3) the similarity of the sand size distribution across the textural discontinuity between the horizons. The following processes are involved in the pedological transformations: (1) development of acidity by oxidation of pyrite, (2) neutralization of acidity initially by the carbonate in shell beds, and later by the hydrolysis of easily weatherable silicate clays. The slightly alkaline river water precipitates kaolinite and later smectite at the contact between the strongly acidic and slightly alkaline environments. This results in the formation of a superficial vertic clay horizon surmounting a sandy horizon. Therefore, we emphasize that the soil morphology results from development and control of acidity and not from changes in past climates.     

Evolution of the soil cover of soccer fields

A soccer field can be considered a soil-like technogenic formation (STF). According to the theory of soil cover patterns, the artificially constructed (anthropogenic) soil cover of a soccer field is an analogue of a relatively homogeneous elementary soil area. However, the spatial homogeneity of the upper part (50–80 cm) of the STF of soccer fields is unstable and is subjected to gradual transformation under the impact of pedogenetic processes, agrotechnical loads, and mechanical loads during the games. This transformation is favored by the initial heterogeneity of the deep (buried) parts of the STF profile. The technogenic factors and elementary pedogenetic processes specify the dynamic functioning regime of the STF. In 50–75 years, the upper part of the STF is transformed into soil-like bodies with properties close to those in zonal soils. Certain micro- and nanopatterns of the soil cover are developed within the field creating its spatial heterogeneity.     

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.     

Contemporary pedogenetic processes in a ferrallitic soil in Uganda,I. Identification

Ferrallitic soils were originally considered to be pedogenetically “dead”, with few pedological processes taking place except perhaps leaching. A study of the Buganda clay loam series, a widespread soil in southern Uganda, showed that although this ferrallitic soil is very highly weathered chemically, two important groups of pedogenetic processes are currently active, differentiating the B from the C horizon. These are alteration of soil structure/physical properties and clay translocation. Leaching and clay mineral transformation are not occurring. It is suggested that the pedogenetic basis for classifying soils as ferrallitic has become outdated and that the criteria used need revision.     

Soils of loamy watersheds of coastal tundra in the north of Yakutia: Pedogenetic conditions and processes

This paper considers regularities governing the formation of automorphic tundra soils on glacial loamy deposits containing relict organic matter mainly represented by very fine plant detritus. Drainage, microtopography, and cryoturbation activity are the major controls of the development of these soils. With an increase in drainage, the following pedogenetic trend is observed on the surface of yedoma (Ice Сomplex) areas: gleyzem–cryozem–cryometamorphic soil. The climate change in the Holocene induced quick transformation of topography and general landscape situation and promoted formation and development of cryogenic soil complexes in the considered territory. Upon the low intensity of pedogenesis, the features and properties of previous soil formation stages are often preserved in the soil profiles; these are: gleyzation, peat accumulation, and cryoturbation.     

Are mangrove forest substrates sediments or soils? A case study in southeastern Brazil

Morphological and analytical data corresponding to several profiles from two mangrove systems in the Brazilian state of São Paulo were examined for evidence of pedogenetic processes. Plant activity exerted a strong effect on the processes occurring in mangrove substrates, especially on the intensity of these processes and, therefore, constitutes one of the major factors involved in the differentiation of sediments and soils. Colonization of substrates by vascular plants leads to drastic changes in physicochemical conditions. The redox processes were much more diverse in the soil than in the sediment (substrate without vegetation); in the former they varied with depth, with oxic or suboxic conditions being observed at the surface and anoxic conditions observed below 30 cm, whereas in the sediment, anoxic conditions were observed throughout. Likewise, the acid–base conditions were more variable in the soils, ranging from strongly acid to neutral, and in the sediment they were close to neutral. Furthermore, different pedogenetic processes were identified: (1) addition of organic matter by accumulation of vegetable debris and dead roots, with formation – in some cases – of a histic epipedon, (2) transfer of soluble iron (Fe²⁺) towards the surface and precipitation in the form of Fe oxyhydroxide, and transfer of the mineral particles due to the bioturbation caused by activity of crabs, (3) transformation of elements such as iron (gleization) and sulphur (sulphidization). Changes undergone in the mangrove substrates were also characterized by simultaneity and intergradations between pedogenesis and diagenesis, especially in the lowermost layers in which authigenesis appears to intensify. Thus, the presence of smectite minerals in the clay fraction may be attributed to authigenic processes that take place in both soils and sediments.     

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

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

Assessment of the mineralogical status of silicate components in chernozems

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

Late Glacial-Holocene genesis of Andosols from the Seaca-Tãtarca (South Gurghiu Mountains, Romania)

The purpose of the research presented here was to find an answer for the possible origin and mode of deposition of soil parent materials for Andosol formation and to link the soilscape variability to the various soil forming factors since the Last Glaciation. Soil formation was studied along a 20‐km climo‐toposequence in the Miocene Andesitic area of the South Gurghiu Mountains (Romania). Six representative soil profiles were chosen from a larger geopedological study on the western slope of the Seaca‐Tãtarca volcano. Based on the macromorphological, micromorphological and chemical properties it was possible to say that the soil profiles are composed of two major types of soil material: a relict type, with a crystalline clay fraction; and a recent type with an amorphous colloidal fraction. It was found that the present‐day distribution of the Andosols on the Seaca‐Tãtarca volcano must be related to the rejuvenation of the soil parent material by processes of aeolian input of frost‐shattered volcaniclasts and by a glacial reworking. It appears that the extension of the glaciated areas during the Pleistocene could have been larger than concluded from geomorphological studies. General Carpathian glacial features are closely related to the altitudinal distribution of the Carpathian Andosols. At the present climatic optimum, the soils of Seaca‐Tãtarca are influenced by pedogenetic processes of freeze‐thaw, oxido‐reduction, strong leaching and internal colluviation, strong accumulation of organic matter and considerable biological activity. Those Andosols that are located in special microtopographic positions with stronger water percolation tend to evolve towards Podzols.     

The effect of five years acid treatment on leaching,soil chemistry and weathering of a humo-ferric podzol

This paper describes the effect of treating a nutrient-poor forest soil in monolith lysimeters with H₂SO ₄, pH 3.0, for 4.75 yr. The lysimeters were instrumented with porous cup probes to distinguish processes occurring in each soil horizon. In the A horizon base cation exchange and sulphate absorption were the principal proton- consuming processes whereas lower down the profile Al³⁺ dissolution from hydrous oxides dominated. Acid treatment thus reduced the amount of amorphous Al in the lower horizons, but exchangeable Al was unaffected. Sulphate absorbtion was positively correlated with the distribution of Al hydrous oxides. High rates of nitrification reduced the differences between acid and control monoliths, but acid treatment significantly reduced soil pH down to 75 cm and reduced the levels of exchangeable base cations in the litter and A horizons. Acid treatment increased the leaching rates of base cations and Al. Consideration of the total base cation content shows that acid treatment increased the rate of weathering by 0.7–1.4 k eq ha^?1 yr^?1. The results should be useful in modelling more realistic rates of acid input to similar soils.     

Mountain-meadow soils of the highlands in the Western Caucasus

The published and author’s data on soil-forming conditions, morphology, substance composition and physicochemical properties, total chemical and mineralogical composition, and micromorphology of mountain-meadow soils of the Western Caucasus Range are analyzed. On the basis of the analytical data obtained, the transformation of minerals and features of chemical element profile patterns developed in the course of soil formation are characterized. The main processes accompanying the transformation of mineral and organic parts of the soil mass and migration of soil-formation products are described. Soil formation is shown to be accompanied by two major elementary soil processes developing with participation of soil biota: humus accumulation and clay formation. Ways to improve the classification of mountain-meadow soils are proposed.     

Early transformation and transfer processes in a Technosol developing on iron industry deposits

Large surface areas covered with man‐made materials are subject to pedogenetic evolution. However, pedogenetic processes in the resulting Technosols are seldom fully assessed. This work was conducted to identify and characterize the processes occurring on deposits of industrial technogenic materials. A former settling pond of the iron and steel industry where a forest has established since termination of the industrial activity approximately 50 years ago was chosen. A 2‐m deep pit was opened, and a series of layers of the soil profile were sampled. The macro‐ and micro‐structure were studied, and soil samples were analysed for structural, chemical and mineralogical assessment (chemical analyses, X‐ray diffraction, infrared and Mössbauer spectroscopies, scanning and transmission electron microscopies coupled with energy dispersion spectrometry). Results showed that the profile was composed of a succession of sub‐horizontal layers arranged in two groups according to their structure and composition, linked to the composition of the industrial effluent. Group 1 was composed of iron‐, carbonate‐ and aluminosilicate‐rich layers exhibiting a compact structure. Group 2 contained manganese‐rich layers with a friable structure. Pedogenetic processes of various intensities were detected at different depths. Besides an accumulation of organic matter at the surface, transformations of minerals were recorded all along the soil profile, with weathering, leaching and precipitation of new phases. Phenomena occurred primarily in specific zones, such as cracks and interfaces between two layers. In conclusion, the soil maintained characteristics of the original industrial material and displayed several stages of pedogenesis, which were controlled chronologically by climatic and biological factors.     

Anthropic pedogenesis of purple rock fragments in Sichuan Basin,China

Considerable amounts of rock fragments are found in many “Purple soils” developed from purple rocks in the Sichuan basin of southwestern China. We describe the effects of anthropic pedogenetic processes on purple rock fragments associated with soil amelioration by determining changes in rock fragment size distribution, transformation of P and K of purple rocks into soils, and the complexing of purple rock particles (soil mineral particles) with organic matter during anthropic pedogenesis of “Purple soils” in Sichuan basin of southwestern China. The pedogenetic capacity of rock fragments can be expressed by the content of < 2.0 mm particles as weathered products of rock fragment disintegration. The pedogenetic capacity of the purple rocks studied ranges from 0.3% to 6.2% under natural conditions. The rates of P and K transformed from purple rocks are closely associated with the pedogenetic capacity of rock fragments(r = 0.891^??; 0.961^??, n = 16). Digging (simulated by sieving) and crop planting facilitate pedogenesis of purple rock fragments and their mineral nutrient transformations. The soil mineral particles preserve 18%–36% of the organic carbon added as corn straw. The organic carbon is complexed after corn straw is mixed with < 1.0 mm soil mineral particles for 1 year. The improvement of newly reclaimed purple soils is enhanced by the complexing effect of organic substances with purple rock particles. The pedogenesis of purple rock in Sichaun basin can be accelerated by anthropic activity, such as tillage, crop planting, fertilization, and land reclamation.     

Temporary storage of soil organic matter and acid neutralizing capacity during the process of pedogenetic acidification of forest soils in Kinki District,Japan

Abstract

Pedogenetic acidification processes in forest soils derived from sedimentary rocks under mesic and thermic soil temperature regimes (MSTR and TSTR; corresponding to mean annual soil temperatures of 8–15°C and 15–22°C, respectively) in the Kinki District were investigated based on titratable alkalinity and acidity characteristics and soil solution composition. According to statistical analyses of the soil properties, the titratable alkalinity required to acidify soils to pH 3.0 was considered to be derived from reactions occurring at the surface of amorphous Al oxides, while titratable acidity at a pH ranging from 5.5 to 8.3 results from dissociation of acidic functional groups of soil humus and/or deprotonation of oxide surfaces. These reactions were generally more prevalent in MSTR soils. Based on the soil solution composition and titratable alkalinity and acidity in the soil profiles, two processes were postulated for pedogenetic acidification, that is, eluvi-illuviation of inorganic Al followed by subsequent adsorption of dissolved organic carbon (DOC) onto the precipitates of Al hydroxides and comigration of Al and DOC in the form of organo-mineral complexes. Both processes were conspicuous in MSTR soils and significantly contributed to soil organic matter storage in the subsoil layers. Pedogenetic acidification in forest soils with MSTR was characterized by an accumulation of acidity in the form of amorphous compounds and/or organo-mineral complexes in the B horizon. It seems, to some extent, similar to podzol formation, at least in terms of Al translocation. Amorphous Al hydroxides protect against further acidification through protonation and/or partial monomerization and can, thus, be regarded as a temporary storage of acid neutralizing capacity of the soil, which would be otherwise leached out directly from the soil profile. In contrast, the acid-buffering reactions of TSTR soils seemed to occur, if at all, mostly at or near the soil surface and the contribution of the B-horizon soils was limited.     

SEM image analysis in the study of a soil chronosequence on fluvial terraces of the middle Guadalquivir (southern Spain)

A Quaternary fluvial chronosequence (Guadalquivir River, southern Spain), consisting of five soil profiles with estimated ages of 300 years (Haplic Fluvisol), 7000 years (Haplic Calcisol), 70 000 years (Cutanic Luvisol), 300 000 years (Lixic Calcisol) and 600 000 years (Cutanic Luvisol), was studied. Increasing soil age was associated with increases in: reddening, development of structure, clay content, dithionite-extractable iron (Fe _d ) and aluminium (Al _d ) and strengthening of X-ray diffraction (XRD) peaks for phyllosilicates and iron oxides; there were also decreases in pH and percentage of carbonates in the fine earth and lower XRD peaks for calcite and dolomite. These changes indicate that the principal pedogenic processes were weathering, clay illuviation, rubefaction and the weathering and leaching of carbonates. We have further characterized the pedogenetic chronosequence by quantification of ultramicrofabrics of ped interiors using image analysis (IA) techniques on images obtained with scanning electron microscopy (SEM). We have estimated morphometric ultramicrofabric parameters for particle clusters, skeleton grains and pore space. These are closely related to analytical, mineralogical and macromorphological properties. In the principal component analysis, the first two principal components of the combined morphological, analytical and mineralogical data accounted for 78% of the total variance. The first component (48%) is loaded by variables associated with clay illuviation, relative accumulation of iron and aluminium sesquioxides and the weathering and leaching of carbonates. The components are related to ultramicrofabric development trends. We tested several chronofunctions derived from analytical and morphometric attributes. The logarithmic model fitted best, and we interpret this as indicating pedogenetic processes that are converging towards a steady state.     

Use of hydraulic conductivity to evaluate the suitability of Vertisols for deep-rooted crops in semiarid parts of central India

Abstract. Detailed morphological, physical, chemical, mineralogical and micromorphological studies were carried out to identify properties that influence the yield of deep-rooted crops in 29 Vertisols of semiarid central India, since existing land evaluation methods are not adequate to explain the yield of cotton obtained by farmers. The studies indicated that among the soil parameters, CaCO₃ in the clay fraction, the exchangeable Ca/Mg ratio, exchangeable sodium percentage (ESP) and saturated hydraulic conductivity (HC) were the yield-influencing factors. The pedogenetic relationships between the semiarid climate, formation of pedogenic calcium carbonate, exchangeable Ca/Mg, ESP and HC have been established. In view of the pedogenetic processes that ultimately impair the drainage of soils, evaluation of Vertisols for deep-rooted crops on the basis of HC alone may help in planning and management of soils, not only in the Indian semiarid tropics, but also in similar climatic areas elsewhere.     

Zur Genese von Schwarzerden auf der Sontheimer Hochterrasse in der Donauniederung bei Ulm

Pedogenesis of chernozems in the upper river terrace of the Danubian river near Ulm (South West Germany) The “chernozem-like” soils in the upper river terrace of the Danubian river near Ulm (FRG) were examinated. Field analyses as well as soil physical and chemical, clay mineralogical and pollen analyses were carried out. The parent material of the soils was identified as loess, on the basis of its texture, clay mineral composition, structure, carbonate content, the presence of loess molluscs, and the location on an upper river terrace with loess findings in the surrounding. Characteristic pedogenetic processes, such as deliming, silicate weathering, formation of oxides and hydroxides, neoformation of clay minerals and clay translocation prove a non-groundwater-influenced development of the soils within at least the last 8000 years. Therefore an accumulation of organic matter under anaerobic conditions during the peat formation in the lower river terrace nearby was not possible. According to this finding, it can be deducted that the humus accumulation may be due to influences of continental climate and forest steppe during the preboreal period, whereby the humus horizons were formed at deeper horizons through bioturbation. After the groundwater level was raised in boreal age, the steppe stage of the soils had ended and the fluctuating levels of groundwater, rich in carbonates, stabilized humic substances. Thus strong degradation of the soils to date was prevented. Therefore the soils under study could be classified as gleyic Chernozems or luvic Phaeozems.     

The fate of phosphorus during pedogenesis

The fate of phosphorus (P) during pedogenesis is considered with particular emphasis on vertical distribution within the profile. Information is based on P fractionation studies involving a range of soil sequences in New Zealand. Forms of P in soil parent materials are discussed in relation to soil P transformations. Soil chronosequences, developed in contrasting environments, provide useful information on the pedogenetic pathways of soil P. Although less well understood, soil toposequences can be used to elucidate the effects of slope and drainage on soil-forming processes which involve P.