Movement of aluminium as an inorganic complex in some podzolised soils,New Zealand

Chemical and mineralogical data are presented for three Spodosols (podzols) and a related Inceptisol (yellow-brown loam). Allophane with an Al/Si atomic ratio close to two is identified in the B horizons of all four soils, and minor amounts of imogolite are present in association with allophane in all but one soil where small-particle gibbsite occurs. Parent materials for these soils are essentially non-vitric. Allophane (Al/Si = 2) has been estimated quantitatively in all soils using oxalate-extractable Si (Si₀) and is selected clay fractions using both Si₀ and infrared spectroscopy. Maximum concentrations of allophane (Al/Si = 2) range from 5% to 18% of fine earth (< 2 mm) fractions and all occur in B horizons. Fe₀ values are low relative to Al₀ values except for the upper horizons of the Inceptisol. Al₀ values peak in B horizons and the ratio pyrophosphate-extractable Al to Al₀ decreases from about 1 in A and upper B horizons to 0.1–0.4 in lower B horizons.An interpretation of the data is consistent with recent proposals that the movement of Al in podzolisation is due primarily to the formation of inorganic complexes with Si. Chemical criteria for spodic horizons should be consistent with the total illuviation of Al and Fe (and perhaps Si), rather than just the organic-bound fraction of Al and Fe in these horizons as indicated by amounts in extractants such as pyrophosphate.     

Oxalate-soluble compounds of Al, Fe, and Si in soils of cold humid regions as a function of weathering

Original and published data on the contents of X-ray amorphous oxalate-soluble compounds of Al, Fe, and Si in mesomorphic eluvial soils of cold, moderately cold, and moderately warm continental humid and semihumid regions are generalized. The groups of soils developed from mafic igneous, metamorphic, and pyroclastic rocks are considered. It is shown that the content of oxalate-soluble oxides (OSOx) in the horizons of their maximal accumulation varies from less than 1% to 20–30%; the Al_ox/Fe_ox ratio varies from 1 to 6.5. The leading factor dictating the amount and quality of the OSOx in the soils is the presence or absence of volcanic glass in the parent materials. The boundary between the soils with and without volcanic glass corresponds to the OSOx content of 5% and the Al₂O_3ox/Fe₂O_3ox ratio equal to 2. These criteria are more reliable than the Al_ox/Fe_ox ratio used by foreign soil scientists to specify Andosols (Al_ox/Fe_ox > 2). The contents of oxalate-soluble oxides of Al and Fe do not depend on the total contents of these oxides in the parent material and seem to be related to the presence of these elements in minerals with different resistance to weathering. Under the natural conditions described in this paper, the content of OSOx shows a very weak response to zonal (temperature-controlled) climatic changes and/or to changes in the degree of humidity and the continentality of the climate.     

Iron oxides in four Red Mediterranean soils on metarhyolite and metadolerite in Kilkis,Greece

The various iron fractions were quantified by selective dissolution (Fe_d, Fe_o, Fe_t) in four Red Mediterranean soils, developed on metarhyolite and metadolerite. They were similar in all profiles. A strong trend of iron removal from the surface horizon and of its subsequent illuvial translocation to the argillic horizons was observed. In all profiles, Fe_o was not related to the organic matter content indicating the Mediterranean xeric soil environment. The Fe_o/Fe_d ratio and the percentage of crystalline iron oxides (Fe_d-Fe_o) suggested that the pedoenvironment in which the profiles P1, P2 were formed, allowed the high crystallization of iron oxides. As indicated by the Fe_d/Fe_t values, the weathering process was more intense in the metarhyolite-developed soils. In contrast, the metadolerite-developed soils present conditions of poorly crystallized iron oxides and a lower degree of development.     

Pedogenic processes of placic and spodic horizons in subtropical subalpine forest soils with contrasting textures

Placic (Bsm) and spodic (Bhs) horizons are common in subalpine or alpine forest soils in Taiwan. Bsm horizons are found more usually in finer textured soils than those with Bhs horizons. To understand the different formation processes in Bsm and Bhs horizons in a humid subtropical ecosystem, we identified micro‐morphological features by using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and electron probe micro‐analysis (EPMA), and determined the physiochemical properties by chemical extractions and clay mineralogy. The study included four pedons with well‐developed Bsm horizons from our previous study and four with well‐developed Bhs horizons at other sites. Both sites were in subtropical mountain forests with similar climate, topography and general geology but over regoliths with distinctly different textures. Micro‐morphology revealed a vughy (small cavities lined with in‐washed materials) microstructure in Bsm horizons but a granular structure with bridge microstructures between coarse grains in Bhs horizons. Chemical analysis revealed more free pedogenic iron (Fe_d) and aluminium (Al_d) in Bsm than in Bhs horizons, but more organically complexed Al (Al_p) in Bhs horizons. Energy dispersive spectrometry revealed predominant Fe, oxygen (O) and carbon (C) in the matrix of the Bsm horizons, whereas Al, silicon (Si) and C were the major elements of interstitial materials in Bhs horizons. Polarizing microscopy and EPMA spectra confirmed the illuvial nature of organic Al complexes in Bhs horizons. The transformation of clay minerals showed more intense podzolization in Bhs horizons than in Bsm horizons. The different formation mechanisms in Bsm and Bhs horizons result from contrasting texture; redox processes are predominant in Bsm horizons because of the clayey texture whereas podzolization is predominant in sandy Bhs horizons.     

Podzol development with time in sandy beach deposits in southern Norway

The coastal areas of SE Norway provide suitable conditions for studying soil development with time, because unweathered land surfaces have continuously been raised above sea level by glacio‐isostatic uplift since the termination of the last ice age. We investigated Podzol development in a chronosequence of six soils on sandy beach deposits with ages ranging from 2,300 to 9,650 y at the W coast of the Oslofjord. The climate in this area is rather mild with a mean annual temperature of 6°C and an annual precipitation of 975 mm (Sandefjord). The youngest soil showed no evidence of podzolization, while slight lightening of the A horizon of the second soil (3,800 years) indicated initial leaching of organic matter (OM). In the 4,300 y–old soil also Fe and humus accumulation in the B horizon were perceptible, but only the 6,600 y–old and older soils exhibited spodic horizons. Accumulation of OM in the A horizons reached a steady state in <2,300 y, while in the B horizons OM accumulated at increasing rates. pH dropped from 6.6 (H₂O)/5.9 (KCl) in the recent beach sand to 4.5 (H₂O)/3.8 (KCl) within approx. 4,500 y (pH_H2O)/2,500 y (pH_KCl) and stayed constant thereafter, which was attributed to sesquioxide buffering. Base saturation showed an exponential decrease with time. Progressive weathering was reflected by increasing Fe_d and Al_d contents, and proceeding podzolization by increasing amounts of pyrophophate‐ and oxalate‐soluble Fe and Al with soil age. These increases could be best described for most Fe and Al fractions by exponential models. Only the increasing amounts of Fe_p could be better described by a power function and those of Fe_o by a linear model.     

Soils and their relationship to aspect and vegetation history in the eastern Southern Alps, Canterbury High Country, South Island, New Zealand

This study focuses on soils in a mountainous catchment area located in the eastern part of the Southern Alps, South Island, New Zealand. The objective was to check the soils for non- or poorly crystalline constituents (metal organic complexes, short-range-order minerals) and if there is a relationship between pedogenesis and aspect and more recent landscape history. The morphology of the soils indicates brown soils (dystric cambisols, dystrudepts) with only few signs of podsolisation. In contrast, selected chemical properties of the soils reveal very strong weathering and leaching. Fe_o/Fe_d ratios are high and exceeding 0.6 in almost every soil horizon. Oxalate-extractable aluminium and silicon show prominent peaks in the lower subsoil horizons with 1.76–2.52% Al_o and up to 0.68% for Si_o on southern aspects. This is considerably higher than the values measured for soils on northern aspects (0.59% to 1.07% Al_o, max. 0.26% Si_o). This aspect relationship is also applying to phosphate retention reaching values of more than 90% on southern aspects and not more than 70% for northern aspects. Additionally, significant movement of organic matter in soils on southern aspects is evident by measurements of organic carbon and pyrophosphate-extractable Al and Fe. Thus soil formation can be regarded as more advanced on southern aspects. Allophane in association with organic matter can be considered as an important constituent in southern aspect subsoils being responsible for the typical andic properties. Metal-humus complexes and ferrihydrite are of subordinate significance. Considering the actual soil forming conditions under scrub-grassland (esp. soil acidity), it is unlikely that weathering and leaching is still strong enough today to allow significant podsolisation and the formation of short-range-order minerals. Under consideration of existing soil data from other studies it is proposed that these components and the podsolisation features are relicts caused by more acidic conditions under former forest cover which supported a stronger weathering and leaching.     

EXTRACTABLE SESQUIOXIDES IN SIX MEDITERRANEAN SOILS DEVELOPED ON BASALT AND SCORIA

Iron, Al, and Mn were extracted by oxalate and dithionite from two Brown Mediterranean Soils, two Red Mediterranean Soils, one Vertisol and one Gley soil, all derived from basalt or scoria in the sub-humid and humid Mediterranean regions of the Golan Heights. Ratios of oxalate: dithionite extracted iron (Fe_o:Fe_d) were low in all soils, indicating that the predominant form of free iron is crystalline. Fe_o accumulates in the argillic B horizons of the Mediterranean soils, while Fe_d accumulates in the surface horizons. A large part of the free iron oxide in the surface horizons of Mediterranean soils is associated with non-clay fractions. While manganese behaves in a manner somewhat similar to that of iron, no definite trends could be discerned in the vertical distribution of free aluminium. In the Vertisol, Fe_o and Mn_o accumulate in the subsoil. Fe_d and Mn_d increase slightly with soil depth. In the Gley soil, amorphous iron accumulates in the surface horizon, total free iron in the bottom horizon. Both amorphous and total free Mn had been depleted from the upper horizons of the Gley soil.     

Pedogenetische Differenzierung von Bodeneigenschaften auf Aggregatebene

Pedogenetic differentiation of soil properties in aggregates Besides the pedogenetic differentiation of soils in horizons a differentiation within horizons across aggregates seems possible. The objective of this study is to check if there is a differentiation of soil properties across aggregates. From a Braunerde, a Podzol-Braunerde, and 2 Podsols from Bavaria and Slovakia aggregates of 10–30 mm in diameter were selected manually from both topsoil and subsoil horizons and mechanically fractionated into a core and a surface fraction. In the aggregate fractions C_org, Al_o, and Fe_d were determined. C_org is generally depleted in the surface fractions of the A-horizons compared to the core fractions. This may be due to favoured microbial degradation of organic matter compared to the aggregate core and preferential leaching of organic C. In the subsoil horizons of the Braunerde C_org is lower in the aggregate surface fraction, in the Podzol, however, it is higher. In Podzols preferential C-input and sorption to aggregate surfaces seems to dominate. Lower Al_o? and Fe_d?concentrations in the aggregate surface fractions of all A-horizons may be explained by preferential acidification of aggregate surfaces as the aggregate surfaces mainly buffer the proton input into structured mineral soils. In the B-horizons only in Braunerde Al_o and Fe_d are lower in the aggregate surface fractions than in the core fractions. The Podzol B-horizons show preferential illuvial enrichment of sesquioxides at aggregate surfaces. Thus, pedogenesis results in the differentiation of soil properties not only between horizons but also within horizons on the level of aggregates. The resulting different chemical properties of aggregate surface and core fractions may affect the sorption capacity of structured soils.     

Iron oxides as weathering indicator and the origin of Luvisols from the Vistula glaciation region in Poland

Purpose

The aim of the research was to determine the effect of lithogenic and pedogenic processes on the formation of Luvisols from the area of Vistula glaciation on the base of profile distribution of iron oxides and total iron in relation to texture and physicochemical properties. The indices of weathering of the soil material in genetic horizons were calculated, and changes in the content and forms of iron oxides were evaluated.

Materials and methods

The predominant type of soil in the study area is Luvisols under agricultural use, formed from silt formations on loam. The analyses were made applying the following methods: grain size composition using the sieve method and hydrometer method, the interpretation of the results was performed according to the World Reference Base for Soil Resources classification, the pH of soils was measured with the potentiometric method, C-organic with the Walkley-Black dichromate method, the content of the following iron forms was determined (total iron (Fe_t) after the mineralization of soils in the mixture of HF and HClO₄ acids), free iron oxides were extracted using dithionite-citrate-bicarbonate method, and amorphous iron oxides after the ammonium oxalate extraction (using the Philips 9100PU apparatus). The clay mineralogy was estimated by X-ray diffraction analysis.

Results and discussion

It was observed that total iron enrichment occurs in argic horizons accompanied by iron depletion in luvic horizons, while the profile distribution of iron is similar to the distribution of clay. The (Fe_d/Fe_t) ratio indicates a low degree of weathering; the highest values were observed in argic (Bt) horizons, which confirms the effect of the process of pedogenesis on the value of that index. In the soils investigated, crystalline iron oxides generally dominate over the amorphous forms. The mineralogical composition of clay fraction separated from the upper part of soils was different as compared to the underlying material.

Conclusions

The results of the study showed that iron contents (together with the other indicators) and its forms can be used to distinguish soil layers of different origin. The depth distribution of Fe_d, Fe_o and Fe_t within soil profiles indicates that the soil material may be of different lithogenic origin in the studied pedons.

     

Effect of north and south exposure on weathering rates and clay mineral formation in Alpine soils

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 Al_o-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.     

Soil organic matter stabilization in acidic forest soils is preferential and soil type-specific

Minerals with large specific surface areas promote the stabilization of soil organic matter (SOM). We analysed three acidic soils (dystric, skeletic Leptic Cambisol; dystric, laxic Leptic Cambisol; skeletic Leptic Entic Podzol) under Norway spruce (Picea abies) forest with different mineral compositions to determine the effects of soil type on carbon (C) stabilization in soil. The relationship between the amount and chemical composition of soil organic matter (SOM), clay content, oxalate‐extractable Fe and Al (Fe_o; Al_o), and dithionite‐extractable Fe (Fe_d) before and after treatment with 10% hydrofluoric acid (HF) in topsoil and subsoil horizons was analysed. Radiocarbon age, ¹³C CPMAS NMR spectra, lignin phenol content and neutral sugar content in the soils before and after HF‐treatment were determined and compared for bulk soil samples and particle size separates. Changes in the chemical composition of SOM after HF‐treatment were small for the A‐horizons. In contrast, for B‐horizons, HF‐soluble (mineral‐associated) and HF‐resistant (non‐mineral‐associated) SOM showed systematic differences in functional C groups. The non‐mineral associated SOM in the B‐horizons was significantly depleted in microbially‐derived sugars, and the contribution of O/N‐alkyl C to total organic C was less after HF‐treatment. The radiocarbon age of the mineral‐associated SOM was younger than that of the HF‐resistant SOM in subsoil horizons with small amounts of oxalate‐extractable Al and Fe. However, in horizons with large amounts of oxalate‐extractable Al and Fe the HF‐soluble SOM was considerably older than the HF‐resistant SOM. In acid subsoils a specific fraction of the organic C pool (O/N‐alkyl C; microbially‐derived sugars) is preferentially stabilized by association with Fe and Al minerals. Stabilization of SOM with the mineral matrix in soils with large amounts of oxalate‐extractable Al_o and Fe_o results in a particularly stable and relatively old C pool, which is potentially stable for thousands of years.     

中国下蜀黄土发育的土壤表层及典型剖面的硫状况

Studies were conducted to examine factors which might influence the status and distribution of S in some surface horizons and typical profiles of soils derived from Xiashu loess on the upper slope (US), middle slope (MS) and lower slope (LS) of Nanjing-Zhenjiang-Yangzhou hilly zone. The total S contents varied from 70.30 to 350.21 mg/kg, and the average for all surface soils was 218.3 mg/kg. The average S contents in the profiles followed the sequence: USo) and the ratio of amorphous iron oxide to free iron oxide (Fe_o/Fe_a), but no significant relationship was found between total S and the ratio of free iron oxide to total iron (Fe_d/Fe_t). Inorganic sulphate in paddy soils (MS and LS) was nearly higher in surface soil than in subsurface soil and subsoil, it, however, remained relatively unchanged with increasing depth for the original soil profile (US). The average organic S accounted for 94% of the total S in the surface soils, but the percentage decreased with depth in the profiles. Like the total S, the organic and inorganic S contents were highly significantly correlated with organic matter, total N, Fe_o and Fe_o/Fe_d ratio, but they were insignificantly related to Fe_d/Fe_t ratio. The C/S and N/S ratios in this study were somewhat lower than the results reported by others. The C/N/S ratios varied considerably within the same profile and among different soils but they fell within the range of values reported worldwide.     

Investigation of soils developed on volcanic materials in Nisyros Island, Greece

Soils that are forming on volcanic parent materials have unique physical and chemical properties and in most cases, on wet and humid climates, are classified as Andisols. The main purpose of this study is to examine if the soils that are forming on volcanic materials under a dry Mediterranean climate, in Nisyros Island (Greece), meet the requirements to be classified as Andisols. Soils from seven sites were sampled and examined for their main physico-chemical properties and selective dissolution analysis. Dithionite–citrate–bicarbonate (DCB) extractable Al and Fe (Ál_d, Fe_d), acid ammonium oxalate extractable Al, Fe, and Si (Ál_o, Fe_o and Si_o), and sodium pyrophosphate extractable Al and Fe (Al_p, Fe_p) were measured. In addition, Al and Si were determined after reaction with hot 0.5 M NaOH, (Al_NaOH and Si_NaOH) and with Tiron-(C₆H₄Na₂O₈S₂), (Al_T and Si_T). P-retention was also measured. The soils are characterised by coarse texture, low organic matter content, low values of cation exchange capacity (CEC), and high pH values. Values of Si_o, Al_o and Fe_o are less than 0.022%, 0.09% and 0.35% respectively, highlighting the lack of noncrystalline components. The ratio (Fe_d–Fe_o)100/Fe_d is quite high expressing the degree of crystallisation of free iron oxides. For all samples tested, values of the Al_o + 1/2Fe_o index are extremely low (< 0.24%). High Si_NaOH and Si_T (arising 2.76% and 2.18% respectively) indicate the presence of silica in amorphous forms. P-retention values are very low (< 12.6%). The results indicated the absence of noncrystalline minerals except for amorphous silica, and do not exhibit andic or vitric soil characteristics to be classified as Andisols.     

Distribution of iron oxides forms on a transect of calcareous soils,north-west of Iran

The iron oxides fractions of four major physiographic units obtained from a transect of calcareous materials were studied to assess the effects of key pedogenic processes and local hydrology conditions as well as physiographic units in controlling iron oxides forms in the north-west of Iran. Samples from different horizons belonging to six pedons were selected and analyzed for soil physicochemical properties, clay minerals, and Fe oxides forms (Fe_d, Fe_o, Fe_p). In general, the soils indicated some variation in the concentration of iron oxides that could be related to rate of weathering, pedogenic accumulations, geomorphologic conditions (as results of different in physiographic units), wet and dry cycle, and organic matter. A wide relative variation in mean values of Fe_d (6.4–9.9 g kg^?1), Fe_o (2.9–4 g kg^?1), and Fe_p (0.68–1.3 g kg^?1) was observed among physiographic units. On the plateau unit, the presence of the most stable geomorphologic conditions and high rate in situ weathering (reflected in clay content), coupled with minor deposition of sediment suggest that the soils have more dynamic conditions than other units, reflecting in the greatest amount Fe_d and the lowest Fe_o/Fe_d ratio. Fe_d content of the soils containing less clay content (15–25%) was significantly different from those with greater clay content (25–35%).     

Colloidal stability in some tropical soils of southeastern Nigeria as affected by iron and aluminium oxides

The stability of microaggregates in soils as opposed to its dispersion is a very important soil phenomenon that checks degradation arising from unguided tillage and soil erosion. Ten soils from southeastern Nigeria were sampled from their typical A and B horizons for the study. The aim was to identify the extent of colloidal stability of the soils and the forms of Fe and Al oxides in the soils contributing to their stability. The soils are mostly Ultisols and Inceptisols formed on sandstones and shale parent materials. The soils are low in soil basic cations including the soil organic carbon (SOC). The major clay mineral is kaolinite while the soil is acid in reaction. The various forms of soil Fe and Al oxides are high with the total forms of Fe and Al being most dominant and > dithionite extracted Fe and Al > oxalate extracted Fe and Al > pyrophosphate extracted Fe and Al. The water-dispersible clay and silt (WDC) and (WDSi) which are index of dispersion in most soils are low to medium thus reflecting in the low to medium dispersion ratio (DR). The clay flocculation index (CFI) and aggregated silt + clay (ASC) were moderate to high implying the high potential stability of the soils. Soil organic carbon did not seem to be contributing much to the stability of the microaggregates while oxalate and pyrophosphate extractable Fe (Fe_ox, Fe_p) and to some extent total Al (Al_t) were among the different forms of oxides that act as aggregating agents. We propose here that rather than SOC acting as a disaggregating agent in the soils, it might have acted in association with these oxides in a linkage or bridge such as C–P–OM–C to ensure stability of the soils.     

Relationship between mineral composition or soil texture and available silicon in alluvial paddy soils on the Shounai Plain,Japan

Abstract

To evaluate the relationship between the amount of available Silicon (Si) in paddy soils and their mineral properties on the Shounai Plain in Japan, which is formed from several parent materials, we evaluated the amount of available Si, the particle size distribution, the oxide composition of crystalline minerals and the amount of oxalate-extractable Si (Si_o), iron (Fe_o) and aluminum (Al_o) in the soil. The amount of available Si in the soil and the oxide content of the crystalline minerals differed among four soil groups that were distinguished by their clay mineral composition. There was no difference in the particle size distribution among the soil groups. The amount of available Si was positively related to the SiO₂/Al₂O₃ ratio of clay, the CaO concentration of silt and fine sand, and the amounts of Si_o, Fe_o and Al_o in the soil. The amount of available Si in the soils was negative correlated with the Na₂O and K₂O concentrations of silt, the K₂O concentration of fine sand, and the coarse sand content. These results suggest that the amount of available Si in soils is affected by the weathering resistivity of their minerals and that the particle size distribution and mineral composition are related to the available Si of the soils. Mineralogical properties, including the particle size distribution and mineral composition such as the SiO₂/Al₂O₃ ratio × clay fraction content and the amounts of CaO and MgO in silt-sized particles, were positively correlated with the amount of available Si in the soil, but these correlations were not found for fine sand-sized particles. The Si_o, Fe_o and SiO₂/Al₂O₃ ratio × clay fraction contents contributed approximately 50% to the amount of available Si in the soils. The amount of available Si in the soil was divided into two groups according to the location of the paddy field. The amount of soil-available Si in the alluvial plain was affected by the geology upstream through the mineral composition.     

Die Bedeutung amorpher AI-Verbindungen für Al-Freisetzungsraten in carbonatfreien,sandigen Böden

The importance of amorphous Al-compounds regarding Al-release rates in carbonate-free, sandy soils In a preceding investigation the kinetics of proton consumption and the release of elements in carbonate-free, sandy forest soil horizons was analyzed by pH-stat-titrations. The soil matrix should reveal losses of Al and DOC equivalent to the amounts mobilized, and several extraction procedures (wet combustion: C_org; Pyrophosphateextraction: Al_p, C_org-p; Oxalate-extraction: Al_o) were applied in order to distinguish between different pools. In eight of the ten horizons investigated the dissolution of Al resulted in equivalent decreases of organically bound Al (Al_p), four of them also exhibited reductions of C_org-p?levels equal to the release of DOC. For the other two horizons, Al mobilization could be attributed to the dissolution of organic and inorganic amorphous Al-compounds, each fraction contributing about half of the total. Like the release of Al and DOC, the losses of Al_p, Al_o and inorganically bound Al (Al_o?Al_p) could be well described as 1st order reactions, the constants of dissolution [h^?1] of Al_p (0.027), Al_o (0.023) and C_org-p (0.026) being in accordance with those of Al-(0.027) and DOC- (0.024) release, respectively. For the dissolution of inorganic Al-compounds the reaction constants (0.066 and 0.052) were calculated to be nearly double.     

Extractable Al and Si compounds in pale-podzolic soils of the Central Forest Reserve: Contents and distribution along the profile and by size fractions

The profile distributions of oxalate- and pyrophosphate-soluble Al compounds and oxalate-soluble Si compounds in the main horizons of pale-podzolic soils of the Central Forest Reserve and the fractions <1. 1–5, and >5 μm have been considered. In the clay-eluvial part of soil profile, the content of these compounds is differentiated by the eluvial–illuvial type with a clear accumulation in the EL horizon compared to the AEL horizon. This distribution is largely ensured by their differentiation in the clay and fine silt fractions, while an accumulative distribution of mobile Al compounds is observed in fractions >5 μm. The high correlation between the Al and Si contents in the Tamm extracts from the clay and fine silt fractions with the (Al_ox–Al_py)/Si_ox molar ratios, which are in the range of 1–3 in the EL horizon, confirms that mobile compounds are accumulated in these fractions in the form of amorphous aluminosilicates. In the AEL and EL horizons, an additional amount of Al can pass into the oxalate solution from the fine fractions due to the dissolution of Al hydroxide interlayers of soil chlorites. The eluvial–illuvial distribution of mobile Al and Si compounds typical for Al–Fe–humus podzols within the clay-illuvial part of profiles of the soils under study can be considered as an example of superimposed evolution.     

Iron in hydromorphic gray forest soils

The amorphous iron content in the upper soil horizons, the profile distribution of iron oxides and hydroxides, and the Schwertmann (Fe_o/Fe_d) ratio can be used as diagnostic criteria for the degree of gleyization in the classification of hydromorphic soils. Drainage removes chemical elements, e.g., nonsilicate Fe, from soils.     

Mineral magnetic properties of a weathering sequence of soils derived from basalt in Eastern China

The magnetic properties and magnetic mineralogy of a weathering sequence of soils developed on basalt parent material from eastern China, were studied by rock magnetism, X-ray diffraction and soil chemical analyses to establish the connection between mineral magnetic properties and pedogenic development in a subtropical region. The magnetic susceptibility of soils formed on basalt varied greatly and did not increase with the degree of pedogenic development. The frequency-dependent susceptibility (χfd) values of soils ranged from 1.0 to 11.1% and increased with the pedogenic development. Highly significant linear relationship was found between the frequency-dependent susceptibility and the Fe_d content (R² = 0.683) and Fe_d/Fe_t ratio (R² = 0.780) in soils, indicating that pedogenic SP ferrimagnetic grains were associated with enrichment of the secondary iron oxide minerals in the weathering process of soil. Rock magnetism analysis showed that the major magnetic carriers in the weakly weathered soil profiles are magnetite and/or maghemite, and the highly developed soil profiles are generally enriched in magnetite/maghemite grains of pedogenic origin and the magnetically hard haematite, indicating that the magnetic component was transformed from a ferrimagnetic phase (magnetite) to antiferromagnetic phase (hematite) during pedogenic development. Results indicated that some of the magnetic parameters of soils, in this case χfd, can be useful for pedogenic comparisons and age correlations in the weathering sequence of soil. It is thus suggested that multiparameter rock magnetic investigations represent a more powerful approach for pedogenesis.