Evaluation of the electro-ultrafiltration technique (EUF) as a measure of the K supplying power of Quebec soils

The electro-ultrafiltration (EUF) method has been used to evaluate the short-term and long-term supplying power of soils for many essential plant nutrients. The objective of this study was to compare the capacity of EUF with other extraction techniques to predict the plant availability of soil K and K fertilizer responsiveness by 10 cuts of alfalfa (Medicago sativa L.) growing over a 366-day period. Increasingly higher average concentrations of soil K were extracted by EUF at 50 V and 20°C (29 mg kg^-1), EUF at 200 V and 20°C (48 mg kg^-1), 0.002 M SrCl₂ (55 mg kg^-1), EUF at 200 V and 80°C (85 mg kg^-1), 0.1 M HCl (105 mg kg^-1), Mehlich 3 (119 mg kg^-1), 1 M NH₄OAc (120 mg kg^-1) and boiling 1 M HNO₃ (601 mg kg^-1). The large content of vermiculitic minerals in the silt and clay fractions is responsible for EUF desorbing more K in 55 minutes than NH₄OAc in 29 out of 30 soils. The total amount of K desorbed by EUF at 80°C was as effective as Mehlich 3-extractable K in predicting K uptake for the first three cuts and was best among the extracting procedures after boiling 1 M HNO₃ in predicting the long-term K supply, the uptake of K from non-exchangeable sources and the relative yield of alfalfa over 10 cuts. The desorption of soil K with EUF provides a better evaluation of the K-supplying power of Quebec soils than the extractants currently used, especially on a long-term basis.Contribution no. 396.     

Effect of growing ryegrass on the distribution of zinc in soil pools

The distribution of zinc between soil pools was measured over 48 weeks in grassed and bare soils using selective extractants. Although changes in the extractable fractions of zinc occurred in all soils, they tended to be less in the bare soils. From weeks 18 to 48 the rate of uptake of zinc by ryegrass ranged from 3.4 to 106 g Zn/week in the 5 soils studied. The CaCl₂-extractable Zn in the soil increased over the 48 weeks, while the amount of acetic acid-, EDTA-and oxalate-extractable Zn decreased. Superimposed on these changes was the effect of growing ryegrass. There was relatively more CaCl₂-Zn, but less acetic acid-Zn and oxalate-Zn, in the grassed soil compared to the bare soil. There was no significant change over time in the difference in the EDTA-Zn pool between grassed and ungrassed soils. Comparison of zinc taken up by the ryegrass and zinc lost to soil, measured by oxalate extraction, suggested that selective extraction was not a good measure of zinc uptake by grass.     

A common chemical extractant for estimating plant-available zinc in different soil types (peaty,red and alluvial)

Summary Relative efficiency of five chemical extractants for the extraction of available Zn in four different soils and its uptake by rice seedlings was studied in a pot culture experiment. The Zn extracted by dithizone-ammonium acetate showed a significant relationship with plant uptake whereas the values for other extractants except NH₄OAc (pH4.8) did not approach the level of significance. Among the soil properties studied, pH and CaCO₃ correlated negatively and organic matter and CEC positively with Zn uptake by rice plants.Contribution from the Soil Science and Agricultural Chemistry Dept., Banaras Hindu University, Varanasi-221005, India.Lecturer and Research Scholar of the Soil Science and Agricultural Chemistry Department, respectively.Lecturer and Research Scholar of the Soil Science and Agricultural Chemistry Department, respectively.     

Responses of microbial components of the rhizosphere to plant management strategies in a semiarid rangeland

Summary Easily soluble heavy-metal fractions from different soils, a garbage-sewage sludge compost and peat were extracted by EUF. Blanks were determined by extracting distilled water. As the rubber seal of the extraction chamber contained Zn, the obtained Zn values were not reliable. The relative standard deviations of extracted micronutrients were 29.1% for Fe and 20.5% for Mn, Fe, Mn, Zn, Cu, Pb, Cd and Cr were not only found in the filters but also in the extracts.The extraction of CrIII and CrVI solutions showed that CrVI mainly migrated into the anode extract. CrIII was found mainly in the cathode filter and cathode extract, a smaller part however was obviously oxidized to CrVI and migrated into the anode extract. Consequently, CrIII and CrVI in soils could not be distinguished unequivocally by EUF.The amounts of Zn, Cu, Pb and Cd extracted by EUF from various substrates were small compared with the quantities extracted by 2N HCl. The heavy metal contents of the leaves were mostly in the order of those of the EUF extract.Several vineyard soils as well as peat were mixed with increasing quantities of Grünsalz (green salt), a fertilizer consisting mainly of iron sulphate. High amounts of Grünsalz (100–200 g/200 g soil) were necessary to raise soluble Fe in calcareous soils. In peat, however, small Grünsalz additions (1 g/50 g peat) were sufficient. Soluble Mn and Cu increased too when Grünsalz was added to soil or peat. These results give valuable information on how grapevine chlorosis can be reduced by the use of Grünsalz or mixtures of peat and Grünsalz.     

Dilute hydrochloric acid as an extractant for available zinc,copper and boron in rice soils

Summary Because zinc deficiency is a widespread disorder of wetland rice and copper deficiency may occur with it, 0.05M HCl was compared with 0.1M HCl, EDTA and DTPA as an extractant for available zinc and copper. It was also compared with the reflux method for boron assay.Thirty-three wetland rice soils were analyzed for zinc and copper by the four methods. Rice was grown on the flooded soils, scored visually for zinc deficiency, and the plants analyzed for zinc and copper content. In the boron study, 53 soils were extracted by the reflux method and the 0.05M HCl procedure. Rice was grown on the flooded soils, scored visually for boron toxicity, and the plants analyzed for boron content.Fourteen of the 16 soils on which rice showed zinc deficiency gave <1.0 mg/kg Zn by the 0.05M HCl method but values far in excess of the critical limits by the other methods. The r values for available and plant zinc were: 0.05M HCl (0.88^**); 0.1M HCl (0.55^**); EDTA (0.43^**); and DTPA (0.31^ns).Twelve of the zinc-deficient soils gave<0.1 mg/kg Cu by the 0.05M HCl method but values exceeding the critical limits by the EDTA and DTPA methods. The r values for available and plant copper were: 0.05M HCl (0.74^**), 0.1M HCl (0.64^**), EDTA (0.28^ns), and DTPA (0.20^ns).The critical limit of 1.0 mg/kg by the 0.05M HCl extraction was confirmed for zinc deficiency and a tentative value of 0.1 mg/kg for copper deficiency proposed.The 0.05M HCl method separated boron-toxic soils from non-toxic soils and gave a better correlation (r=0.91^**) between available and plant boron than the reflux extraction (r=0.84^**). The toxic limit by the 0.05M HCl method was provisionally set at 4 mg/kg.     

Sulfur in Ghanain soils

Sulfur availability in twenty selected surface soils (0–22 cm), which varied in both physical and chemical properties and sampled under cultivated and uncultivated management in the various ecological zones of Ghana, was studied. Texture varied from coarse sand to clay, with 16–85% sand and 10–51% clay. Organic C varied from 0.45 to 2.24% and total N from 0.034 to 0.215%; soil pH (0.01M CaCl₂) from 3.69 to 7.43 and total S from 44 to 273 ppm. Inorganic sulfate formed 2.3 to 14.8% of the total S, HI-reducible S 4.4 to 28.2, C-bonded S 4.4 to 28.2 and unidentified organic S 12.7 to 63.2%. Sulfur availability was assessed by chemical extraction methods and electroultrafiltration technique as follows: (i) extraction with Ca(H₂PO₄)₂·H₂O solution containing 500 ppm P, (ii) extraction with 0.1M LiCl and (iii) electroultrafiltration (EUF) at 80°C, 400 V for 10 min and also on seven of the soils the standard EUF fractionation procedure of Neméth. Ca(H₂PO₄)₂-extractable S was not significantly correlated with LiCl-extractable S nor with any of the EUF values. LiCl-extractable S was not significantly correlated with sulfate extractable by and EUF?1+2+3 fractions (r=0.911^**). Dry matter yield of oat seedlings and EUF?1+2+3 fractions (r=0.911^**). Dry matter yield of oat seedlings was not correlated with any of the availability indexes. Total S uptake was significantly correlated with LiCl-extractable S (r=0.629^** without S and 0.729^** with S applied) and with EUF-80°C, 400 V/10 min (r=0.561^**), EUF-1 (r=0.953^***) and EUF-2 (r=0.912^**). On all the soils, more S was taken up by oat plants than could be accounted for by the inorganic S and S mineralized from organic S during an incubation period of 4 weeks.     

A comparison of electro-ultrafiltration and quantity/intensity measurements of soil potassium with its uptake by ryegrass in Scottish soils

Summary Electro-ultrafiltration (EUF) and quantity/intensity (Q/I) parameters of soil K were compared for 14 soils from each of three soil series. The K desorbed by EUF during the first 10 min (K₁₀) was closely correlated with the equilibrium activity ratio (AR₀) for soils of the same series, but differences between series reflected the soil K-buffering capacity, indicating that K₁₀ includes loosely held exchangeable K and is not strictly an intensity measurement. EUF values were compared with conventional soil test methods for predicting K-uptake and dry-matter yield of ryegrass grown in the glasshouse. Correlation coefficients between K uptake at the first cut were 0.80 for K₁₀, 0.88 for K_a (the initially labile K derived from the Q/I curve), 0.92 for K₃₅ (desorbed by EUF in 35 min) and 0.97 for K_ex (1.0M ammonium acetate extraction).     

Rice yield in relation to electroultrafiltration extractable soil potassium

Summary Potassium in wetland rice soils from five different locations in the Philippines was analyzed using the electroultrafiltration (EUF) technique and by extraction withN NH₄ acetate (pH 7). The soils contained low exchangeable K and responded to K application. The K soil test values were calibrated against the rice response to K application under field conditions. EUF extractable soil K correlated highly significantly with the rice yield response to K fertilizer, whereas the NH₄ acetate extractable K (exchangeable K) did not. Under limiting K supply in soils, rice yield depends more on the EUF-K than on the exchangeable K. Maximum grain yields were obtained when the EUF-K values after harvest and before wetland preparation were above 30 ppm K.     

Evaluation of chemical methods for estimating available zinc and response of green gram (Phaseolus aureus roxb) to applied zinc in non-calcareous soils

Summary Studies were conducted in 22 non-calcareous soils (India) to evaluate various extractants,viz. (6N HCl, 0.1N HCl, EDTA (NH₄)₂CO₃, EDTA NH₄OAc, DTPA+CaCl₂ and 1M MgCl₂) to find critical levels of soil and plant Zn for green gram (Phaseolus aureus Roxb.). The order of extractability by the different extractants was 6N HCl>0.1N HCl>EDTA (NH₄)₂CO₃<EDTA NH₄OAc DTPA+CaCl₂>1M MgCl₂. Critical levels of 0.48 ppm DTPA × CaCl₂ extractable Zn, 0.80 ppm EDTA NH₄OAc extractable Zn, 0.70 ppm EDTA (NH₄)₂CO₃ extractable Zn, and 2.2 ppm 0.1N HCl extractable Zn were estimated for the soils tested. The critical Zn concentration in 6 weeks old plants was found to be 19 ppm. The 0.1N HCl method gave the best correlation (r=0.588^**) between extractable Zn and Bray's per cent yield, while with DTPA+CaCl₂, it was slightly low (r=0.542^**). The DTPA + CaCl₂ method gave significant (r=0.73^**) correlation with plant Zn concentration. The 0.1N HCl gave the higher correlation with Zn uptake (r=0.661^**) than DTPA (r=0.634^**) 6N HCl and 1M MgCl₂ method gave nonsignificant positive relationship with Bray's per cent yield. For noncalcareous soils apart from the common use of DTPA+CaCl₂, 0.1N HCl can also be used for predicting soil available Zn. The use of 0.1N HCl would be much cheaper than DTPA and other extractants used in the study.     

Solubility and mobility of copper,zinc and lead in acidic environments

Understanding the chemical speciation of metals in solution is necessary for evaluating their toxicity and mobility in soils. Soil samples from the Powder River Basin, Wyoming were extracted with distilled deionised H₂O. Soil water extracts were subjected to chemical speciation to determine the relative distribution and chemical forms of copper (Cu), zinc (Zn) and lead (Pb) in acidic environments. As pyrite oxidised, the pH decreased from 6.6 to 2.4, concentration of dissolved sulfate (S_T) increased from 259 to 4,388 mg L^-1 and concentration of dissolved organic carbon (DOC) decreased from 56.9 to 14.4 mg L^-1. Dissolved Cu concentrations ranged from 0.06 to 0.42 mg L^-1 and dissolved Zn concentrations ranged from 0.084 to 4.60 mg L^-1. Dissolved concentrations of Pb were found to be 0.003 to 0.046 mg L^-1. Chemical speciation indicated that at near neutral pH, dissolved metal concentration in soil water extracts was dominated by DOC- metal complexes. At low pH, dissolved metal concentration in soil water extracts was dominated by free ionic forms (e.g. Cu²⁺, Zn²⁺, Pb²⁺) followed by ion pairs (e.g. CuSO₄ ⁰, ZnSO _inf4 ^sup0 , PbSO _in4 ^sup0 ). Results obtained in this study suggest that as soil pH decreased, the availability and mobility of metal ions increased due to the chemical form in which these metal ions are present in soil solutions.     

Soil microbial activities and heavy metal mobility in long-term contaminated soils after addition of EDTA and EDDS

A 40-day incubation experiment was carried out in order to evaluate the microbial activities and heavy metal availability in long-term contaminated arable and grassland soils after addition of EDTA (ethylenediaminetetraacetic acid) or EDDS ([S,S]-ethylenediaminedisuccinic acid). Soils with similar contamination of heavy metal from the vicinity of a lead smelter were used in the experiment. The soil microbial carbon (C_mic) decreased significantly after addition of EDTA in the arable soil (CM1); lesser effects were observed in the grassland soil (CM2). Addition of EDDS caused a decrease of C_mic during the first 10 days of incubation. In the later phases of the experiment, C_mic increased, and even exceeded the amounts found in the control soils. Respiratory activities and metabolic quotients (qCO₂) increased after the addition of the chelating agents into the soils. Higher respiratory activities and qCO₂ were observed in the EDTA-treated soils. The readily available heavy metal fractions were extracted with NH₄NO₃ solution. Readily mobilizable heavy metal fractions of Cd, Pb, Zn, and (in part) Cu increased during the first 3-10 days of incubation in the presence of EDTA. The addition of EDDS particularly increased concentrations of available Cu. Significant correlations between NH₄NO₃-extractable metals, soil respiratory activities, and qCO₂ were found in both soil treatments with EDTA and EDDS. This indicates that enhanced metal mobility seriously affects the microbial processes in experimental soils. In addition, the relationships between NH₄NO₃-extractable Cd, Cu, and the microbial biomass were found in the CM1 soil amended with EDTA.     

The use of DGT for prediction of plant available copper, zinc and phosphorus in agricultural soils

Soil chemical extractions are widely used to predict the nutritional status of soils. However, the correlation between extracted elements and plant uptake is often poor, especially if compared over a range of soil types. The aim of this study was to examine a new method called Diffusive Gradients in Thin films (DGT), which measures the diffusive supply of elements, thereby mimicking a plant root. The ability of DGT to assess plant-available P, Zn and Cu was tested in a wide range of typical Scandinavian agricultural soils along with conventional methods (EDTA and DTPA for Cu and Zn; NaHCO₃ for P and soil solution concentrations). Extracted soil concentrations were compared to that of the element in the youngest fully developed leaf of barley (Hordeum vulgare L.) grown in pots. For Zn and P, only DGT could predict plant uptake while conventional extraction methods and soil solution analyses performed poorly. All soil tests could predict Cu concentration in leaves, but the DGT technique proved to be most accurate followed by the soil solution concentration of Cu. We conclude that DGT is much more accurate at predicting plant-available P, Zn and Cu than commonly used methods for analysing plant-available nutrients in soil.     

Copper and zinc fractions affecting microorganisms in long-term sludge-amended soils

The influences of Zn and Cu on soil enzyme activities (acid phosphatase, alkaline phosphatase, arylsulfatase, cellulase, dehydrogenase, protease (z-FLase), urease, beta-D-glucosidase and beta-D-fructofuranosidase (invertase)) and microbial biomass carbon were investigated in agricultural soils amended with municipal sewage sludge or compost since 1978. The trace metals in the soils were fractionated using a sequential extraction method. Long-term application of the sewage sludge and composts caused accumulations of Cu and Zn in the soils, ranging from 140 to 144 and from 216 to 292 mg kg(-1), respectively. The percentage of Cu was highest in the NaOH- and HNO3-extractable fractions (44-51% and 38-46%, respectively), while the percentage of Zn was highest in the HNO3- and EDTA-extractable fractions (65-83% and 11-32%, respectively). Although the percentage of the bioavailable fractions (sum of KNO3 + H2O-, NaOH-, and EDTA-extractable amounts) of Cu (53-64%) was higher than that of Zn (15-37%), the percentage of the most labile fractions (KNO3 + H2O) of Zn (2.1-5.9%) was larger than that of Cu (1.1-2.4%). The size of the microbial biomass carbon increased with the application of sewage sludge or compost. For some enzymes, however, the ratio of the enzyme activity to microbial biomass was lower in the soils amended with sewage sludge or compost than that in the control soil. The soil enzyme activities were more adversely affected by Zn than by Cu. From a multiple regression analysis, it was found that dehydrogenase, urease, and beta-D-glucosidase activities were reduced by the KNO3 + H2O-extractable fraction of Zn in the soils. These microbial activities seem to be sensitive to Zn stress, indicating the possibility that they might be useful bioindicators for evaluation of the toxic effects of Zn on microorganisms in the soils.     

Simultaneous extraction of soil phytoavailable cadmium,copper, and lead by chelating resin membrane

Cadmium, copper, and lead were extracted from suspensions of contaminated soils using metal chelating exchange resin membranes. Nine soils with widely varying properties and Cd, Cu and Pb levels were tested. Soil suspensions made up with 4 g in 40 mL deionized water were equilibrated with 5 cm² Ca-saturated Chelex exchange resin membrane which was retained inside a polypropylene bag and shaken at 150 rpm for 24 hrs. Resin membrane extractable Cd, Cu and Pb of the soils were correlated with Cd, Cu, and Pb uptake by young wheat seedlings grown in these soils and compared with soil Cd, Cu, and Pb extracted by 0.1 M HCl, 0.01 M CaCl₂, and 0.005 M Diethylenetriamine pentaacetic acid (DTPA). The amounts of Cd, Cu and Pb extracted by the Ca-saturated Chelex membrane from all tested soils correlated well with those absorbed by young wheat seedlings. The Ca-saturated Chelex membrane extractable Cd, Cu and Pb of the soil had the strongest correlation with plant uptake Cd, Cu and Pb among the extraction methods we tested. It was demonstrated that the Ca-saturated Chelex membrane extraction is an appropriate method in simultaneously estimating Cd, Cu and Pb phytoavailability of soil and is applicable to a wide range of soils.     

Effects of biochar amendments on speciation and bioavailability of heavy metals in coal-mine-contaminated soil

An incubation experiment was executed on applying biochar as a soil remediation amendment to discuss an effect of the various addition rates on the speciation and bioavailability of heavy metals in mining-contaminated soil. The result showed that the content of Cd in soil was 9.51 times higher than the Huainan soil background values. The contents of Cu, Zn and As were 2.97, 1.60 and 1.42 times the background values, respectively, and the total contents of all heavy metals were higher than the standard values of soil environment quality GB15618-1995 set by the China Ministry of Environmental Protection. Speciation analysis indicated that Cu and Cd were mainly associated with the reducible fraction, while Zn and As were dominated by the residual fraction. After biochar was added to contaminated soil, the residual fractions of heavy metals increased, while the acid-soluble fractions reduced. According to the results of CaCl₂ extraction experiment, CaCl₂-extractable concentrations of Cu, Zn, As, and Cd were observed with a biochar dosage rate of 10%, which were 57.26%, 51.37%, 6.94% and 42.04% lower than those of control soil samples, respectively, but there were no obvious changes of CaCl₂-extractable As.     

Copper,Lead, Cadmium,and Zinc Sorption By Waterlogged and Air-Dry Soil

Competitive sorption of copper (Cu), lead (Pb), cadmium (Cd), and zinc (Zn) was studied in three soils of contrasting chemical and physical properties under air-dry and waterlogged conditions. Competitive sorption was determined using the standard batch technique using six solutions, each with Cu, Pb, Cd, and Zn concentrations of approximately 0, 2.5, 5, 10, 20, and 50?mg L^?1Waterlogged soils tended to sorb higher amounts of added Cu, Pb, Zn and Cd relative to soils in the air-dry condition; however, this increase in sorption was generally not statistically (p<0.05) significant. The magnitude of sorption under both waterlogged and air-dry conditions was affected by the type and amount of soil materials involved in metal sorption processes, and competition between other metals for the sorption sites. Metal sorption was closely correlated with soil properties such as cation exchange capacity, organic carbon, and Fe and Mn hydrous oxides. Exchangeable Al may have markedly reduced metal sorption due to its strong affinity for the sorption sites, while increases in exchangeable Mn may have enhanced Zn and Cd sorption. Heavy metal sorption was best described as a combination of both specific and nonspecific interactions. The extractability of Cu, Pb, Cd, and Zn under waterlogged and air-dry conditions was also studied. Three solutions containing these metals were mixed with each soil to achieve a final concentration of 0, 50, and 500?mg kg^?1. Each soil was extracted every 7 days using 1?M MgCl₂ (pH 7) to determine metal extractability. Metal extractability initially decreased then increased due to waterlogging. The increased extractability of added metals was closely related to increased solubility of Fe and Mn suggesting that dissolution of Fe and Mn, oxides under reducing conditions caused a release of previously sorbed Cu, Pb, Cd, and Zn.     

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.     

EUF-analysis of tea soils of Southern India and tea productivity

Summary The relationship between EUF extractable nutrients and conventional soil test extractable nutrients in the acid soils of Southern India on one hand and that between EUF values and tea productivity on the other are described. Close correlation exists between EUF-NO₃–N at 20°C and CuSO₄–Ag₂SO₄-extractable NO₃–N (r=0.98^***), EUF-N_org and Morgan's reagent extractable NH₄–N (r=0.97^***), total EUF-N and CuSO₄–Ag₂SO₄-extractable NO₃–N plus Morgan's reagent NH₄–N (r=0.96^***), EUF-P at 20°C and modified Bray II-P (r=0.93^***) and EUF-P at 20°C plus that at 80°C and modified Bray II-P (r=0.91^***). The EUF-K at 20°C shows close correlation with NH₄OAc–K (r=0.80^***), Ag-thiourea-K (r=0.86^***) and Morgan's reagent-K (r=0.84^***) whereas the EUF-K at 80°C shows close correlation with the difference in K contents of NH₄OAc–K and Ag-thiourea-K (r=0.92^***) or of NH₄OAc–K and Morgan's reagent-K (r=0.93^***) and fixed NH₄–N (r=0.89^***). EUF-Ca, EUF-Mg and EUF-Mn do not show any relationship with conventional soil test values. Tea productivity is strongly associated with EUF-N and EUF-P extracted at 20°C.     

Partitioning of Zn,Cd, Pb,and Cu in organic-rich soil profiles in the vicinity of a zinc smelter

Abstract

A five-step sequential extraction procedure was applied to organic-rich soil samples from five soil profiles situated 1–8 km from a zinc smelter. The partitioning of Zn, Cd, Pb, and Cu into five operationally defined fractions (exchangeable, “carbonate’’-bound, reducible, oxidizable, and residual) was studied at different soil depths down to 35cm. In the surface soil (0–1 cm) a major part of Pb and Cu was extracted in the oxidizable fraction, whereas for Zn and Cd slightly more was extracted in the ‘‘carbonate”-fraction than in the other four fractions. Extracted metal proportions in the oxidizable fraction were respectively of the order of 30%, 20%, 50%, and 80% for Zn, Cd, Pb, and Cu in the surface soil for all sites, but these proportions decreased with soil depth. In the surface soil less than 20% of all the elements were extracted in the residual fraction, but the proportions associated with this fraction generally increased with soil depth. In the C-horizon, differences in extracted proportions of Pb and Cu in the residual fraction were probably due to geochemical factors, whereas for Zn the low extracted proportion at a highly contaminated site (20%) may be due to Zn migration to the C-horizon at this site. For Cd the extracted proportions in the C-horizon were lower than for the other elements, generally below 20%, presumably because Cd is weaker in terms of its adsorption to the soil than the other elements studied. Total concentrations of the metals decreased strongly with increasing distance from the smelter, but less systematic differences were observed for their distributions among fractions. Potentially bioavailable metal proportions (exchangeable + “carbonate”-bound fraction) in the surface soil were about 50%, 60%, 20%, and 10% for Zn, Cd, Pb, and Cu, respectively. In C-horizon soil the mobility sequence Cd>Zn>Pb = Cu was generally observed. The present results indicate that the concentrations and chemical fractionation of Zn, Pb, and Cd in these soils represent a considerable risk to natural terrestrial food chains.     

The critical level of copper in sierozem soils of haryana as evaluated with different extractants

Summary The relative efficiency of seven extractants for estimating available Cu in sierozem soils of Haryana was studied. Bulk samples of 15 soils ranging in neutral normal amm. acetate extractable Cu from 0.12 to 0.20 ppm were subjected to screen-house study. The quantities of Cu extracted with neutral normal amm. acetate, Morgan’s reagent (pH 4.8)N ammonium acetate (pH 4.8), 0.1N HCl, 0.02M EDTA, critrate-EDTA and DTPA from soils were examined for their correlation with responses of maize in terms of Bray’s percentage yield and percentage Cu uptake. The highest coefficient of correlation was obtained between Cu extractable with neutral 1N NH₄OAc and Bray’s per cent yield and per cent Cu uptake. All other methods showed lower values of correlation. The critical level of available Cu estimated with use of neutral normal NH₄OAc was 0.16 ppm. Below this value, responses to applied Cu can be expected.