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1.
Soil organic matter stabilization in acidic forest soils is preferential and soil type-specific 总被引：1，自引：0，他引：1
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 (Feo; Alo), and dithionite‐extractable Fe (Fed) 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 Alo and Feo results in a particularly stable and relatively old C pool, which is potentially stable for thousands of years. 相似文献
2.
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 (Áld, Fed), acid ammonium oxalate extractable Al, Fe, and Si (Álo, Feo and Sio), and sodium pyrophosphate extractable Al and Fe (Alp, Fep) were measured. In addition, Al and Si were determined after reaction with hot 0.5 M NaOH, (AlNaOH and SiNaOH) and with Tiron-(C6H4Na2O8S2), (AlT and SiT). 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 Sio, Alo and Feo are less than 0.022%, 0.09% and 0.35% respectively, highlighting the lack of noncrystalline components. The ratio (Fed–Feo)100/Fed is quite high expressing the degree of crystallisation of free iron oxides. For all samples tested, values of the Alo + 1/2Feo index are extremely low (< 0.24%). High SiNaOH and SiT (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. 相似文献
3.
The island of Milos (Greece), part of the South Aegean volcanic arc with a typical Mediterranean climate, is covered with volcanic deposits of different ages. The objective of this study was to investigate the physicochemical and mineralogical properties of the soils developing on these volcanic deposits and their classification. Samples were taken from seven locations of soil on different parent material and of different ages. There were substantial differences in their particle size distribution, with sand ranging from 19% to 92%, silt from 3.5% to 50%, and clay from 5% to 46%. Organic matter content was low (< 2.0%). The soil pH ranged from 5.6 to 8.0. In two of the profiles, CaCO3 equivalents of 1.4% to 24.6% were found and a calcic horizon identified. The cation exchange capacity (CEC) and specific surface area (SSA) varied between profiles ranging from 3 cmol(+) kg− 1 to 47 cmol(+) kg− 1 and 30 m2 g− 1 to 380 m2 g− 1, respectively. The soils exhibited high base saturation. The amounts of Al, Fe and Si extracted with ammonium oxalate (Αlo, Feo and Sio) were particularly low (< 0.1%, < 0.17%, and < 0.1%, respectively) which demonstrates the absence of amorphous clay-silicate minerals (allophane). Fe extracted with dithionite citrate bicarbonate — DCB (Fed) was greater than Feo sharing the dominance of crystalline Fe oxides. Al and Si extracted with hot 0.5 M NaOH (Al2Ο3NaOH and SiΟ2NaOH) and with Τiron-C6H4Na2O8S2, (Al2Ο3Τ and SiΟ2Τ). SiΟ2NaOH and SiΟ2Τ were particularly high (mean values 3.4% and 4.5%, respectively), showing that amorphous silica was present. The clay fraction of the soil was dominated by the presence of 2:1 (vermiculite and smectite) and 1:1 (kaolinite) clay-silicates. Alo+ 1/2Feo was low (< 0.18%), while the P-retention in most soils was less than 15%. These soils do not exhibit andic properties and hence cannot be classified as Andisols. The silica saturation index (ISS) may be used for these soils to describe a pedogenetic environment rich in Si which favours the formation of pedogenic amorphous silica. The climate is the major determinant of the evolution of these soils. 相似文献
4.
Rodrigo Neculman Cornelia Rumpel Francisco Matus Roberto Godoy Markus Steffens María de la Luz Mora 《Biology and Fertility of Soils》2013,49(6):681-689
Recent studies with Andisols show that the carbon (C) stabilization capacity evolves with soil age relative to the evolution of the mineral phase. However, it is not clear how soil mineralogical changes during pedogenesis are related to the composition of soil organic matter (SOM) and 14C activity as an indicator for the mean residence time of soil organic matter (SOM). In the present study, we analyzed the contribution of allophane and metal–SOM complexes to soil C stabilization. Soil organic matter was analyzed with solid-state 13C nuclear magnetic resonance spectroscopy. Additionally, the soil was extracted with Na-pyrophosphate (Alp, Fep) and oxalate (Alo, Sio, and Feo). Results supported the hypothesis that allophane plays a key role for SOM stabilization in deep and oldest soil, while SOM stabilization by metal (Al and Fe) complexation is more important in the surface horizons and in younger soils. The metal/Cp ratio (Cp extracted in Na-pyrophosphate), soil pH, and radiocarbon age seemed to be important indicators for formation of SOM–metal complexes or allophane in top- and subsoils of Andisols. Changes in main mineral stabilization agents with soil age do not influence SOM composition. We suggest that the combination of several chemical parameters (Alp, Fep and Cp, metal/Cp ratio, and pH) which change through soil age controls SOM stabilization. 相似文献
5.
Four soils were treated with HNO3, CaCO3 and K2SO4 to enable observation of the response of the soil solution composition and the solution A1 ion activity (Al3+) to the treatments and to time. The clay fraction of three of the soils was dominated by illite, kaolinite and quartz. The fourth was minated by kaolinite and iron oxides. The initial pH in 0.01 M CaCl2 varied between 4.0 and 5.0 and the organic carbon content from 0.7 to 1.1%. The soil solutions from soils dominated by kaolinite, illite and quartz were generally supersaturated with respect to quartz and well ordered kaolinite, and unsaturated with respect to illite. The soil solutions from the soil dominated by kaolin and iron oxide were generally unsaturated with respect to quartz but still saturated with respect to ell crystallized kaolin. Within mineral groups such as Al2SiO5 compounds, A12Si2O5(OH)4 (kaolinite group), and Al(OH)3 (A1 oxide) minerals, the more soluble forms became less supersaturated or unsaturated with time for many treatments. Lime treatment usually increased the ion activity product of AI(OH)3 in all soils, and of minerals with the composition, Al2SiO5, in the illite/kaolinite soils. Acid treatment reduced the apparent solubility of Al(OH)3, and the A1 silicates in the Al2SiO5, and Al2, Si2, O5,(OH)4, mineral groups on all soils. These results are interpreted to indicate that lime treatment led to the formation of trace quantities of more soluble A1 minerals that subsequently controlled (Al3+), whereas acid treatment dissolved trace quantities of such minerals leaving less soluble minerals to control (Al3+). The results suggest that, in mineral soils such as these, (Al3+) is under the control of inorganic dissolution and precipitation processes. These processes conform to expectations given the free energy of various inorganic aluminium compounds. Furthermore the sequence of dissolution and formation processes appears to be governed by the Gay-Lussac—Ostwald step rule. 相似文献
6.
7.
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. 相似文献
8.
Susumu S. Abe 《Soil Science and Plant Nutrition》2016,62(2):127-132
The present study aimed to assess the dynamics of oxyhydroxides via termite mounds in a tropical savannah of Central Nigeria, where the soils often contain oxyhydroxides as a major component of soil minerals. To this end, the quantities of oxyhydroxides stored in mounds built by Macrotermes bellicosus (Smeathman) were compared to those stored in surface (Ap1) soils, and their turnover rates were estimated. Both the mound wall and nest of M. bellicosus were enriched two- to 10-fold with acidified ammonium oxalate soluble iron (Feo) and aluminum (Alo) and dithionite-citrate-bicarbonate (DCB) soluble iron (Fed) and aluminum (Ald) relative to the adjacent surface soil horizon. These oxyhydroxide contents were positively correlated with the clay content (P < 0.05), suggesting that M. bellicosus preferentially used silicate clay-associated oxyhydroxides for mound construction. The Fed, Ald and DCB-soluble manganese (Mnd) preserved in the M. bellicosus mounds ran up to 112 ± 25.6, 5.72 ± 1.41 and 2.17 ± 0.68 kg ha?1, accounting for 1.91 ± 0.23%, 1.00 ± 0.60% and 0.35 ± 0.09% of the total amount stored in the surface soil horizon, respectively. Furthermore, the estimated turnover rates of Fed, Ald and Mnd were 6.6, 0.33 and 0.14 kg ha?1 year?1, respectively. These findings suggest that the mound-building termites significantly impacted the dynamics of free oxyhydroxides in an African savannah soil. 相似文献
9.
In previous studies, Al extracted by acid ammonium acetate (Ala) or Na-pyrophosphate (Alp), rather than silt or clay content and climate conditions, was the most important factor that controls organic matter (OM) levels in volcanic soils. Here, the hypothesis was tested that Ala is a comparable method (as much as CuCl2) to quantify the proportion of Al bound to OM in allophanic soils. As far as we know, there are no previous antecedents in which selective dissolution method has been compared with this extractant. Secondly, we examine the effects of (a) Al, (b) silt plus clay content (particles size 0-53 µm) and (c) clay mineralogy on the control of organic carbon (OC) level in Chilean volcanic soils. This was achieved by sampling 16 soils series (11 Andisols, one Alfisol and four Ultisols, USDA classification) including 48 soil pedons up to 0.4 m depth. Soils were analyzed for Ala, Alp, oxalate (Alo, Sio and Feo), cold NaOH (Aln) and un-buffered salts, CuCl2 (AlCu), LaCl3 (AlLa) and KCl (Alk). We also measured the Al-humus as soluble C fraction after pyrophosphate extraction and the C associated to the silt plus clay fraction after sonication and gravity decantation. The statistical package (S)MATR was used to examine bivariate linear regressions among soil properties by computing the standardized major axis (SMA). Our results indicate that Ala had a good correspondence with Alp (R2 = 0.76) in the top soil with Ala/Alp ratio of 0.19 and both extractans presented significant and positively relationship with soil OC (R2 > 0.62). Acid ammonium acetate was as effective as AlCu to determine the Al-OM in allophanic soils. It is cheaper than AlCu and Alp and 0.5 h shaking is required compared to 2 h of AlCu and 16 h of Alp. The efficiency of the extraction was: Aln ≥ Alo > Alp > AlCu ≥ Ala > AlLa > Alk. We also found that allophane content (estimated by Al/Si ratio) was strongly correlated (R2 = 0.82) with the OC in the fine silt plus clay and that Al-humus together with C in the finest particles explained (R2 > 0.60) the largest proportion of variation of soil OC across studied soils. 相似文献
10.
Salar Rezapour A. A. Jafarzadeh Abbas Samadi Sh. Oustan 《Archives of Agronomy and Soil Science》2013,59(2):165-182
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 (Fed, Feo, Fep). 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 Fed (6.4–9.9 g kg?1), Feo (2.9–4 g kg?1), and Fep (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 Fed and the lowest Feo/Fed ratio. Fed content of the soils containing less clay content (15–25%) was significantly different from those with greater clay content (25–35%). 相似文献
11.
Yukiya Horikawa Tetsuro Kitamura Toshimasa Honna 《Soil Science and Plant Nutrition》2013,59(6):779-786
Abstract A method to determine the contents of imogolite and Al-rich allophane (Sil Al ? 1 : 2) in volcanic ash soils was presented. The method is based on the (1) assessment of the presence of Al-rich allophane in clays by successsive extraction with dithionite-citrate and oxalate-oxalic acid, (2) trimethylsilylation of soil clay with a mixture of hexamethyldisiloxane, HCl, and isopropyl alcohol, and determination of the content of monomeric Si based on the trimethylsilyl derivative of monomeric orthosilicate anion by gas / liquid chromatography, (3) determination of the total content of imogolite and Al-rich allophane based on the content of monomeric Si from imogolite, (4) determination of the imogolite content by Thermogravimetry (TG )-Differential Thermal Analysis (DTA) based on the weight loss due to endothermic dehydroxylation with maximum values at ca. 386°C, (5) calculation of the Al-rich allophane content by subtracting the imogolite content from the total content of these minerals, and (6) evaluation of the imogolite and Al-rich allophane content of soil by multiplying clay content of soil and the two mineral content of clay. The trimethylsilylation analysis was found to be reproducible, and the estimated total amounts of two minerals in clays by this method were adequately approximated to those evaluated from the amount of Si (= Sio) extracted with oxalate-oxalic acid after extraction with dithionite-citrate. The variation in the abmldance of two minerals in the soil horizons of volcanic ash soils from the San'in region indicated that this method is suitable for the profile-study of volcanic ash soils. 相似文献
12.
Luis Valério Prandel Nívea Maria Piccolomini Dias Sérgio da Costa Saab André Maurício Brinatti Neyde Fabíola Balarezo Giarola Luiz Fernando Pires 《Journal of Soils and Sediments》2017,17(8):2144-2155
Purpose
Brazilian soils that present extremely hard sub-superficial horizons when dry and friable when humid are similar to the Australian and South African hardsetting horizons whose hardness can be mainly related to low crystallinity. Studies involving refinement by the Rietveld method with X-ray diffraction (RM-XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and their relation have not been carried out in hardsetting horizon soils. Thus, the objective of this study is to obtain information about the kaolinite in the hardsetting horizon of a Yellow Argisol clay fraction, taking into consideration the results of isomorphic substitution, crystallite average size, and microstrains, relating them to particle image analysis regarding their morphology and size.Materials and methods
Soil samples were collected in the hardsetting horizon of a Yellow Argisol in the Coastal Tablelands region, which covers the whole Brazilian Northeast coast and part of the Southeast region. The sample was powdered, sieved, and submitted to dispersion and physical fractioning process by sedimentation. The clay fraction was analyzed by RM-XRD, AFM, and SEM techniques.Results and discussion
The RM-XRD provided improvement of indices with isomorphic substitutions in the goethite [Fe0.70Al0.30O(OH)], kaolinite [Al1.44Fe0.56Si2O5(OH)4], and halloysite [Al1.42Fe0.58Si2O5(OH)4]; 29 nm crystallite average size; 5 × 10?3 microstrain; and 49.5% kaolinite. AFM analyses indicated particle average size from 80 to 250 nm and average height from 60 to 80 nm. By relating this data, it was possible to estimate that the particles under analysis are kaolinite composed of 3 to 9 crystallites and stacking of 88 to 112 layers.Conclusions
The process, analyses, and comparisons such as crystallographic and morphologic information about the kaolinite mineral particles contribute to the comprehension of the hardsetting horizon soil nature as well as other soils that present minerals with a high degree of isomorphic substitution.13.
Chemical and mineralogical properties of five soil profiles of a catena in Iperu, Western State of Nigeria, are reported. The pH values of the subsoils are extremely acid. Acidity decreases with improved drainage in the subsoils (pH 4.0–5.8). The cation exchange capacity (C.E.C.) of the soils range from 3.0 to 16.2 me/100g of soil. The silt: silt+clay ratio, calcium: magnesium ratio and Fe2O3:Al2O3 ratio are used as weathering indices. The low values of the silt: silt + clay index indicate that the soils must have undergone advanced weathering. The magnitude of the Ca: Mg ratio indicates that more calcium than magnesium is available in the soils. The values for sodium and potassium are extremely low. More iron than aluminium was extracted from the soils by the dithionite-citrate method. Kaolinite is the most abundant clay mineral. Halloysite, interstratified clay materials, vermiculite, quartz, and mica are present in considerable amounts. The silt fraction in which quartz is the most abundant mineral, also contain some kaolinite and mica. 相似文献
14.
We tested whether a ‘Lockerbraunerde’ from the heights of the Zittauer Gebirge in Eastern Saxony exhibited andic properties and classified it according to the rules of the World Reference Base for Soil Resources (WRB, 1998). To achieve this, we characterized a selected soil by means of routine soil analysis; selective dissolution procedures; X‐ray diffraction (XRD); X‐ray fluorescence (XRF), and Transmission Electron Microscopy (TEM). We used field criteria (Thixotropy; NaF‐field test) to obtain a map of the spatial distribution of soils with potential andic properties. We found that the soil fulfilled all requirements to be classified as an Andosol. The composition of the colloidal phases was exactly intermediate between sil‐andic and alu‐andic. At the same time, the soil had a spodic horizon [determined through the depth function of the Alo+½Feo criterion]. As there was no indication of vertical translocation of metal‐organic complexes, but sufficient evidence to suggest the downward movement of mobile Al/Si‐phases, we maintain to classify the soil as an Endoskeleti‐Umbric Andosol and propose the existence of a pedogenetic pathway intermediate between Podsolisation and Andosolization. We conclude that the spodic horizon in the WRB is not well defined because of the dominance of the Alo+½Feo criterion over morphological evidence. We further suggest the German soil taxonomy to be modified to better represent soils containing short range order minerals. 相似文献
15.
Understanding soil water dynamics and storage is important to avoid crop failure on highly weathered, porous and leached soils. The aim of the study was to relate soil moisture characteristics to particle-size distributions and chemical properties. On average, Atterberg limits were below 25% in the A-horizon and not more than26.56% in the B-horizon, whereas soil bulk density was between 1.27 and 1.66Mgm?3. The saturated hydraulic conductivity (Ksat) was generally between 0.20 and 5.43 cm h?1 in the top soil and <1.31 cm h?1 in the subsoil. The higher Ksat values for the A-horizons were attributed to the influence soil microorganisms operating more in that horizon. The amount of water retained at field capacity or at permanent wilting point was greater in the B-horizons than in the A-horizons, suggesting that clay accumulation in the B-horizon and evapotranspiration effects in the A-horizon may have influenced water retention in the soils. Soil moisture parameters were positively related to clay content, silt content, exchangeable Mg2+, Fe2O3 and Al2O3, and negatively related to sand content, SiO2, sodium absorption ratio, exchangeable sodium percentage and bulk density. The low clay content may explain why drainage was so rapid in the soils. 相似文献
16.
中国亚热带红壤团聚体稳定性与土壤化学性质的关系 总被引：16，自引：1，他引：16
The stability of aggregates in the surface soil is crucial to soil erosion and runoff generation. Thus, to understand the stability and the breakdown mechanisms of soil aggregates as well as the relationship between aggregate stability and selected soil chemical properties, such as different forms of Fe and Al oxides, organic matter, CEC and clay content, the aggregates of slightly and severely eroded red soils derived from Quaternary red clay in subtropical China were analyzed using the routine wet sieving and the Le Bissonnais methods. The results indicated that the aggregates of the severely eroded soils were more stable than those of the slightly eroded soils. Different aggregate breakdown mechanisms resulted in different particle size distribution. The slaking from entrapped air in aggregates severely destroyed the soil aggregates, especially in the slightly eroded soils. Meanwhile, mechanical breakdown and microcracking had little effect on the aggregates compared to slaking. The fragments resulting from slaking were mainly microaggregates that increased in size with increasing clay content. The main fragment size of the slightly eroded soils was 1.0-0.2 mm, while for the severely eroded soils it was 5.0-2.0 mm and 1.0-0.5 mm. Overall, more than 20% of the fragments were smaller than 0.2 mm. In addition, aggregate stability was positively and often significantly correlated with Fed, Ald, Feo and clay content, but significantly and negatively correlated to SOC. 相似文献
17.
本文应用标准化数据—斜交距离—误差平方和聚类分析法对甘肃成县34个土壤剖面进行了数值分析研究。研究结果表明,供试34个剖面可分为五个土壤类型。对五类土壤的pH值、有机质、代换量、SiO2、Al2O3、Fe2O3、CaCO3及粘粒含量八项主要指标进行方差分析的结果表明,除pH、代换量和SiO2含量未达类型间F测验显著水平外,其他各项指标均达显著或极显著水平。各类土壤在地理分布、植被类型、田间石灰反应等特性上也有明显的差异,并且每一类土壤都具有一定的发生学意义。并分别对应于棕壤、淋溶褐土、褐土、碳酸盐褐土和潮土五种发生学类型。 相似文献
18.
试论中国淋溶土的成土过程与基本特性 总被引：2，自引：2，他引：2
淋溶土是我国的一类重要土壤，总面积约１２．５万ｋｍ＾２。在我国现行的土壤分类系统中，有几个土类－暗棕壤、棕壤、酸性棕壤、白浆土以及部分褐土可归属于淋溶土＾１）。这些土壤大都是温带针阔叶混交林下的森林土壤，生物地球化学循环别具特征。据３０个剖面的统计分析，其Ｂ／Ａ层粘粒含量比值，从暗中壤－棕壤－黄棕壤，为１．４７－１．８８－２．５３，经统计土壤发育过程中粘粒的生成量（或损失量）相差七倍。上述几种土壤 相似文献
19.
D. L. MOKMA M. L. JACKSON J. K. SYERS F. R. GIBBONS 《European Journal of Soil Science》1973,24(2):199-214
The mineralogical composition and retention properties for radioisotopes (20Sr and 137Cs) of soils developed in five basalt flows of age varying from 6000 years to about four million years occurring in western Victoria were investigated. The trend of mineral weathering has been almost exclusively to amorphous material, kaolinite-plus-halloysite, and chlorite, the more soluble products of weathering having been removed. The most significant changes in clay mineralogical composition with time are the progressive decrease in the Si02/Al2O3 molar ratio of the amorphous material in the clay fraction of the surface horizons, from an initial value of approximately 4 to values of approximately 2, and the progressive increase in the amount of kaolinite-plus-halloysite, both in the topsoil and at depth, with age of the basalt flow. The amount of kaolinite plus halloysite increases from approximately 20 per cent of the clay of soil developed in the basalt flow 6000 years old to approximately 50 per cent of that of soil in basalt about four million years old. Evidence for the presence of halloysite was obtained by electron microscopy studies. The amorphous material and chlorite contents, each of which constitutes between 20 and 50 per cent of the clay fractions, decrease concurrently with the increase in kaolinite-plushalloysite content. Fixation of Sr by whole soil samples was controlled by the organic matter and free iron oxide contents rather than by the mineralogy of the samples. A high proportion of the added Cs was sorbed by whole soil samples. Much of the sorbed Cs was not readily replaced by CaCl, washings but was replaced in part by subsequent washing with NaCl of pH 5.3 and almost entirely by subsequent NH4Cl washings. Much of the Sr and Cs deposited on these soils by rainfall and dry fall-out would be sorbed; the ease of replacement suggests that these elements would be available for further movement through the food chain. 相似文献
20.
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. Feo/Fed 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% Alo and up to 0.68% for Sio on southern aspects. This is considerably higher than the values measured for soils on northern aspects (0.59% to 1.07% Alo, max. 0.26% Sio). 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. 相似文献