Influence of anions on dispersion and physical properties of the A horizon of a Red-brown earth

Three groups of anions were distinguished in order of effectiveness with respect to the dispersion and flocculation of soil samples treated with Fe(III) polycations: phosphate and fulvate citrate, oxalate, silicate and tartrate and salicylate, catechol, aspartate, lactate and acetate. This was also the order of the amount of anion adsorbed by the soil. The addition of phosphate and fulvate to soil samples with a net charge of zero lowered the zero point of charge producing particles with a net negative charge. This increased the amount of dispersible clay present from 0 to 9% by weight of soil. The sorption of phosphate and fulvate by soil samples with a net positive charge reduced the zero point of charge and caused flocculation of dispersed clay. Electrophoretic and electron microscopic studies confirmed the dispersion-flocculation phenomena.Treatments which produced dispersed clay led to increased bulk densities, plastic limits and moduli of rupture but lower porosities, water holding capacities and hydraulic conductivities. The sorption of anions on soil samples with a net charge of zero reduced friability.     

Origin of the effect of ph on the saturated hydraulic conductivity of non‐sodic soils

Abstract

The effect of pH on the saturated hydraulic conductivity (K) of repacked columns of two non‐sodic soils (Healaugh and Fagaga soils) was examined. The K value was greater for the Fagaga soil than for the Healaugh soil which is attributed to the difference in the amount of free iron oxides between the soils. The K values reached a maximum when the pH was close to the point of zero net charge (PZNC) (3.7 and 4.8 for the Healaugh and the Fagaga soil, respectively) and decreased on either side of these pH values. The effect of pH on K was related to its effect on surface charge. As the pH of variable‐charge soils approaches the PZNC, the net surface charge decreases resulting in flocculation and maintenance of a high K. Conversely, as the pH deviates from the PZNC, the net surface charge increases, resulting in dispersion and a decrease in K. There was a negative relationship between the amount of dispersed clay and the K values, suggesting that clay dispersion and the resulting clogging of pores decreases K in these soils.     

伊毛缟石对蒙脱土和高岭土分散凝聚特性的影响

[目的]探究伊毛缟石对蒙脱土和高岭土分散凝聚特性的影响,为水土保持和环境保护工作提供理论依据。[方法]采用浊度法测定黏土的分散性、离子交换法测定黏土电荷特性、电子显微镜观察等实验方法,将蒙脱土和高岭土溶液分别按一定比例混合伊毛缟石溶液,观察伊毛缟石对蒙脱土和高岭土分散凝聚特性的影响。[结果]伊毛缟石和蒙脱土的1∶1混合溶液,在全部pH值范围内保持凝聚;未脱铁处理的高岭土在pH值为5.9以下凝聚,在pH值为6.0以上分散,添加约5%的伊毛缟石使它的分散凝聚特性逆转。[结论]从微观上看,无论在酸性还是碱性条件下,伊毛缟石混合溶液都呈凝聚状态。酸性时,伊毛缟石的可变电荷和结晶性黏土矿物的永久电荷之间的引力形成凝聚;碱性时,伊毛缟石的表面变成中性形成凝聚。     

海南岛五指山土壤指纹电荷特征及影响因素研究

采用指纹电荷法(chargefingerprint)研究了海南岛五指山土壤指纹电荷特征及其与土壤有机质、pH、土壤黏粒含量、交换性H、交换性Al等之间的关系。结果表明:在本研究所设定的土壤pH范围(7.0、6.4、5.8、5.2、4.6、4.0)内,土壤指纹电荷随土壤pH的降低而减少;土壤指纹电荷与土壤有机质、pH、交换性H、交换性Al等之间极显著相关。研究显示,土壤黏粒含量对土壤养分的保持能力在低pH条件下比在高pH条件下显得更为重要。在实际工作中可用有机质含量、pH、黏粒含量(体积%)、交换性H、交换性Al含量等常规理化指标来计算出指纹电荷,作为判断土壤养分保持能力及预测土壤酸化影响的一个重要指标。     

可变电荷土壤对酸雨敏感度的影响因子

The sensitivity of a large number of variable charge soils to acid rain was evaluated through examining pH-H₂SO₄ input curves. Two derivative parameters, the consumption of hydrogen ions by the soil and the acidtolerant limit as defined as the quantity of sulfuric acid required to bring the soil to pH 3.5 in a 0.001mol L^-1 Ca(NO₃)₂ solution, were used. The sensitivity of variable charge soils was higher than that of constant charge soils, due to the predominance of kaolinite in clay mineralogical composition. Among these soils the sensitivity was generally of the order lateritic red soil > red soil > latosol. For a given type of soil within the same region the sensitivity was affected by parent material, due to differences in clay minerals and texture. The sensitivity of surface soil may be lower or higher than that of subsoil, depending on whether organic matter or texture plays the dominant role in determining the buffering capacity. Paddy soils consumed more acid within lower range of acid input when compared with upland soils, due to the presence of more exchangeable bases, but consumed less acid within higher acid input range, caused by the decrease in clay content.     

土壤电荷对盐桥的液接电位的长距离影响

Jenny^[3]等和Coleman等^[2]发现,当将参比电极的盐桥插入土壤悬液中时,带电荷的土壤颗粒可以使盐桥中阳离子和阴离子的淌度发生改变,因而在与土壤溶液的接触界面产生一个液接(扩散)电位.这个液接电位受一系列因素的影响.^[1]一般认为,这个液接电位与土壤胶体双电层的存在有关.在胶体化学上.普遍的概念是双电层的(有效)厚度为数百至数千埃.     

Dispersion and zeta potential of pure clays as related to net particle charge under varying pH, electrolyte concentration and cation type

The effect of changing pH and electrolyte concentration on the dispersion and zeta potential of Na-and Ca-forms of kaolinite, illite and smectite was investigated in relation to changes in their net negative charge. The percentage of dispersible Na-clay and the percentage increase in net negative charge was positively correlated with pH, but the slopes varied from clay to clay. In general, the net negative charge was the primary factor in clay dispersion, and the pH affected clay dispersion by changing the net charge on clay particles. Na-smectite had larger net charge at all pHs than Na-illite and Na-kaolinite, and it always had larger flocculation values. The role of electrolyte concentration could be due to its effect both on flocculation and variable charge component of the clay minerals. The zeta potential at different pHs also reflected the same trend of clay dispersion with net particle charge. In Ca-clays the trends were similar to Na-clays up to pH 7.0. In more alkaline solution CaCO₃ formation led to charge reduction on clay particles, resulting in flocculation and reduction of zeta potential. At similar pHs the electrophoretic mobilities of all the clays showed constant potential behaviour. However, the zeta potentials of Ca-clays were always smaller than those of sodic clays because the clays were more aggregated. Net particle charge was the most important factor in controlling clay dispersion for the whole range of pH and ionic strength and for all types of cations.     

不同黏粒含量对黄土渗透系数影响的试验研究

[目的]开展不同黏粒含量对黄土渗透系数影响的试验研究,揭示黏粒含量对渗透系数的影响及其微观机理,为黄土及其渗透性相关的理论与工程实践提供科学依据。[方法]通过自制负压湿筛装置筛取不同黏粒含量的黄土试样,利用激光粒度仪对土样的黏粒含量进行跟踪测定,采用静压法将不同黏粒含量的黄土试样制成天然干密度水平下的不同含水率试样进行饱和渗透试验。[结果]黏粒含量对黄土渗透性能有较大影响,在同一含水率条件下,随黏粒含量的增多,黄土的渗透性逐渐降低,渗透系数与黏粒含量呈指数函数负相关关系;在黏粒含量一定时,渗透系数随着初始含水率的增加而减小,呈指数函数负相关关系;SEM分析结果表明,随着黏粒含量的增加,黄土试样微观结构由分散结构变为致密结构,部分颗粒的接触方式由支架接触变为镶嵌接触,颗粒连接由葱皮连接或桥接变为嵌埋连接,相应地孔隙则由支架大孔变为黏粒间微小孔隙,从而一定程度上降低了黄土的渗透性。[结论]黄土渗透系数受黏粒含量、含水率的影响规律相似,可通过微观结构对其影响机理进行解释。     

Amelioration Effects of Pedogenetic Acidification Process on Physical Properties of Soils in Japanese Non-Volcanic Areas with Special Reference to Charge Characteristics

The charge characteristics and physical properties of acid soils were compared with those of reference clays to elucidate the effect of the pedogenetic acidification process on soil physicochemical properties. The soil physics such as clay dispersibility and aggregate stability of the acid soils are considered to be ameliorated by acidification process, which is attributable to the increase in amorphous Al hydroxides and interlayering of 2:1 clays. This means that the pedogenetic acidification process plays an important role in maintaining a desirable soil structure in Japanese non-volcanic areas from the aspect of environmental conservation. The involved mechanism was discussed with special reference to the modification of charge characteristics of clays and binding agents between soil particles.     

Distribution of organic matter and adenosine triphosphate after fractionation of soils by physical procedures

A mildly leached soil and a calcareous clay soil were dispersed using ultrasound. In the mildly leached soil, organic carbon, nitrogen and ATP (which was used as a guide of the soil microbial biomass) were concentrated in the finer fractions. In the calcareous clay, organic carbon and nitrogen were concentrated in the silt fraction.When slurries of the same soils were shaken vigourously in a wrist action shaker the soils were more completely dispersed but the recovery of ATP was only 30% compared with 90% after ultrasonic dispersion. It is concluded that the vigorous shaking of a soil slurry is destructive with respect to the biomass and smears cell contents, including ATP, across the colloidal fractions.The use of ¹⁴C showed that organisms, and metabolic products after incubation of [¹⁴C]glucose, existed mainly in larger aggregates (> 250 μm dia), silt and clay sized materials. Following physical dispersion the ¹⁴C shifted to silt and clay fractions.It is concluded that while fine clay may be a source of the metabolic products of organisms, the silt fraction a source of cells, and macroorganic matter contains most of the plant debris, the association of microorganisms with inorganic colloids is such that “clean” fractionations of biological components in soils cannot be realized.     

土壤电化学性质的研究Ⅴ.土壤对阳离子的结合能与土壤电荷的关系

带电的土壤胶体与离子之间的相互作用.是土壤电化学研究的中心问题.对于带净负电荷的大多数土壤来说,其与阳离子的结合强度,应该决定于土壤的电荷特点、阳离子的本性、和影响二者的相互作用的环境条件.     

Organic matter available for denitrification in different soil fractions: effect of freeze/thaw cycles and straw disposal

The 0 to 20-cm surface layer of a sandy loam soil was sampled in early autumn from plots where straw had either been removed or incorporated annually for 22 years. Denitrification in whole soils, 1–2-mm wet-stable aggregates, clay and silt size fractions was determined by acetylene blocking during anaerobic incubation with excess nitrate. Thus available organic matter was the limiting factor. Samples were exposed to one or two freeze/thaw cycles, or used unfrozen. K₂SO₄-extractable carbon (C) was determined before and after CHCI, fumigation. Freeze/thaw increased denitrification in whole soils and in aggregates. In aggregates and in whole soil without straw the increase in denitrification was similar following two freeze/thaw cycles, and well above the amount that could be fed by extractable soil C. In whole soils with straw addition, an extra denitrification increase occurred at first thaw only. This straw-induced denitrification surplus was matched by a decline in soil microbial biomass. For other samples and treatments, the freeze/thaw released C from additional organic matter sources. The availability of C in clay for denitrification was twice that of silt-associated C. Straw disposal generally had no effect on the bioavailability of particle-bound C. In contrast to whole soils and aggregates, the availability of organic matter in clay and silt after one freeze/thaw cycle was only half that observed from unfrozen samples. The effect of freeze/thaw on whole soils and aggregates may be to release organic matter available for denitrification by killing the microbial biomass and by disintegrating aggregates. However, the impact of freeze/thaw on completely dispersed samples such as clay and silt may be to promote the formation of granular structures (micro-aggregation) in which organic matter may become less accessible to denitrifiers.     

MIGRATION AND AGGREGATION OF Na AND Ca CLAYS BY THE FREEZING OF DISPERSED AND FLOCCULATED SUSPENSIONS

The ability of clay to move ahead of an ice-liquid interface depends on the rate of freezing, the particle size, the release of dissolved air from the water through its probable effect on local freezing rates, and on the electrolyte and its concentration through their effects on interparticle forces and particle mobility. A freezing-rate of 1 cm per hour did not move flocculated clay in most cases, but moved dispersed clay up to 0.7 cm before being trapped in the ice with released air. Aggregates of clay (0.1 to 1 mm) were produced by freezing. After thawing they swelled and dispersed depending on the electrolyte and its concentration in a similar manner to aggregates formed by drying.     

Pesticide sorption and diffusion in natural clay loam aggregates

Pesticide sorption in soils is controlled by time-dependent processes such as diffusion into soil aggregates and microscopic sorbent particles. This study examines the rate-controlling step for time-dependent sorption in clay loam aggregates. Aggregates (5 mm) were stabilized with alginate, and adsorption of azoxystrobin, chlorotoluron, and cyanazine was measured in batch systems equilibrated for periods between 1 h and 7 days. Stepwise desorption was measured at 1- or 3-day intervals following 1 or 7 days of adsorption. Time-dependent adsorption was also measured on dispersed soil. Results were interpreted using process-based modeling. Adsorption on dispersed soil was described by intraparticle sorption and diffusion. Adsorption in the aggregates was much less than in suspension, suggesting that part of the sorption capacity of the dispersed soil was not available within the aggregates (approximately 50%). Adsorption and desorption were reversible and could be described by pore diffusion into the aggregate with effective diffusion coefficients between 0.5 x 10(-10) and 1 x 10(-10) m2 s(-1), a factor 3-6 slower than estimated theoretically. Intraparticle diffusion did not seem to contribute to sorption in the aggregates at this time scale. Apparent hysteresis was explained by nonattainment of equilibrium during the adsorption and desorption steps.     

Complexed organic matter controls soil physical properties

It is shown that, for mineral soils, it is not the total amount of organic carbon (or organic matter) that controls soil physical behaviour but the amount of complexed organic carbon (COC). We assume that this complex is formed by the association of unit mass (i.e. 1 g) of organic carbon with n grams of clay. Analysis of data from two French and two Polish databases shows that, for these soils, n = 10. A consequence of this is that in soils with small contents of organic carbon (OC), such as arable soils, COC is proportional to OC. However, in soils with large contents of organic carbon, such as pasture soils, COC is proportional to the clay content. This explains why we find that soil bulk density is significantly correlated with OC in French arable soils but with the clay content in French pasture soils. The use of COC instead of OC enables the arable and pasture soils to be considered on the same scale.

Water retention data were fitted to a double-exponential equation which allows both the matrix and structural porosities to be estimated. It is shown that in soils with low contents of organic carbon, the carbon content is positively correlated with the matrix porosity. In contrast, in soils with high contents of organic carbon, the matrix porosity is constant at its maximum value and the structural porosity is not significantly correlated with either the total organic carbon or the non-complexed organic carbon (NCOC). It is suggested that the complexed organic carbon can be considered as being sequestered. The soil clay content can similarly be partitioned between clay that is complexed with organic carbon and clay that is not complexed. It is shown that non-complexed clay is more easily dispersed in water than clay that is complexed with organic carbon. These findings indicate how improved pedo-transfer functions for the prediction of soil physical properties may be produced. Such functions need to use the values of complexed and non-complexed organic carbon and clay which must be determined by algorithms. The values produced by the algorithms may then be used in the improved pedo-transfer functions.     

土壤电化学性质的研究Ⅲ.红壤胶体的电荷特征

土壤胶体的电荷性质,与土壤的一系列物理化学性质有密切关系。红壤的某些与肥力有关的物理化学性质,与其它类型土壤有所不同。例如,它的阳离子交换量较小,而阴离子吸附量则较大,分散性较弱,胀缩性也较小。红壤在物理化学性质方面的这些特点,大多是由其胶体的电荷特点所引起。     

POTASSIUM-CALCIUM EXCHANGE EQUILIBRIA IN SOILS: THE LOCATION OF NON-SPECIFIC (GAPON) AND SPECIFIC EXCHANGE SITES

Several studies (e.g. Bolt et al., 1963; Beckett, 1964a) of the exchange equilibria between K and Ca on soil colloids or pure clay minerals have drawn attention to the presence of sites with different affinities for K. There is so far no evidence to indicate the location of sites with the highest affinity, though several workers (e.g. van Schouwenburg and Schuffelen, 1963) have assumed that they lie on the edge-faces of stacks of clay plates, or in the spaces between the expanded leaves of partially weathered stacks of clay plates. Earlier work has resolved the K: Ca exchange isotherms of soils and clays into a curved part at low values of aK/√aCa, attributed to exchange at sites with a high specific affinity for K, and an upper linear part commonly described by the Gapon equation and attributed to non-specific sites. The present work on soil clays and clay minerals shows that Na hexametaphosphate or changes in pH affect the curved but not the linear part; cetyl trimethyl ammonium bromide and changes in the amount or charge of exchangeable Al affect the linear but not the curved part of the isotherms. At low pH, the linear but not the curved part of the kaolinite isotherm obeys Schofield's Ratio Law. Grinding has more effect on the curved than on the linear part. So the specific sites are attributed to the edges or peripheral interstices of stacks of clay plates, and the non-specific sites to their planar surfaces. The specific sites take up K more slowly from solution than the non-specific sites. The isotherms of completely dispersed bentonites have no curved part. The specific sites are attributed to the wedge-shaped interstices opened between clay plates by weathering, from which exchange is diffusion-controlled. Added organic cations reduce the numbers of both kinds of site; peroxide treatment increases them. This paper confirms that the exchange sites with highest affinity for K are indeed associated with the edges, rather than the faces, of stacks of clay plates.     

Potential contributions of smectite clays and organic matter to pesticide retention in soils.

Soil organic matter (SOM) is often considered the dominant sorptive phase for organic contaminants and pesticides in soil-water systems. This is evidenced by the widespread use of organic-matter-normalized sorption coefficients (K(OM)) to predict soil-water distribution of pesticides, an approach that ignores the potential contribution of soil minerals to sorption. To gain additional perspective on the potential contributions of clays and SOM to pesticide retention in soils, we measured sorption of seven pesticides by a K-saturated reference smectite clay (SWy-2) and SOM (represented by a muck soil). In addition, we measured the adsorption of atrazine by five different K-saturated smectites and Ca-saturated SWy-2. On a unit mass basis, the K-SWy-2 clay was a more effective sorbent than SOM for 4,6-dinitro-o-cresol (DNOC), dichlobenil, and carbaryl of the seven pesticides evaluated, of which, DNOC was sorbed to the greatest extent. Atrazine was sorbed to a similar extent by K-SWy-2 and SOM. Parathion, diuron, and biphenyl were sorbed to a greater extent by SOM than by K-SWy-2. Atrazine was adsorbed by Ca-SWy-2 to a much lesser extent than by K-SWy-2. This appears to be related to the larger hydration sphere of Ca(2+) (compared to that of K(+)) which shrinks the effective size of the adsorption domains between exchangeable cations, and which expands the clay layers beyond the apparently optimal spacing of approximately 12.2 A for sorption of aromatic pesticide structures. Although a simple relation between atrazine adsorption by different K-smectites and charge properties of clay was not observed, the highest charge clay was the least effective sorbent; a higher charge density would result in a loss of adsorption domains. These results indicate that for certain pesticides, expandable soil clays have the potential to be an equal or dominant sorptive phase when compared to SOM for pesticide retention in soil.     

Effect of cell surface characteristics on the adhesion of bacteria to soil particles

Summary We investigated the adhesion to a sandy soil and a clay loam soil of a series of Lactobacillus strains with various cell surface characteristics. Measurable adhesion occurred within 30 s of contact time. No further increase in the number of bacteria adhering to the soil was observed after 15–20 min. The fraction of bacteria adhering to the soil was independent of the initial concentration of bacteria in solution. Bacteria adhering to the soil could be removed by washing the soil immediately after the adhesion test. Bacterial cell surface hydrophobicity, as determined by the bacterial adherence to octane and polystyrene, was the major parameter influencing the adhesion to the sandy soil. The cell surface charge of the bacteria was of minor importance in the adhesion to the sandy soil. The adhesion of the bacteria to the clay loam soil was higher than to the sandy soil and increased in the presence of divalent ions. This indicates that electrostatic interactions also influence the adhesion of bacteria to clay particles.     

土壤电化学性质的研究——Ⅹ.红壤胶体的表面性状和离子专性吸附对表面电荷性质的影响

根据可变电荷和永久电荷共存的土壤体系的模式,研究了一个砖红壤和一个红壤胶体的表面电荷特性。由于两种土壤胶体的矿物成分和铁铝氧化物的含量不同,砖红壤胶体的pH。值、ZPNC和IEP都高于红壤胶体者。红壤胶体的永久负电荷量多,其pH₀与ZPNC的差值也大。土壤加3%的有机质淹水培育4个月后,胶体的腐殖质含量增加不足0.5%,对胶体的pH₀的影响不明显。砖红壤胶体用磷酸盐或硅酸盐处理后,表面正电荷减少,负电荷增多,pH₀值和IEP都降低。磷酸盐的效应较硅酸盐为甚。不同浓度的KCl溶液中存在少量SO₄^2-时,砖红壤胶体的正电荷减少,负电荷增加,ZPNC和pH₀值降低;如存在少量Ca²⁺,则pH₀值升高。以单一的K₂SO₄、为支持电解质时,pH₀值较KCl者为高。