A simple rapid method for the measurement of exchangeable cations and effective cation exchange capacity

Abstract

A simple single‐extraction procedure for measuring exchangeable cations and effective CEC (ECEC, the CEC at natural pH and ionic strength) has been developed for routine advisory soil analysis. The method is based on the use of Sr (1.26M SrCl₂) to displace exchangeable cations and effective CEC is taken as the sum of the exchangeable cations. A ten minute shaking time at 5 g:80 ml, soil solution ratio, was found to be optimum. Good agreement was found between the proposed method and the standard neutral IN ammonium acetate leaching procedure with correlation coefficients (r) for the individual cations Mg, Ca, Na and K of 0.99***, 0.99***, 0.83*** and 0.96*** respectively. Strontium chloride extracted more Al but less Mn (P<0.01) than IN KC1, but because of the low levels of these cations in relation to the total cations present, there was still a good relationship (r= 0.99) between ECEC determined by 1.26M SrCl₂ and that determined as the sum of ammonium acetate extractable Mg, Ca, Na and K plus IN KCl‐extracted Al and Mn.     

Zur Bestimmung austauschbarer Kationen in sauren Waldböden

On the determination of exchangeable cations in acid forest soils Different samples from acid forest soils were percolated with large amounts of H₂O. Significant amounts of anions, especially sulfate, were found in the percolates mainly accompanied by Na. K, Ca and Mg (M_b-cations). The dissolution of Al-Sulfates and subsequent exchange of M_b-cations by Al as dominant mechanism is proposed. Thus the common method for determination of the cation exchange capacity (CEC) of acid forest soils, the percolation with NH₄Cl may overestimate the CEC. The overestimation may be related to the sulfate content of the soil and also influences the calculation of relative CEC proportions of individual cations.     

Comparison of Prewashing Procedures for the Assessment of Phosphate Rock Dissolution in Soils

When evaluating phosphate rock (PR) dissolution, previous to the extraction with sodium hydroxide (NaOH), dry soil samples with PR were extracted with three solutions to remove exchangeable and solution calcium (Ca) [sodium chloride (NaCl) 1 M, buffered NaCl with ethylenediaminetetraacetic acid (EDTA) (NaCl–EDTA), and NaCl buffered at pH 7 with triethanolamine (TEA) (NaCl–TEA)] for comparison with the extraction of soil samples without any prewash. In acidic soils, up to 51% of applied P was recovered during the NaCl extraction because of the high exchangeable acidity released during the extraction. In soils with exchangeable Ca>2 cmol₍₊₎kg^?1, high EDTA quantities also promoted PR dissolution. The NaCl–TEA solution efficiently removed Ca, avoiding PR dissolution and P retention by calcium hydroxide [Ca(OH)₂] during the NaOH extraction. Thus, when evaluating PR dissolution we recommend the use of NaCl–TEA to remove Ca. We also recommend the same procedure when applying the Chang and Jackson fractionation to calcareous soils and soils submitted to PR application.     

SPECIFIC EFFECT OF MAGNESIUM ON THE HYDRAULIC CONDUCTIVITY OF SODIC SOILS

Exchangeable Mg does not have a specific effect on the hydraulic conductivity (HC) and clay dispersion in calcareous soils. Conversely, in well-weathered soils, which do not contain CaCO₃, a specific effect of exchangeable Mg is evident, on both HC losses and clay dispersion, when the Na/Mg soils are leached with distilled water (simulating rain water). Soil clays, when Mg-saturated, are chemically more stable and do not release electrolytes into the solutions: they thus disperse more easily when leached with distilled water. The presence of exchangeable Mg enhances the dissolution of CaCO₃ in calcareous soils, and the electrolytes prevent the dispersion of the clay and HC losses in the Na/Mg calcareous soils.     

Relationship between water soluble and exchangeable soil cations for estimating plant uptake and leaching potential

Abstract

The relationship between water soluble and exchangeable cations (Ca, Mg, Na, and K) was investigated for surface horizons of 195 soils including many taxonomic categories and a wide range in physical and chemical properties from around the world. This will provide information on exchangeable soil cation solubility for use in estimating plant uptake and leaching potential. Amounts of water soluble and exchangeable cations were not consistently related (r² of 0.50, 0.08, 0.77, and 0.49 for Ca, Mg, Na, and K). High correlations were biased by high water soluble and exchangeable cation levels of a few soils that had 3.8‐ and 2.5‐fold greater mean than median values. The ratio of exchangeable to water soluble cations was closely related to cation saturation (r² of 0.87, 0.95, 0.95, and 0.93 for Ca, Mg, Na, and K, respectively). As the degree of saturation of the exchange complex by a certain cation increased, solubility Increased. A change in saturation had less effect on K than on Na, Mg, and Ca solubility. Only exchangeable soil cations (NH₄OAc extractable) are routinely measured and reported in soil survey reports, thus, water soluble levels may be determined from cation saturation. This will allow estimation of the amounts of cation that can potentially move in solution through the soil or be taken up by plants. Use of cation saturation, in addition to exchangeable content, will better characterize soil cation availability by representing quantity, intensity, and buffer factors.     

Cation exchange capacity measurements

Abstract

Soil cation exchange capacity (CEC) measurements are important criteria for soil fertility management, vaste disposal on soils, and soil taxonomy. The objective of this research was to compare CEC values for arable Ultisols from the humid region of the United States as determined by procedures varying widely in their chemical conditions during measurement. Exchangeable cation quantities determined in the course of two of the CEC procedures were also evaluated. The six procedures evaluated were: (1) summation of N NH₄OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus BaCl₂ ‐ TEA (pH 8.0) exchangeable acidity; (2) N Ca(OAc)₂ (pH 7.0) saturation with Mg(OAc)₂ (pH 7.0) displacement of Ca²⁺; (3) N NH₄OAc (pH 7.0) saturation with NaCl displacement of NH₄ ⁺; (4) N MgCl₂ saturation with N KCl displacement of Mg²⁺; (5) compulsive exchange of Mg²⁺ for Ba²⁺; and (6) summation of N NH₄OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus N KCl exchangeable AJ. The unbuffered procedures reflect the pH dependent CEC component to a greater degree than the buffered methods. The compulsive exchange and the summation of N NH₄OAc exchangeable cations plus N KCl exchangeable Al procedures gave CEC estimates of the same magnitude that reflect differences in soil pH and texture. The buffered procedures, particularly the summation of N NH₄OAc exchangeable cations plus BaCl₂ ‐ TEA (pH 8.0) exchangeable acidity, indicated inflated CEC values for these acid Ultisols that are seldom limed above pH 6.5. Exchangeable soil Ca and Mg levels determined from extraction with 0.1 M BaCl₂ were consistently greater than values for the N NH₄Oac (pH 7.0) extractions. The Ba²⁺ ion is apparently a more efficient displacing agent than the NH₄ ⁺ ion. Also, the potential for dissolving unreacted limestone is greater for the Ba₂ ⁺ procedures than in the NH₄ ⁺ extraction.     

Comparison of extractants for the determination of available phosphorus,potassium, calcium,magnesium and sodium in some Ethiopian and German soils

Abstract

A study was conducted with the purpose of comparing the efficiency of Mehlich 1, Mehlich 3, and calcium acetate lactate (CAL) extractants for the deter‐ mination of available phosphorus (P) and exchangeable cations [potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na)] on 22 Ethiopian and 10 German agricultural soils. The Olsen and NH₄OAc extractants were used as standards against which P and exchangeable cations values were compared. Results showed that, in general, highly significant correlations were found between all of the methods for available P and exchangeable cations determination on the Ethiopian soils. The highest correlation was, however, found with the Mehlich 3 extractant. On the ten soils from Germany, the Olsen method did not give significant cor‐ relation with the CAL method for P determination. The CAL and Mehlich 3 extrac‐ tants were also not good indicators of Na availability when compared with the NH₄OAc method. It can be generalized that the Mehlich 3 is a suitable extractant for P, K, Ca, Mg, and Na in Ethiopian soils, but further study is recommended to confirm these findings under field conditions.     

Ionic equilibria,selectivity and diffusion of cations in soil as influenced by anion additions

Abstract

An experiment was carried under controlled conditions to investigate the influence of the anions, H₂PO₄ ^‐. and Cl on the ionic equilibria, selectivity and effective diffusion of Rb, K, Na, Ca, Mg in two Indiana soils.

Additon of anions to the soils increased the concentration of cations in soil solution. In both the soils receiving H₂PO₄ ^‐, lower cation concentrations were found in the soil solution than in those receiving Cl^‐ . Additon of H₂PO₄ ^‐and Cl^‐ reduced the ion selectivity coefficient, k, for various homovalent (Rb/K, Rb/Na, K/Na, Ca/Mg) and mono‐divalent ion pairs (Rb/Ca, Rb/Mg, K/Ca, K/Mg). In Zanesville soil treatments receiving H₂PO₄ ^‐ had lower k values for mono‐divalent cations than treatments receiving Cl^‐. However, no such conclusions could be drawn for Raub soil. Soils treated with H₂PO₄ ^‐ had higher k values for homovalent cations than Cl^‐ treated soils. The differences in the selectivity of adsorption in these two soils might be attributable to the differences in the type and nature of exchange materials and cation concentrations on the exchange phase.

Addition of H₂PO₄ ^‐ or Cl^‐ enhanced the magnitude of effective diffusion coefficient. (De) of all the cations under considerations. The magnitude of effective diffusion coefficient for cations was lower for H₂PO₄ ^‐ treated soils than Cl^‐ treated soils. Such a reduction in De is related to the reduction in cation concentration in soil solution thereby increasing the buffer capacity for the ions under consideration.     

Relationship between chemical and mineralogical properties and the rapid response to acid load of soils in humid Asia: Japan,Thailand and Indonesia

Abstract

It is essential to determine the relationship between soil chemical and mineralogical properties and soil response to acid load to understand the acid-neutralizing capacity and cation behavior of different ecosystems. For 46 soil samples from a subsurface horizon in humid Asia, that is, Japan, Thailand and Indonesia, exchangeable cations, total bases and oxalate-extractable Al (Al_o) were determined, and acid titration was conducted to investigate the rapid soil response to acid load. The acid titration experiment indicated three types of soil response: (1) the release of base cations (particularly Ca and Mg) strongly correlated with exchangeable bases, which dominated the tropical soil samples, (2) the release of Al correlated with Al_o content, which dominated the Japanese soil samples, (3) acid and anion adsorption in soil samples with low acid-neutralizing capacity. To gain further information on the source of soil alkalinity, a column experiment with HCl was conducted using eight selected soil samples in which first-order kinetics were assumed to simulate the time-courses of cation release. In the column experiment, the amounts of Ca and Mg released were close to the exchangeable amounts, and Al_o dissolved more rapidly than Al in crystalline minerals. The rate constants of cation release were large for Ca and Mg, and small for Al, clearly indicating a difference between the exchange and dissolution reactions. Thus, rapid soil response to acid load differed among the soils. A cation exchange reaction was dominant in the tropical soils. In some tropical soils, Ca and Mg were present in exchangeable forms at a higher ratio in the total amounts and they were considered to be easily utilized by plants, but leached out from the soils. In the Japanese soils, including the Andisols, secondary mineral dissolution was conspicuous, resulting in a large acid-neutralizing capacity. In both the tropical and Japanese soils with low acid-neutralizing capacity, anion adsorption mainly contributed to acid neutralization.     

EFFECT OF SOIL pH AND ORGANIC MATTER ON LABILE ALUMINIUM IN SOILS UNDER PERMANENT GRASS

The rates of extraction of Na, K, Mg, Ca, and Al with 1M NH₄ NO₃ from the mineral-and organic-rich layers of some Park Grass (Rothamsted) soils were measured at the pH of the soil. Below pH 3.7 exchangeable Al, derived from the kinetics curve, increases with decreasing soil pH and is less in the organic-rich layer. The sum of the basic exchangeable cations, ∑(Na + K + Mg + Ca), increases with increasing soil pH and is more in the organic-rich layer. The extraction of exchangeable Al obeys first order kinetics, the rate constant being similar for all the soils (mean value 36 ± 7 × 10^?6|s^?1), which implies that exchangeable Al is released from surfaces with similar properties for the adsorption of Al, and that the rate is not affected by soil pH and organic matter. The rate of extraction of non-exchangeable Al is the same in the mineral-and organic-rich layers of each soil, and is maximal at about pH 3.7, decreasing sharply at more and less acid pH values.     

鹅凰嶂山地雨林土壤阳离子交换量和交换性盐基离子分布特征

  目的  探究广东阳春鹅凰嶂山地雨林土壤阳离子交换量和交换性盐基离子的空间分布特征,了解该区域森林土壤的保肥能力及其影响因子。  方法  以鹅凰嶂山地雨林内不同位置、不同土层土壤作为研究对象,分析土壤阳离子交换量和交换性盐基离子空间分布格局、剖面垂直分布规律。  结果  鹅凰嶂山地雨林土壤阳离子交换量5.46 ± 0.97 cmol(+) kg?1,交换性阳离子呈现明显表聚现象;土壤交换性盐基总量在表层土（0 ~ 10 cm）中呈现阴坡 > 阳坡、下坡位 > 中坡位 > 上坡位的规律,土壤盐基离子含量基本呈现K+ > Mg2+ > Ca2+ > Na+的趋势,且Ca2+/Mg2+ < 1.6;土壤阳离子交换量、交换性盐基总量与土壤总有机碳含量呈极显著正相关。  结论  鹅凰嶂山地雨林土壤的保肥能力较差,且存在生理性缺钙的风险,阳坡尤为明显;同时存在土壤有机质稳定性不高导致阳离子交换量下降的潜在风险。     

The importance of exchangeable cations and resin-sink characteristics in the release of soil phosphorus

The significance of exchangeable cations in the release of phosphorus by sequential extraction with water was evaluated in 11 acid (_pH 5.0–6.3) New Zealand soils contrasting in P status and P retention. The release of P from Na-saturated soil exceeded that from the original Ca-dominated soils by up to four-fold. Possible explanations for the larger P release in the Na system include: (i) desorption of P induced by increased surface negative potential associated with the exchange of Na for Ca/Mg, and/or (ii) accelerated dissolution of Ca phosphate compounds or complexes resulting from the creation of a sink for Ca.
The potential of a series of anion- and cation-exchange resin systems (AER and CER, respectively) as sinks for labile soil P was also examined. For all soils studied, P extracted by AER-HCO₃ 3 and that removed by sequential extraction with water. Also, the amounts of P extracted by AER-OH/CER-H and NaCl/ H₂O were closely correlated ( r = 0.95**), suggesting similar release mechanisms. The results obtained indicate that charge-balancing cations, particularly Ca which is the predominant exchangeable cation in the majority of soils, exerts a more significant control on soil P equilibria in acid soils than is commonly recognized.     

A comparison of buffered and unbuffered ammonium salts to determine exchangeable base cations in acid soils

Abstract

In soil samples from two study sites in southern Norway, exchangeable cations were determined using two different ammonium (NH₄)‐salts as extractant. As expected, the cation exchange capacity (CEC) determined in 1M ammonium acetate (NH₄OAc), buffered at pH 7.0 was higher than the CEC measured in ammonium nitrate (NH₄NO₃). By contrast, the amount of exchangeable calcium (Ca), magnesium (Mg), and barium (Ba) was lowest in the NH₄OAc extract, in particular in the upper soil horizons high in organic matter (O‐ and E‐horizon). This suggests that NH₄ in 1M NH₄OAc does not compete effectively with multivalent base cations. The relatively high levels of exchangeable base cations in NH₄NO₃ could not be explained by increased weathering. An increase in selectivity of especially divalent cations may explain the relatively low amount of exchangeable base cations extracted by NH₄OAc, as this involves increased deprotonation and thus a higher negative charge.     

A comparison of methods for measuring extractable Ca,Mg, K,Na, Mn,Al, Fe,and P from New England forest soils

Abstract

An experiment was designed to evaluate several of the commonly used extractants and methods for determining “available”; elements in soils. The purpose of the study was to evaluate the suitability of these extraction procedures for use on forest soils typical for New England commercial forests. The extraction procedures selected included NH₄OAc pH 4.8, NH₄OAc pH 7.0, NH₄Cl, Double Acid, Bray, and Mehlich methods. The elements measured varied somewhat by procedure but included the base cations, Al, Fe, Mn, and P. As a bioassay of element availability, a greenhouse study was conducted using six forest soil materials from different horizon types (i.e. O, Ap, B) and three conifer seedling species (red spruce, balsam fir, and white pine). Relatively small differences among extraction procedures were found among the methods used for exchangeable Ca, Mg, K, and Na. Large differences, however, were found among the different horizon types in the amount of exchangeable base cations present. In contrast, significant differences were found among extraction procedures for Al, Fe, Mn, and P depending on the degree of buffering and acidity of the extracting solution. Of the elements measured in this study, only P appeared to be growth limiting with the NH₄OAc pH 4.8 being best correlated with P uptake by seedlings. Further work under field conditions over longer time periods is required to evaluate these methods for measuring P availability in forest soils     

A computer‐assisted method for CEC estimation and quality control in a routine soil‐test operation

Abstract

Cation‐exchange capacity (CEC) of 30 Alabama soils was estimated by two different methods based or routine soil‐test results consisting of soil‐water pH, Adams‐Evans buffer pH, and Mehlich‐1 extractable cations (K, Mg, and Ca), which were obtained automatically by a computerized data acquisition system. In one method, CEC was calculated by solving a quadratic equation involving soil‐water and buffer pH's; in the other, CEC was estimated as the summation of extractable cations and exchangeable acidity. The two estimated CEC's agreed well with each other and also had the same magnitude as CEC determined by the normal NaOAc, pH 8.2 method. By averaging the two calculated values, an even closer estimation of the measured CEC was found. These calculations and comparisons can be accomplished quickly and efficiently by a minicomputer via a simple FORTRAN program.

In addition, a discrepancy between the two estimated CEC's would indicate possible errors in analytical determinations and/or the inadequacy of the soil testing procedures. Therefore, an additional means for quality control in a routine soil‐test operation can be obtained by comparing the two CEC values.     

AB‐DTPA cation extraction in Spanish soil samples

Abstract

Since only one extraction is required to determine a large number of nutrients, many laboratories employ universal extractants to determine the available nutrients in a soil sample. This paper compares the universal ammonium bicarbonate‐DTPA (AB‐DTPA) method developed by Soltanpour and Schwab (1977) with the traditional methods, ammonium acetate (NH₄OAc) test for exchangeable cations and the Lindsay and Norwell (1969) test for the micronutrients. Results from the analysis of 28 soils by these methods were compared. Most soils were selected from those used by the Spanish Working Group for the Standardization of Analytical Methods. In most cases, statistical correlations between methods presented good agreement for each element, but depending on the soil pH range, some elements needed two correlations. Also, when results for wet and dry soils were compared, variability was lower when the AB‐DTPA extraction method was used. We concluded that, besides being faster, the AB‐DTPA method is valid for Spanish soils, even for calcium (Ca) extraction in calcareous soils, where the ammonium acetate method fails due to excessive Ca solubilization.     

A Rapid and Simple Manifold to Study Exchangeable Cations and Cation Exchange Capacity in 24 Soil Samples Simultaneously

ABSTRACT

The outcomes of this work highlight the development and validation of a rapid and simple manifold for determination of exchangeable cations [calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K)] and cation exchange capacity (CEC) in soil. First, the performance of the manifold was evaluated to determine the best conditions to use: filter assembly, volume and number of aliquots of extracting solution, and the use of vacuum. Second, the analytical performance was study from trueness and precision analysis. For that, soil samples with assigned values, an in house reference material and unknown soil samples, were used, comparing their results with those obtained using the classical extraction method (agitation, centrifugation, and filtration). The performance study showed that a filter system assembled with S&S Nº859 type filter paper, cotton, and plastic piece is better to the other studied options. Four aliquots of 10 mL extracting solution and a few seconds of vacuum between additions is recommended to achieve the best recovery. The extraction procedure proposed using the manifold demonstrated to be accurate, and so can effectively replace the classical method for the extraction of exchangeable cations and CEC in soils. Regarding simplicity, rapidity, and simultaneity, the manifold method could be the method of choice for extraction up to 24 samples. Moreover, the manifold method significantly reduces the laboratory supplies and instrument used in the extraction steps in the classical method, attaining better efficiency and reducing costs associated to this stage of the analysis.     

Waste water renovation through soil percolation

A laboratory experiment simulating high-rate effluent renovation by soil percolation involved leaching secondary sewage effluent through columns of three differing soils. Analyses of P in 22 leachate collections and distribution of both organic and inorganic P in column sections revealed the mechanisms of P removal, the influence of differing soil properties, and the effect of continuous utilization. Renovation of effluent P was greatest with percolation through columns of acid Milner soil which contains abundant Al and Fe, and, although Squilax soil removed more P from initial leachings due to its higher exchangeable Ca content, Glenmore soil was the more suitable of these two alkaline soils over the long term. The leachate N0₀3-N levels were lower than the original N0₃-N content of effluent for the first ten leachings but N0₃-N enrichment occurred for the last effluent percolations through all three soils. Analyses of Ca, Mg, K, and Na in leachates and soil columns indicated losses of exchangeable cations from the calcareous Squilax and Glenmore soils enriched effluent content and the accumulation of the cations in the acid soil reduced concentrations in effluent that passed through Milner soil.     

Determination of CEC and exchangeable Ca and Mg in non-saline calcareous soils

A method is proposed for determination of CEC and exchangeable cations in non-saline calcareous soils. The saturating solution used, 0.5 d Lithium formate in 80% methanol at pH 8.2, does not dissolve CaCO₃.The method is simple and less laborious than any other known method.     

Exchangeable cations and CEC determinations of some highly weathered soils

Abstract

Eight methods to determine exchangeable cations and cation exchange capacity (CEC) were compared for some highly weathered benchmark soils of Alabama. The methods were: (1) 1N NH₄OAc at pH 7.0 by replacement (for CEC only), (2) 1N NH₄OAc at pH 7.0 (summation of basic cations plus 1N KCl extractable Al), (3) 1N NH₄OAc at pH 7.0 (summation of basic cations plus exchangeable H⁺), (4) 0.1M BaCl₂ (summation of basic cations plus exchangeable Mn, Fe and Al), (5) Mehlich 1 (summation of basic cations plus 1N KCl extractable Al), (6) Mehlich 1 (summation of basic cations plus exchangeable H⁺), (7) Mehlich 3 (summation of basic cations plus 1N KCl extractable Al), and (8) Mehlich 3 (summation of basic cations plus exchangeable H⁺). The 0.1M BaCl₂ was chosen as the standard method for the highly weathered soils and the other methods compared to it. The results indicated that the 1N NH₄OAc replacement method gave significantly higher CEC values compared to the summation methods. This was probably due to the overestimation of the field CEC caused by measurement of pH dependent cation exchange sites in these soils. There was, however, close agreement between the BaCl₂ method and the summation methods that included extractable Al. The generally good agreement between these summation methods suggests that the Mehlich 1 and Mehlich 3 extractants, commonly used to determine available nutrients in the southeastem USA, may also be used to measure effective CEC of some acid‐rich sesquioxide benchmark soils of Alabama. However, 1N KCl extractable Al as opposed to exchangeable H⁺ should be included in the computation.