氧化铁对红壤电荷性质的影响

作者研究了6种土壤去除游离氧化铁前后在不同pH时正电荷、负电荷和净电荷以及净电荷零点(ZPNC)的变化。结果表明,6种红壤都带有相当量的正电荷。土壤经去铁处理后,正电荷大量减少或消失:5种红壤在高pH时出现对Cl^-的负吸附;5种红壤的负电荷在实验pH范围内(3-7.5)较原土明显增加。去铁处理使净电荷零点(ZPNC)明显降低。采自昆明由玄武岩发育的铁质红壤与上述不同,去铁后负电荷稍有减少,净负电荷变化很小,对Cl^-未出现负吸附。     

中南地区几种土壤的表面电荷特性Ⅲ.土壤的电荷量,电荷零点(PZC)和净电荷零点(PZNC)

研究了中南地区3种土壤的电荷量、电荷零点(PZC)和净电荷零点(PZNC)等表面电荷性质及其与土壤矿质组成的关系.结果表明:(1)从赤红壤、红壤到黄棕壤,永久负电荷量(CECp)趋于增大,主要与土壤的粘土矿物组成和粘粒含量有关;可变负电荷量(CECv)变异趋势不明显,主要与土壤氧化铁铝的组成及含量有关;可变负电荷量占负电荷总量的比例趋于降低;正电荷量趋于减小.(2)供试赤红壤、红壤和黄棕壤的PZC分别为3.90、3.35～3.50和2.96～3.12;赤红壤和红壤的PZNC分别为3.85和2.15～2.84,黄棕壤不存在PZNC.(3)初步提出可变电荷土壤表面电荷性质的指标为:PZC>3.0、PZNC>2.0、PZC朠ZNC<1.0和CECv/CEC8.2>0.4.     

几种有机酸对恒电荷和可变电荷土壤吸附Cu2+的影响

以恒电荷土壤(黄褐土和黄棕壤)和可变电荷土壤(红壤和砖红壤)为供试材料,研究了乙酸、草酸、酒石酸和柠檬酸对土壤吸附重金属铜离子(Cu2 )的影响。结果表明,在相同酒石酸浓度下,土壤对酒石酸的吸附量依次为黄棕壤(2 1 8mmolkg-1) >红壤(15 4mmolkg-1) >砖红壤(9 5mmolkg-1) ,土壤吸附有机酸后负电荷量增加,相同条件下增幅为砖红壤>红壤>黄棕壤;无有机酸配体时,供试土壤对Cu2 的吸附量为黄褐土>黄棕壤>砖红壤>红壤;加入有机酸时,随有机酸浓度增高,土壤对Cu2 的吸附一般表现为“峰”形曲线,峰所对应的有机酸浓度因有机酸类型而异,且随土壤可变电荷性质增强而增高;土壤吸附有机酸后对Cu2 的次级吸附不同于有机酸与铜共存时的竞争吸附,且因土壤性质表现迥异。这些结果意味着在存在有机酸配体的根际环境中,恒电荷土壤与可变电荷土壤对Cu2 的吸附明显不同,并将影响重金属离子在根际的转化与有效性     

SURFACE CHARGE CHARACTERISTICS OF SOILS IN CENTRAL AND SOUTHERN CHINA

研究了中南地区3种土壤的电荷量、电荷零点（PZC）和净电荷零点（PZNC）等表面电荷性质及其与土壤矿质组成的关系。结果表明（1）从赤红壤、红壤到黄棕壤,永久负电荷量（CECp）趋于增大,主要与土壤的粘土矿物组成和粘粒含量有关;可变负电荷量（CECv）变异趋势不明显,主要与土壤氧化铁铝的组成及含量有关;可变负电荷量占负电荷总量的比例趋于降低;正电荷量趋于减小。（2）供试赤红壤、红壤和黄棕壤的PZC分别为3.90、3.35～3.50和2.96～3.12;赤红壤和红壤的PZNC分别为3.85和2.15～2.84,黄棕壤不存在PZNC。（3）初步提出可变电荷土壤表面电荷性质的指标为PZC>3.0、PZNC>2.0、PZC朠ZNC<1.0和CECv/CEC8.2>0.4。     

低分子量有机酸对砖红壤表面电荷的影响

本文研究了4种低分子量有机酸对砖红壤表面电荷性质的影响,结果表明存在于体系中的有机酸增加了表面负电荷量,同时减少表面正电荷的量。在低有机酸加入量下,有机酸对正电荷的影响程度比其对负电荷的影响程度大得多。4种酸对土壤表面电荷影响的大小顺序为:柠檬酸>苹果酸>草酸>醋酸。有机酸对表面电荷的影响随体系pH而变化,它们对正电荷的影响程序随pH的增加而减小,而对负电荷的的影响呈相反的变化趋势。有机酸主要通过其阴离子在土壤表面的吸附来影响土壤的表面电荷性质。     

中南地区几种土壤的表面电荷特性 Ⅲ.土壤的电荷量,电荷零点(PZC)和净电荷零点(PZNC)

研究了中南地区３种土壤的电荷量,电荷零点和净电荷零点等表面电荷性质及其与土壤矿物组成的关系,结果表明：（１）从赤红壤,红壤到黄棕壤,永久负电荷量趋于增大,主要与土壤的粘土矿物组成和粘粒含量有关,可变负电荷量变异有明显,     

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。     

我国几种地带性土壤无机胶体的表面电荷特性

研究了用返滴定法测定我国七个不同地带土壤无机胶体的表面电荷特性。结果表明 :( 1 )返滴定法测定的供试土壤无机胶体可变电荷量随纬度升高而逐渐上升。这主要与供试土壤粘土矿物、铁铝氧化物组成及含量有关。一般来说 ,土壤层状硅酸盐粘土含量越多 ,永久负电荷量和其可变负电荷量越大 ;铁铝氧化物含量越高 ,可变负电荷量越低。( 2 )七个地带性土壤无机胶体的Qv pH曲线上在pH5左右有一峰值 ,这可能与供试土壤胶体中铁铝氧化物的ZPC及供试土样层状硅酸盐的边面Si OH基吸附H 及Al OH基离解H 有关     

氧化铁的存在方式对土壤和黏土矿物胶体动电电位的影响

土壤表面带有电荷是土壤胶体的基本特征,也是土壤具有保肥能力的主要原因。可变电荷土壤由于矿物组成的特点,其表面电荷特征与恒电荷土壤有很大不同。在通常的pH条件下这类土壤中的硅酸盐矿物带负电荷,而铁、铝氧化物带正电荷,因此,可变电荷土壤中存在两类带相反电荷的胶体颗粒,两者之间存在相互作用。Qafoku和Sumner[1]发现当用很稀的CsCl溶液(0.5mmol L-1)对美国老成土进行淋溶实验时,淋出液中Cs+和Cl-的浓度在开始阶段几乎保持不变,而且较加入的淋溶液低很多,淋出液的电导率(EC)较加入的淋溶液的电导率也低得多。此现象无法用传统的离子交换理论和形成离子对模型来解释,他们提出可变电荷     

CrO42-对两种可变电荷土壤表面电荷的影响

对两种可变电荷土壤的研究结果表明,加入铬酸根(CrO42-)能增加土壤的表面负电荷,减小土壤的表面正电荷的量。CrO42-对表面正电荷的影响程度随体系pH的增加而减小,对负电荷的影响呈相反的趋势。CrO42-对表面电荷的影响程度也随其加入量的增加而增加。CrO42-主要通过自身的吸附来影响土壤的表面电荷,因为伴随着土壤表面电荷的变化,CrO42-在土壤中发生明显的吸附。而且土壤对CrO42-的吸附量随其加入量的增加而增加,随pH的升高而减小,与土壤电荷的变化趋势基本一致。     

磷酸盐吸附对可变电荷土壤正负电荷的影响

本文研究了华南地区不同类型的可变电荷土壤，并对磷酸盐的吸附量和吸附磷后土壤的正、负电荷的变化，以及ｐＨ和游离氧化铁对这种变化的影响进行了研究。结果表明，土壤吸磷量与土壤游离氧化铁含量成良好的正相关。土壤吸磷后正电荷减少，负电荷增加，土壤电荷量与吸磷量之间呈抛物线状相关。吸附１摩尔磷酸盐对土壤净负电荷的贡献在０．３－１．０摩尔之间。土壤中的游离氧化铁使吸附的磷对土壤负电荷的贡献减少。     

Surface chemical properties and pedogenesis of tropical soils derived from basalts with different ages in Hainan,China

Limited information is available on the changes of surface chemical properties of tropical soils with time during the pedogenesis. Soil samples of three profiles derived from basalts of 10, 1330 and 2290 kilo annum (ka) in age were collected from adjacent locations in a tropical region of Hainan Province, China. The changes in soil surface chemical properties and the mineralogy of the soil clay fraction with time were investigated using ion adsorption, micro-electrophoresis, and X-ray diffraction analysis. The content of 2:1-type clay minerals decreased, while those of kaolinite and gibbsite increased with increasing basalt age and degree of soil development. The content of pedogenic free iron (Fe) oxides and the ratio of free Fe oxides/total Fe oxides increased with soil development stage, while soil poorly crystalline Fe and aluminum (Al) oxides had an opposite trend. The positive surface charge of the soils increased with increasing basalt age and degree of soil development; this was consistent with the change in their contents of free Fe/Al oxides. However, the value of negative surface charge had an opposite behavior. The soil derived from 10-ka-basalt had much more negative charge than soils derived from 1330- and 2290-ka-basalt. Soil net surface charge and zeta potential of the soil clay-fraction decreased with the increase in basalt age. Both net charge–pH curves and zeta potential–pH curves shifted to positive values with increased basalt age and degree of soil development. Increasing age also elevated the point of zero net charge of the soil and the isoelectric point of soil colloids.     

Growth of Cocoa Planted on Highly Weathered Soil as Affected by Application of Basalt and/or Compost

Oxisols, which are highly weathered, occupy a large area of Malaysia. These soils are infertile because of low pH, calcium (Ca), magnesium (Mg), and potassium (K) levels but high aluminum (Al) content. The infertility can be ameliorated by applying soil amendments. A study was conducted to determine the effects of basalt and/or rice husk compost application on cocoa growth planted on an Oxisol. The results showed that either basalt or rice husk compost and their combinations were effective ameliorants. Basalt application increased soil pH and exchangeable Ca and Mg while decreasing exchangeable Al. Accordingly, soil solution Ca, Mg, and K increased and Al and manganese (Mn) concentrations decreased. Silicate released from basalt was able to lower the pHo (the pH at which the net charge of the variable charge minerals is zero), indicating a negative charge was being generated, which led to increase in the cation exchange capacity (CEC) of the Oxisol. The improvement in soil fertility because of application of the amendments had improved cocoa growth. Leaf K and P of the cocoa planted on the basalt-treated soils were within the sufficient range for cocoa growth. Rice husk compost applied at a rate of less than 20 t ha^?1 in this trial was not able to supply sufficient N to the cocoa. Basalt application at an appropriate rate effectively ameliorates acidic soil infertility, but it takes time to realize the positive effects of application as it slowly dissolves under field conditions.     

Evaluation of relationship between dispersibility of soils and charge characteristics using a modified ion adsorption method; An example of soils from Wakayama Prefecture,Japan

The relationship between the charge characteristics and the dispersibility of soils from reclaimed land (highly dispersive) and adjacent forest area (physically stable) was investigated.

To evaluate the amount of soil charges quantitatively, the measurement based on cation and anion adsorption (ion adsorption method) was attempted in two ways, where special attention was paid to the solution concentration. In the conventional ion adsorption method, the treatments with concentrated solutions (1 mol L^-1) were included in the process. In the modified method, soils were treated with dilute solutions (5 mmol L^-1), in taking account of the soil solution concentration in humid temperate regions. The amount of charges derived from the modified method was smaller than that from the conventional one, especially in the high pH zone. In a preliminary experiment, the extraction of polyvalent cations from soils was found to be significantly affected by the salt concentration. Thus, the use of solutions with an excessively high concentration was considered to result in an error in the estimation of the active charges in soils which would contribute to the dispersion behavior in the field.

The applicability of the modified method for analyzing the dispersion behavior of soils was evaluated by relating the dispersibility of silts and clays at different pHs with the charge characteristics determined under the same ionic strength. The dispersion ratio of silts of the reclaimed land reached maximum values at pH 5.5, above which the ratio decreased, whereas the ratio of clays began to increase in the pH range above 6. The dispersion ratio of silts of the forest area increased in the pH range above 6, whereas that of clays remained constant at a low level in all the pH ranges below 7. The changes in the dispersibility of silt plus clay fractions corresponded to total charge characteristics determined by the modified method. Thus, the evaluation of soil charges by the modified ion adsorption method was considered to be effective to predict soil dispersibility under field conditions, indicating that it could replace electrokinetic analyses such as electrophoresis in studies on the dispersion/flocculation behavior of soils.     

Nitrate Mobility in Variable-Charge Tropical Soils

ABSTRACT

Nitrate (NO₃ ^–-N) leaching in tropical soils, which are more weathered, is influenced by their mineralogical, physical, and chemical characteristics. Thus, the present study aimed to evaluate the effect of the variation of net electrical charge on the mobility of nitrate, applied as potassium nitrate (KNO₃) or calcium nitrate (Ca(NO₃)₂), in samples from A and B horizons of three Red-Yellow Latosols (Oxisols), with different mineralogical and textural characteristics. Hydrochloric acid (HCl) or sodium hydroxide (NaOH) volumes were added to previously sterilized soil samples in order to condition five hydrogen potential (pH) values, obtaining different net electrical charges. The experiment was carried out with leaching columns under laboratory conditions. The soil columns were percolated with solutions of KNO₃ or Ca(NO₃)₂ or water (control). An increase in positive net charges was significant and varied according to the soil and percolating solution; in general, it resulted in an increase of up to 50% in nitrate adsorption in some soils. Larger amounts of adsorbed nitrate were observed in the columns filled with the B horizon of the clayey gibbsitic Red-Yellow Latosol, showing adsorption of 85% for a positive net charge of 2 cmol_c kg^?1. Regarding kaolinitic soils, lower adsorption was observed in the medium-textured kaolinitic Red-Yellow Latosol, which had lower clay content and positive net charge. Application of Ca(NO₃)₂, as a percolating solution, increased nitrate adsorption compared to the application of KNO₃. This effect may be attributed to the increase in positive net charge promoted by calcium (Ca²⁺), being more evident for the highest negative net charges.     

Soil pH on mobility of imazaquin in oxisols with positive balance of charges

The influence of soil pH on the leaching potential of the ionizable herbicide imazaquin was assessed on the profile of two highly weathered soils having a net positive charge in the B horizon, in contrast to a soil having a net negative charge in the whole profile, using packed soil column experiments. Imazaquin leached to a large extent and faster at Kd values lower than 1.0 L kg(-1), a much more lenient limit than usually proposed for pesticides in the literature (Kd < 5.0 L kg(-1)). The amount of imazaquin leached increased with soil pH. As the soil pH increased, the percentage of imazaquin in the anionic forms, the negative surface potential of the soils, as well as imazaquin water solubility also increased, thus reducing sorption because of repulsive electrostatic forces (hydrophilic interactions). For all surface samples (0-0.2 m), imazaquin did not leach at soil pH values lower than pKa (3.8) and more than 80% of the applied amount was leached at pH values higher than 5.5. For subsurface samples from the acric soils, imazaquin only began to leach at soil pH values > zero point of salt effects (ZPSE > 5.7). In conclusion, the use of surface K(oc) values to predict the amount of imazaquin leached within soil profiles having a positive balance of charges may greatly overestimate its actual leaching potential.     

可变电荷土壤中铜离子的解吸

研究了我国四种可变电荷土壤红壤、赤红壤、砖红壤和铁质砖红壤以及二种恒电荷土壤黄棕壤和黑土中吸附性铜离子的解吸特征。研究结果表明 ,可变电荷土壤吸附的一部分铜离子可以被去离子水解吸 ,而且在pH～解吸率曲线上在一定pH值时出现解吸率最大值。在最大值时不同土壤中铜离子解吸率的大小与土壤中氧化铁的含量有关。氧化铁的含量越高 ,在最大值时铜离子的解吸率越大。当用中性电解质解吸可变电荷土壤吸附的铜离子时 ,电解质的浓度越大 ,解吸率越低。与此相反 ,恒电荷土壤吸附的铜离子不能被去离子水解吸 ,只能被中性电解质解吸 ,且电解质的浓度越高 ,解吸率越大。这表明 ,可变电荷土壤中吸附性铜离子的解吸规律 ,完全不同于恒电荷土壤中者。本文初步讨论了其原因     

Effect of removal of free oxides on changes in dispersibility and charge characteristics of soils

Changes in dispersibility and charge characteristics of two soils with different colloidal properties were investigated after various extracting treatments of free oxides. The soil samples were taken from the upland field in a reclaimed area (highly dispersive) and from the B horizon of an adjacent forest area (physically stable), both of which derived from the same parent material. Special attention was paid to selective extraction of Al and Fe oxides. After the extraction of free oxides by conventional methods such as DCB or oxalate treatment, dispersibility of the soils which always became too high made it difficult to relate the amounts of removed oxides with the changes in dispersibility. Thus, extractions by milder treatments were designed in order to remove varying amounts of free oxides using several organic salt solutions. Among the treatments, citrate and oxalate extracted more Al oxides, followed by tartrate. Dithionite, acetate, and NaCl extracted only trace amounts of Al oxides. This order seemed to be controlled by the stability constants of organo-Al complexes. The changes in dispersibility of the residual soil were related to the amount of extracted Al, especially for the forest soil, but not to Fe or Si. After these treatments, the amount of positive charges of the soil decreased while that of negative charges increased. For instance, the amount of total charges of the forest soil after DCB treatment was 1.5 times larger than that of the non-treated soil at the dispersion pH, which was mainly attributed to the removal of Al oxides. Although the amount of removed Al oxides was relatively small, the changes in dispersibility of the residual forest soil were drastic, indicating that free oxides (mainly Al) removed by milder treatments were the most external, active fractions. This interpretation suggests the practical importance of the release of amorphous sesquioxides in the natural weathering process in preventing the dispersion of potentially dispersive soils.