Optimization of DTPA and calcium chloride extractants for assessing extractable metal fraction in polluted soils

Abstract

Metal availability in soils is often assessed by means of extraction with chemical solutions, among others the chelating agent DTPA (diethylenetriaminepentaacetic acid) and the non‐buffered salt calcium chloride (CaCl₂). The same procedures are used for polluted soils that were originally created to assess the nutrient status of arable soils. We studied the influence of various parameters (type of shaker, shaking time, soil to solution ratio, and concentration of chemical extractant) and modify the DTPA and CaCl₂ extraction procedures to make them suitable for the study of polluted soils. The chosen extraction ratio and extractant concentration were the followings: 8 g/20 mL of 0.1 MCaCl₂ and 2 g/20 mL of 0.005 M DTPA. The optimized procedures were applied to nine soil samples affected by different sources of pollution (mine works, vehicle emissions, and various industries). Cadmium (Cd) showed the highest extractability with both extractants. Depending on the soil, copper (Cu) and zinc (Zn) (using DPTA) and Cu and manganese (Mn) (using CaCl₂) were the followings in the extractable amounts. Cadmium, Cu, and Zn were highly correlated in both extractions and with total contents.     

Comparison of a hot water and cold 0.01 M Cacl2 extraction procedures for the determination of boron in soil

Abstract

In 100 different soils, hot (100C) water extractable boron was determined and the results were compared with boron data after extraction of the same soil samples with cold (20C) 0.01 M CaCl₂. Since the boron concentrations in cold soil extracts are too low for direct determination, the extracted boron was converted into BF4‐ and subsequently extracted with a liquid anion exchanger, Aliquat 336, into xylene, and measured by ICP‐AES. A linear relation with R² = 0.74 was found between the two tested procedures. It is, therefore, concluded that with a cold 0.01 M CaCl₂ extraction equally valuable soil boron values can be obtained as with the more difficult to standardize hot water extraction procedure.     

Phosphate adsorption by soils 1. Influence of time and ionic environment on phosphate adsorption

Abstract

The influence of reaction time and ionic environments, on phosphate adsorption were studied using one calcareous soil from India, and one calcareous and two latosols from Hawaii.

Phosphorus adsorption by soils has a initial rapid phase followed by a slow process. For plant nutrition studies, where emphasis is on P concentration of solutions from which plants derive P, isotherms should be constructed using data obtained after near‐equilibration has been attained. This condition does not obtain in a few hours and may require 6 days or more.

Calcium chloride as suspending electrolyte always gave lower phosphate solubility than when KC1 was used as electrolyte. Phosphate retention increased with increasing ionic strength. The necessity for obtaining clear supernatant solutions and the desirability for maintaining reasonable constant equilibrium conditions make 0.01 M CaCl₂ a reasonable choice for constructing P sorption isotherms, even though 0.01 M CaCl₂ is not representative of Ca concentrations in many soil solutions. Saturation extracts of soils investigated here were in the range 0.0002 to 0.005 M Ca.

Adsorption of calcium by highly weathered soils was high suggesting specific adsorption. Calcium adsorption was increased by phosphate additions to a Hydrandept.     

Microwave digestion of fertilizers and soil amendments

Abstract

The trace element pollution hazard of the continuous and large scale application of fertilizers and other amendments to soils depends in part on the chemical composition of these materials. Complete sample dissolution is generally required prior to total elemental analyses. The objectives of this study were to evaluate closed vessel microwave digestion procedures, using HNO₃, HF, H₂O₂, and H₃BO₃, for the total dissolution of fertilizers and soil amendments and to develop a general digestion guide for individual samples. Twenty‐six materials, including commercial fertilizers, rock phosphate, liming materials, organic sources, and a soil sample were studied. More than 99.5% of each of these materials could be dissolved. Commercial nitrogen (N) fertilizers, most of the ammonium phosphates, and a potassium chloride sample could be completely dissolved using exclusively HNO₃. The other samples required HNO₃ and HF, used either in mixtures or consecutively in a stepwise procedure. The sewage sludge materials, the soil sample, and one of the rock phosphates were the only samples that could not be totally dissolved. No improvement in the digestions was observed by including H₂O₂. No significant contamination was evident during the digestions and satisfactory recoveries of 14 trace elements were obtained in digests of 2 standard reference materials. The proposed dissolution procedures are simple and safe. The usual quickness of microwave procedures was partially sacrificed to obtain a more complete dissolution of the samples. Digests obtained with these procedures could be potentially analyzed for other analytes, with the obvious exceptions of N, fluorine (F), and boron (B).     

Extraction of soil phosphorus with calcium chloride solution for prediction of plant availability

Abstract

Soil and vegetative samples of ley and cereals were collected four times during the growing season from field and pot trials with different phosphorus (P) fertilisation levels. The soil samples, dried and of field moisture condition, respectively, were extracted by 0.01M calcium chloride (CaCl₂) at two different soil:extractant ratios (1:2 and 1:10), and analysed by inductively coupled plasma emission spectrometry (ICP) for content of P. The plant samples were digested in concentrated nitric acid (HNO₃) and the P content determined by ICP. Calcium chloride‐extractable P content was lowest in the middle of the growing season, while plant P was highest in the beginning of the season. Phosphorus extracted by CaCl₂ solution was higher at a soil:extractant ratio of 1:10 than at 1:2, and also when drying the soil before extraction. A soil:extractant ratio of 1:2 minimizes the risk of coming too near the limit of determination. However, if organic soils are also to be included, a ratio of 1:10 has to be used in order not to have all the solution absorbed by some types of soils. The solution of ammonium lactate/acetic acid (AL) extracted nearly two powers of ten more P than CaCl₂ solution. There was a good relationship between the methods. If calcareous or very acid soils had been included, a less good relation would have been expected. Plant P content varied more in straw than in grain between different treatments. Measuring CaCl₂‐extractable P with ICP might be able to predict plant uptake of P by plants. This would be a great advantage when using 0.01M CaCl₂ as a universal extradant.     

Ability of different soil extraction methods to predict potassium release from soil in ley over three consecutive years

To avoid over‐fertilization of potassium (K) and thereby a mineral composition in the grass crop not optimal for animal health, estimation of K release from soil is important. The analytical methods should therefore predict the total K release. Furthermore, to minimize costs for the farmers they should provide information which remains valid over a period of several years. The relationship between different soil extraction procedures for K and K uptake in ley for three subsequent years after soil sampling was studied in 19 field experiments on a range of mineral soil types in Norway. Potassium determined with solutions that extracted exchangeable K or parts of exchangeable K (0.01 M CaCl₂, 0.5 M NaHCO₃, 1 M NH₄oAc, or ammonium acetate lactate) was significantly (p < 0.05) related to the K yield only in the 1st yr after soil sampling. Potassium extracted with boiling in 1 M or 2 M HNO₃ was significantly related to the K yield only in the 2nd and 3rd yr. Potassium extracted with cold 2 M HCl, boiling 0.1 M HNO₃ or 0.5 M HNO₃ was significantly related to the K yield in all 3 yr after soil sampling. Among these extractants, 0.1 M and 0.5 M HNO₃‐extractable K were better predictors of K uptake than 2 M HCl‐extractable K. These three extractants release some non‐exchangeable K in addition to exchangeable K. The fraction of 1 M HNO₃‐K extractable with 0.1 M HNO₃ varied from 4% to 45%, whereas from 15% to 78% of 1 M HNO₃‐K was extractable with 0.5 M HNO₃. Consequently, the more easily releasable fraction of K extracted by boiling with 1 M HNO₃ varied considerably between different sites.     

Vergleich zwischen Perkolation und Extraktion mit 1 M NH4Cl‐Lösung zur Bestimmung der effektiven Kationenaustauschkapazität (KAKeff) von Böden

Comparison between percolation and extraction with 1 M NH₄Cl solution to determine the effective cation exchange capacity (CEC_eff) of soils A simple method is proposed for the determination of the effective cation exchange capacity (CEC_eff). The soil is extracted with 1 M NH₄Cl‐solution, manually shaken for three times, and the exchangeable cations are determined by ICP‐OES and pH‐measurement. Comparison with corresponding results of the percolation method (n = 110 samples) shows good agreement in reproducibility, exchangeable cations (except Fe and Na), base saturation and CEC_eff.     

Soil Test to Predict the Copper Availability in Pasture Soils

Abstract

The proportion of copper (Cu) that can be extracted by soil test extractants varied with the soil matrix. The plant‐available forms of Cu and the efficiency of various soil test extractants [(0.01 M Ca(NO₃)₂, 0.1 M NaNO₃, 0.01 M CaCl₂, 1.0 M NH₄NO₃, 0.1 M HCl, 0.02 M SrCl₂, Mehlich‐1 (M1), Mehlich‐3 (M3), and TEA‐DTPA.)] to predict the availability of Cu for two contrasting pasture soils were treated with two sources of Cu fertilizers (CuSO₄ and CuO). The efficiency of various chemical reagents in extracting the Cu from the soil followed this order: TEA‐DTPA>Mehlich‐3>Mehlich‐1>0.02 M SrCl₂>0.1 M HCl>1.0 M NH₄NO₃>0.01 M CaCl₂>0.1 M NaNO₃>0.01 M Ca(NO₃)₂. The ratios of exchangeable: organic: oxide bound: residual forms of Cu in M1, M3, and TEA‐DTPA for the Manawatu soil are 1:20:25:4, 1:14:8:2, and 1:56:35:8, respectively, and for the Ngamoka soil are 1:14:6:4, 1:9:5:2, and 1:55:26:17, respectively. The ratios of different forms of Cu suggest that the Cu is residing mainly in the organic form, and it decreases in the order: organic>oxide>residual>exchangeable. There was a highly significant relationship between the concentrations of Cu extracted by the three soil test extractants. The determination of the coefficients obtained from the regression relationship between the amounts of Cu extracted by M1, M3, and TEA‐DTPA reagents suggests that the behavior of extractants was similar. But M3 demonstrated a greater increase of Cu from the exchangeable form and organic complexes due to the dual activity of EDTA and acids for the different fractions and is best suited for predicting the available Cu in pasture soils.     

Comparison of Iron Oxide–Impregnated Paper Strips with Other Extractants in Determining Available Soil Phosphorus

Abstract

Iron oxide–coated strips (P_i) can serve as a sink to continuously remove phosphorus (P) from solution. In this way, P extraction is analogous to the P absorption by plant roots. The objective of this study was to compare the iron oxide–coated paper strips with other chemical extraction methods to estimate the plant P availability for corn (Zea mays) growing in the greenhouse in some soils of Hamadan province of Iran. Sixteen soil samples with different physicochemical properties were analyzed for available P using Olsen, Colwell, Mehlich‐1, 0.01 M CaCl₂, AB‐DTPA, and 0.1 M HCl methods and p_i. Furthermore, the effects of two P levels (0 and 200 mg P kg^?1) on the plant indices (P uptake, relative yield, and plant responses) were studied in a greenhouse experiment using 10 soil samples. The results showed that the amount of extractable P decreased in the order of 0.01 M CaCl₂<AB‐DTPA<p_i<Olsen<Colwell<Mehlich‐1<0.1 M HCl. The amount of P extracted by the p_i method was significantly correlated with other extractants. The amounts of P extracted by all chemical methods were significantly correlated. The results of a pot experiment showed that the amount of P extracted by the p_i method was significantly correlated with the plant P uptake. However, the other methods were not significantly correlated with P uptake. The results of this experiment showed that p_i method was able to predict the plant availability of soil P.     

Applicability of 0.01 M CaCl2 as a single extraction solution for the assessment of the nutrient status of soils and other diagnostic purposes

Abstract

The applicability of 0.01 M CaCl₂ solution as a single extraction agent for soils as a basis for fertilizer recommendation was tested on a variety of soils both from the Netherlands and from some tropical countries. Air‐dry soil samples were subjected to extraction with 0.01 M CaCl₂ and to several conventional extraction procedures, and the results were compared. In the soil suspensions pH was measured, whereas in the extracts Na, K, Mg, P, different extractable N‐forms and Zn were measured. The values found in CaCl₂ extracts are discussed in relation to results of other extraction procedures and as to their potential value in soil quality assessment. It is concluded that a single extraction procedure with 0.01 M CaCl₂ can be applied for fertilizer recommendation purposes. The possibility of determining different extractable N‐forms (NH₄, NO₃, soluble organic N) significantly enhances the value of the method in predicting the N‐fertilizer needs. Furthermore it was found that the concentration of Zn in 0.01 M CaCl₂ extracts was a good indicator of phytotoxicity in a polluted area. Additional advantages of this extraction are low costs, simplicity and repro‐ducibility.     

Change Point in Phosphorus Release from Variously Managed Soils with Contrasting Properties

Abstract

Investigating the relation between concentration or release of phosphorus (P) into soil solution (CaCl₂‐P, determined by 0.01 M CaCl₂ extraction of soils) and soil test phosphorus (Olsen P, or 0.5 N NaHCO₃‐extractable soil phosphorus) for 10 widely ranging and variously managed soils from central Italy, a change point was evident where the slopes of two linear relationships meet. In other words, it was possible to distinguish two sections of the plots of CaCl₂‐P against Olsen P, for which increases of CaCl₂‐P per unit of soil test P increase were significantly (p<0.05) greater above than below these change points. Values of change point ranged from 14.8 to 253.1 mg kg^?1 Olsen P and were very closely correlated (p<0.001) to phosphorus sorption capacity of soils. Similar change points were also previously observed when Olsen P (and also Mehlich 3 P) of surface soils was related to the P concentration of surface runoff and subsurface drainage. Because insufficient data are available relating P in surface soils and amount of P loss by overland, subsurface, or drainage flow, using the CaCl₂ extraction of soil can be convenient to determine a change point in soil test P, which may be used in support of agricultural and environmental P management.     

Estimation of plant available manganese in acidic subsoil horizons

Abstract

General agreement does not exist as to the most appropriate method to estimate plant available Mn in soils. In the current investigation soil and soil solution Mn were measured in limed and unlimed treatments of 11 acidic subsoil horizons and related to plant Mn concentrations, Mn uptake and growth of subterranean clover (Trifolium subterraneum L. cv. Mt. Barker) and switchgrass (Panicum virgatum cv. Cave‐in‐Rock). Manganese measurements were taken at planting and harvest and included: Mn extracted by 1M NH₄OAc (pH 7), 0.01M CaCl₂, 0.05M CaCl₂, 0.033M H₃PO₄, 0.005M DTPA, 0.2% hydroquinone in 1M NH₄OAc (pH 7), 0.01M NH₂ OH.HCl 4 2 in 0.01M HNO₃, total soil solution Mn and concentrations and 2+ activities of Mn²⁺ calculated from the GEOCHEM program. Measured and calculated values of soil solution Mn generally gave the best correlations with subterranean clover and switchgrass Mn concentrations and Mn uptake. Root Mn concentrations were highly correlated with soil solution Mn measurements taken at harvest with r=0.97 and r=0.95 (p<0.01) for subterranean clover and switchgrass respectively. The Mn extracted by 0.01M CaCl was also significantly correlated (p<0.01) with plant Mn concentrations and Mn uptake and proved to be better than the other extractants in estimating plant available Mn. Although Mn concentrations as high as 1769 mg/kg (shoots) and 8489 rag/kg (roots) were found in subterranean clover, Mn did not appear to be the major factor limiting growth. Measures of soil and soil solution Mn were not strongly correlated with yield. Both Al toxicities and Ca deficiencies seemed to be more important than Mn toxicities in limiting growth of subterranean clover and switchgrass in these horizons.     

A comparison of different indices for nitrogen mineralization

Indices of N mineralization in soils of contrasting texture, pH, and organic matter contents were compared at different dates during the growing season. The indices were derived from a 12-week aerobic incubation, determination of the amount of microbial biomass at the start of the incubation, determination of the increase in NH ₄ ⁺ after boiling with 2 M KCl for 2h, and extraction of total soluble N with 0.01 M CaCl₂. Cumulative mineral N increased linearly with time in the course of the incubations. Rates of mineralization in soil samples taken in March 1989 and 1990 were significantly correlated with soluble organic N, while correlations between the mineralization rate and the increase in NH ₄ ⁺ after boiling with 2 M KCl for 2 h were poor for sandy soils and absent for loamy soils. Correlations between NH ₄ ⁺ after boiling with 2 M KCl for 2h and the soil N concentration were highly significant, but no general relationship was found between the mineralization rate and the soil N concentration. Neither biomass N nor biomass C was significantly correlated with the mineralization rate or with one of the chemical indices. Among the methods tested, soluble organic N extracted with 0.01 M CaCl₂ was the only method with any promise for routine measurement of the mineralization capacity of the individual sites.     

Plant availability and leaching of (heavy) metals from ammonium‐, calcium‐, carbohydrate‐, and citric acid‐treated uranium‐mine‐dump soil

Remediation of an uranium‐mine soil from Settendorf (East Germany) includes phytoextraction under conditions which make its heavy metals more plant‐available but less leachable. A second way is active inhibition of heavy metal uptake by the plant. In a pot trial with Chinese cabbage (Brassica chinensis L.), planted and unplanted soil samples were daily irrigated with deionized water or aqueous solutions with a total of (g (kg soil)^–1) CaCl₂ (0.26 Ca), NH₄Cl (1.39), casein, sucrose, citric acid (13), and an extract of rape (B. napus L.) shoots (13 DW) in a phytotron for 26 d. Water‐irrigated plants were also treated with a 50 mM citric acid solution (10.5 g (kg soil)^–1) 6 and 7 d prior to harvesting. Total elements in plant tissue and soluble elements in aqueous extracts from control and postharvest soils were determined by ICP‐AES. Supplements of NH , and the NH ‐generating casein and rape extract reduced soil pH during nitrification, and increased plant uptake of Cd, Cu, Ni, and Zn. Citric acid at 50 mM adjusted soil to pH 4.5–6.0 and enhanced uptake of all elements. Long‐term application of sucrose and citric acid increased pH and inhibited uptake of Cd, Cr, Cu, Ni, and Zn. Contemporarily, leaching of heavy metals and humic substances was lowest with Ca and NH and highest with sucrose and citric acid amendments. It is concluded that Chinese cabbage grown for chelate‐assisted phytoextraction should be supplied with Ca and NH to obtain a high plant biomass on soil with a low hazard of leaching. Metal uptake should be stimulated by application of chelator 7 d prior to harvesting. Undesired uptake of heavy metals by Chinese cabbage determined as food should be inhibited with carbohydrate amendments. Long‐term application of NH or chelator, which reduces the solubility of certain elements but increases their uptake moderately, is recommended as a tool for continuous phytoextraction technologies.     

Effect of some soil properties on extractable boron content in argentine pampas soils

Abstract

The influence of some soil properties on hot 0.02 M calcium chloride (CaCl₂) extractable boron in the Argentine Pampas was studied. The selected soils represent an extensive area in the middle west of the country where most of the grain crops are produced. Soils have all developed on loess and cover a wide range of organic matter, pH, and exchangeable calcium. The most representative soils are Typic Argiudolls and Typic Haplustolls. Two hundred soil samples were taken in order to characterize their 0.02 M CaCl₂ extractable boron content and study the boron behavior with regard to other soils properties and environmental conditions. The amounts of extracted boron on all samples had a significant correlation with soil organic carbon (positive), and soil pH (negative). The regression equation between extractable boron and organic carbon content was y=0.1021+0.3722 OC R²: 0.51. Since solubility in hot CaCl₂, 0,02 M is considered an availability index, these results support the hypothesis that organic carbon content is the main boron reserve for plants. When a multiple regression was calculated, both variables organic carbon and pH explained 57% of variation in extractable boron. The studied area can be subdivided into regions with different boron content, within each region the relationship between boron content and organic carbon and pH were also different. The exchangeable calcium content had a light influence especially in the subsuperficial layer. The influence of environmental conditions on boron content and its relationship with soil properties were discussed.     

The determination of hot‐water‐soluble boron in some acid Oregon soils using a modified azomethine‐H procedure

Abstract

A method is proposed for determination of hot‐water‐soluble boron in acid soils from western Oregon. The soil sample is boiled in 0.02 M CaCl₂, filtered, and B determined using azomethine‐H. Soils extracted in this way yielded extracts with little color in them and the predicted error due to this color was 0.00–0.07 ppm B. The use of charcoal as a decolorizing agent resulted in comparatively high predicted errors.

Inductively‐coupled plasma emission spectroscopic (ICP) analysis of distilled water and 0.02 M CaCl₂ extracts indicated that the extractable B level was not affected by the presence of CaCl₂. Azomethine‐H yielded comparable values to ICP but the curcumin method tended to give high values for hot‐water‐soluble B.     

Air Drying Affects Extractable Sulfate in Soils of Variable Charge: Test of Two Extraction and Two Quantification Methods

Abstract

Fertilizer recommendations need to be based on reliable soil sulfate determinations. Airdrying samples changes irreversibly many properties of soils with variable charge and might affect the extractable sulfate. In this study, sulfate extracted from air‐dry and field‐moist samples was compared. Two extracting solutions [water and 00.1 M Ca(H₂PO₄) ₂] and two quantification methods (turbidimetry and ion chromatography) were assayed on A and B horizon samples of five Humic Acrisols from southeast Mexico. Air drying increased water‐extractable sulfate in Ah horizons, whereas in Bt horizons, it increased the 00.1 M Ca(H₂PO₄)₂‐extractable sulfate. Airdrying increased dissolved organic carbon contents in all samples and increased soil acidity and oxalate extractable iron in 70 and 60% of the samples, respectively. Results showed larger coefficients of variation in air‐dried samples. Turbidimetry resulted less sensible than ion chromatography. To enhance sensitivity and reproducibility, particularly organic soil samples should be analyzed field‐moist and by ion chromatography.     

Extraction of phosphorus,potassium, calcium,and magnesium from soils by an ion‐exchange resin procedure

Abstract

A procedure for the simultaneous extraction of phosphorus, potassium, calcium and magnesium from soils, by an ion‐exchange resin procedure applicable to large‐scale advisory soil testing, is described. The important steps are the disaggregation of soil by shaking in water during 15 minutes with a glass marble, the transference of the elements from the soil to a sodium bicarbonate treated mixture of anion and cation exchange resins during a 16‐hour shaking period, the separation of the resin from the soil by sieving and extraction of the elements from the resin.

The results of resin extractable calcium, magnesium and potassium were comparable to the results of these elements extracted with 1M NH₄OAc, to calcium and magnesium extracted with 1M KCl, and to potassium extracted with 0.025M H₂SO₄.

For phosphorus the resin extractable values were not comparable to the results obtained by the former routine method, based on the extraction with 0.025M H₂SO₄. The results of resin extractable P presented closer correlation with cotton response to phosphorus application in 28 field experiments (r = 0.85**) as compared with 0.025M H₂SO₄ extractable P (r = 0.68**), and also with P uptake by flooded rice in a pot experiment with eight lowland soil samples (r = 0.98**), as compared with extraction with 0.0125M H₂SO₄ in 0.050M HCl, for which the correlation was not significant. The reasons for the superiority of the extraction of P with the described procedure are discussed.     

Field-based partition coefficients for trace elements in soil solutions

A total of 48 elements was detected in the soil solutions centrifuged from two acid sandy (humus-iron podzol) profiles from southern England. Concentrations ranged from mm for the major ions to mm for trace metals such as U and the rare earth elements. Field-based solid/solution partition coefficients, K_d, were determined by calculating the ratio of the amount of an element extracted by 0.43 m HNO₃ or a neutral salt (0.01 m CaCl₂ or 0.1 m Ba(NO₃)₂) to the concentration in the soil solution. These partition coefficients did not show the expected trend in selectivity. For example, Cd consistently had one of the highest K_d values, higher even than Cu. This was thought to be due in part to the nature of the K_d which reflects a balance between binding to the soil solids and to the dissolved organic carbon (DOC), which is present at relatively high concentrations (1–20 mm ) in the soil solutions. Because of the underlying functional similarity between metal binding by the solid and dissolved organic matter, the partition coefficient (and hence element mobility) will be relatively insensitive to changes in pH and metal-ion activity in the soil solution.