Effect of clay,organic matter and CaCO3 content on zinc adsorption by soils

Summary Zinc adsorption was studied in suspensions of six soils of different physicochemical characteristics in dilute ZnSO₄ solutions. At low concentrations, Zn²⁺ adsorption was described by the Langmuir adsorption equation. The calculated Langmuir adsorption maxima were related positively to clay and carbonate content and negatively with organic matter content of soils. Multiple regression analysis revealed that zinc adsorption maxima can be predicted with good precision from information in soil survey reports. When the added Zn²⁺ exceeded the adsorption maximum, the solid phase of zinc controlling its concentration in solution was either zinc hydroxide or carbonate so long as soil carbonates were present. The values of zinc potential also indicated that soils retain Zn²⁺ more strongly than Zn(OH)₂ or carbonate. Postgraduate student Professor of Soils. Professor of Soils.     

Phosphate fertilization reduces zinc adsorption by calcareous soils

Summary Zinc adsorption isotherms were constructed for three calcereous soils which varied in carbonate contents, texture, and past history of phosphate fertilization. The equilibrium conditions were 25°C, 0.01 M CaCl₂ and 6 days.Higher phosphate fertilization of the soils reduced Zn adsorption. The effect of P was more in the soil with lower carbonate content which suggested that soil carbonates played a dominant role in the Zn adsorption characteristics of the soils.The adsorption data conformed to the Langmuir equation. Constants (k and b) calculated from the Langmuir isotherm showed that bonding energies (k) were inversely related to extractable P; i.e. higher Zn adsorption was associated with lower bonding energy. The Zn adsorption maxima (b) were higher for the soils with higher calcium carbonate equivalent.Adsorbed Zn was extracted with a single extraction of 0.005 M DTPA. The recovery was 91 percent for the Tandojam soil, 82 percent for the Tarnab soil, and 63 percent for the Kala shah Kaku soil, indicating that most of the adsorbed Zn is not irreversibly fixed by the soils and can be utilized by plant during growth.The results suggest that P-induced Zn deficiency could not be ascribed to precipitation of Zn as insoluble Zn-P compounds in soils. The increased Zn solubility with P fertilization is the evidence that P-Zn interaction does not reside in the growing medium external to plant.The work is part of Ph.D. thesis submitted to the University of Hawaii, Honolulu, U.S.A.     

Phosphorus adsorption characteristics of Hawaiian soils and their relationships to equilibrium phosphorus concentrations required for maximum growth of Millet

Summary Phosphorus adsor tion isotherms were constructed for six Latosols and one calcareous soil from Hawaii which differed greatly in their phosphorus adsorption capacities. Equilibration was in 0.01M CaCl₂ at 25°C for 6 or 8 days. P adsorption properties of the soils were characterised employing the linear form of Langmuir's equation and also by calculating the amount of P adsorbed between equilibrium concentrations of 0.25 to 0.35 ppm (estimates of P buffering capacities), following the procedure of Oaanne and Shaw¹³. The isotherms of all the soils were found to fit the Langmuir equation at low equilibrium concentrations (< 5 ppm) and the P adsorption maxima ranged from 520 to 10 500 ppm. The buffering capacity estimates correlated closely (r = 0.950) with the adsorption maxima of soils. However, in two soils, the estimates were much lower than expected from their adsorption maxima.Millet (Pennisetum typhoides) was grown in these soils in pots, at 6 phosphorus levels corresponding to 6 equilibrium concentrations chosen from the phosphorus adsorption isotherms. Equilibrium concentrations at maximum growth of millet (C_max) in Latosols varied inversely with the adsorption maxima of the soils. The relationship between these two parameters was expressed by the equation CmaX = a,b^–k, where C_max = equilibrium P concentration at maximum growth of millet, b = P adsorption maximum and a and k are constants. Quantitative expression of the constants are useful as they enable predictions of CmaX for a particular crop from the phosphorus adsorption maximum. This relation was found to hold also for the data on limed acid soils published by Woodruff and Kamprath²⁰.A part of the Ph.D. Thesis approved by the University of Hawaii, Honolulu, Hawaii, U.S.A. (1971).     

Cadmium and zinc adsorption maxima of geochemically anomalous soils (Oxisols) in Jamaica

Abstract

Soil samples were collected from a Miocene limestone area of Jamaica (Manchester Parish) where unusual accumulations of Cd and other metals have been described previously. The source of the metals is natural (geological). The soils are aluminous Oxisols and, geochemically, are closely similar to local karst bauxite deposits. For comparison a karst bauxite sample was collected from Alabama (USA) and an Ultisol sample from South Carolina (USA). All the Jamaican soils were in the pH range neutral to slightly alkaline and CaCO₃ contents ranged from 1.3 to 23.1%. Mean total Cd = 102.5 mg/kg (range 13.6-191.8 mg/kg) and mean Zn = 362.6 (range = 125.8-683.3) mg/kg. These values are higher than world averages. The mean readily exchangeable Cd was 0.05 (range 0.01-0.15) mmol/kg and for Zn mean = 0.02 (range 0.01-0.02) mmol/kg. Adsorption data were obtained experimentally and modelled using the Langmuir isotherm. For the Manchester soils the mean Cd adsorption maximum was 9.15 (range 2.26-32.0) mmol/kg; the values were higher than the karst bauxite sample (0.08 mmol/kg) or the Ultisol (0.08 mmol/kg). Reliable Zn isotherms were not obtained for all soils; for three Manchester soils the mean Zn sorption maximum was 2.99 mmol/kg compared with 3.13 mmol/kg for Cd in the same three soils. Mean Al and Fe values are 38.7% Al₂O₃ and 17.7% Fe₂O₃ compared with the Ultisol (14.5% Al₂O₃ 11.3% Fe₂O₃) and the bauxite (52.6% Al₂O₃, 0.7%Fe₂O₃). Interpretation of the major element values and the known mineralogy of the soils implies that the high adsorption maxima of the Manchester soils can best be explained by their calcareous nature. It is concluded that the Manchester soils have ample adsorption capacity to trap any incoming Cd or Zn solutes.     

Reaction of labelled65ZnCl2,65ZnEDTA and65ZnDTPA with different clay-systems and some alluvial Egyptian soils

Summary The clay fraction separated from an alluvial Egyptian soil and montmorillonite clay mineral were equilibrated with CaCl₂ or NaCl solution then treated with humic acid isolated from composted clover straw to obtain different clay systems: Ca-clay, Ca-clay-HA, Na-clay, Na-clay-HA, Ca-mont and Ca-mont-HA. These clays as well as seven soil samples were reacted with different amounts of labelled⁶⁵ZnCl₂,⁶⁵ZnEDTA and⁶⁵ZnDTPA. The effectiveness of these Zn-sources for maintaining soluble Zn²⁺ ions in the equilibrium solution was the greatest for ZnDTPA and the lowest for ZnCl₂. Ca-clay provided greater Zn sorption capacity than Na-clay, and complexing the clay with humic acid depressed its capacity for Zn sorption. At the pH of the clay-systems (pH=6.5), the possibilities of Zn(OH)₂ formation were reduced especially in the presence of Zn-chelates. Reactions of⁶⁵ZnE DTA and⁶⁵ZnDTPA with the seven soils produced higher levels of soluble Zn²⁺ ions in the equilibrium solution rather than⁶⁵ZnCl₂ meanwhile ZnDTPA was more effective than ZnEDTA. The calculated Zn(OH)₂ ion product in the solution of ZnCl₂-soil systems indicated the precipitation of Zn as Zn(OH)₂. However, this was not valid in the Zn-chelates-soil systems. The results also revealed the role of soil carbonate, organic matter and soil texture as soil variables affecting Zn sorption by natural soils.     

The Role of CEC and pH in Cd Retention from Soils of North of Iran

Cadmium (Cd) is a critical environmental chemical in which sorption reactions control its entry into soil solution. The aim of the present study was to evaluate Cd sorption characteristics of some soils of the northern part of Iran with a wide range of physicochemical properties. Duplicates of each sample were equilibrated with solutions containing 5 to 500 mg Cd L^?1 with 0.01 M CaCl₂ as background solution. The quantity of Cd retention was calculated as the difference between initial and equilibrated Cd concentration. Sorption isotherms including Freundlich, Langmuir, Temkin, Dubinin-Radushkevich, and Redlich-Peterson were used to evaluate the behavior of Cd sorption. Cadmium sorption data were well fitted to Langmuir, Freundlich, and Redlich-Peterson isotherms. The constant of Freundlich equation (k_F ) and adsorption maxima (b_L ) of Langmuir equation were related to pH and cation exchange capacity (CEC). The maximum buffering capacity (K_d ) was significantly correlated with pH (R² = 0.52, p ≤ 0.001) and calcium carbonate equivalent (CCE) (R² = 0.63, p ≤ 0.001). Redlich-Peterson constants (k_RP and a_RP ) were significantly correlated with pH (R² k_RP = 0.30, p ≤ 0.007) and (R² a_RP = 0.27, p ≤ 0.012). It seemed that pH, CEC, and CCE were the main soil properties regulating Cd retention behavior of the studied soils.     

Vertical stratification in sediments from a young oligotrophic South African impoundment: implications in phosphorus cycling

Changes at the mud surface in Midmar Dam, following impoundment, were studied by examining vertical profiles of selected parameters in sediment cores. Distinct stratification in organic carbon, pH and exchangeable Al³⁺ was evident. Phosphate adsorption characteristics in the stratified sediments was quantified using Langmuir adsorption isotherms. The adsorption maxima and bonding energy constants in the surface sediments (0–3 cm) were markedly lower than those below 3 cm, indicating that the surface layers are less efficient at binding phosphate than the deeper layers. Radiotracer experiments indicate that the layers comprising the top 3 cm of sediment predominate in PO₄-P exchange with the overlying water.     

Immobilization and phytoavailability of cadmium in variable charge soils. II. Effect of lime addition

The effect of pH-increases due to Ca(OH)₂ and KOH addition on the adsorption of cadmium (Cd) was examined in two soils which varied in their variable-charge components. The effect of Ca(OH)₂ on immobilization and phytoavailability of Cd from one of the soils, treated with various levels of Cd (0–10 mg Cd kg^–1 soil), was further evaluated using mustard (Brassica juncea L.) plants. Cadmium immobilization in soil was evaluated by a chemical fractionation scheme. The addition of Ca(OH)₂ and KOH increased the soil pH, thereby increasing the adsorption of Cd, the effect being more pronounced in the soil dominated by variable charge components. There was a greater increase in Cd²⁺ adsorption in the KOH-treated than the Ca(OH)₂-treated soil, which is attributed to the greater competition of Ca²⁺ for adsorption. Increasing addition of Cd enhanced Cd concentration in plants, resulting in decreased plant growth (i.e., phytotoxicity). Although addition of Ca(OH)₂ effectively reduced Cd phytotoxicity, Cd uptake increased at the highest level, probably due to decreased Cd²⁺ adsorption resulting from increased Ca²⁺ competition. There was a significant inverse relationship between dry matter yield and Cd concentration in soil solution. Addition of Ca(OH)₂ decreased the concentration of the soluble + exchangeable Cd fraction but increased the concentration of inorganic-bound Cd fractions in soil. Since there was no direct evidence for CdCO₃ or Cd(OH)₂ precipitation in the variable charge soil used for the plant growth experiment, alleviation of phytotoxicity can be attributed primarily to immobilization of Cd by enhanced pH-induced increases in negative charge.     

Influence of organic matter and solute concentration on nitrate sorption in batch and diffusion-cell experiments

Nitrate sorption potentials of three surface soils (soils-1-3) were evaluated under different solute concentrations, i.e. 1-100 mg L⁻¹. Batch and diffusion-cell adsorption experiments were conducted to delineate the diffusion property and maximum specific nitrate adsorption capacity (MSNAC) of the soils. Ho’s pseudo-second order model well fitted the batch adsorption kinetics data (R² > 0.99). Subsequently, the MSNAC was estimated using Langmuir and Freundlich isotherms; however, the best-fit was obtained with Langmuir isotherm. Interestingly, the batch adsorption experiments over-estimated the MSNAC of the soils compared with the diffusion-cell tests. On the other hand, a proportionate increase in the MSNAC was observed with the increase in soil organic matter content (OM) under the batch and diffusion-cell tests. Therefore, increasing the soil OM by the application of natural compost could stop nitrate leaching from agricultural fields and also increase the fertility of soil.     

A study of the impacts of Zn and Cu on two rhizobial species in soils of a long-term field experiment

Two agriculturally important species of rhizobia, Rhizobium leguminosarum biovar viciae (pea rhizobia) and R. leguminosarum bv. trifolii (white clover rhizobia), were enumerated in soils of a long-term field experiment to which sewage sludges contaminated predominantly with Zn or Cu, or Zn plus Cu, were added in the past. In addition to total soil Zn and Cu concentrations, soil pore water soluble Zn and free Zn²⁺, and soluble Cu concentrations are reported. Pea and white clover rhizobia were greatly reduced in soils containing ≥200 mg Zn kg^-1, and soil pore water soluble Zn and free Zn²⁺ concentrations ≥7 and ≥3 mg l^-1, respectively, in soils of pH 5.9–6. Copper also reduced rhizobial numbers, but only at high total soil concentrations (>250 mg kg^-1) and not to the same extent as Zn. Yields of field grown peas decreased significantly as total soil Zn, soil pore water soluble Zn and free Zn⁺² increased (R² = 0.79, 0.75 and 0.75, respectively; P < 0.001). A 50% reduction in seed yield occurred at a total soil Zn concentration of about 290 mg kg^-1, in soils of pH 5.9–6. The corresponding soil pore water soluble Zn and free Zn²⁺ concentrations were about 9 and 4 mg l^-1, respectively. Pea seed yields were not significantly correlated with total soil Cu (R² = 0.33) or soil pore water soluble Cu (R² = 0.39). Yield reductions were due to a combination of greatly reduced numbers of free-living rhizobia in the soil due to Zn toxicity, thus indirectly affecting N₂-fixation, and Zn phytotoxicity. These effects were exacerbated in slightly acidic soils due to increased solubility of Zn, and to some extent Cu, and an increase in the free Zn²⁺ fraction in soil pore water. The current United Kingdom, German and United States limits for Zn and Cu in soils are discussed in view of the current study. None of these limits are based on toxicity thresholds in soil pore water, which may have wider validity for different soil types and at different pH values than total soil concentrations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Distribution of zinc fractions and their transformation in submerged rice soils

Distribution of different forms of Zn in 16 acid alluvial rice growing soils of West Bengal (India) and their transformation on submergence were studied. The results showed that more than 84% of total Zn occurred in the relatively inactive clay lattice-bound form while a smaller fractionviz. 1.1, 1.6, 11.1 and 2.0 per cent of the total occurred as water-soluble plus exchangeable, organic complexed, amorphous sesquioxide-bound and crystalline sesquioxide bound forms, respectively. All these four Zn forms showed significant negative correlations with soil pH (r=−0.48^**, −0.39^*, −0.61^** and −0.67^**, respectively), while the latter two Zn forms showed significant positive correlations with Fe₂O₃ (0.68^** and 0.88^***) and Al₂O₃ (0.89^*** and 0.75^***) content of the soils. The different Zn forms were found to have positive and significant correlations amongst each other, suggesting the existence of a dynamic equilibrium of these forms in soil. Submergence caused an increase in the amorphous sesquioxide-bound form of Zn and a decrease in each of the other three forms. The magnitude of such decreases in water-soluble plus exchangeable and crystalline sesquioxide-bound forms was found to be correlated negatively with initial pH values of the soils and positively with the increase in the amorphous sesquioxide-bound form, indicating their adsorption on the surface of the freshly formed hydrated oxides of Fe, which view was supported by the existence of significant positive correlation between the increase in the amorphous sesquioxide-bound form of Zn and that in AlCl₃-extractable iron. The existence of a positive correlation between the decrease in crystalline sesquioxide-bound Zn and that in Fe₂O₃ content in soil suggested that on waterlogging the soil Zn occluded in the cry talline sesquioxide was released as a result of reduction of Fe₂O₃.     

Evaluation of Iodide and Iodate for Adsorption–Desorption Characteristics and Bioavailability in Three Types of Soil

Adsorption–desorption of iodine in two forms, viz., iodide (I⁻) and iodate (IO₃⁻), in three types of soil were investigated. The soils were: red soil developed on Quaternary red earths (REQ)— clayey, kaolintic thermic plinthite Aquult, Inceptisol soil (IS) and alluvial soil (AS)—Fluvio-marine yellow loamy soil. The isothermal curves of iodine adsorption on soils were described by Langmuir and Freundlich equation, and the maximum adsorption values (y _m) were obtained from the simple Langmuir model. As compared with the iodide, the iodate was adsorbed in higher amounts by the soils tested. Among three soils, the REQ soil adsorbed more iodine (I⁻ and IO₃⁻) than the IS and AS. The distribution coefficient (K _d) of iodine in the soils decreased exponentially with increasing iodine loading concentration. Desorption of iodine in soil was increased correspondingly with increasing adsorption values. The REQ soil had a greater affinity for iodine than the IS and AS at the same iodine loadings. In the pot experiment cultivated with pakchoi (Brassica chinensis L.) and added with two exogenous iodine sources, the iodide form was quickly taken up by pakchoi and caused more toxicity to the vegetable. The rate of iodine loss from soil was higher for iodide form as compared with the iodate. The iodine bioavailability was the highest but the persistence was the weakest in AS among the three soils tested, and the REQ soil showed just the opposite trend to that of the AS soil. This study is of theoretical importance to understand the relationship between iodine adsorption–desorption characteristics and their bioavailability in different soils and it also has practical implications for seeking effective alternatives of iodine biofortification to prevent iodine deficiency disorders.     

Chemistry of Cr in some Swedish soils

The effect of Si(OH)₄ on Cr toxicity and elemental concentrations in ryegrass were investigated in a growth chamber using an acid and a neutral mineral soil. Each soil was treated with 50 mg Cr, as CrO₃, kg⁻¹ soil dry weight, singly, or in combination with 25 mg Si as Si(OH)₄. Plants growing in unamended soils were used as controls. Chromium toxicity, expressed as decrease in shoot or root dry weight, was increased by the Si. This increase was accompanied by a higher Cr uptake particularly on the acid soil. The shoot and root dry weights were significantly correlated (P=1%) with the concentration of Cr, where r=−0.80 and −0.65, respectively. Uptake of Al, Cu, Fe, P and Zn did not show any consistent relationship to the magnitude of Cr toxicity.     

Quantitative relationship between zinc transport and plant uptake

Summary The importance of the Zn buffer power and its influence on the Zn concentration in soil solution was investigated in a simulatory experiment where the soil in question, previously treated with Zn and compacted to known bulk density, was eluted with 0.01M CaCl₂ under constant hydraulic head. The data so obtained were correlated with Zn, uptake by maize. The correlation coefficient for effluent Znvs total Zn uptake improved, remarkably when the corresponding Zn buffer power was also incorporated into the computations. It is concluded from this and the earlier investigation² that the Zn buffer power is the most important parameter governing Zn uptake by maize.     

Phosphorus characteristics correlate with soil fertility of albic luvisols

The information on phosphorus (P) characteristics of albic luvisols and their effect on plant P uptake is limited. Twelve soils representing typical albic luvisols were collected from farmland of four regions in northeast China, each with various levels of soil fertility. Phosphorus fractions, P adsorption and P supply capacity of the soils were analysed and were correlated with soil fertility and plant P nutrition. Total P in these soils ranged from 0.62–0.91 g kg^–1, and comprised 37–51% organic P, and 49–63% in inorganic forms among which the percentage of occluded P was the greatest, followed by Fe-P, Ca-P, Al-P and loosely bound P was the lowest (<1%). Whereas the % of organic P was not clearly affected by fertility, the % of occluded P increased with fertility. By contrast, both % and contents of other P forms decreased with decreasing soil fertility. Soil P adsorption maxima calculated from Langmuir isotherm ranged from 484 to 912 mg kg^–1. Soils with low fertility had the strongest P adsorption, and those with medium fertility had the weakest in all collection regions. The supply capacity of P was positively related to soil fertility. Plant growth correlated positively with P forms with available P correlating best, followed by Fe-P and P supply capacity. Organic C correlated with available P, Fe-P, total P, Al-P and P supply capacity but not with organic P. The results suggest that though the albic luvisols contained high total P, they had low P availability, and P application is required for optimal crop production on these soils.     

Effects of soil acidification and subsequent leaching on levels of extractable nutrients in a soil

Summary The effects of soil acidification (pH values from 6.5 to 3.8), and subsequent leaching, on levels of extractable nutrients in a soil were studied in a laboratory experiment. Below pH 5.5, acidification resulted in large increases in the amounts of exchangeable Al in the soil. Simultaneously, exchangeable cations were displayed from exchange sites and Ca, Mg, K and Na in soil solution increased markedly. With increasing soil acidification, increasing amounts of cations were leached; the magnitude of leaching loss was in the same order as the cations were present in the soil: Ca²⁺>Mg²⁺>K⁺>Na⁺. Soil acidification appeared to inhibit nitrification since in the unleached soils, levels of NO ₃ ⁻ clearly declined below pH 5.5 and at the same time levels of NH ₄ ⁺ increased greatly. Significant amounts of NH ₄ ⁺ and larger amounts of NO ₃ ⁻ , were removed from the soil during leaching. Concentrations of NaHCO₃-extractable phosphate remained unchanged between pH 4.3 and 6.0 but were raised at higher and lower pH values. No leaching losses of phosphate were detected. For the unleached soils, levels of EDTA-extractable Mn and Zn increased as the soil was acidified whilst levels of extractable Fe were first decreased and then increased greatly and those for Cu were decreased slightly between pH 6.5 and 6.0 and then unaffected by further acidification. Significant leaching losses of Mn and Zn were observed at pH values below 5.5 but losses of Fe were very small and those of Cu were not detectable.     

Effects of Surface-Modified Nano-Scale Carbon Black on Cu and Zn Fractionations in Contaminated Soil

Cu contamination soil (547 mg kg^–1) was mixed separately with the surface-modified nano-scale carbon black (MCB) and placed in the ratios (w/w) of 0, 1%, 3%, and 5% in pots, together with 0.33 g KH₂PO₄and 0.35 g urea/pot. Each pot contained 20 ryegrass seedlings (Lolium multiflorum). Greenhouse cultivation experiments were conducted to examine the effect of the MCB on Cu and Zn fractionations in soil, accumulation in shoot and growth of ryegrass. The results showed that the biomass of ryegrass shoot and root increased with the increasing of MCB adding amount (p < 0.05). The Cu and Zn accumulation in ryegrass shoot and the concentrations of DTPA extractable Cu and Zn in soil were significantly decreased with the increasing of MCB adding amount (p < 0.05). The metal contents of exchangeable and bound to carbonates (EC-Cu or EC-Zn) in the treatments with MCB were generally lower than those without MCB, and decreased with the increasing of MCB adding amount (p < 0.05). There was a positive linear correlation between the Cu and Zn accumulation in ryegrass shoot and the EC-Cu and EC-Zn in soil. The present results indicated the MCB could be applied for the remediation the soils polluted by Cu and Zn.     

施用鸡粪对土壤与小白菜中Cu和Zn累积的影响

我国鸡饲养量已占世界总量的24%,鸡饲料添加剂中高含量的Cu和Zn随鸡粪排出体外,鸡粪作为优良的有机肥大量施用于菜园土壤,会导致土壤和蔬菜中重金属Cu和Zn的含量过高,进而通过食物链影响动物和人类健康。研究含高Cu和高Zn的鸡粪施入土壤后典型蔬菜对Cu和Zn的富集和转运,对于阐明鸡粪中Cu和Zn的土壤环境行为和蔬菜的健康风险评价具有重要的科学价值,同时可为蔬菜安全生产提供参考。本研究以Cu和Zn浓度分别为1137.3 mg/kg和1503.4 mg/kg的鸡粪堆肥作为实验材料,设置5个鸡粪施用处理,即11、22、44、89 g/kg和222 g/kg,相当于25、50、100、200 t/hm2和500 t/hm2,以不施鸡粪处理为对照。通过小白菜盆栽实验,研究了施用鸡粪对土壤与小白菜中Cu和Zn的影响。结果表明：土壤全Cu和全Zn含量范围分别为58.6—203.4 mg/kg和78.1—431.6 mg/kg;EDTA-Cu为12.7—119.8 mg/kg,EDTA-Zn为15.6—215.1 mg/kg。鸡粪施用量大于50 t/hm2时,土壤中Cu和Zn全量均较对照显著提高。小白菜地上、地下部以及整株Cu和Zn的含量都随鸡粪施用量的增加而提高,且地下部Cu、Zn的含量均高于地上部,同时小白菜各部分Zn的含量都高于Cu。鸡粪施用量大于100 t/hm2处理的小白菜地上部Cu含量显著高于对照处理,但是各处理小白菜中地上部的Zn含量与对照相比,均无显著性差异。施鸡粪量为大于50 t/hm2时,地下部分Cu含量较对照显著增加,而施鸡粪量大于100 t/hm2时,地下部分Zn含量显著增加。土壤有效态的Cu（EDTA-Cu）与植物各部分吸收Cu的相关性较好,但土壤有效态的Zn（EDTA-Zn）与植物各部分吸收Zn的相关性较差。随着鸡粪施用量的增加,小白菜对土壤中Cu的富集系数由11%增加到15%,对Zn富集系数却由47%下降到19%,小白菜对Cu和Zn的转运系数分别下降36%和51%。小白菜地上、地下部及整株的Zn/Cu都随鸡粪施用量的增加而减小,说明小白菜对Cu、Zn吸收转运能力的差异随着鸡粪施用量的增加而下降。     

Zinc phytoavailability after remediation in soils contaminated by sphalerite-containing pyritic sludge

Zinc can be toxic to plants growing on soils in areas of the Guadiamar River valley (southwestern Spain) affected by the spillage of pyritic sludge in April 1998. The shoots and the soil around the roots of two wild plants (viz. Amaranthus blitoides S. Wats., November 2000; and Xanthium strumarium L., June 2001) growing in the sludge-affected areas were sampled with the purpose of relating Zn phytoavailability to soil properties. The soils were calcareous and non-calcareous Entisols and Inceptisols which, after remediation, contained ploughed-in residual sludge and unevenly distributed industrial lime. Chemical extracts from the soils suggested that much of the sphalerite (ZnS) originally present in the sludge had weathered and Zn was partly bound to carbonates and Fe oxides, the total Zn concentration ranging from 37 to 2407 mg kg ^–1. To identify the soil properties that influenced Zn phytoavailability under controlled conditions, the soil samples (n=63) were homogenized and oilseed rape (Brassica napus var. Karola) was pot-grown on them in a growth chamber. The concentrations of Zn in oilseed rape shoots and roots were below phytotoxic levels, with mean ± standard deviation values of 142 ± 128 and 244 ± 328 mg kg ^–1 dry matter, respectively. Citrate/bicarbonate-extractable Zn in soil (Zn _cb) was found to be the best predictor for the Zn concentration in both shoots and roots. Also, the Zn _cb/Olsen P ratio exhibited a high predictive power for Zn in shoots as the likely result of the Zn-P interaction in soil. The shoot Zn concentration in the wild plants, generally lay below phytotoxic levels (the mean ± standard deviation values were 261 ± 255 and 200 ± 228 mg kg ^–1 dry matter for Amaranthus blitoides and Xanthium strumarium, respectively) and was not correlated with soil properties – by exception, there was slight correlation between the Zn concentration in Amaranthus blitoides and Zn _cb/Olsen P. Such a lack of correlation can be ascribed to the local small-scale soil heterogeneity caused by remediation practices. The Zn concentration in wild plants growing on CaCO ₃-poor soils was weakly correlated with Zn _cb/Olsen P; no similar correlation was found in CaCO ₃-rich soils, however. The wild plants growing on CaCO ₃-poor and CaCO ₃-rich soils differed little in Zn concentration; this suggests that further addition of lime to reduce Zn phytoavailability may be unjustified.     

Assessment of Metal Availability in Soils from a Pb-Zn Mine Site of South-Central Spain

Heavy metal pollution of the soils around an abandoned Pb-Zn mine site located in the Alcudia Valley (South Central Spain) have been characterized by analysis of extractable and total metal concentrations in 60 samples of arable, pasture, and mine lands. The samples showed a broad range of size-particle distribution, cation exchange capacity, and pH values as well as high levels of total metal concentrations (up to 98510 mg kg^?1 of Pb, up to 20912 mg kg^?1 of Zn, and up to 61 mg kg^?1 of Cd). In order to assess the potential availability of metals the metal partitioning in two different soil size fractions (<2 mm and <63 μm) was determined using EDTA and CaCl₂ as sequestering reagents. The average contents of Pb, Zn, and Cd in the <63 μm particle size fraction for both extractions were higher than those of the <2 mm fraction due to the high metal adsorption capacity of the fine soil particles. Concentrations of heavy metals extracted by CaCl₂ were up to three orders of magnitude lower than those extracted by EDTA, because CaCl₂ only extracts the easily mobile fraction. Metal concentrations extracted by both procedures in the two granulometric fractions increased with total metal concentrations, thus increasing the potential environmental risk associated to heavy metal pollution.