Influences of aluminum ions on the determination of zpc (zero point of charge) of variable charge soils

Influence of Al dissolution on soil ZPC (zero point of charge) measured by a potentio-metric titration (PT) method and a modified salt titration (STPT) method was examined using two strongly weathered soils from Thailand and two volcanic ash soils from Japan. The amount of dissolved Al ions increased with the increase in the concentration of a supporting electrolyte for the strongly weathered soils, while the increase was negligible for the volcanic ash soils.

ZPC value of the strongly weathered soils determined by the PT method was lower than that by the STPT method, due to the greater Al dissolution associated with the higher electrolyte concentration used in the PT method. Al ions adsorbed onto the soil surface would shift the ZPC to a higher pH value not as a result of the formation of hydroxy Al polymers, but due to the blocking of permanent negative charge sites, which could otherwise lower the ZPC. The σp value, as a measure of permanent charge or the amount of 11 or O11 adsorbed by a soil required to attain the ZPC, could be used to describe this phenomenon.

In the STPT method, the salt concentration was not high enough to causc a significant Al dissolution at the ZPC, which is considered to be a more suitable condition than in the PT method because the ZPC value can be evaluated at a low salt concentration as in the ease of field conditions for crop production. Thus, the STPT method is rccommendcd for the determination of the ZPC.     

Charge distribution of selected venezuelan soils with some pedogenic and agrotechnological implications

Abstract

A study of the electrical charge distribution of selected Venezuelan soils (two Oxisols, two Ultisols, and one Alfisol) by potentiometric titration (PT) and ion adsorption (IA) procedures, showed that all soils have a predominance of negative charge at their natural pH level and within the experimental pH range used (3.5–7.5). The only exception was the Amazonas 2 soil, which has a point of zero net charge (PZNC) at pH 3.5. Potentiometric titration (PT) results allowed us to find the point of zero salt effect (PZSE) of these soils, which is related to their pedogenetic development. The order found, from older to younger, was: Guanipa (Oxisol) > Amazonas (Oxisol) > Lomas de Cubiro (Ultisol) > Altos de Pipe (Ultisol) > Barinas (Alfisol). The Stoop's method, used to determine the PZSE of the soils, was found to be a more efficient and shorter way than PT for this purpose. Ion adsorption (IA) was a more realistic way than PT to determine charge distribution for the studied soils. The soils were classified according to their charge distribution, following Gillman and Sinclair (4), as type 1 (Barinas, Lomas de Cubiro, Altos de Pipe, Amazonas 1) and type 2 (Amazonas 2 and Guanipa). This classification has agrotechnological and management implications related to the effect of added amendments, fertilizer and pollutants that would interact as ions in these soils. The low anion exchange capacity (AEC) of all these soils means low absorption capacity for non‐specifically adsorbed anions, and therefore, their probable ease of leaching down through the soil profile.     

Retarded leaching of nitrate in acid soils from the tropics: measurement of the effective anion exchange capacity

Delay in the leaching of nitrate was measured in laboratory columns of repacked soils (Oxisols, Alfisols, Ultisols and Inceptisols) from South America, Africa and South-East Asia. Between one and five pore volumes were required for the frontal displacement of chloride by nitrate (2 mM adjusted to the natural pH of the soil). The delay was in good agreement with that calculated from charge (0 to 1.7 cmol positive charge kg^?1). Measurement of charge by batch equilibration with 0.5 M and then 2 mM NH₄CI at the pH of the soil overestimated the effective charge, probably due to removal of sulphate in the washings. A leaching method using only 2 mM NH₄CI gave a better estimate.     

Predicting value of diagnostic soil properties on actual and potential cation exchange capacity (CEC) in andisols and andic soils

Abstract

Relationships between charge variation and diagnostic soil properties were studied in Andisols and andic subgroups of Inceptisols and Ultisols. Charge variation was calculated as the difference between “field” or actual cation exchange capacity (CECa), and potential CEC (1M NH₄OAc, pH 7). Methods used to estimate CECa (effective CEC, silver thiourea) were higly correlated. The relative charge variation was greater than 70% in Andisols with very low content of layer silicates. Active Al (Alo) was positively correlated with CEC‐NH₄ and negatively correlated with CECa. This result contributed to the explanation of the negative trend correlation observed between actual and potential CEC. The ratio CECa/Alo showed low values (<8) in Andisols. This parameter was also tested in 25 samples of Andisols described elsewhere. The predicting value of both Alo and CECa for a rough estimation of variable charge seemed apparent from the results obtained.     

Charge characteristics and exchangeable cation status of Korean Ultisols and Alfisols and Thai Ultisols and Oxisols

The charge characteristics of A₁ or Ap and B₂ horizon samples of total 23 Ultisols, Alfisols and Oxisols in Korea and Thailand were studied by measuring the retention of NH₄⁺ and NO₃^? at different pH values (4–8) and NH₄NO₃ concentrations (0.1–0.005 m ). The magnitude of their negative charge (σ^?; meq/100g) was dependent on pH and NH₄NO₃ concentration (C; m ) as represented by a regression equation: log σ^?=apH +blogC +c. The values of the coefficient a (0.04–0.226), b (0.03–0.264) and c (–0.676–1.262) were correlated with the kinds of the soil and horizon and with the region where the soil exists. The retention of NO₃^? was less than 1 and 2–3 meq/100 g for the A₁ or Ap and B₂ horizon samples, respectively. The sum of exchangeable base and Al (‘effective’ CEC) was close to and higher than the magnitude of permanent charge (=σ^? measured at pH = 4.3 and at C = 0.005 m ) for one-third and two-thirds of samples, respectively. A σ^? value of 16 meq/100 g clay at pH = 7 and C = 0.01 m was found appropriate to separate the B₂ horizons of Thai Ultisols and Oxisols from those of Korean Ultisols and Alfisols. Korean Alfisols and Ultisols and Thai Ultisols were distinguished from each other on the status of exchangeable base and Al     

Mineralogy and factors controlling charge development of three Oxisols developed from different parent materials

Three Oxisols, developed from serpentinite (Sungai Mas Series), basalt (Kuantan Series) and andesite (Segamat Series), selected to represent the most common Oxisols in Malaysia were sampled and studied. The objectives of this study were: (i) to determine mineralogical composition and factors responsible for changes in point of zero charge (pH₀) of the variable charge component of three Oxisols; (ii) to use pH₀ values to assess degree of chemical weathering; and (iii) to determine the magnitude of variable charge using corrected back-titration technique. The mineralogical composition was determined by X-ray diffraction analysis (XRD). The pH₀ was determined by potentiometric titration in different electrolyte strengths. The magnitude of variable charge generation as a function of soil pH was measured using corrected back-titration to allow elimination of charge overestimation caused by solid dissolution and hydrolysis reactions. The results showed that the mineralogical composition were similar (kaolinite, goethite, hematite and gibbsite) between profiles but different in proportion, except for gibbsite which was absent in the andesite-derived soil. The sequential removal of soil organic matter (SOM), iron oxides and SOM together with iron oxides resulted in the changes of pH₀ from 3.9–5.7 to 5.3–6.7, 2.6–3.7 and 3.3–4.5, respectively. These pH₀ changes indicate SOM and sesquioxides are masking mineral surfaces and are factors responsible for lowering and increasing pH₀ values, respectively. Regression correlation (R² = 0.87^??) showed that for every 1% organic C may decrease 1.0 unit of pH₀ value. The pH₀ values, after SOM removal, are in the order of Sungai Mas ～ Segamat > Kuantan Series. This suggests that the serpentinite and andesite-derived soils have achieved a relatively similar degree of chemical weathering and they are more weathered than the basalt-derived soil. The charge measured by corrected back-titration is 1.5–3.8 cmol_c kg^? 1 at pH 4.5 and increases to 4.2–10.8 cmol_c kg^? 1 at pH 6.5, indicating that the three Oxisols mainly bear variable charge. Charge overestimation resulted from dissolution and hydrolysis reactions during potentiometric titration ranges from 36 to 160%, depending on pH values (the lower the pH the higher is the overestimation). Hence, back-titration is a reliable technique to correct charge overestimation when using the traditional potentiometric titration for highly weathered tropical soils.     

Effect of P application on CEC,amounts of extractable nutrients,and corn yield in a Hydric Melanudand in the Philippines

In soils, next to nitrogen, phosphorus (P) is the second major growth-limiting factor for plants (Fox 1979). It is probably the most deficient soil-derived plant nutrient in Oxisols, Ultisols, acid Alfisols, and Andisols and the proper development of crops is frequently impossible without the application of P. P deficiency is a major nutritional problem in variable charge soils, especially the Andisols, where applied P is usually converted into an unavailable form. The P added to Andisols in fertilizers is readily sorbed to form noncrystal-line aluminum phosphate materials (Nanzyo 1987). Most uncultivated Andisols also show a very low P fertility and very low recovery of applied P fertilizers by crops (Shoji et al. 1993). In fact, P fixation is one of the growth-limiting factors for crops cultivated in Brazil (Fageria and Filho 1987).     

The effects of time of incubation on the relation between charge and pH of soil

Samples of two Andisols and two Ultisols from southern Chile were incubated with acid or with lime for up to 60 d at 25°C or for 1 day at 40°C or at 60°C. The changes in positive and negative charge were measured. The Andisols reacted slowly at 25°C. They lost protons to the solution at high _pH, thus increasing the negative charge on the soils and decreasing the pH of the solution. They gained protons at low _pH, thus increasing the positive charge on the soils and increasing the _pH of the solution. The Ultisols reacted more quickly but again charge and _pH changed through time. For all samples, the rate of reaction was increased by incubating at 60°C. Brief incubation at 60°C produces a similar relation to that obtained after longer incubation at 25°C. This provides a convenient means by which measurements can be made more quickly.     

Classifying soils at the ultimate stage of weathering in the tropics

Oxisols cover ≈ 23% of the land surface in the tropics and are utilized extensively for agricultural purposes in the tropical countries. Under the variable input types of agricultural systems practiced locally, some of these soils still appear to have problems in terms of proper soil classification and subsequently hinder attempts to implement sustainable agro‐management protocols. The definition for Oxisols in Soil Survey Staff (1999) indicates that additional input is still required to refine the definition in order to resolve some of the outstanding classification problems. Therefore, the objective of this study is to examine the properties of some Oxisols and closely related soils in order to evaluate the classification of these soils. Soils from Brazil, several countries in Africa, and Malaysia were used in this study. Field observations provided the first indication that some of the presently classified kandi‐Alfisols and kandi‐Ultisols were closer to Oxisols in terms of their properties. Water‐retention differences and apparent CEC of the subsurface horizons also supported this idea. The types of extractable Fe oxides and external specific surface areas of the clay fractions showed that many kandic horizons have surface properties that are similar to the oxic horizons. Micromorphology indicated that the genetic transition from the argillic to the oxic involves a diminishing expression of the argillic. Properties, such as CEC, become dominant. The kandic horizon is therefore inferred as a transition to the oxic horizon. It is proposed that the Oxisols be keyed out based only on the presence of an oxic horizon and an iso–soil temperature regime. The presence of a kandic horizon will be reflected at lower levels in Oxisols. The Oxisols will now be exclusive to the intertropical belt with an iso–soil temperature regime. The geographic extend of the Oxisols would increase and that of kandi‐Alfisols and Ultisols would decrease. A few kandi‐Alfisols and Ultisols in the intertropical area will have low CEC which would fail the weatherable mineral contents. The kandic subgroups of some Alfisols and Ultisols will be transitional between the low (< 16 cmol_c [kg clay]^–1)‐ and high (> 24 cmol_c [kg clay]^–1)‐activity clay soils. The proposed changes to classification will contribute to a better differentiation of the landscape units in the field. Testing of the proposed classification on some Malaysian soils showed that the new definition for Oxisols provides a better basis for the classification of the local soils and the development of meaningful soil‐management groups for plantations.     

一种改进的盐滴定法测定氧化锰矿物的电荷零点

以针铁矿为对照，采用电位滴定法（PT）、快速电位滴定法（RPT）、盐滴定法（ST）和改进的盐滴定法（IST）研究了几种氧化锰矿物的电荷零点（PZC）。结果表明：PT法测得酸性水钠锰矿、锰钾矿和钙锰矿的PZC分别为1．18、1．98和3．98，RPT法的结果分别为1．75、2．10和3．50。而ST法测得氧化锰矿物的△pH与横轴没有交点，但延长加入0．5ml 2mol L^-1 KCI溶液后的平衡时间至24h，获得上述样品的PZC分别为0．98、1．72和3．31。经典ST法通过改进，可以测定氧化锰矿物的PZC，其方法简单，结果与PT、RPT法有可比性。     

Enzyme activities as affected by soil properties and land use in a tropical watershed

Enzyme activities play key roles in the biochemical functioning of soils, including soil organic matter formation and degradation, nutrient cycling, and decomposition of xenobiotics. Knowledge of enzyme activities can be used to describe changes in soil quality due to land use management and for understanding soil ecosystem functioning. In this study, we report the activities of the glycosidases (β-glucosidase, α-galactosidase, and β-glucosaminidase), acid phosphatase, and arylsulfatase, involved in C (C and N for β-glucosaminidase), P, and S cycling, respectively, as affected by soil order and land use within a watershed in north-central Puerto Rico (Caribbean). Representative surface soil (0–15 cm) samples were taken from 84.6% of the total land area (45,067 ha) of the watershed using a completely randomized design. The activity of α-galactosidase was greater in soils classified as Oxisols than in soils classified as Ultisols and Inceptisols, and it was not affected by land use. The activity of β-glucosidase was greater in Oxisols compared to the Inceptisols and Ultisols, and it showed this response according to land use: pasture > forest > agriculture. The activity of β-glucosaminidase was higher in Oxisols than the other soil orders, and it was higher under pasture compared to forest and agriculture. Acid phosphatase and arylsulfatase activities were greater in Oxisols and Ultisols than in Inceptisols, and they decreased in this order due to land use: forest = pasture > agriculture. As a group, β-glucosaminidase, β-glucosidase, and acid phosphatase activities separated the sites under forest and pasture from those under agriculture in a three-dimensional plot. Thus, enzyme activities in Inceptisols under agriculture could be increased to levels comparable to other soil orders with conservative practices similar to those under pasture and secondary forest growth. Our findings demonstrate that within this watershed, acid and low fertility soils such as Oxisols and Ultisols have in general higher enzyme activities than less weathered tropical soils of the order Inceptisols, probably due to their higher organic matter content and finer texture; and that the activities of these enzymes respond to management with agricultural practices decreasing key soil biochemical reactions of soil functioning.     

Comparison of Copper,Manganese, and Zinc Extraction with Mehlich 1, Mehlich 3, and DTPA Solutions for Soils of the Brazilian Coastal Tablelands

Deficiency of micronutrients is increasing in crop plants in recent years in Oxisols and Ultisols in the tropics. The predominant soils in the coastal tablelands of Brazil are Ultisols and Oxisols, with low cation exchange capacity and kaolinitic clay mineralogy. Soil copper (Cu), manganese (Mn), and zinc (Zn) extracted by the Mehlich 1 solution, currently used in the regional soil-testing laboratories, were compared with those extracted by the Mehlich 3 and diethylenetriaminepentaacetic acid (DTPA) solutions in a greenhouse experiment with 10 soil samples (0–20 cm deep) collected from representative Ultisols and Oxisols from various locations in the region. Corn was grown as a test crop, and its dry matter and micronutrient uptake was measured at 30 days of growth. Soil Cu, Mn, and Zn extracted with the three solutions were significantly correlated (0.65–0.95 range for r values), with the Mehlich 3 solution extracting greater quantities than the Mehlich 1 and DTPA solutions. Zinc and Cu taken up by corn plants were significantly related to their soil-extractable levels measured at harvest with all three of the solutions, except for Zn DTPA. However, similar relations between plant uptake and soil extractable Mn were poor, except for DTPA extracting solution.     

Surface charge characteristics of volcanic‐ash‐soils from Spain. Effect of organic matter and mineralogical composition

Abstract

Surface charge characteristics of several Spanish Andosols were investigated. The relationship between these characteristics and the mineralogical composition and organic matter content of the soils were also taken into account.

The electro‐chemical behaviour of the soils was similar to that of many metallic oxides, in which the surface charge is determined exclusively by the activity of potential determining H and OH^‐ ions in the bulk solution.

The ZPC of the soils varies between 3.7 and 5.1 and always remains below the zero point of titration (between 0.6 and 10 meq/100g). These low ZPC values seem to be related to the high content of organic matter in the soils, but no clear correlation between both values has been found.

The mineralogical composition and the percentage of amorphous oxides in the soils, on the other hand, had an effect on the charge characteristics’. A correlation coefficient (r=0.801) was found between the Al₂O₃% and ZPC value of the soils.     

土壤胶体中氧化物表面性质的初步研究

我们以蒙脱石为对照,测定了以水合氧化物型表面为主的试样四个方面的表面性质:电荷零点(ZPC)、滴定曲线、羟基释放量及不同pH条件下对NH₄⁺和Cl^-的吸附。结果表明,在pH 4—9范围内,氧化物型表面提供可变正电荷1—8 meq/100g,提供可变负电荷3—15meq/100g;三二氧化物使土壤的ZPC升高,而永久负电荷和有机质使土壤的ZPC降低。作为粘土酸,氧化物表面的酸性较弱,其表面质子逐步解离,使滴定曲线不出现突跃。氧化物表面的羟基和水合基密度很高,增加了土壤对离子的专性吸附能力。土壤中常见的氧化物型表面主要来自Fe,Al氧化物及非品质矿物,就它们的化学式而言,主要有Si—OH、Fe—OH及Al—OH,它们可存在于同一土壤中,在土壤常见的pH范围内,具有低ZPC的Si—OH亚表面提供可变负电荷,具有高ZPC的Fe—OH和Al—OH亚表面提供可变正电荷。     

Zero Point of Charge of Organo—Mineral Complexes

Five soil sapmles collected from China and two soil samples from Pakistan with widely different origin and characterstics were used to study the zero point of charge(ZPC) of soil colloids.The results showed that the value of zero point of charge of H-clay complexes was lower than that of H-clays in all the samples.Natural clay complexes had the highest ZPC as compared to -Hclay complex and H-clay in alfisol,closer to H-clays rather than H-clay complexes in oxisol and udult.The Delta Value of ZPT(zero point of titration )to ZPC was higher in H-Clay complexes than in H-Clays.     

不同pH条件下黄壤胶体凝聚的动态光散射研究

土壤胶体的凝聚或分散紧密地联系着许多环境问题,并受胶体表面电荷性质的调控.以黄壤为实验材料,利用动态光散射技术研究pH作用下该可变电荷胶体颗粒的凝聚动力学.结果发现:土壤胶体的凝聚与否强烈依赖于pH.不同浓度HNO3和KOH诱发的土壤胶体凝聚均表现出慢速和快速凝聚特征,在快速凝聚中,HNO3作用较KOH作用的黄壤胶体平均凝聚速率更高、变化更快,表明表面电荷中和诱发的凝聚远大于压缩双电层诱发的凝聚.通过快速平均凝聚速率变化的反转点对应的pH,估计电荷零点(Zero pointof charge,ZPC),提供了一个实验测定ZPC的新方法.     

Nitrogen flux patterns through Oxisols and Ultisols in tropical forests of Cameroon,Central Africa

We lack an understanding of nitrogen (N) cycles in tropical forests of Africa, although the environmental conditions in this region, such as soil type, vegetation, and climate, are distinct when compared with other tropical forests. Herein, we simultaneously quantified N fluxes through precipitation, throughfall, and 0-, 15-, and 30-cm soil solutions, as well as litterfall, in two forests with different soil acidity (Ultisols at the MV village (exchangeable Al³⁺ in 0–30 cm, 126 kmol_c ha^–1) and Oxisols at the AD village (exchangeable Al³⁺ in 0–30 cm, 59.8 kmol_c ha^–1)) over 2 years in Cameroon. The N fluxes to the O horizon via litterfall plus throughfall were similar for both sites (MV and AD, 243 and 273 kg N ha^–1 yr^–1, respectively). Those values were remarkably large relative to other tropical forests, reflecting the dominance of legumes in this region. The total dissolved N flux from the O horizon at the MV was 28 kg N ha^–1 yr^–1, while it was 127 kg N ha^–1 yr^–1 mainly as NO₃^–-N (~80%) at the AD. The distinctly different pattern of N cycles could be caused by stronger soil acidity at the MV, which was considered to promote a superficial root mat formation in the O horizon despite the marked dry season (fine root biomass in the O horizon and its proportion to the 1-m-soil profile: 1.5 Mg ha^–1 and 31% at the MV; 0.3 Mg ha^–1 and 9% at the AD). Combined with the published data for N fluxes in tropical forests, we have shown that Oxisols, in combination with N-fixing species, have large N fluxes from the O horizon; meanwhile, Ultisols do not have large fluxes because of plant uptake through the root mat in the O horizon. Consequently, our results suggest that soil type can be a major factor influencing the pattern of N fluxes from the O horizon via the effects of soil acidity, thereby determining the contrasting plant–soil N cycles in the tropical forests of Africa.     

Linking Amazonian secondary succession forest growth to soil properties

The Amazon Basin has suffered extensive deforestation in the past 30 years. Deforestation typically leads to changes in climate, biodiversity, hydrological cycle, and soil degradation. Vegetation succession plays an important role in soil restoration through accumulation of vegetation biomass and improved soil/plant interaction. However, relationships between succession and soil properties are not well known. For example, how does vegetation succession affect nutrient accumulation? Which soil factors are important in influencing vegetation growth? What is the best way to evaluate soil fertility in the Amazon basin? This paper focuses on the interrelationships between secondary succession and soil properties. Field soil sample data and vegetation inventory data were collected in two regions of Brazilian Amazonia (Altamira and Bragantina). Soil nutrients and texture were analyzed at successional forest sites. Multiple regression models were used to identify the important soil properties affecting vegetation growth, and a soil evaluation factor (SEF) was developed for evaluating soil fertility in Alfisols, Ultisols, and Oxisols, which differ in the ways they affect vegetation growth. For example, the upper 40 cm of soil is most important for vegetation growth in Alfisols, but in Ultisols and Oxisols deeper horizons significantly influence vegetation growth rates. Accumulation of vegetation biomass increased soil fertility and improved soil physical structure in Alfisols but did not completely compensate for the nutrient losses in Ultisols and Oxisols; however, it significantly reduced the rate of nutrient loss. Copyright © 2002 John Wiley & Sons, Ltd.     

SURFACE CHEMISTRY OF THE HYDRANDEPTS AND ITS RELATION TO NITRATE ADSORPTION AS AFFECTED BY PROFILE DEPTH AND DEHYDRATION1

The pH₀ and ZPC of two Hydiandepts were determined by potentiomettic titiation in NaCl and by ion adsorption measurements from NH₄NO₃, respectively. The decrease of pH, pH₀, and ZPC due to drying was explained by the hydrolysis reaction. Partial drying, high organic matter content, and low Al₂ O₃ concentration in the surface soil were responsible for its low pH, pH₀ and ZPC. The high pH₀ of subsoils was attributed to the presence of amorphous aluminosilicates and mixed polymeric gels of Fe(III) and A1 with high water content. The significant decrease of nitrate adsorption due to dehydration is discussed in relation to the change in pH, pH₀, ZPC, and surface area on drying.     

有机-无机复合体的电荷零点

Five soil samples collected from China and two soil samples from Pakistan with widely different origin and characteristics were used to study the zero point of charge (ZPC) of soil colloids. The results showed that the value of zero point of charge of H-clay complexes was lower than that of H-clays in all the samples. Natural clay complexes had the highest ZPC as compared to H-clay complex and H-clay in alfisol, closer to H-clays rather than H-clay complexes in oxisol and udult. The delta value of ZPT (zero point of titration) to ZPC was higher in H-clay complexes than in H-clays.