Characteristics of Clay Minerals in Podzols and Podzolic Soils

The clay minerals in Podzols and podzolic soils developed under coniferous forests in the Subarctic and Cool-temperate zones are characterized by the predominance of smectite and/or mica-smectite interstratified minerals in the eluvial horizons and chlorite-vermiculite intergrade in the illuvial horizons. A large amount of vermiculite is present in the eluvial horizons of some podzolic soils in the Cool-temperate zone. The illuvial horizons of these soils also contain free iron oxides such as goethite. Imogolite and allophane are present in the illuvial horizons of several soils derived from volcanic ashes. It is suggested that the critical bioclimate for the release of interlayered aluminum from the 2:1-type minerals lies between the Cool- and Warm-temperate zone. In the eluvial horizons of Podzols and podzolic soils, mica minerals and chlorite, as primary minerals, have been transformed to smectite through the pedogenic process. Based on previous studies on the structure and degradation of the dioctahedral mica minerals, it is considered that smectite is transformed from 1M-type mica minerals directly, and from 2M-type mica minerals via mica-smectite interstratifled minerals. The formation of a smectite lattice in the eluvial horizon should be a clay-mineralogical indicator of podzolization.     

Classification of pedogenic cementation in Podzols by pocket penetrometry

According to the German Soil Taxonomy, the formation of cemented horizons in Podzols is restricted to the precipitation of iron oxides. However, in iron‐poor sandy substrates, also illuviation of only organic compounds can form cemented horizons with penetration resistances of up to 14 kg cm⁻². We present a reproducible field test for classifying pedogenic cementation in Podzols and suggest considering cemented horizons (Bmh and Bhm) in the upcoming edition of the Guidelines for Soil Mapping.     

Podzol formation in sandy soils of Finland

Podzolization occurs quickly in acidic parent materials with addition of acidic litter from coniferous trees. This study was conducted to evaluate Podzol formation and estimate lengths of time required to meet morphological and chemical criteria of podzolic B horizon and spodic horizon in Finland. Soil color, organic C, ODOE, and extractable Al and Fe were measured in a seven-pedon chronosequence (230–1800 years) and four older pedons (8300–11,300 years). The bulk mineralogical composition of the BC and C horizons was uniform with quartz, plagioclase and K-feldspar as main components and amphibole, illite and chlorite as minor components. The fine (<5 μm) fraction of selected samples was primarily amorphous allophone-like material with some mixed-layered illite–vermiculite. All pedons in the study met the criteria for albic horizons according to the FAO–Unesco, World Reference Base (WRB) and Soil Taxonomy systems. According to the FAO–Unesco system, all pedons had spodic B horizons and were classified as Podzols. According to the WRB system, none of pedons of the chronosequence had spodic horizons, whereas the older pedons met the criteria for a spodic horizon. About 4780 years were required to form a spodic horizon according to the WRB system. The oldest pedon of the chronosequence and the older pedons had spodic horizons according to Soil Taxonomy, but the younger pedons failed to meet the spodic horizon criteria. About 1520 years were required to form a spodic horizon that met the color and organic C criteria of Soil Taxonomy, whereas it took about 4780 years to meet the required accumulation of Fe and Al. This study points out the discrepancy between the color criteria and the criteria reflecting the accumulation of Al, Fe and organic matter in the B horizon.     

Profilmorphologische Studie zur,disharmonischen’ Polygenese von Podsolen

Profile-morphological study of the ‘disharmonic’ polygenesis of Podzols Based on the relevant literature and his own research findings the author points out the diversity of soils designated as Podzols in the past and the present. Older Podzols which have passed through several phases of development (polygenesis) not infrequently show illuvial horizons with iron oxides and/or clay minerals which were obviously washed out earlier than the humus substances. This is demonstrated by photographs. Whereas previous attempts to explain these facts were based on changes in pedogenetic parameters (pH, redox potential, density) or vegetation (= harmonic development) the author suggests taking Holocene climatic changes into consideration (= disharmonic development). By analogy with the formation of clay-illuvial horizons of ‘Lessivé-Braunerden’ (so-called ‘Parabraunerde-Braunerden’ after AG Boden, 1994) on till and loess in Central Europe, which the author considers to be relict formations developed under the warm-humid climatic conditions of the Atlanticum, we can — in very sandy soils — assume a similar process of percolative sesquioxide-transfer during this period. If further investigations come to the conclusion that such transport of colloids took place without the participation of organic complex-forming substances this process should no longer be interpreted as a phase of podzolisation, but either attributed to lessivation or designated by a new pedogenetic term (ferralluviation, Ferralluvisol).     

Discrimination of Australian soil horizons and classes from their visible–near infrared spectra

A soil's reflectance spectrum in the visible and near infrared is rich in information. It is an integrative property of the soil that measures its colour, the abundance of iron oxides, clay minerals and carbonates, the amount of water and organic matter and its particle size. We explored the merit of discriminating between soil horizons, of which we had 13 654 samples, and soil orders from the Australian Soil Classification, of which we had samples from 1697 profiles with designated horizons, by analysing quantitatively their diffuse reflectance spectra in the visible‐near infrared (vis–NIR) range (350–2500 nm). We re‐sampled the spectra to 10‐nm intervals and converted them to logarithms of deviations from their convex hulls. We then transformed them to canonical variates, which we display as scatter diagrams in low‐order canonical planes. The minerals, colour and organic constituents thought to be responsible for their discrimination are identified. Each spectrum was re‐examined and allocated to the group whose centroid was nearest in the canonical space. Topsoil horizons (A, A2 and transitional AB and AC horizons) were distinguishable from subsoils (B, C and transitional BC horizons). Vertosols, Ferrosols, Podosols (Podzols), Organosols, Calcarosols, Rudosols, Sodosols, Hydrosols, Kandosols and Kurosols were in general well separated from other soil orders and were assigned to their own orders such that 80% or more were correctly allocated. These orders possess characteristics that are easily distinguished by vis–NIR spectroscopy. Re‐allocations to other orders were interpretable and could be related to identifying features of the ASC classification. Our results show that spectra distinguish soil horizons and soil type. They suggest that vis–NIR spectroscopy could make an important contribution to the definition and identification of classes in an effective system of soil classification.     

Accumulation of organo‐metallic complexes in laterites and the formation of Aluandic Andosols in the Nilgiri Hills (southern India): similarities and differences with Umbric Podzols

We have investigated the speciation and distribution of iron (Fe) and aluminium (Al) between minerals and organic species in A and B horizons of two Aluandic Andosols with X‐ray diffraction, thermal analyses, visible diffuse reflectance and Fourier transform infrared (FTIR) spectroscopies, together with selective and total chemical extractions. The two Aluandic Andosols of the Nilgiri Highlands (south India) have formed at the expense of intensively weathered lateritic formations of the Eocene. Data revealed that Al and Fe were predominantly stored in end‐weathering products of laterites, mainly as gibbsite and Fe (hydr)oxides in B horizons of the Aluandic Andosols. These secondary minerals are gradually replaced by organo‐metallic complexes in the topsoil A horizons exhibiting andic properties. We then indicate that formation of the organo‐metallic complexes results from weathering of the dominant crystalline Al‐ and Fe‐(hydr)oxides mediated by the organic ligands and complexation of the polyvalent metals following the accumulation of organic matter. Such weathering and complexation mechanisms are therefore similar to those recently ascribed to deferralitization and the formation of freely drained Umbric Podzols (Humus‐Podzols) in the upper Amazon Basin. In the present case, large supplies of both Al‐ and Fe‐bearing minerals provide large metal:carbon ratios that prevent the mobility of the organo‐metallic complexes and induce the formation of Aluandic Andosols rather than Podzols.     

Bodenentwicklung am Rande oligotropher Moore im Raum Berlin

Soil development in the surrounding of oligotrophic mires in the Berlin region Polygenetic soils, surrounding oligotrophic kettle hole mires in the valley and aeolian sand areas of the Berlin region, were investigated. The typical soil catena is formed by the sequence of Ombric Histosol (Niedermoor), Ombric Histosol/Albi‐gleyic Podzol (Moor‐Podsol‐Gley), Albi‐gleyic Podzol (Nasspodsol‐Gley), Gleyic Podzol (Podsol‐Gley), and Dystri‐gleyic Arenosol (Gley‐Podsol‐Braunerde) (German soil classifications in parenthesis). Field and laboratory work showed, that the investigated soils were strongly related to each other and that their development depends on the trophy of the mire and groundwater fluctuations during the Holocene. Compared with the Bh‐horizon of terrestrial soils the Gh‐horizon is nearly free of Fe and Mn, but very rich in pedogenic Al‐oxides and rich in organic matter. The genesis of the soils is explained as follows: 1. The development of different Gleyic Podzols was due to rise of groundwater. Consequently the Bh and Bs horizons of Podzols surrounding the mire were converted to Gh and Gr horizons. 2. Humic substances and Al in the Gh and Gr horizons were not re‐mobilized due to the rise of groundwater, whereas Fe and Mn were reduced and removed by groundwater. 3. At the periphery of the mire Fe was enriched in the Go horizon of the Gley‐Podzols but not Mn. 4. The fact that the mire is completely surrounded by Podzol‐Gleys, indicates, that movement of the groundwater from the central parts of mires towards the periphery is an essential pedogenetic factor.     

Tracing Pb Pollution Penetration in Temperate Podzols

We combine high‐resolution soil sampling with lead (Pb) analyses (concentrations and stable isotopes) in two temperate podzols, together with previous data obtained with selective Al and Fe dissolution techniques. We aim to assess how atmospheric Pb is incorporated into the soils during pedogenesis. Partial least squares modelling for Pb concentrations shows that the podzolization process has the largest effect on Pb concentration (80·3% of the variance). The proportion of inorganic secondary compounds, the input of fresh organic matter from the soil surface and the relative abundance of Fe versus Al are responsible for a small part of the Pb concentration variance. Lead isotopic composition (²⁰⁶Pb/²⁰⁷Pb ratios) depends on soil organic matter content either fresh/poorly humified (57·3% of the variance) or humified (24·7% of the variance). The Pb linked to inorganic compounds and the overall podzolization process play a minor role in isotopic signature (5·3 and 3·7% of the variance respectively). Soil pH appears to be the controlling variable of the different transport and retention mechanisms. The relatively low isotopic ratios observed in spodic horizons result from geogenic Pb released through the preferential dissolution of the isotopically distinct most weatherable minerals of the parent material in the eluvial horizons, which undergoes downward mobilization. An accurate knowledge of soil reactive components and formation mechanisms is essential to a correct diagnose of the scope of Pb pollution and a more effective design of remediation strategies. Copyright © 2017 John Wiley & Sons, Ltd.     

Changes in soil morphology of Podzols affected by alkaline fly ash blown out from the dumping site of an electric power plant

Purpose

The impacts of fly ash on the chemistry of forest floors were previously described in literature, while impacts on soil properties were less recognised. Soil investigations were focussed mainly on increases of pH and base saturations in surface horizons. The purpose of this study was to describe the influence of alkaline fly ash blown out from the dumping site of a lignite-fired power plant on pH changes of ectohumus horizons of Podzols and the morphology of deeper horizons.

Materials and methods

We investigated the soil profiles of Podzols derived from loose quartz sand and developed under pine forest surrounding the dumping site of the power plant Be?chatów, central Poland. In the vicinity of the fly ash dumping site, five Podzol profiles located at a distance of 50 m from the dumping site were investigated, as well as soil profiles located along the transect set at distances of 50, 300, 800 and 2000 m from the dumping site. Control profiles were located at a distance of 7.3 km from the dumping site. Soil morphology was described in the field and the following properties were determined: soil texture, hydrolytic acidity, exchangeable cations, total organic carbon and total nitrogen content.

Results and discussion

The pH values of Podzol ectohumus horizons located close to the dumping site ranged from 6.01 to 7.34 compared to a range of 3.08–3.72 in the control. Ectohumus horizon located 300 m from the dumping site showed a pH range of 4.13–4.26, while at a distance of 800 m, the pH values did not differ from those of the control site. The upper part of the eluvial soil horizons located close to the dumping site had been transformed into transitional AE horizons in which humic substances translocated from ectohumus horizons were accumulated. Moreover, the organic carbon content of this horizon increased compared to the carbon content of the illuvial Bs horizon located below it. Under the influence of alkalisation of upper horizons, the illuvial Bhs horizons vanished and were transformed into Bs horizons.

Conclusions

Changes in soils affected by fly ashes are connected with alkalinisation of ectohumus horizons. Podzolisation processes can be reduced or even completely stopped regarding the distance from the dumping site. Eluvial Podzol horizons located close to the dumping site may be transformed into AE horizons in which humic substances translocated from ectohumus horizons are accumulated. Due to transformation and translocation of organic components, Bhs horizons can be transformed into Bs horizons.

     

Ermittlung von analytischen Kriterien zur bodentypologischen Einordnung tiefreichend humoser Sandböden im Westmünsterland

Determination of analytical criteria for classification of sandy soils with deepreaching humus contents in the region of Westmünsterland While mapping agricultural areas in the region of Westmünsterland a problem of soil classification became obvious. There are widespread sandy soils of brown to greybrown colour, which have unusually high contents of humus down to several decimeters depth. Several chemical and physical laboratory investigations were carried out to answer the question of natural or anthropogenic origin. Based on the characteristics of diagnostic horizons from certain classifiable soils like Kultosole espec. Plaggenesche (Plaggepts/Anthrosols, 7 profiles) and Spodosols/Podzols (8 profiles) clearly differentiating characteristics should be derived. Comparing with datas from subsoil horizons of the questionable 11 profiles these should be attached to one of the former groups. Univariate and multivariate statistic methods like discriminant and cluster analysis were used to evaluate the analytical laboratory results. It was possible to attach 5 of 11 systematic questionable soil profiles to the group of Kultosole/Plaggenesch. As there is no better fitting systematical classification (like deepreaching humous Brown Earth o.s.) the remainder must be classified as Brown Earth or Podzol-Brown Earth.     

Soil altitudinal sequence on base-poor parent material in a montane cloud forest in Sierra Juárez, Southern Mexico

The soils of montane cloud forests (MCF) are still insufficiently studied. A number of researchers report Podzols to be the main soil group for MCF ecosystems; however, a great deal of contradictory data exists. We studied an altitudinal sequence of soils formed on ferrous chlorite shale under natural MCF vegetation in Sierra Juárez, Southern Mexico, from 1500 to 2500 m asl. The soils of the upper part of the toposequence were Folic Stagnic Podzols, with inclusions of Folic Stagnosols in local depressions, while the soils of the lower part of the toposequence were Folic Cambisols (Humic, Hyperdystric). All the soils in the toposequence were extremely acid, and had thick organic surface horizon. Mineral horizons of all soils were poor both in exchangeable and total reserves of bases; the bases were concentrated mainly in organic topsoil. With decreasing altitude both the thickness of albic horizons, the depth of the maximum acid oxalate-extractable Fe and Al concentrations, and the difference in clay content between the eluvial and illuvial horizons decreased. In the upper part of the toposequence the composition of soil clays was similar to that of parent material (chlorite and mica), with some mixed-layered 2:1 minerals. However, gibbsite and kaolinite were also present in the soils of the other site within the same upper MCF belt. The phenomenon was ascribed to parent material heterogenity. In the medium and lower parts of the toposequence gibbsite and kaolinite were the dominant minerals. We consider that the main pedogenic processes in the study area are raw humus accumulation, weathering in situ, podzolization, and iron reduction due to water stagnation in mineral topsoil. The intensity of weathering decreases, while the extent of water stagnation increases with altitude. To a great extent the genesis and altitudinal distribution of the soils in the MCF depends on parent material.     

Feedback processes in soil genesis

Feedback can be defined as the returning of a part of the effects of a given process to its beginning or to a preceding stage so as to reinforce or modify that process. Feedback processes are self-accelerating because of continuous reinforcement of the causes starting them. Up to a certain moment, reinforcement is proportional to the effects (or output) of the process. Later, de-acceleration and termination come as one of several factors (or reactants) in the process become limiting, e.g., depletion of easily weatherable minerals, hence cessation of clay formation. In soils there are many feedback, self-terminating processes such as accumulation of organic matter in Mollisols, clay accumulation in Argids, and development of windows in duripans and dayas in soils with petrocalcic horizons. The occurrence and constancy of some morphological features in many soil profiles and soilscapes can be explained by this concept.     

Soil mixing and genesis as affected by tree uprooting in three temperate forests

The purpose of this study was to identify general patterns of pedoturbation by tree uprooting in three different, forested landscapes and to quantify post‐disturbance pedogenesis. Specifically, our study illustrates how the effects of ‘tree‐throw’ on soils gradually become diminished over time by post‐uprooting pedogenesis. We studied soil development within 46 pit‐mounds in two regions of the Czech Republic, one on Haplic Cambisols and one on Entic Podzols. A third study site was in Michigan, USA, on Albic Podzols. Uprooting events were dated by using tree censuses, dendrochronology and radiometry. These dates provided information on several chronosequences of pedogenesis in the post‐uprooting pits and mounds, dating back to 1816 AD (dendrochronological dating, Haplic Cambisols), 322 AD (median of calibration age, ¹⁴C age = 1720 ± 35 BP, Entic Podzols) and 4077 BC (¹⁴C age = 5260 ± 30 BP, Albic Podzols). Post‐uprooting pedogenesis was most rapid in pits and slowest on mounds. Linear chronofunction models were the most applicable for pedogenesis, regardless of whether the soils were in pit or mound microsites. These models allowed us to estimate the time required for horizons in such disturbed sites to obtain the equivalent thicknesses of those in undisturbed sites. These ranged from 5 (O horizon in pits on the Haplic Cambisols) to > 16 000 years (E horizon on mounds on the Albic Podzols). On the Albic Podzols, development of eluvial and spodic horizon thicknesses suggested that pathways involving divergent pedogenesis may occur at these small and localized spatial scales.     

Andic properties in soils developed from nonvolcanic materials in Central Bhutan

A number of soils are described in the literature as having andic and spodic soil properties, but have developed in nonvolcanic and nonallophanic materials and lack typical Podzol eluvial and illuvial horizons. They cover a wide range of parent materials and different types of climate. They have always been regarded as restricted to small areas. They were assigned to Andisols/Andosols, Podzols/Spodosols, or andic Inceptisols in the WRB and Soil Taxonomy and sometimes also named Cryptopodzols or Lockerbraunerden. Recent soil surveys in Bhutan, E Himalayas, show these soils are widespread at altitudes between 2200–3500 m asl and are spanning several bioclimatic zones. The aim of this study is the detailed characterization of specific properties and processes of formation by physical and chemical analyses, NMR spectroscopy, column experiments, SEM, XRD, and ¹⁴C dating in one of these soils in E central Bhutan. The results indicate advanced soil development with high amounts of oxidic Fe and Al compounds, low bulk densities (partly <0.5 g cm^–3), P retention >85%, and a dominance of Al‐hydroxy‐interlayered phyllosilicates. Scanning electron microscopy of sand fractions indicate microaggregates highly resistant to dispersion. Column experiments show podzolization with mobilization and translocation of DOM, Fe, and Al. Nuclear‐magnetic resonance spectroscopy and ¹⁴C ages of 16,000 BP indicate stabilization of DOM. Applying classification criteria, these soils appear to have andic and spodic features, but are neither Andosols nor Podzols senso strictu. Especially the role of Fe seems to be underestimated with regard to the specific soil‐forming processes. Because of their widespread occurrence and distinct properties, we suggest either a simplification of the criteria for existing soil types or a clearly defined separation of volcanic and nonvolcanic/nonallophanic Andosols.     

Mineralogic evolution in hydromorphic sandy soils and podzols in “landes du médoc”, France

Soils of the nearly level “Landes du Médoc” in southwestern France have a pattern of alternating bodies of hydromorphic podzols (Haplaquods) and low humic hydromorphic soils (Psammaquents). The soils are formed in a sedimentary mantle of coarse, quartzose sands with a slight microrelief consisting of low, elongated ridges and shallow, intervening troughs. The water table is at shallow depths throughout the plain, even at the surface in places. The podzols on the crests of the low ridges have distinct A₂ and cemented B₂ h horizons. Podzols persist down the sides of ridges but going downslope first lose the A₂ horizon and then the cementation of the Bh horizon. Soils in the shallow troughs have A₁ and Cg horizons without B horizons.The fine silt (2–20 μm) and clay (0–2 μm) fractions of the parent sand contain primary trioctahedral chlorite, mica, feldspars, and quartz, with the last mineral predominant. During soil development, the first three minerals undergo weathering at different rates and to different extents. Chlorite is most strongly weathered, followed in order by plagioclases and K-minerals. In the fine silt fraction, weathering seems to occur mostly by fragmentation of particles. In the clay fraction, the phyllosilicates successively form irregularly interstratified minerals with contractible but not expandable vermiculitic layers, interstratified minerals with contractible and expandable smectitic layers, and finally smectites.The extent to which the silicate minerals are weathered becomes progressively greater from the low humic hydromorphic soils to the podzols with friable Bh horizons to the podzols with cemented Bh horizons. Smectite is present only in the A₂ horizons of these last podzols.The aluminum release by weathering of silicate minerals is translocated in part in the form of organo-metal complexes into the Bh horizons of the podzols. Greatest concentrations of Al are associated with coatings of monomorphic organic matter on mineral grains in the cemented Bh horizons, in which some Al has also crystallized into gibbsite. That mineral was not detected in friable B horizons of podzols nor in the low humic hydromorphic soil. Contrary to expectations, the mobile Al did not enter interlayer spaces of expanding 2:1 clay minerals.     

Estimation of soil weathering stage and acid neutralizing capacity in a toposequence Luvisol–Cambisol on loess under deciduous forest in Belgium

Soils derived from loess are extensive in Europe and are well suited for forestry. They are suspected to be poor acid buffers, however. We have estimated the weathering stage and acid neutralizing capacity of acid soils under forest in a toposequence on loess in the Belgian silt belt. The soils vary distinctly in morphology and physico‐chemical properties according to their topographic position. Dystric Cambisols have developed in colluvial deposits in the dry valley floors, whereas Dystric Luvisols have formed on the slopes in a rejuvenated material. The Cambisols are more acid and less saturated in bases than are Luvisols. They are strongly depleted of clay and contain less weatherable minerals. Easily weatherable minerals are concentrated mainly in the clay fraction of both soil types. Clay minerals of size < 2 μm therefore act as major sinks for protons in these soils. A simplified expression taking into account the total reserve in bases, total aluminium and iron occluded in silicates is used to estimate acid neutralizing capacity. Our estimates confirm that these acid loessic soils are indeed poor acid buffers. They show that the Dystric Cambisols depleted of clay are sensitive to potential acidification, whether natural or man‐made.     

Podzolization as a deferralitization process: dynamics and chemistry of ground and surface waters in an Acrisol – Podzol sequence of the upper Amazon Basin

Hydrochemical processes involved in the development of hydromorphic Podzols are a major concern for the upper Amazon Basin because of the extent of the areas affected by such processes and the large amounts of organic carbon and associated metals exported to the rivers. The dynamics and chemical composition of ground and surface waters were studied along an Acrisol‐Podzol sequence lying in an open depression of a plateau. Water levels were monitored along the sequence over a period of 2 years by means of piezometers. Water was sampled in zero‐tension lysimeters for groundwater and for surface water in the drainage network of the depression. The pH and concentrations of organic carbon and major elements (Si, Fe and Al) were determined. The contrasted changes reported for concentrations of Si, organic carbon and metals (Fe, Al) mainly reflect the dynamics of the groundwater and the weathering conditions that prevail in the soils. Iron is released by the reductive dissolution of Fe oxides, mostly in the Bg horizons of the upslope Acrisols. It moves laterally under the control of hydraulic gradients and migrates through the iron‐depleted Podzols where it is exported to the river network. Aluminium is released from the dissolution of Al‐bearing minerals (gibbsite and kaolinite) at the margin of the podzolic area but is immobilized as organo‐Al complexes in spodic horizons. In downslope positions, the quick recharge of the groundwater and large release of organic compounds lead to acidification and a loss of metals (mainly Al), previously stored in the Podzols.     

Clay minerals in a soil chronosequence derived from basalt on Hainan Island, China and its implication for pedogenesis

A soil chronosequence consisting of six profiles formed on quartz tholeiite basalt ranging in age from 10,000 years to 1. 8 Million years (My) was studied here. Soil clays were identified using XRD diffractogram decomposition methods for samples obtained from the A and C horizons of profiles. The results showed that kaolinite minerals dominated in all the clay fractions. Gibbsite was prominent in the C horizons in the soils from older rocks. Clays in the A horizon of relatively young soils showed an initial stage of illite formation, followed by smectite mixed layer minerals (illite-smectites and then vermiculite-illite) and finally by vermiculite. The initial presence of illite is interesting as there is no magmatic micaceous or phyllosilicate phase in these basalts and the formation of illite we attribute to a secondary process, probably created by alkali transport by plant materials. The change in 2:1 clay mineralogy reflects the overall change in Si/Al ratios in the soils over longer periods of weathering. In all cases gibbsite is more abundant in the C horizons than the A horizons. The difference in gibbsite content between the A and C horizons we attribute to plant transport of siliceous phytolite material to the surface. Continued high rainfall over long periods of time removed the alkali faster than the plants could bring it to the surface, which led to continuous lowering of 2:1 minerals from younger to older in the soil chronosequence. Nevertheless a 2:1, silica-rich mineral persists in the clay assemblages although in very minor amounts.     

A hardpan podzol at Yarner Wood, Devon

Podzols under sessile oak at Yarner Wood National Nature Reserve have extraordinarily hard and compact grey subsurface (Ea) horizons. The parent material is solifluxion debris from sandstones and siltstones of the Culm Measures (Lower Carboniferous) into which small amounts of loess have been incorporated. The general morphological, micro-morphological and chemical features of these soils, which are classified as hardpan stagnopodzols, are outlined and compared with those of adjoining brown podzolic soils. The evidence shows that the compaction is due only to close packing of particles and not to cementation. The genesis of the hardpan stagnopodzols and their relationship to other hardpan soils elsewhere in the world is discussed and the creation of a'Densi-'Great Group within Soil Taxonomy is proposed.     

Biological influences on the morphology and micromorphology of selected Podzols (Spodosols) and Cambisols (Inceptisols) from the eastern United States and north-east Scotland

Biological activities greatly influence the formation of many soils, especially forest soils under cool humid climates. The objective of this study was to investigate the effects of vegetation and soil biota on the formation of selected soils. Field morphology, micromorphology, and carbon and organic matter analysis were determined on six Podzols (Spodosols) and two Cambisols (Inceptisols) from the eastern United States and north-east Scotland. Humification of plant material by soil fauna and fungi occurs in all organic horizons. Thick organic coatings are observed on soil peds and rock fragments from the E1 to the Bs horizon in a Haplic Podzol from Clingmans Dome Mt., TN. Thin sections reveal large accumulations of root material in different stages of decomposition in the spodic horizons of a Haplic Podzol from Whiteface Mt., NY. Organic carbon ranges from 5.4 to 8.5% in the spodic B horizons of the Whiteface Mt. Podzol. Earthworms and enchytraeids have a great effect on the structure of the surface and subsurface horizons in the Dystric Cambisols from Huntly and Clashindarroch Forests, Scotland and a Cambic Podzol from the Corrie Burn Basin, Scotland. Podzols from Speymouth Forest, Scotland (Gleyic Podzol), Clingmans Dome Mt., and Whiteface Mt. have thick organic horizons. The Podzols from the Flatwoods in Georgia, the Pine Barrens in New Jersey, the Corrie Burn Basin, and the Cambisol from Huntly Forest have only A horizons at the surface. The Clashindarroch Forest soil has a very thin organic horizon. Warm and humid climates and sandy parent material are responsible for thick E horizons and lack of thick organic horizons in the Flatwoods (Carbic Podzol) and Pine Barrens (Ferric Podzol) soils. Earthworms and enchytraeids thrive in the Corrie Burn Basin and Huntly Forest soils due to the vegetation and the highly weathered basic parent material. The site at Clashindarroch once carried oak, and then birch forest, both of which produce a mild litter and also encourage earthworm and enchytraeids. This fauna is responsible for much mixing of the topsoil. The present conifer vegetation will eventually produce a deep litter and cause podzolization.