Catalysis of Dissolved and Adsorbed Iron in Soil Suspension for Chromium（Ⅵ） Reduction by Sulfide

The kinetics of Cr（Ⅵ） reduction by sulfide in soil suspensions with various pHs, soil compositions, and Fe（Ⅱ） concentrations was examined using batch anaeroblc experimental systems at constant temperature. The results showed that the reaction rate of Cr（Ⅵ） reduction was in the order of red soil 〈 yellow-brown soil 〈 chernozem and was proportional to the concentration of HCl-extractable iron in the soils. Dissolved and adsorbed iron in soil suspensions played an important role in accelerating Cr（Ⅵ） reduction. The reaction involved in the Cr（Ⅵ） reduction by Fe（Ⅱ） to produce Fe（ⅡI）, which was reduced to Fe（Ⅱ） again by sulfide, could represent the catalytic pathway until about 70% of the initially present Cr（Ⅵ） was reduced. The catalysis occurred because the one-step reduction of Cr（Ⅵ） by sulfide was slower than the two-step process consisting of rapid Cr（Ⅵ） reduction by Fe（Ⅱ） followed by Fe（Ⅲ） reduction by sulfide. In essence, Fe（Ⅱ）/Fe（Ⅲ） species shuttle electrons from sulfide to Cr（Ⅵ）, facilitating the reaction. The effect of iron, however, could be completely blocked by adding a strong Fe（Ⅱ）-complexing ligand, 1,10-phenanthroline, to the soil suspensions. In all the experiments, initial sulfide concentration was much higher than initial Cr（Ⅵ） concentration. The plots of In e[Cr（Ⅵ）] versus reaction time were linear up to approximately 70% of Cr（Ⅵ） reduction, suggesting a first-order reaction kinetics with respect to Cr（Ⅵ）. Elemental sulfur, the product of sulfide oxidation, was found to accelerate Cr（Ⅵ） reduction at a later stage of the reaction, resulting in deviation from linearity for the In c[Cr（Ⅵ）] versus time plots.     

Catalysis of Manganese（Ⅱ） on Chromium（Ⅵ） Reduction by Citrate

The catalysis of manganese（Ⅱ） （Mn^2＋） on chromium（Ⅵ） （Cr^6＋） reduction by citrate was studied through batch experiments with the concentration of citrate greatly in excess of Cr^6＋ at 25 ℃ and in pH ranges of 4.0 go 5.0. Results showed that at pH 4.5 within 22 h direct reduction of Cr^6＋ by citrate was not observed, bug for the same time when Mn^2＋ （50 to 200 μmol L^-1） was added, nearly all Cr^6＋ was reduced, with the higher initial Mn^2＋ concentration having faster Cr^6＋ reduction. In the initial stage of the reaction, the Cr^6＋ reduction could be described with a pseudo-first-order kinetics equation. In the lager stage of the reaction, plots of lnc（Cr^6＋） versus t, where c（Cr^6＋） is the Cr^6＋ concentration in the reaction and t is the reaction time, deviated from the initial linear trend. The deviations suggested that the pseudo-first-order kinetics did not apply go the whole experimental period and that some reaction intermediates could have greatly accelerated Cr^6＋ reduction by citrate. The catalysis of the intermediates increased with the reaction time and gradually reached stability. Then, the plot of lnc（Cr^6＋） versus t in the presence of Mn^2＋ was linear again, with the rate constant increasing by 102 times compared with the absence of Mn^2＋. Complexation between Mn^2＋ and citrate was likely a prerequisite for the catalysis of Mn^2＋ on the reaction. Additional experiments showed that introducing eghylenediaminegegraacegic acid （EDTA） into the reaction system strongly suppressed the catalysis of Mn^2＋.     

二价锰离子对柠檬酸还原六价铬的催化作用

The catalysis of manganese(Ⅱ) (Mn²⁺) on chromium(Ⅵ) (Cr⁶⁺) reduction by citrate was studied through batch experiments with the concentration of citrate greatly in excess of Cr⁶⁺ at 25℃ and in pH ranges of 4.0 to 5.0. Results showed that at pH 4.5 within 22 h direct reduction of Cr⁶⁺ by citrate was not observed, but for the same time when Mn²⁺ (50 to 200μmol L^-1) was added, nearly all Cr⁶⁺ was reduced, with the higher initial Mn²⁺ concentration having faster Cr⁶⁺ reduction. In the initial stage of the reaction, the Cr⁶⁺ reduction could be described with a pseudo-first-order kinetics equation. In the later stage of the reaction, plots of lnc(Cr⁶⁺) versus t, where c(Cr⁶⁺) is the Cr⁶⁺ concentration in the reaction and t is the reaction time, deviated from the initial linear trend. The deviations suggested that the pseudo-first-order kinetics did not apply to the whole experimental period and that some reaction intermediates could have greatly accelerated Cr⁶⁺ reduction by citrate. The catalysis of the intermediates increased with the reaction time and gradually reached stability. Then, the plot of lnc(Cr⁶⁺) versus t in the presence of Mn²⁺ was linear again, with the rate constant increasing by 102 times compared with the absence of Mn²⁺. Complexation between Mn²⁺ and citrate was likely a prerequisite for the catalysis of Mn²⁺ on the reaction. Additional experiments showed that introducing ethylenediaminetetraacetic acid (EDTA) into the reaction system strongly suppressed the catalysis of Mn²⁺.     

外生菌根真菌Laccaria bicolor S238N增强花旗松生长及其对磷钾吸收的能力

Two variable charge soils were submerged after the addition of 30g/kg of organic matter to examine the differences in behavior between iron and manganese with respect to reduction and the distribution of different froms of the reduced elements.The reduction of manganese proceeded almost synchronously with the fall in redox potential,while the reduction of iron showed a remarkable lag behind the Eh change.Once formed,the distribution of water-soluble,exchangeable and precipitatied forms of ferrous iron was controlled by pH,CEC of the soil and total concentration of the element.For manganous ions,the proportions of water-soluble and exchangeable forms in total Mn^2 were larger than those for ferrous ions.The reduction of the two elements led to a mobilization of them,and such effect persisted even after drying of the soil,i.e.,the content of amorphous Fe became higher than that of the original soil.     

VA菌根对土壤酸度的耐性

The ammonification,nitrifcation and denitrification in maize rhizosphere of alluvial sols were compared with those in the bulk soil after exposure to different kinds of heavy metals.The addition of cadmium at low levels (2 mg kg^-1 and 5 mg kg^-1）could stimulate the ammonification and nitrification in the soils,while inhibition influences were found at high levels of Cd addition (10 mg kg^-1 and 20mg kg^-1），The relationship between microbial activity and cadmium concentration varied with the kind of microorganisms.The nitrifying bacteria were more sensitive to cadmium pollution than the ammonifying bacteria.When Cd( Ⅱ），Cu（Ⅱ）and Cr（Ⅵ）wer compared at the same addition concentration of 20 mg kg^-1 soil,Cd(Ⅱ） was the most effective inhibitor of ammonification and denitrification. among the three investigated heavy metals,and Cr（Ⅵ）had the most strong inhibitory influence on the nitrifying bacteria.The microbial activities in rhizosphere were higher than those in the bulk soil for most of the treatments.Cr(Ⅵ)proved to be the most effective in enhacing the microbial activities in rhizosphere,and this could be caused by the poitive reduction of Cr(Ⅵ）to Cr(Ⅲ）in rhizosphere,and the relatively sufficient existence of organic matter which intensified the adsorption of the metal,It seemed that the rhizosphere had some mitigation effect on heavy metal toxicity.     

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.     

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.     

黑土轻组分C与团聚体水稳性的关系

To evaluate the role of kaolinite and variable charge soils on the hydrolytic reaction of Al, the hydrolysis of Al ions in suspensions of a kaolinite and an Oxisol influenced by organic anions was investigated using changes of pH, Al adsorption, and desorption of pre-adsorbed Al. Kaolinite and the Oxisol promoted the hydrolytic reaction of Al above a certain initial Al concentration （0.1 mmol L^-1 for kaolinite and 0.3 mmol L^-1 for the Oxisol）. The Al hydrolysis accelerated by kaolinite and the Oxisol increased with an increase in initial concentration of Al and was observed in the range of pH from 3.7 to 4.7 for kaolinite and 3.9 to 4.9 for the Oxisol. The acceleration of Al hydrolysis also increased with the increase of solution pH, reached a maximum value at pH 4.5, and then decreased sharply. Al hydrolysis was promoted mainly through selective adsorption for hydroxy-Al. Soil free iron oxides compensated a portion of the soil negative charge or masked some soil surface negative sites leading to a decrease in Al adsorption, which retarded acceleration to some extent. For the Oxisol organic anions increased the proportion of adsorbed Al^3＋ in total adsorbed Al with the increase in soil negative surface charge and eliminated or reduced the acceleration of Al hydrolysis. Different organic anions inhibited the hydrolysis of Al in the order： citrate 〉 oxalate 〉 acetate （under initial pH of 4.5）. The formation of Al-organic complexes in solution also inhibited the hydrolysis of Al.     

高岭石和氧化土悬液中铝的水解行为及有机酸对铝水解反应的影响

To evaluate the role of kaolinite and variable charge soils on the hydrolytic reaction of Al, the hydrolysis of Al ions in suspensions of a kaolinite and an Oxisol influenced by organic anions was investigated using changes of pH, Al adsorption, and desorption of pre-adsorbed Al. Kaolinite and the Oxisol promoted the hydrolytic reaction of Al above a certain initial Al concentration (0.1 mmol L^-1 for kaolinite and 0.3 mmol L^-1 for the Oxisol). The Al hydrolysis accelerated by kaolinite and the Oxisol increased with an increase in initial concentration of Al and was observed in the range of pH from 3.7 to 4.7 for kaolinite and 3.9 to 4.9 for the Oxisol. The acceleration of Al hydrolysis also increased with the increase of solution pH, reached a maximum value at pH 4.5, and then decreased sharply. Al hydrolysis was promoted mainly through selective adsorption for hydroxy-Al. Soil free iron oxides compensated a portion of the soil negative charge or masked some soil surface negative sites leading to a decrease in Al adsorption, which retarded acceleration to some extent. For the Oxisol organic anions increased the proportion of adsorbed Al³⁺ in total adsorbed Al with the increase in soil negative surface charge and eliminated or reduced the acceleration of Al hydrolysis. Different organic anions inhibited the hydrolysis of Al in the order: citrate > oxalate > acetate (under initial pH of 4.5). The formation of Al-organic complexes in solution also inhibited the hydrolysis of Al.     

活化过硫酸盐和芬顿反应修复有机磷农药污染土壤的比较研究

Organophosphorus pesticides (OPs) are one of the most regular pollutants and frequently detected in the contaminated sites,so developing an efficient method for the treatment of OPs is highly required.The aim of the present study was to compare the effectiveness of persulfate (PS) activation and Fenton reaction in remediating the soil polluted with OPs.The polluted soil used in this study was sampled from an abandoned insecticide factory in Nantong,Jiangsu Province of China,mainly containing chloropyrifos (CP) and 4-bromo-2-chlorophenol (BCP,the raw material of profenofos) with total concentration of about 30 000 mg kg-1.The results showed that both BCP and CP were efficiently degraded by base activation of PS,and increasing the ratio of NaOH/PS enhanced CP degradation,but slightly decreased BCP degradation.The greatest degradation rates for CP and BCP were 92％ and 97％,respectively,with 7.0 mol L-1 NaOH and 0.21 mol L-1 PS and a soil-to-liquid ratio of 1:1.Furthermore,ferrous iron activation of PS also degraded BCP efficiently,but only 60％ of CP was degraded under the same reaction conditions.These results indicated that base activation of PS was more feasible than Fe2+ activation and Fenton reaction in remediating the soil polluted with OPs.The high degradation rate for CP may be linked to the initial hydrolyzation of CP by base to 3,5,6-trichloro-2-pyridinol,which can be further rapidly degraded by free radicals generated from base activation of PS.     

氧化节杆菌生物降解苯并芘

A pot experiment was conducted with multi-metal (Pb, Cd, Cu, and Zn) contaminated acidic soil to investigate changes in available metal burden resulting from the application of industrial wastes (fly ash and steel slag). The efficiency of amendments-induced metal stabilization was evaluated by diffusive gradients in thin films (DGT), sequential extraction, and plant uptake. The stability of remediation was assessed by an acidification test and by chemical equilibrium modeling. Addition of fly ash (20 g kg-1 ) and steel slag (3 g kg-1 ) resulted in similar increase in soil pH. Both amendments significantly decreased the concentrations of metals measured with DGT (C DGT) and the metal uptake by Oryza sativa L. Significant correlations were found between C DGT and the concentration of a combination of metal fractions (exchangeable, bound to carbonates, and bound to Fe/Mn oxides), unraveling the labile species that participate in the flux of metal resupply. The capability of metal resupply, as reflected by the R (ratio of C DGT to pore water metal concentration) values, significantly decreased in the amended soils. The C DGT correlated well with the plant uptake, suggesting that DGT is a good indicator for bioavailability. Acidification raised the extractable metal concentration in amended soil but the concentration did not return to the pre-amendment level. Equilibrium modeling indicated that the soil amendments induced the precipitation of several Fe, Al and Ca minerals, which may play a positive role in metal stabilization. Chemical stabilization with alkaline amendments could be an effective and stable soil remediation strategy for attenuating metal bioavailability and reducing plant metal uptake.     

有机物料对淹水土壤中施入的镉形态的影响

The effect of three organic materials(rice straw,Chinese milk vetch and pig manure)on the fractionation of cadmium added into two soils(a red soil and a fluvo-aquic soil) was studied using submerged incubation experiment.The organic materials increased soil soild organic carbon(SOC),pH value,the concentration of active Si in all the treatments and active Fe and Mn in some treatments.Accumulated SOC caused directly the increase of Cd bound to solid organic matter and consequently the decrease of exchangeable Cd.Higher active Si and pH,as well as lower Eh,were also responsible for the reduction of exchangeable Cd.Cd bound to mn oxide was positively correlated with pH values and rose significantly after one-month incubation,but decreased after three-month incubation.Cd bound to amporphous Fe oxide increased with the incubation time,but was not affected significantly by adding organic materials.     

电析土壤微粒悬浮液的维恩(Wien)效应及其影响因子

The electrical conductivity of suspensions and their supernatants from the electrodialyzed clay fractions of latosol, yellow-brown soil and black soil equilibrated with nitrate solutions were determined at different field strengths using a short high-voltage pulse apparatus to demonstrate the Wien effect in soil suspensions and to investigate factors affecting it. It was found that Wien effect was much stronger in suspensions with a clay content of 30 g kg-1 from the soils equilibrated with a 1 × 10-4 KNO3 solution than in their supernatants.The threshold field strength (TFS), at which the relative conductivity is equal to 1.05, i.e., the Wien effect begins to be obvious, of the yellow-brown soil suspensions (clay content of 30 g kg-1) equilibrated with different nitrate solutions of a concentration of 1 × 10-4/z mol L-1 , where z is the valence, varied with the type of nitrates, being lowest for NaNO3 (47 kV cm-1) and highest for Ca(NO3)2 (98 kV cm-1). At high field strengths (larger than 130 kV cm-1), the relative conductivities of yellow-brown soil suspensions containing different nitrates diminished in the order: NaNO3 ＞ KNO3 ＞ Mg(NO3)2 ＞ Zn(NO3)2 ＞ Ca(NO3)2. The rates and intensities of the Wien effect in the suspensions of the three soils equilibrated with 5 × 10-5 molL-1 Ca(NO3)2 solution were in the order of the yellow-brown soil ＞ the latosol ＞ the black soil. The results for the yellow-brown soil suspensions (clay concentration of 30 g kg-1) equilibrated with KNO3 solutions of various concentrations clearly demonstrated that the more dilute the solution, the lower the TFS, and the larger the relative conductivity of the suspensions at high field strengths. The results for yellow-brown soil suspensions with different clay concentrations indicated that as the clay concentration increased, the low field electrical conductivity, EC0, also increased, but the TFS decreased, and the Wien effect increased.     

4种湿地植物根系泌氧由根诱导的pH,Eh和Fe(II)变化和根际土壤中铅和锌的组分研究

A rhizobox experiment was conducted to compare iron (Fe) oxidation and changes of pH, redox potential (Eh) and fractions of zinc (Zn) and lead (Pb) in rhizosphere and non-rhizosphere soils of four emergent-rooted wetland plants (Echinodorus macrophyllus, Eleocharis geniculata, Hydrocotyle vulgaris and Veronica serpyllifolia) with different radial oxygen loss (ROL) from roots. The results indicated that all these wetland plants decreased pH and concentration of Fe(Ⅱ) but increased the Eh in the rhizosphere soils. Pb and Zn were transformed from unstable fractions to more stable fractions in the rhizosphere soils, so decreasing their potential metal mobility factors (MF). Among the four plants, E. macrophyllus, with the highest ROL and root biomass, possessed the greatest ability in formation of Fe plaque and in the reduction of heavy metal MFs in the rhizosphere soil. Wetland plants, with higher ROLs and root biomass, may thus be effective in decreasing potential long-term heavy metal bioavailabilities.     

一株在微生物燃料电池中可以利用喹啉发电的产电假单胞杆菌Q1的产电特性研究

A rhizobox experiment was conducted to compare iron (Fe) oxidation and changes of pH, redox potential (Eh) and fractions of zinc (Zn) and lead (Pb) in rhizosphere and non-rhizosphere soils of four emergent-rooted wetland plants (Echinodorus macrophyllus, Eleocharis geniculata, Hydrocotyle vulgaris and Veronica serpyllifolia) with different radial oxygen loss (ROL) from roots. The results indicated that all these wetland plants decreased pH and concentration of Fe(Ⅱ) but increased the Eh in the rhizosphere soils. Pb and Zn were transformed from unstable fractions to more stable fractions in the rhizosphere soils, so decreasing their potential metal mobility factors (MF). Among the four plants, E. macrophyllus, with the highest ROL and root biomass, possessed the greatest ability in formation of Fe plaque and in the reduction of heavy metal MFs in the rhizosphere soil. Wetland plants, with higher ROLs and root biomass, may thus be effective in decreasing potential long-term heavy metal bioavailabilities.     

影响土壤中铬, 锰的氧化还原反应的环境因素

Disposal of chromium(Cr) hexavalent form,Cr(VI),in soils as additions in organic fertilizers,liming materials or plant nutrient sources can be dangerous since Cr(VI) can be highly toxic to plants,animals,and humans.In order to explore soil conditions that lead to Cr(VI) generation,this study were performed using a Paleudult(Dystic Nitosol) from a region that has a high concentration of tannery operations in the Rio Grande do Sul State,southern Brazil.Three laboratory incubation experiments were carried out to examine the influences of soil moisture content and concentration of cobalt and organic matter additions on soil Cr(VI) formation and release and manganese(Mn) oxide reduction with a salt of chromium chloride(CrCl 3) and tannery sludge as inorganic and organic sources of Cr(III),respectively.The amount of Cr(III) oxidation depended on the concentration of easily reducible Mn oxides and the oxidation was more intense at the soil water contents in which Mn(III/IV) oxides were more stable.Soluble organic compounds in soil decreased Cr(VI) formation due to Cr(III) complexation.This mechanism also resulted in the decrease in the oxidation of Cr(III) due to the tannery sludge additions.Chromium(III) oxidation to Cr(VI) at the solid/solution interface involved the following mechanisms:the formation of a precursor complex on manganese(Mn) oxide surfaces,followed by electron transfer from Cr(III) to Mn(III or IV),the formation of a successor complex with Mn(II) and Cr(VI),and the breakdown of the successor complex and release of Mn(II) and Cr(VI) into the soil solution.     

澳洲东部三种沿海漫滩酸性硫酸盐土壤中铁一硫化物的分布

The distribution of iron monosulifde (quantified as acid volatile sulfur:SAV) was compared with geochemical properties that are known to affect its formation and accumulation in three coastal Holocene acid sulfate soils (ASS) at Tuckean Swamp,Mc Leods Creek and Bungawalbyn Swamp respectively,These properties included pH,reactive iron(FeR),pore-water sulfate(SO4^2-) and organic carbon(OC).Iron monosulfide was concentrated at the oxic/anoxic boundary,the Tuckean Swamp and McLeods Creek sites are Holocene sediments,whereas the Bungawalbyn Swamp is a Holocene peat.The concentration of SAV averaged 0.2 g kg^-1 in a 0.5m thick soil layer at the Tuckean Swamp,but was an order of magnitude lower in the oxic/anoxic transition layers at McLeods Creek and Bungawalbyn Swamp,The SAV mineral greigite(Fe3S4) was identified in the Tuckean Swamp by X-ray diffraction and scanning electron microscopy with quantitative energy dispersive X-ray analysis(SEM-EDX),Very small concentrations of greigite were also observed in the McLeods Creek,based on crystal morphology and elemental composition.The concentration of SAV was a small fraction of the total reduced sulfur,representing at most 3% of the pyrite sulfur,However,the presence of this highly reactive sulfide mineral,distributed within pores where oxygen diffusion is most rapid,has important implications to the potential rate of acid production from these sediments.     

亚热带土壤不同矿物组分中铬的吸附

Safe application of chromium (Cr)-containing organic industrial wastes to soil requires considering the ability of the soil to adsorb Cr.In this study,the maximum Cr adsorption capacity was assessed for the bulk samples and their clay and iron-free clay fractions of four subtropical soils differing in mineralogy.To this end,the samples were supplied with Cr(Ⅲ) nitrate solutions at pH 4.5 or 5.5.The results of Cr(Ⅲ) adsorption fitted to a Freundlich equation and the adsorption capacity was positively correlated with soil organic matter and iron oxide contents.The clay fractions adsorbed more Cr per unit mass than the bulk soils and the iron-free clay fractions.The Cr(Ⅲ) adsorption capacity increased with increasing soil pH due to more charges on adsorbing surfaces.Our results suggest that the soils rich in organic matter and iron oxides and having a pH above 4.5 are suitable for application of Cr(Ⅲ)-loaded industrial wastes.     

Direct Determination of Potassium-Sodium Activity Ratio in Soil Suspension with Two Ion-Selective Electrodes

A K^ -selective electrode and a Na^ -selective electrode were used to construct a measuring cell without liquid-junction for the determination of the ion activity ratio of K^ to Na^ in soil suspensions.The measured cell potential was not affected by the total electrolyte concentration when the total cation concentration was 10^-1-10^-3 mol L^-1 and the concentration ratio Ck /CNa was 10:1 to 1:50.When the concentration ratios were equal to 1 and the total electrolyte concentrations were 10^-2 and 10^-3 mol L^-1,the ion activity ratio measurenent would not be affected by pH in the pH range of 3.5 to 11.5 and 4.4 to 11 respectively.Ions other than H^ have no remarkable influence on the measurement.The ion activity ratio of K^ to Na^ measured directly in soil suspension agree well with those in centrifuged supernant solution.The relative deviation was within 4%.From the measured ion activity ratio,the difference of the bonding energies of K^ and Na^ ions was calculated.     

钙盐诱导下土壤锰和铁的释放及其对胡椒的生物有效性

Releases of manganese and iron ions from an albic soil (Albic-Udic Luvisol), a yellow-red soil (Hap-Udic Ferrisol) and a yellow-brown soil (Arp-Udic Luvisol) induced by calcium salt addition and their bioavailability to pepper (Capsicum frutescens L.) were studied in a pot experiment. Addition of Ca(NO₃)₂ decreased soil pH and increased both exchangeable and DTPA (diethylenetriamine pentaacetic acid)-extractable Mn and Fe in soils. Meanwhile, total Mn accumulation in the shoots of Capsicum frutescens L. on the salt-treated soils increased significantly (P< 0.01) compared with the control, suggesting that salt addition to soil induced Mn toxicity in Capsicum frutescens L. Although exchangeable and DTPA-extractable Fe increased also in the salt-treated soils, Fe uptake by the shoots of Capsicum frutescens L. decreased. The effect of added salts in soils on dry matter weight of pepper varied with the soil characteristics, showing different buffer capacities of the soils for salt toxicity in an order of yellow-brown soil > albic soil > yellow-red soil. Fe/Mn ratio in shoots of Capsicum frutescens L. decreased with increasing salt addition for all the soils, which was ascribed to the antagonistic effect of Mn on Fe accumulation. The ratio of Fe/Mn in the tissue was a better indicator of the appearance of Mn toxicity symptoms than Mn concentration alone.