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1.
Glomalin is a glycoprotein produced by the hyphae of arbuscular mycorrhizal fungi (AMF). The chemical methods usually employed to extract glomalin from the soil obtain something more than this pure glycoprotein, and therefore it would be better to call this fraction soil protein related to glomalin (SPRG) or glomalin associated with humic substances (GAHS). On this account, its isolation is controversial. The SPGR or GAHS has a significant influence on the physical, chemical, and biological properties of soils and could then be considered as an indicator of soil use change. In the present study, the storage of SPRG was evaluated, as well as carbon (C) associated with the latter (CG) and the content of soil organic C (SOC) in cultivated tepetates in the State of Mexico. Tepetates are hardened volcanic tuffs of the fragipan type, ameliorated for agricultural production. The specific objectives of the present study were (1) to evaluate the SPRG levels in tepetates, (2) measure the contribution of carbon (C) made by the SPRG to soil organic C (SOC), and (3) compare the extraction of SPRG with sodium pyrophosphate and sodium citrate. The samples used in this experiment came from 87 tepetate-cultivated plots (0–20 cm) located in the Texcoco River basin, State of Mexico. The levels of SPRG were observed among traces, 2.3 mg g–1 for citrate and up to 5.6 mg g–1 for pyrophosphate. The latter reactive allowed us to extract nearly three times more SPRG and two times more C-SPRG than sodium citrate (P?=?0.05) in the tepetates having about 4% of SOC; yet when the latter was less than 0.5%, the extraction levels with both solutions were similar. The SPRG and CG were closely correlated with SOC (r > 0.90). Tepetates have levels of SPRG similar to those observed in arid soils.  相似文献   

2.
Fahlerden dominate large areas of the young and old moraine landscapes of N and E Germany. Fahlerden (part of Fahlerden corresponds to Albeluvisols) and their transitional subtypes are supposed to have a higher intensity of clay illuviation than Parabraunerden (Luvisols). Besides this macroscopic feature reflecting periglacial influence, micromorphological features such as lenticular platy microstructure, vesicles, and fragments of clay coatings in Bt streaks document the initiation of Fahlerde genesis, which began in the Late Glacial. A model of Fahlerde genesis chronologically connects sedimentological and periglacial processes, vegetation development, and soil‐forming processes like decalcification, clay illuviation, and humification. The classification criterion of larger differences in clay contents between E and Bt horizons to distinguish Fahlerden from Parabraunerden needs to be reconsidered, because most Fahlerden have developed in stratified parent material in periglacially influenced landscapes. The interpretation of a soil data base listing data of both soil types distributed in Brandenburg demonstrates that the difference in clay contents between E and Bt horizons may even be smaller in Fahlerden than in Parabraunerden.  相似文献   

3.
Peter Kühn   《CATENA》2003,54(3):537
In the German soil science literature, Luvisols formed in Weichselian sediments (except from the Early Weichselian) are normally regarded as purely Holocene soils with the main period of development assumed to have been during the Atlantic phase. Although debated at some length since the 1960s, the genesis of the widespread albic Luvisols, with a simplified Ap/Bw/(Eb)/(EBtb)/Btb(g)/C horizon sequence and developed on the flat and slightly undulating till plains of the north German Mecklenburgian Stage (deglaciation 14 000 BP), has yet to be clarified. Periglacial climate during the Late Weichselian led to the formation of sand-filled wedge-shaped structures penetrating Bt horizons. Systematic micromorphologic investigations of soil profiles with sand wedges revealed the occurrence of numerous fragments of rounded limpid clay coatings within periglacial formed lenticular microplates as well as in and at the margins of the sand wedge infillings. Assuming the Younger Dryas as the latest possible phase of formation, the lenticular microplates and the undisturbed sand wedges postdate clay illuviation. Undisrupted clay coatings next to fragmented clay coatings prove a subsequent Holocene clay illuviation. Clay illuviation must have occurred at least in warmer phases of the Late Glacial, together with the already accepted pedogenic processes of decalcification, organic matter accumulation (Ahb horizons), podzolisation and silicate weathering (Bwb horizons) on sites not influenced by groundwater.  相似文献   

4.
The micromorphology of eluvial and glossic areas with weak soi1, strength from the upper fragipan, and the upper parts of grey polygonal zones, in some argillic brown earths (Glossic Fragiudalfs) from north-east England shows unstable void walls stripped of clay with remnants of ferri-argillans, pale grey grainy clay coatings and darker grainy coatings. These occur alongside loose surface residues of skeleton grains and thin grey fine silt coatings of quartz and muscovite. SEM and EDAX studies of coating surfaces, and optical microscopy, SEM and EDXRA of very thin polished sections, show that some grainy clay coatings form as alteration rims of ferri-argillans through localized waterlogging, iron oxide loss and micro-erosion leading to micropitting and disoriented fabrics. The inclusion of coarse clay to fine silt-sized quartz, feldspar and muscovite in other grainy coatings suggests either alteration of impure ferri-argillans or accumulation of degradational products derived from elsewhere on void walls. This is more certainly the case for dark grainy coatings in layered compound illuviation coatings adjacent to glossic areas. These fragipans are degrading from the top downwards by processes which are partly a consequence of the effects that the fragipan has on water percolation and root penetration. The destabilization of void walls, the degradation of ferri-argillans and the remobilization of clay to form glossic features did not begin until seasonal waterlogging in parts of the upper pan was sufficient to mobilize iron.  相似文献   

5.
A paleosol with Mousterian tools in aeolianites at the Habonim site (Carmel Coastal plain, Israel) is a complex pedosedimentary sequence which records a succession of soil-forming episodes and stages of coastal dune instability. We identified three strong soils and one accretionary soil within Mousterian pedocomplex via micromorphological techniques, coupled with FTIR and SEM/EDAX. In the lowermost, red sandy soil (hamra) in Unit IV, decalcification led to the formation of micritic coatings, disrupted by faunal churning, while rubefication resulted in red ferric segregations. Illuviation of ferruginious clay in the form of clay coatings is lacking, probably due to its strong incorporation into the matrix. Redox features were intensified in the pseudogley of the next stage (Unit III). Polyphase calcitic features here indicate that illuviation of clay pre-dates illuviation of micrite and its later recrystallization into sparitic calcite. Further deterioration of drainage conditions and increased accumulation of fine particles led to the formation of vertisol (Unit II). Paleovertisol is characterized by a maximum of clay, stress-originated microfabric, abundant Mn precipitates and calcitic pseudomorphs. The peak of landscape instability occurred later and is recorded in the upper Unit I, in which micromorphological signs of colluvial and aeolian processes are juxtaposed with various ferric accumulations, associated with gleying. The final episode occurred at a time of climatic instability, devegetation, and probably, a simultaneous groundwater rise in the littoral zone.  相似文献   

6.
Clay illuviation in Red Mediterranean soils   总被引：2，自引：0，他引：2  
N. Fedoroff   《CATENA》1997,28(3-4)
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.  相似文献   

7.
Texture is one of the major criterions in soil classification, probably because it has a decisive influence on soil properties. This is particularly true for volcanic ash soils. Most ashes are largely composed of sand and silt particles with little clay (11, 15). The ash weathers very rapidly (1), and clay site particles less than 2 microns in diameter occur even within a few months, as shown by Ishii at the authors' laboratory. Those clay size particles produced in the early stage of weathering are slightly weathered ones (2), and are still subject to rapid weathering, losing bases and silica under humid and well drained conditions. In consequence the clay fraction of volcanic ash soils is composed of particles which vary in degree of weathering from slightly altered glass and feldspar to true clay mineraloids and minerals. The clay fraction of younger soils as a whole is less and that of older ones is more weathered. Weathering brings a remarkable change in the properties of volcanic ash soils; for example, an inerease in soil acidity, lowering of base saturation and bulk density, or accumlation of organic matter. These changes must exert a great influence on soil fertility directly or indirectly.  相似文献   

8.
Some aspects of the genesis of terrae rossae are still subject to controversy while others related to the genesis of the mineral fraction have been studied very little. We have studied four terrae rossae over limestone (two Chromic‐Leptic Luvisols, a Rhodi‐Leptic Luvisol and a Chromi‐Leptic Cambisol) in Sierra Gádor (Almería, southern Spain), in particular the various formation processes by (i) examination of their morphological, analytical and mineralogical characteristics (including crystallochemical parameters of the mica), (ii) examination of the insoluble residue of the gravel and rock, (iii) scanning electron microscopy (SEM) of sand and silt grains, and (iv) examination of the geochemistry of the soil solution. We have investigated the autochthonous or allochthonous nature of the soil material (fine earth and gravel) in relation to the rocky substrate, concluding that both origins are possible. Our SEM study of the morphology of the quartz grains shows that some are insoluble residue and some are probably wind blown from desert and coastal sources. The micas in the fine earth fractions are inherited from the insoluble residue. Comparison of the crystallochemical parameters of micas in the insoluble residue and the soil clay shows that the clay has more SiIV and (Fe, Mg)VI, and less AlIV, AlVI and x (layer charge) than the insoluble residue. It also has fewer polytypes 2M1 and more 1M and has a smaller crystal size, especially in B horizons. The kaolinite is of varied origins including neoformation and inheritance from underlying rock. Some of the kaolinite and some mica has been blown in from elsewhere, probably from desert and coastal sources. The soils have undergone other typical processes of terrae rossae including dissolution of carbonate, illuviation of clay and iron oxides, and rubifaction.  相似文献   

9.
The Pleistocene volcanic paleosols of Armenia and Mexico combine the features of both arid and humid pedogeneses. They were studied in order to reconstruct the environmental conditions during the period of the initial settlement of humans in these areas. The main attention was paid to the micromorphological analysis of the pedogenic features. The pedocomplexes studied in Armenia have been forming since the Early Pleistocene. They bear evidences of humid (weathering, clay illuviation, and gleying) and arid (calcification) pedogeneses alternating in different soil layers and pointing to climatic cycles. The nonuniform lithology of the soil profiles is related to pulsating volcanic activity. Mexican paleosols of the Late Pleistocene period are similar to the lower layers of the soils in Armenia with respect to the features characteristic of the humid and arid phases of pedogenesis. This allows us to suggest that the early stages of the formation of the Armenian pedocomplex proceeded under warmer paleoclimatic conditions similar to those of a tropical climate. It is shown that the arid pedogenesis may erase the features produced during the previous stage of humid pedogenesis. The studied paleosols are characterized by the destruction of the features inherited from the humid phase (the clayey groundmass and illuviation coatings) by the newly forming calcite. Paleopedological records point to the fact that the paleoenvironmental conditions during the periods of the initial settlement of humans in both regions differed significantly from the modern environmental conditions in these regions.  相似文献   

10.
World Reference Base for Soil Resources (WRB) was published in 1998 and has begun to be used all over the world. We examined the definitions of andic and vitric horizons and qualifiers (lower-level units) of Andosols in the WRB by using the Tohoku University World Andosol Database (TUWAD) and proposed several revisions. Among 5 items of the definition for the andic horizon, we considered that the requirements of clay and volcanic glass contents should be deleted due to the difficulty in their accurate determination with the progression of soil weathering. In relation to this revision, correction of vitric horizon was also proposed. Although two major types of andic horizons, silandic and aluandic, are specified in the andic horizon definition, the aluandic type is not included in the qualifiers. Because aluandic volcanic ash soils have unique properties and are extensively distributed, the aluandic qualifier should be included in the lower level units of Andosols. Soil texture is used for the definition of arenic, luvic and vatic qualifiers. Therefore, these qualifiers should be modified or deleted. Both melanic and fulvic qualifiers are required to obtain the Munsell color value (moist) and chroma of 2 or less. To distinguish fulvic Andosols from melanic Andosols, the Munsell color and melanic index requirements for a fulvic horizon should be modified. Since Andosols with buried non-Andosols occur in a significantly large area, the thaptic qualifier should be used.  相似文献   

11.
Content, Transformation and Neoformation of Clay Minerals in near shore Sediments of the North Sea From literature and our own results, approximate quantitative values are given on the mineral content of clay and silt fractions of marine sediments from the Wadden Sea. Besides this, the extent of clay mineral transformation and neoformation in a marine environment is discussed. According to our knowledge, the extent of clay mineral transformation and neoformation must be unimportant because the sea water and pore solution of the sediments seems to be - with the exception of a small Mg-surplus — something like an equilibrium solution for three-and fourlayer minerals, which neither favors a considerable base fixation nor base release. Therefore illite neoformation during halmyrolysis or early diagenesis seems to be impossible because of unfavourable relations of potassium to all other cations in the sea water. Obviously the neoformation of illite is connected with later diagenesis. The processes of clay mineral neoformation in a marine evironment are probably restricted to the formation of amorphous (Mg-) Fe-Si-particles, which may be first steps in the formation of chamosites, chlorites or smectites.  相似文献   

12.
Field observations and laboratory analyses of podzols developed on sandy Triassic parent material in the Vosges have demonstrated clay accumulation in the upper parts of spodic horizons, especially in the Bh horizons. To see whether clay accumulation corresponds to real clay illuviation, two types of podzol profiles have been studied. The first is an iron podzol, called “podzol forestier”, because it has been entirely developed under climax forest environment. The second, an iron-humus podzol, called “podzol de dégradation”, was first developed under forest and more recently (the last 1000 to 2000 years) under heath vegetation. Methods used in the study of the two profiles were the “isoquartz” alteration balance, clay mineral identification by X-ray analyses and micromorphholigical examination.For the podzol forestier, the data strongly support a hypothesis of illuviation of very fine micaceous clays (vermiculite), especially the ferriargillans in the Bh horizon. Consequently, it is believed that illuviation of the greatest part of clays promoted differentiation of podzol horizons. Podzolization is strongly redistributive.In the podzol de dégradation, the identified clay minerals are the same as in the podzol forestier but the pedological features in the Bh horizon correspond to those of classic spodic horizons (mixed concentration and grain coatings). Moreover, podzolization is geochemically strongly subtractive in this second type of podzol.Inasmuch as the podzols de dégradation are developed from the podzols forestiers, the authors define an evolutionary time-sequence: the first phase of forest soil genesis is regulated by the double process of clay illuviation and redistributive podzolization. The following degradation phase connected to the particular nature of heath vegetation and to abundant chelating organic compounds induces the disruption of the ferriargillans previously formed in the Bh horizon, the formation of an agglomeroplasmic fabric microstructure and above all, the elimination of hydrolyzed products of minerals from the profile. During this last phase, a strongly subtractive podzolization prevails over clay illuviation.  相似文献   

13.
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.  相似文献   

14.
MICROMORPHOLOGICAL QUANTIFICATION OF CLAY ILLUVIATION   总被引：2，自引：0，他引：2  
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.  相似文献   

15.
According to the World Reference Base for Soil Resources (IUSS Working Group WRB, 2006), the differentiation of Acrisols and Alisols is based on the cation‐exchange capacity of clay, which cannot be directly determined in the field, but needs expensive and time‐consuming soil‐chemical analyses. This is an unsatisfactory situation for pedologists, who urgently require a rapid field method to distinguish illuviation‐type reference soil groups (Alisols, Acrisols, Luvisols, Lixisols). In this study, we tested the ability of gamma‐ray spectrometry to separate major WRB reference soil groups in the field. The underlying hypothesis is that Alisols and Acrisols are distinguished by their clay mineral composition, which should be reflected by geochemistry and consequently gamma‐ray radiation (i.e., K‐containing illite vs. K‐free kaolinite). Highly significant differences in their gamma‐ray spectrum for K, Th, and U were found for limestone and its soils. Especially the K and Th signatures allowed a clear separation of Acrisols and Alisols. In general, the surface radiation was sufficient to separate these soils. Best results were revealed considering parent rock and the whole soil profile. This means by using a portable radiometer and a pH meter, all illuviation‐type reference soil groups could be distinguished in this case. If applicable at other sites, this approach could enormously reduce expenditures for soil‐chemical analysis needed to assist soil classification.  相似文献   

16.
《CATENA》2001,43(1):49-62
A comparison was made between soils on north- and south-facing slopes of six cinder cones in the Springerville volcanic field (SVF), Arizona, in order to determine the influence of slope aspect on soil weathering processes. Twenty-four soil pedons were sampled on different aspects of six cinder cones. To control for the influence of slope on pedogenesis, all sample sites possessed slopes of 17±2°. Soil weathering processes were characterized by solum depth, texture, and Ca:Zr chemical weathering indices. Quartz and mica were used to identify eolian additions to the volcanic soils. Accelerated rates of weathering and soil development were found to occur in soils on south-facing slopes while no trend with aspect was found for eolian additions. Accelerated rates of weathering and soil development may influence cinder cone degradation and cone morphology.  相似文献   

17.
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18.
Whether some soils observed in Morocco prior to the 1966 conference on Mediterranean soils held in Madrid had argillic horizons was the subject of active discussions. Textural differences between A- and B-horizons were obvious. Consequently, individual horizons of a number of profiles were sampled for micromorphological study. No clay films were observed in thin sections representing the B-horizons free in carbonate. Peds had pressure faces and internal striations in the matrix. Microchurning and swelling and shrinking are believed to have obliterated evidence of clay illuviation in the B-horizons, but clay coatings were observed at greater depth in well-developed Bca-horizons.  相似文献   

19.
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.  相似文献   

20.
A comparison was made between two soil climosequences on north- and south-facing slopes in northern Italy to determine the influence of slope aspect on soil processes. The climosequences span an elevational gradient ranging from moderate (1200 m a.s.l.) to high alpine (2420 m a.s.l.) climate zones on surfaces having an age of about 15 000 years. The soils were investigated with respect to organic C, oxalate and dithionite extractable Fe, Al and Si, elemental losses (Ca, Mg, K, Na, Fe, Al, Si, Mn) and clay minerals. The stocks of soil org. C as well as of oxalate-extractable Fe and Al was greatest in the subalpine zone near the timberline. There are no clear differences in organic C content between the soils on north- and south-facing sites. Fe-oxalate and to a lesser extent Alo-stocks were, however, greater on north-facing sites, indicating that weathering is greater there. Eluviation and illuviation of Al and Fe within the soil profile, typical for podzolisation, was more distinctly expressed on the N slopes. The probability of ITM (Imogolite-type-material) formation in the soil seemed to be greater on south-facing sites. On the north-facing sites, element leaching was most intense in the subalpine zone close to the timberline while on the south-facing sites this was only the case for the base cations. The N slopes exhibited higher leaching of elements which generally indicates a higher weathering intensity. On south-facing sites, typical podzolisation processes were measurable only above 2000 m a.s.l. The development of smectites is also a reflection of the weathering intensity; smectite was discernible in the surface horizon at all sites on N slopes but the highest amount was detected in the sub-alpine climate zone. For the south-facing sites only in the alpine climate zone could smectite be detected. Higher temperatures and an increased number of freeze-thaw cycles on south-facing slopes should theoretically enhance rates of chemical weathering. This could, however, not be confirmed with our measurements. The degree of chemical weathering increases from the south- to the north-facing sites that are characterised by lower temperatures, lower evapotranspiration and consequently by a higher humidity. Although precipitation in Alpine regions is abundant, the availability and flux of water through the soil is the prime factor in weathering intensity.  相似文献   

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