不同氧化还原条件下土壤性质对非石灰性土壤中锌溶解动力学的影响

Zinc(Zn) deficiency in paddy soils is often a problem for rice production.Flooding can decrease metal availability in some noncalcareous soils through different mechanisms associated with soil redox status.Laboratory experiments were performed in order to better understand the processes that governed the dynamics of Zn in non-calcareous paddy soils at varying redox potentials(Eh).Airdried non-calcareous soil samples collected from four different paddy field sites in the Philippines were submerged and incubated in a reaction cell with continuous stirring and nitrogen purging for 4 weeks,and then purged with compressed air for another week to reoxidize the system.The Eh of the four soils started at 120 to 300 mV,decreased to —220 to —300 mV after 100 to 250 h of reduction,and was maintained at this low plateau for about 2 weeks before increasing again upon reoxidation.Zinc solubility showed contrasting patterns in the four soils,with two of the soils showing a decrease in soluble Zn as the Eh became low,probably due to zinc sulfide(ZnS) precipitation.In contrast,the other two soils showed that Zn solubility was maintained during the reduced phase which could be due to the competition with iron(Fe) for precipitation with sulfide.Differences in the relative amounts of S,Fe,and manganese(Mn) oxides in the four soils apparently influenced the pattern of Zn solubility after flooding.     

The solubility of cations in soils

Water-soluble and exchangeable basic cations, and electrical conductivity, were measured in temperate and tropical soils. The ‘availability’ of cations in temperate soils is a function of both the amounts of exchangeable ions and the electrical conductivity of the solution, especially for divalent cations. In tropical soils the solubility of Ca and Mg seems less clear. The implications for some management problems are discussed.     

Aluminium sulphate solubility in acid forest soils in Denmark

Ion leaching in 3 sandy spruce forest soils of different origin and pH was investigated in the laboratory. Zero-tension lysimeters containing undisturbed soil columns of varying soil depth were subjected to H₂SO₄ loadings for a period of 9 weeks. The analysis of the resulting leachate supports the hypothesis that Al-sulphate minerals may form in acidic soils when exposed to acid (H₂SO₄) deposition. In the B horizon of a glaciofluvial sandy soil (pH 4.2), both H⁺ and sulphate ions were retained to maintain 2pH + PSO₄ = 11.9 in the leachate solutions. This relation between H⁺ and sulphate activity may be due to an adsorption mechanism or a precipitation mechanism. The precipitation mechanism is favored by the good fit of leachate composition to the conditions for jurbanite [AlOHSO₄] formation from gibbsite [Al(OH)₃]. In the B horizon of a sandy till at pH 3.7, the Al in soil solution (0.5 mmol L^?1) was leached with sulphate. As the sulphate load was increased, some sulphate was retained. This may also be due to the dissolution and precipitation of an Al-sulphate mineral. The ion activity products of leachate solutions from the B horizon of this soil were close to the pK_s reported for jurbanite. The conditions for the possible existence and/or formation of Al-sulphate minerals in acidic soils are discussed.     

Minerals controlling arsenic distribution in floodplain soils

As a consequence of intensive mining of the western Erzgebirge since medieval times, floodplain soils of the Mulde river contain large concentrations of arsenic (As) (>50 mg kg⁻¹). Arsenic in soil is often bound to poorly crystalline Fe and Mn (hydr)oxides, which may dissolve under reducing conditions. Part of the As may also exist in primary minerals, predominately sulphides, or in secondary minerals formed upon weathering. In order to better understand the impact of seasonal flooding, we surveyed As‐bearing mineral phases, especially of iron (Fe) (hydr)oxides. Because Fe (hydr)oxides are clay‐sized, soil samples were fractionated into six particle‐size fractions. The fractions were digested with aqua regia for determination of total element concentrations, extracted with hydroxylammonium chloride (NH₃OHCl; selective for Mn (hydr)oxides and NH₄ oxalate), and analysed by X‐ray diffraction and scanning electron microscopy. The largely similar distribution of As and lead (Pb) suggested the potential co‐existence of the two elements in primary or secondary mineral phases. However, neither As–Pb minerals nor any other As mineral were detected. Association with Mn oxides was negligible. The predominant As‐bearing phases were poorly crystalline Fe (hydr)oxides, which also incorporated large amounts of Pb and were affected by redox dynamics.     

The control of aluminium solubility in some acidic Australian soils

The variation in the solubility of aluminium in some acid soils of south-eastern Australia has been investigated. The hypothesis was that leaching of silicic acid influenced the extent of clay decomposition, and hence aluminium solubility, in accord with Le Chatelier's principle. In lower rainfall areas (< 800 mm) control of Al solubility was consistent with a poorly crystalline kaolinite as the source phase, while at higher rainfall (> 1200 mm) it was consistent with gibbsite control. However, soluble silica concentrations were too high for gibbsite and kaolinite to be thermodynamically stable phases. The hypothesis was modified to take account of a quasi-equilibrium in the open soil system, in which clay dissolution and A1 solubility appear to depend on the relative rates of H⁺ input and of silica leaching. These may result in a supersaturated, or possibly even undersaturated system, at any point in time. The relative sizes of the organic sink and mineral Al source determine the influence of organic matter on Al solubility.     

Modelling pH buffering and aluminium solubility in European forest soils

The pH buffering and aluminium solubility characteristics of acid soil are important in determining the soil's response to changes in precipitation acidity. The chemistry of soil organic matter (humic substances) plays a key role in both processes, yet is complex and still poorly understood. Nevertheless, models of humic substance chemistry have been developed, one of which is WHAM–S, which contains a model (Model V) of proton and metal binding at discrete sites on humic substances and considers electrostatic effects on the binding strength. Here we have tested the ability of WHAM–S to model solution pH and Al using batch titration studies on organic and mineral soil horizons from forested sites in Norway, Germany and Spain, with ambient pH values from 3.73 to 5.73. We optimized the model predictions by adjusting the amounts of soil aluminium and humic substances within defined limits, taking the contents of copper chloride‐extractable Al and the base‐extractable organic matter as starting values. The model simulated both pH and dissolved Al well with optimized amounts of aluminium and humic substances within the defined limits (root mean squared error for pH from 0.01 to 0.22, for p[Al]_aq (total dissolved Al) from 0.03 to 0.49, five data points). Control of dissolved Al by dissolved organic matter was important particularly at above‐ambient pH. In two mineral horizons we improved the fits by assuming that Al could precipitate as Al(OH)₃. The optimized model also gave reasonable predictions of pH and dissolved Al in supernatants obtained by repeated leaching of the soil horizons. The results show that humic substances dominate the control of pH and dissolved Al in most of the horizons studied. Control by Al(OH)₃ occurs but is the exception.     

Nitrification in three soils amended with zinc sulfate

Zinc as ZnSO₄ was added to three soils at rates of 0, 10, 100 and 1000 μg Zn g^?1 soil. The soils were uniformly treated with 100 μg Ng^?1 as nh₄cl, incubated at 30°C and NH₄⁺-N and (NO₃^? + NO₂^?)-N determined weekly for 7 weeks. Nitrification in all three soils was totally inhibited by 1000 μg Zn g^?1. At the 100 μg Zn g^?1 rate, nitrification was significantly reduced in two of the three soils during some part of the incubation. This differential effect on nitrification at the 100 μg Zn g^?1 rate was related to differences in soil properties. These results imply that, with respect to nitrification, care should-be taken not to apply Zn-containing materials indiscriminately to soils.     

Solubility and speciation of zinc in calcareous soils

Water, Air, & Soil Pollution - The objective of this study was to evaluate the formation of a probable Zn solid phase in soils. Thermodynamic solubility isotherms revealed that ZnFe2O4, Zn2SiO4...     

Fractionation of zinc in some New Zealand soils

Abstract

The amounts and forms of zinc in twenty surface soils from Canterbury and Southland, New Zealand were determined using a sequential fractionation scheme. Total soil zinc concentrations ranged from 38.1 mg#lbkg^‐1 to 113.8 mg#lbkg^‐1. Although the proportions of zinc found in individual fractions varied between soils, on average approximately 3% occurred as exchangeable zinc, 5% as organic‐bound zinc, 9%, 18%, 24% was associated with manganese, amorphous iron and crystalline iron oxides, respectively, and 40% was in the residual fraction. In a group of soils formed in greywacke alluvium or loess, exchangeable zinc was inversely related to soil pH. Within the same group of soils, those of similar age with greater concentrations of total and organic‐bound zinc were present in imperfectly‐ and poorly‐drained soils compared with well‐drained soils. Zinc extracted from the soils with a range of reagents used to assess ‘plant available’ zinc was correlated strongly with the concentrations of zinc present in the exchangeable and organic‐bound zinc fractions.     

Aluminium solubility mechanisms in moderately acid Bs horizons of podzolized soils

The processes controlling the retention and release of aluminium in acid forest soils are still subject to controversy, and therefore a universal hypothesis as to what mechanisms are operating has not been firmly established. By studying the Bs horizons of Swedish and Swiss podzolized soils, and by analysing data in the literature, we have found that aluminium hydroxide, and in some cases also poorly ordered imogolite, may control Al solubility in moderately acid (pH > 4.2–4.3) Bs horizons. The strongest evidence in support of the presence of a quickly reacting Al(OH)₃ pool came from the temperature dependence of Al solubility in a Bs horizon, which was consistent with the reaction enthalpy of an Al(OH)₃ phase such as gibbsite, and from the observation that the ion activity product for Al(OH)₃ was the same regardless of whether equilibrium was reached from over‐ or undersaturation. The pool of Al(OH)₃ is commonly small and may be completely dissolved after large additions of acid. This may be explained by the continuing redissolution of reactive Al(OH)₃ to form less soluble imogolite‐type phases. By using the same methods it was found that soil suspensions did not reach equilibrium with poorly ordered imogolite even after 17 days. Thus, imogolite probably does not control Al solubility in the short term in many soils despite the common occurrence of this mineral. This is due to the relatively slow kinetics of imogolite formation and dissolution, especially at low temperatures and at small solution H₄SiO₄ concentrations.     

Mechanisms of pentachlorophenol adsorption by soils

The precipitation and adsorption of pentachlorophenol (PCP) on allophane was confirmed by adsorption experiments carried out at various pll values. The precipitation of PCP took place around base-unsaturated clay particles when the concentration of PCP exceeded solubility. The adsorption of PCP involves anion exchange reaction as well as physical adsorption due to van der Waals' force, and the PCP adsorbed as anions is released with greater when washed with deionized water.

Allopbane of Andosols appears to adsorb PCP largely as anions, while humus, balloysite, and allophane (molar SiO₂/Al₂O₃ ratio about 2) seem to adsorb PCP mostly as molecules. The precipitation of PCP in mlcell might participate in the adsorption. PCP mixed with layer silicate day minerals such as illite, montmorillonite, and kaolinite sublimated by about 200°C. In contrast to this, PCP mixed or adsorbed on allophane did not sublimate by 200°C but burnt out between 250 and 500°C showing a strong exothermic reaction.     

The distribution of zinc in selected soils in Louisiana

Abstract

The zinc (Zn) content of ten selected soils in Louisiana was partitioned into the following fractions: water‐soluble, exchangeable, chelated, organic and residual. In seven of the soils, water‐soluble > exchangeable < chelated < organic < residual Zn. In three of the soils, water‐soluble < exchangeable < chelated < organic < residual Zn.

The ten soils contained an average of 1.7, 0.9, 2.6, 4.4 and 86.4 per cent of the total in the water‐soluble, exchangeable, chelated, organic and residual mineral Zn fractions respectively.     

The solubility and plant uptake of chromium from heated soils

Abstract

The effects of heating on the solubility and plant uptake of Cr from three soils variously influenced by ultramafic parent materials were evaluated. Chromium extracted by 2 M HNO₃ and by M KCl increased with degree of serpentine influence and with temperature of ignition in air. In contrast, solubility of the element was only slightly influenced by ignition in a N₂ atmosphere. Heating enhanced the solubility of soil Cr by at least two oxidative reactions: (1) the destruction of a relatively heat‐stable, probably organic, complex with the release of Cr(III), and (2) the oxidation of free Cr(III) to Cr(VI).

Corn (Zea mays L.) grew poorly in the ignited soils, but normally in ignited and leached soils. Growth depression from ignition was related to shoot Cr levels (r² = 0.494) and is attributed to the readily absorbed and translocated chromate formed at elevated temperatures. Under more usual soil conditions, as in the untreated and ignited then leached soils, the less readily soluble forms of the element are the principal contributors to available Cr.     

伊朗一些石灰性土壤中锌解吸动态研究

Desorption of zinc (Zn) from soil is an important factor governing Zn concentration in the soil solution and Zn availability to plants. Batch experiments were performed to study the kinetics of Zn desorption by diethylenetriaminepentaacetic acid (DTPA) from 15 calcareous soil samples taken from Golestan Province in northern Iran. Soils were equilibrated with 0.005 mol L-1 DTPA solutions for 0.25 to 192 h. The results showed that the extraction process consisted of rapid extraction in the first 2 h followed by much slower extraction for the remainder of the experiment. Desorption kinetic data was fitted to pseudo-first-order kinetic model. The experimental data were found to deviate from the straight line of the pseudo-first-order plots after 2 h. The model of two first-order reactions was fitted to the kinetic data and allowed to distinguish two pools for Zn: a labile fraction (Q1 ), quickly extracted with a rate constant k1 , and a slowly labile fraction (Q2 ), more slowly extracted with a rate constant k2 . The applicability of pseudo-second-order model in describing the kinetic data of Zn desorption was also evaluated.     

Characterization of zinc adsorption sites in two mineral soils

The adsorption of Zn, as compared with Mg, on two mineral soils, which differed in their major cation-exchange materials and with and without Ca-saturation, was measured in the presence of free CaCl₂.

The adsorption of Zn as well as Mg occurred on cation-exchange sites. The Zn adsorption data conformed to a two-term Langmuir equation. The presence of two kinds of adsorption sites and their numbers and bonding energies were deduced. However, the Langmuir approach was not adopted on the basis of comparison between the total number of the adsorption sites for Zn deduced and the CEC of the soils.

As an alternative approach, the selectivity coefficient as defined by the equation:

was calculated for each adsorption equilibrium and plotted against the amount of Zn adsorbed. This [Zn]_soil plot was used to estimate the capacities of the soil to adsorb Zn with specified affinities. The value varied between 1 and 1,000, whereas the corresponding value varied only between 0.5 and 1. The value was dependent upon the amount of Zn adsorbed, the status of exchangeable cations, and the major cation-exchange materials (montmorillonite VS. allophane-imogolite) in the soils. The importance of surface OH groups in allophane-imogolite as specific adsorption sites for Zn was suggested.     

Estimation of critical limit for zinc in rice soils

Abstract

Twenty surface soil samples wore collectod from Nalnltal Tarai (foot‐ hills of Himalya) where ‘Khaira’ disease (Zn deficiency disease of rice) was prevalent. Rice (Oryza sativa L. variety IR ‐ 8) was grown in pots for 8 weeks after transplanting. Experiments were carried out to find the suitability of five soil Zn extractants viz. dilute acid (HC1 ‐ H₂SO₄) mixture, DTPA‐ (NH₄) ₂CO₃, pH 7.3, dithizono, NH₄ ‐ Ac, pH 4.6 and MgCl₂. Critical limits of available Zn in soils were established for rice crop by old and new Cate and Nelson procedures.

Zn extracted from the soil with NH₄ ‐ Ac, pH 4.6, dithlzono, MgCl₂, and DTPA‐(NH₄) ₂CO₃, pH 7.3 was significantly correlated with the uptake of Zn by the rice plants. The correlation of Zn uptake with dilute acid mixture extractable Zn was not significant. The extractant which extracted more Zn gave higher values of critical limit and vice versa. It is concluded that all extracting solutions except dilute acid mixture were found to be suitable for predicting available Zn in rice soils of Taral.     

Estimation of critical limit for zinc in rice soils

Abstract

Twenty surface soil samples were collected from Nainital Tarai (foothills of Himalya) where “Khaira”; disease (Zn deficiency of rice) is prevalent. Rice (Oryza sativa L. variety IR‐8) was grown in pots for 8 weeks after transplanting. Experiments were conducted to determine the suitability of five soil Zn extractants: dilute acid (HCl + H₂SO₄) mixture; DTPA‐(NH₄) ₂CO₃, pH 7.3; dithizone; NH₄OAc, pH 4.6; and 2N MgCl₂ to predict Zn deficiency. Critical values for soil available Zn were established for rice by the old and new Cate and Nelson procedures¹.

Zinc extracted from the soils with dithizone; NH₄OAc, pH 4.6; 0.2N MgCl₂. and DTPA‐(NH₄) ₂CO₃ pH 7.3 was significantly correlated with the uptake of Zn by the rice plants. The correlation between Zn extracted with the dilute acid (HCl + H₂SO₄) mixture and plant Zn was not statistically significant. The ex‐tractants which extracted greater quantities of Zn gave higher critical values and vice versa. It is concluded that all extracting solutions except the dilute acid (HCl + H₂SO₄) mixture were found to he suitable for predicting available Zn in rice soils of Tarai.     

Mobility and leachability of zinc in two soils treated with six organic zinc complexes

A study of soil columns was conducted to evaluate Zn movement potential in two reconstructed soil profiles. Zn-phenolate, Zn-EDDHA, Zn-EDTA, Zn-lignosulfonate, Zn-polyflavonoid, and Zn-heptagluconate were applied in the upper zone of the column. The different physicochemical properties of the two soils and the micronutrient source may influence Zn leaching, the distribution of Zn among soil fractions, and the Zn available to the plant in the depth of the layers. In Aquic Haploxeralf soil, the application of six fertilizers produced little migration and very small leaching of Zn in the soil profiles. In Calcic Haploxeralf soil, Zn-EDTA migrated and was distributed throughout the soil columns. This Zn chelate produces a loss of Zn by leaching, which was 36% of the added Zn. In the latter soil, Zn leached very little with the other five fertilizer treatments. The same as for these organic Zn complexes, the retention of added Zn indicated the potential of metal accumulation in the A(p) horizons of the two soil profiles. A large portion of applied Zn was available to plants [diethylenetriaminepentaacetic acid (DTPA) and Mehlich-3 extractable Zn] in the depths reached by the different commercial formulations. The relationship between the two methods was highly significant (Mehlich-3-Zn = 1.25 + 1.13 DTPA-Zn, R(2) = 99.19%). When Zn was added as Zn-EDTA, the amounts of the most labile fractions (water-soluble plus exchangeable and organically complexed Zn) increased throughout the entire profile column in comparison with the control columns, although in the B(t) horizon of the Aquic Haploxeralf soil they increased only slightly.     

Conditions related to solubility of rare and minor elements in forest soils

Soil solutions expelled by high‐speed centrifugation (13900 g) of intact soil sample cores at field moisture from 30 forest topsoils (A horizons of mainly Dystric and Eutric Cambisols, according to the FAO‐Unesco system) low in clay were subjected to analysis of 60 elements, using ICP‐MS and ICP‐AES. Concentrations measured were related to soil and soil solution properties assumed to be important for the solubility of elements, using stepwise regression analysis. On an average two thirds of the variability in soil solution concentration of elements were accounted for by, in particular, organic C concentrations, pH and/or nitrate concentrations of the solutions, varying among elements from 19 to 90 %. Concentrations of elements strongly positively related to soil solution acidity were Al, Be, Ge, Li, Ni, Pb, and Zn, strongly negatively related to acidity were Ca, Mo, and W. Most positively related to nitrate concentrations in soil solutions were B, Ba, Cd, Mg, Mn, and Sr; negatively were Nb, Ta, and Ti. Concentrations of organic C in the soil solutions correlated positively, often quite closely, with most of the other elements studied, including La, all the lanthanides, and with Ag, Br, Cr, Fe, Ga, Hf, Hg, In, P, Th, U, Y, and Zr. Soluble organic compounds were apparently ’︁carriers’ of these elements in the soil solution. The concentrations of elements in HNO₃ digests of the soils usually accounted for just little or no statistical variability of their soil solution concentrations.     

Influence of applied zinc and organic matter on zinc desorption kinetics in calcareous soils

Zinc (Zn) desorption from an exchange complex to solution, the release of Zn from organic matter (OM), crystalline minerals and other precipitates into the solution phase, is the process that controls Zn mobility in soils. An experiment was conducted to determine the pattern of Zn desorption and the soil characteristics affecting it. Desorption of Zn in 15 calcareous soils from southern Iran, treated with 10 mg Zn kg soil^?1 as zinc sulfate (ZnSO₄?7H₂O) and 10 g organic matter (OM) kg^?1 as feedlot cattle manure, equilibrated and extracted with diethylenetriamine pentaacetic acid (DTPA), was studied. Eight kinetic models were evaluated to describe the rate of Zn desorption of soil extracted with DTPA. There was a rapid rate of desorption during the first 4 h followed by a slower rate during the next 12 h. Two-constant rate and simple Elovich models were determined as the best models describing Zn desorption kinetics. Zinc desorption increased as Zn was applied, whereas it decreased with applied OM. The constants of the simple Elovich (β_s) and two-constant rate equations (a and b) were closely correlated with cation-exchange capacity (CEC), OM and pH, which affect Zn solubility, sorption–desorption and diffusion in soils.