Evaluation of magnetic iron oxides as sediment tracers in water erosion experiments

Water erosion is one of the major concerns with regard to sustainability of agricultural systems in Mediterranean countries (e.g. olive farming areas in Southern Spain). The limitations of the technologies traditionally used in erosion measurement has created increased interest in the use of innovative erosion tracers useful for monitoring erosion and determining deposition rates in the field. In this work, we evaluated the potential of magnetic iron oxide (Fe₃O₄) as a soil tracer. Particle size distribution of the magnetic iron oxide, mobility under drainage conditions and the effect of the aggregate size distribution in blank and tagged soils were studied. The use of magnetic iron oxide to estimate soil losses at small-scale was also examined using a portable rainfall simulator and measuring magnetic susceptibility before and after each simulated rainfall. The properties of the magnetic iron oxide, including a particle size distribution similar to that of soil aggregates, strong binding to soil particles, little mobility in soil, very high magnetic susceptibility relative to the typically low background values of the studied soils, innocuous to environment and low cost, make it an effective soil tracer for estimating soil losses at a small-scale.     

Long-term reactions of Ni, Zn and Cd with iron oxyhydroxides depend on crystallinity and structure and on metal concentrations

Iron oxyhydroxides are long-term sinks for toxic trace metals and are suggested as factors to explain long-term metal immobilization in soil. It is unknown how crystallinity and crystal structure of iron (Fe) oxyhydroxides affect the long-term kinetics of trace metal adsorption. Adsorption kinetics of nickel (Ni), zinc (Zn) and cadmium (Cd) on to four synthetic Fe oxyhydroxides (hydrous ferric oxide (HFO), ferrihydrite (FH), goethite (GT), haematite (HT)) were characterized in suspensions during 70 days at different initial metal concentrations and various pH values (3.8–7.0) maintained within 0.2 units. The slow reactions, defined as those occurring beyond day 1 were most pronounced in GT and least in HT. The extent of the slow reaction was surprisingly unrelated to crystallinity or microporosity as determined by N₂ adsorption. Freundlich adsorption isotherms fitted to the data show that ageing between 1 and 70 days decreases metal concentrations in solution by factors of 2–30 (Ni), 1–20 (Zn) and 1–4 (Cd) depending on the type of oxyhydroxide. These factors become significantly larger at smaller concentrations for Ni and Zn in some oxyhydroxides and this concentration dependency suggests that slow reactions are not only related to diffusion. The short-term adsorption strength of carrier-free metal radio-isotopes was similar at 1 or 70 days after reaction with these iron oxyhydroxides and excludes the possibility that long-term reactions are related to solid-phase transformations or changes in solution properties. The extent of slow reactions in GT decreased with decreasing pH and was less than a factor 2 within 70 days at pH 3.7. The results confirm that slow reactions in Fe oxyhydroxides can explain lessened metal availability by ageing in pH neutral soils. The uncertainty of their actual structure and crystallinity in soils does not allow quantitative predictions based on the behaviour of synthetic oxyhydroxides.     

旱作褐土中铁氧化物的厌氧还原动力学特征

异化铁还原是厌氧环境中有机物降解的重要微生物过程,不仅影响Cr、U等无机污染物在环境中的迁移,还与CH4、N2O、H2S等温室气体的释放关系密切.本文选择7个旱作褐土样品,采用泥浆厌氧恒温培养的方法,研究了旱作褐土中氧化铁的厌氧还原特征,结果表明旱作褐土在淹水条件下可以发生铁氧化物的异化还原,其还原潜势介于4.47～5.95 mg g-1之间,还原速率常数介于0.15 ～0.27 d-1之间.褐土中部分晶态铁氧化物可在这一过程中被还原,游离铁的平均还原率为41.95％.经过40 d厌氧培养后,99.26％的NO3-和88.82％的SO42-被还原.还原过程的速率常数κ、Vmax、Tmax随着土壤有机碳含量增加而增加,还原潜势与土壤SO42-含量呈显著负相关关系.     

水稻根际中铁的形态转化

本文以熟化红壤性水稻土、淀浆白土、红壤和赤红壤为样品,研究了植稻后根际中铁的形态转化.结果表明,两种水稻土根际中无定形氧化铁、游离氧化铁、络合态铁、土壤中氧化铁的活化度及两种红壤上根际中的络合态铁均低于非根际土;而两种红壤上其余各项在根际内外分布趋势均与水稻土相反.用穆斯堡尔谱仪分析表明,所有根际土与非根际土相比,四极矩分裂增大,内磁场下降,说明根际中氧化铁被活化.同时,水稻土上根际中Fe²⁺增多,赤红壤中根际出现新矿物磁赤铁矿.根际中铁被活化,可能会影响根际中重金属等污染物的吸附和解吸特性、植物的铁素营养及对其它养分的吸收.     

Accumulation of free oxyhydroxides in termite (Macrotermes bellicosus (Smeathman)) mounds and the implications for their dynamics in an African savannah Ultisol

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 (Fe_o) and aluminum (Al_o) and dithionite-citrate-bicarbonate (DCB) soluble iron (Fe_d) and aluminum (Al_d) 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 Fe_d, Al_d and DCB-soluble manganese (Mn_d) 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 Fe_d, Al_d and Mn_d 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.     

Retention of cobalt by an oxisol in relation to the content of iron and manganese oxides

Abstract

The study aims at determining the cobalt retention properties of various soil components. Therefore, cobalt (Co) sorptions and extractions were carried out using an Oxisol sample before (untreated) and after successive removal of organic matter and active manganese (Mn) oxides (H₂O₂‐treated) and iron (Fe) oxides (H₂O₂+CBD‐treated). A synthetic goethite was included for comparison. Sorption of the four sorbents was determined over a range of Co concentrations (initially 10^‐8 M to 10^‐4 M), pH values (3 to 8) and reaction times (2 hours to 504 hours). The Co species sorbed was Co(ll), since oxygen exclusion during sorption had no effect on the amount sorbed. The pH‐dependent sorption curve (sorption edge) was shifted to lower pH at decreasing initial Co concentration and increasing reaction time. The displacements, in particular of the sorption edges corresponding to the lowest initial Co concentrations, to successively higher pH following removal of Mn oxides, organic matter and Fe oxides could be attributed to sorption onto sites of decreasing Co affinity [Mn oxides (and organic matter) > Fe oxides > kaolinite]. Extractions of sorbed Co at pH 5.5–7.5 with 2 M HCI showed that the extractability decreased with increasing sorption time and decreasing initial Co concentration. The untreated and H₂O₂‐treated soil samples retained sorbed Co at least as firmly as the synthetic goethite, whereas the H₂O₂+CBD‐treated sample (kaolinite) was clearly less effective. The results emphasized the importance of the soil Mn and Fe oxides for Co retention in soils but also the necessity of taken interior sorption sites into consideration.     

Effect of iron oxide on phosphate sorption by calcite and calcareous soils

Pure calcite (AR grade CaCO₃) was treated with ferrous perchlorate solution to give a surface coating of iron (Fe) oxide. Maximum sorption (x_m) of phosphate (P) by the calcite increased from 18.2 to 160 mg P kg^?1 as the amount of coating increased from 0.00 to 16.0 g Fe₂O₃, kg^?1 CaCO₃. Evidence for Fe oxide coatings on carbonate minerals in two Sudanese soils was obtained by optical microscopy and electron-probe microanalysis. The relative contributions of carbonate and Fe oxide minerals, and Fe oxide coatings to P sorption in these soils were calculated, based on an assumed model of oxide distribution. Separate-phase Fe oxide was the major contributor (30–40%) to P sorption in the soils; the Fe oxide coatings on carbonate minerals were only minor contributors (< 6%), and the contribution of uncoated carbonate minerals was found to be negligible (<1 %). These results suggest a very minor role for carbonate minerals, even when coated with Fe oxide, in the sorption of P by these calcareous, Sudanese soils.     

Modelling the effects of ageing on Cd,Zn, Ni and Cu solubility in soils using an assemblage model

Ageing reactions can reduce trace metal solubility and can explain natural attenuation of contaminated soils. We modelled ageing reactions in soil with an assemblage model that considers slow reactions in Fe‐oxyhydroxides and reversible sorption on organic matter and clay minerals. Metal adsorption kinetics on Fe‐oxyhydroxides was obtained from data with synthetic oxyhydroxides. Metal solubility and isotopic exchangeability data were obtained from 28 soils amended with Ni, Zn, Cu and Cd metal salts and monitored for 850 days. The assemblage model was constructed in WHAM 6.0 and used soil properties and dissolved organic matter as input data. The model was first validated to predict dissolved metal concentrations, based on the concentration of isotopic exchangeable metals. The model overestimated metal solubility without parameter adjustment by mean factors of 4–7, and successful fits were obtained by increasing the specific surface area of Fe‐oxyhydroxides from measured values of synthetic systems to a value of 600 m² g^?1 recommended by other authors. The effect of ageing on the isotopic exchangeable metal fraction was subsequently modelled starting from the predicted fraction of metals present on Fe‐oxyhydroxides immediately after soil spiking. The observed isotopic exchangeable metal fractions of Ni, Zn and Cd agreed reasonably well with predicted values. The model predicts that ageing reactions are more pronounced at higher pH because metal sorption is increasingly directed to oxyhydroxide surfaces with increasing soil pH. Modelling fixation of Cu requires more information on fixation of that metal in organic matter.     

Phosphorus adsorption by a range of western Australian soils related to soil properties

Abstract

The capacity of 36 Western Australian soils to adsorb phosphorus (P) was measured by three different methods: P retention index (PRI), P buffering capacity (PBC), and P adsorption (PA). The P adsorption values measured by all three methods varied markedly with soil type. When the P adsorption values were correlated with several soil properties, using simple and multiple linear regressions, PRI, PBC, or PA values were found to be significantly correlated with the aluminium oxide content of the soils. In addition, PBC and PRI was correlated with organic carbon content. The role of aluminium oxide (Al₂O₃) in the soil was apparently more important in determining the P adsorption capacity of the soils than that of iron (Fe), even though the iron oxide (Fe₂O₃)content of all the soils studied was consistently higher than the aluminium oxide content. The relationship between P adsorption and the selected soil properties, as determined by multiple linear regression, explained 45–59% of the variation: arabic PRI = ‐10.87 + 9.94 organic C (%) + 160.02 Al₂O₃ (%), r² = 0.45.

arabic PBC = ‐0.004 + 1.532 organic C (%) + 22.26 Al₂O₃ (%), r² = 0.57.

arabic PA = 3.52 + 248.75 Al₂O₃ (%), r² = 0.59.

     

土壤对镉的吸附与解吸——Ⅰ.土壤组份对镉的吸附和解吸的影响

采用选择溶解法研究了有机质、游离铁、无定型硅、铝等土壤组份对青黑土、黄棕壤、红壤和砖红壤胶体吸附和解吸Cd的影响。结果表明,去除有机质后胶体吸附Cd减少,这可能是由于交换吸附的减少所致;游离铁的去除使得黄棕壤、红壤和砖红壤的吸附量显著减少,显示了在这些土壤中游离氧化铁专性吸附的重要性;随着无定形铝含量的上升,吸附量下降,这是因为铝离子占据了高能量的吸附位。经不同处理后的土壤胶体,其Cd的解吸顺序(解吸%)大致为:去无定型硅、铝者>去游离铁者>去有机质者>原胶体,但在不同土壤和不同pH条件下该顺序略有差别。研究结果为控制和改造土壤Cd污染提供了理论依据。     

Mycorrhizal (Rhizophagus Intraradices) Symbiosis and Fe and Zn Availability in Calcareous Soil

Greenhouse experiment was conducted to assess the iron (Fe) and zinc (Zn) fractionation patterns in soils of arbuscular mycorrhizal (AM) fungus-inoculated and uninoculated maize plants fertilized with varying levels of Fe and Zn. Soil samples were collected for Fe and Zn fractions and available Fe, Zn and phosphorus (P) contents besides organic and biomass carbon (BMC), soil enzymes and glomalin. Major portion of Fe and Zn fractionations was found to occur in the residual form. Mycorrhizal symbiosis increased the organically bound forms of Fe and Zn while reducing the crystalline oxide, residual Fe and Zn fractions, indicating the transformation of unavailable forms into available forms. Soil enzymes, viz. dehydrogenase and acid phosphatase activities in M+ soils, were significantly higher than M? soil consistently. Overall, the data suggest that mycorrhizal symbiosis enhanced the availability of Fe and Zn as a result of preferential fractionation and biochemical changes that may alleviate micronutrient deficiencies in calcareous soil.

Abbreviations: AM: arbuscular mycorrhiza; Fe: Iron; Zn: Zinc; P: Phosphorous; Amox-Zn: amorphous oxide bound zinc; Cryox-Zn: crystalline oxide bound zinc; DAS: days after sowing; DTPA: diethylene Triamine Penta Acetic Acid; MnO₂-Zn: manganese oxide bound zinc; OC-Zn: organically bound zinc; WSEX: water soluble plus exchangeable zinc; MnO₂ Fe: manganese oxide bound iron; OC-Fe: Organically bound iron; WSEX Fe: water soluble plus exchangeable iron.     

岷江上游杂谷脑河谷土壤发生特征与系统分类研究

为了解岷江上游杂谷脑河谷的土壤发生特征及类型归属，以位于四川阿坝藏族羌族自治州理县杂谷脑河谷的8个典型土壤剖面为研究对象，通过野外成土因素调查与土壤形态特征观测及室内土壤物理、化学性质分析，依据《中国土壤系统分类检索(第三版)》(简称系统分类)与《中国土壤(1998)》(简称发生分类)鉴定其类型。研究表明，8个剖面均为温性土壤温度状况、半干润土壤水分状况；土壤色调为7.5YR和10YR，部分剖面表层明度和彩度均低于3.5，达到暗沃表层的颜色要求；土壤颗粒组成以粉粒含量最高、砂粒次之、黏粒最低，质地为壤土或粉质壤土；土壤结构主要为亚角块状，部分剖面表层为团粒结构；部分剖面中具有腐殖质、黏粒胶膜及假菌丝体等新生体，形成黏化层和钙积层；均具石灰性，主要为碱性到强碱性反应；有机碳含量范围1.64 ~ 61.45 g/kg，部分剖面含量至上而下逐渐降低，具有均腐质特性；游离铁含量为10.78 ~ 19.57 g/kg，个别剖面B层均在14 g/kg以上，具有铁质特性；有效磷含量为1.2 ~ 43.1 mg/kg，个别符合肥熟表层和磷质耕作淀积层的有效磷含量要求。供试土壤在中国土壤系统分类中归属于人为土、均腐土、淋溶土和雏形土4个土纲的4个亚纲、7个土类和8个亚类，在中国土壤发生分类中属于半淋溶土纲下褐土土类的燥褐土亚类(对应于系统分类的石灰肥熟旱耕人为土、普通简育干润雏形土和普通暗沃干润雏形土3个亚类)及石灰性褐土亚类(对应于系统分类的普通暗厚干润均腐土、普通简育干润淋溶土、钙积暗厚干润均腐土、普通钙积干润淋溶土和普通铁质干润淋溶土5个亚类)。中国土壤系统分类具有更强的土壤类型区分能力。     

Effect of silicate fertilizer on reducing methane emission during rice cultivation

Slag-type silicate fertilizer, which contains high amount of active iron oxide, a potential source of electron acceptor, was applied at the rate of 0, 2, 6, 10, and 20 Mg ha⁻¹ to reduce methane (CH₄) emission from rice planted in potted soils. Methane emission rates measured by closed chamber method decreased significantly with increasing levels of silicate fertilizer application during rice cultivation. Soil redox potential (Eh) decreased rapidly after flooding, but floodwater pH and soil pH increased significantly with increasing levels of silicate fertilizer application. Iron concentrations in potted soils and in percolated water significantly increased with the increasing levels of silicate fertilizer application, which acted as oxidizing agents and electron acceptors, and thereby suppressed CH₄ emissions. Silicate fertilization significantly decreased CH₄ production activity, while it increased carbon dioxide (CO₂) production activity. Rice plant growth, yield parameters, and grain yield were positively influenced by silicate application levels. The maximum increase in grain yield (17% yield increase over the control) was found with 10 Mg ha⁻¹ silicate application along with 28% reduction in total CH₄ flux during rice cultivation. It is, therefore, concluded that slag-type silicate fertilizer could be a suitable soil amendment for reducing CH₄ emissions as well as sustaining rice productivity and restoring the soil nutrient balance in rice paddy soil.     

The cause of redness in some buried and non-buried soils in eastern England

Relationships were examined between colours and the amounts of extractable-iron or of individual iron oxides present in <2μm fractions of samples from buried and non-buried soils in eastern England. Colour was expressed in terms of a redness rating (RR). Oxalate-extractable iron (Fe_o), dithionite-extractable iron (Fe_d) and goethite contents were not significantly correlated with RR. There was, however, a strong correlation between RR and hematite content. These preliminary results provide some justification for the assumptions concerning relationships between reddish colours and hematite content, which are implicit in the paleo-argillic concept of the Soil Survey of England and Wales. However, reddish colours (particularly within the 7.5 YR and possibly the 5 YR hue range) should not be used in isolation as an indiscriminate indicator of pre-Devensian pedogenesis in Britain.     

Methanotrophs are favored under hypoxia in ammonium-fertilized soils

Methanotrophy of arable soils is affected by N fertilization, but the knowledge about the effect of oxygen level is poorly understood; soil aeration can fluctuate and zones of low oxygen are widespread in soil. We monitored CH₄ oxidation in three mineral soils (Eutric Cambisol, Haplic Podzol, Mollic Gleysol) under laboratory conditions by varying the O₂ level (from 20 to 2% O₂), with or without NH₄⁺ (100 mg N kg^?1). In controls (without NH₄⁺), CH₄ was oxidized completely in the O₂ range from oxia (20% O₂) to high hypoxia (5% O₂), while the process was inhibited under microoxia (2% O₂). Ammonium application decreased CH₄ consumption in all soils. This negative effect was stronger at 20% and 2% O₂ than under hypoxia. The highest CH₄ oxidation rates and the shortest initial (lag) phases in both control and NH₄⁺-amended soils were observed under high (5% O₂) and low (10% O₂) hypoxia.     

Microscale Zn and Pb distribution patterns in subsurface soil horizons: an indication for metal transport dynamics

In many studies on soil pollution, authors conclude that there is no downward migration of metal elements if no evidence for enrichment can be inferred from profiles of total metal contents. We assessed possible transfer of mobile and less mobile metal pollutants to depth in subsurface horizons of a heavy metal contaminated soil, by a study of specific pedofeatures in thin sections by optical microscopy, and their corresponding Zn and Pb distribution patterns by synchrotron‐based X‐ray microfluorescence. In the B horizon (70 cm depth), Zn accumulation was predominantly associated with clay–iron coatings. Strong correlation was found between Zn and Fe (r = 0.94), Zn and Mn (r = 0.75), Zn and Ti (r = 0.84), and Zn and K (r = 0.88), but significant correlation was absent between Zn and Pb. In the C horizon (100 cm depth), clear Pb accumulation was observed in distinct iron coatings, with large correlation coefficients found between Pb and Fe (r = 0.94–0.75), whereas correlation between Zn and Fe was absent. Detected Zn concentrations were small and attributed to the local natural geochemical background. These results were then compared with data of the composition of gravitational soil water collected in other soils from the same study area. Thus, Zn accumulation in the B horizon was ascribed to interception of dissolved Zn²⁺ by negatively charged constituents of clay–iron coatings. In contrast, Pb accumulation in C horizons was related to precipitation of Pb‐bearing iron colloids leading to neoformed, optically pure iron oxyhydroxide crystals and coatings. We demonstrate very localized accumulation of almost immobile Pb which occurs at greater depth than the more mobile Zn. The common, but strongly localized, occurrence of Pb‐bearing iron coatings in the soil groundmass explained the absence of changes in the total Pb concentrations of the C horizon compared with the concentrations in the B horizon.     

Significance of hydrous iron oxides in enhancing P sorption of soils with the addition of sodium hydrosulfite (Na2S2O4)

Phosphorus sorption (P_sor) of soils is affected by redox conditions. It has been shown that P_sor of lowland soils at a pH value of about 4.3 increases when a small amount of sodium hydrosulfite (Na₂S₂O₄) is added and decreases when an excess amount of (Na₂S₂O₄) is added to the mixture of a soil and P solution. Hydrous Fe-Al oxides, manganese dioxide (MnO₂) exchangeable Ca, models of reactive components with P in soils, were examined to identify the factors responsible for the increase of P_sor in lowland soils when a small amount of Na₂S₂O₄ was added. For clarifying the contribution of the hydrous Fe-Al oxides, goethite and 7 hydrous Fe-Al oxides (Fe/Al atomic ratio: 1/0, 5/1, 2/1, 1/1, 1/2, 1/5, and 0/1) were used. The P_sor of all these materials increased when they were treated with a small amount of Na₂S₂O₄ although the increase was the smallest for the hydrous Al oxide among the 7 oxides. Thus, the hydrous Fe oxides, and Al oxide to a smaller extent, play an important role in the increase in P_sor of the lowland soils treated with a small amount of Na₂S₂O₄ The P_sor of the hydrous Fe oxides was not appreciably affected by the addition of MnO₂. The increase in P_sor of the Ca-saturated Hachirogata soil was almost the same as that of the Nasaturated Hachirogata soil, indicating that exchangeable Ca did not affect appreciably the increase of P_sor in reduced soils at a pH value of about 4.3.     

Multivariate analyses and spatial distribution of Manganese minerals in soils close to an abandoned Manganese mine

Four hundred soil samples were obtained from a 4 km² area close to the abandoned Kgwakgwe Mn oxide ore mine in order to investigate the environmental association of Mn minerals and concentrations in the soils. Manganese minerals and Mn concentrations in samples were identified by X‐ray diffractometry and atomic absorption spectrometry, respectively, and results statistically analysed. Bixbyte, Mn₂O₃; braunite, Mn⁺²MnSiO₁₂; ramsdellite, MnO₂; pyrolusite, β‐MnO₂ and cryptomelane, K_{2 − x}Mn₈O₁₆ were identified in soil samples at the study site but none of these minerals found in soil samples from the control site. Manganese concentrations in samples from the study area were significantly higher than those from the control site. Statistical data yielded seven clusters with distribution of the Mn minerals and concentrations as follows: cluster 1 dominated by Mn concentrations in soil, cluster 2 by none of the seven Mn minerals, cluster 3 by pyrolusite, cluster 4 by braunite, cluster 5 by cryptomelane, cluster 6 by bixbyite and cluster 7 by ramsdellite. Very weak associations of these minerals were depicted from their correlations. The clusters had a bearing on the spatial distribution of the different minerals. Comparing results obtained from the control site, and geological materials, to the soils from the study area, it is certain that Mn minerals and high Mn concentrations in soils originated from the surrounding geological materials. The mining activities most possibly have affected Mn concentrations' and minerals' occurrences in the soils at the study area. Copyright © 2009 John Wiley & Sons, Ltd.     

皖南山地主要土壤的特征和分类问题

本文研究了皖南山地主要土壤的特征和分类。结果表明,本区土壤风化和淋溶作用强,富铝化特征明显,且随海拔高度的增加,土壤特征有差异。海拔600-700m以下的土壤,B层颜色以红棕色和亮红棕色(5YR5/6-5/8)为主,粉砂/粘粒值小于1.00,风化淋溶系数小于0.35,盐基饱和度小于35%,粘粒SiO₂/Al₂O₃多小于2.4。粘粒矿物以高岭石为主。氧化铁的活化度和络合度低,表层HA/FA小于0.35。该类土壤定为黄红壤(红壤土类中的一个亚类)。海拔600-700m以上的土壤,B层颜色以黄色(2.5Y8/6)和亮黄棕色(10YR6/6-6/8)为主,粉砂/粘粒值大于1.00,风化淋溶系数大于0.35,盐基饱和度小于35%,粘粒SiO₂/Al₂O₃一般大于2.3。粘粒矿物以蛭石和高岭石为主,并有较多的三水铝石出现。氧化铁的活化度和络合度高,表层HA/FA值0.35-0.75。该类土壤定为黄壤。从粘粒矿物组成和SiO₂/Al₂O₃,判断,皖南山地上部不存在山地黄棕壤和山地棕壤。土壤垂直带谱主要由黄红壤和黄壤构成。     

Soil solution aluminium activity related to theoretical A1 mineral solubilities in four Australian soils

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.