Organic Amendment Effects on the Transformation and Fractionation of Aluminum in Acidic Sandy Soil

Addition of organic amendments can alleviate the level of aluminum (Al) phytotoxicity in acid soils by affecting the nature and quantity of Al species. This study evaluated the transformation of Al in an acidic sandy Alaquod soil amended with composts (10 and 50 g kg^?1 soil of yard waste, yard + municipal waste, GreenEdge^®, and synthetic humic acid) based on soil Al fractionation by single and sequential extractions. Though the organic compost amendments increased total Al in soil, they alleviated Al potential toxicity in acidic soil by increasing soil pH and converting exchangeable Al to organically bound and other noncrystalline fractions, stressing the benefits of amending composts to improve acid soil fertility. The single‐extraction method appears to be more reliable for exchangeable Al than sequential extraction because of the use of nonbuffered pH extract solution.     

红壤中铝的形态

以改进的连续分级提取方法,用１ｍｏｌ／Ｌ,ＫＣｌ,０．２ｍｏｌ／Ｌ,ＨＣｌ,０．１ｍｏｌ／Ｌ Ｎａ４Ｐ２Ｏ７（ｐＨ８．５）,ＤＣＢ溶液,０．３３ｍｏｌ／Ｌ,柠檬酸钠和０．５ｍｏｌ／Ｌ ＮａＯＨ为提取剂,把红壤中可提取的非晶态铝区分为交换态铝,肿附态无机羟基铝,有机配合态铝,氧化铁结合态铝,层间铝和非晶态铝硅酸盐。     

Estimating non‐crystalline and crystalline aluminum and iron by selective dissolution in a riparian forest soil

Abstract

We compared sequential and separate extraction procedures for estimating non‐crystalline and crystalline aluminum (Al) and iron (Fe) in a floodplain forest soil. We used 0.2M acid ammonium oxalate (pH 3.0) to estimate non‐crystalline Al and Fe, dithionite‐citrate‐bicarbonate to estimate crystalline Fe, and 0.1M sodium hydroxide (NaOH) to estimate crystalline Al. Both separate and various combinations of sequential extractions were compared, as well as variations in soil:solution ratio, extraction time, extraction temperature, and the use of field‐moist versus dried soils. A sequential oxalate/NaOH extraction, using 0.4 g dry weight equivalent of field‐moist soil and a soil:solution ratio of 1:100, gave the best estimate of non‐crystalline Al and Fe and crystalline Al, while a separate 16 hour DCB extraction at room temperature, using 0.8 g dry weight equivalent of field‐moist soil and a soil:solution ratio of 1:50, gave the best estimate for non‐crystalline plus crystalline Fe. A sequential oxalate/NaOH extraction followed by a separate DCB extraction is a relatively simple procedure for estimating amounts of non‐crystalline and crystalline Al and Fe in large numbers of soil samples.     

Aluminum Forms in Solid Phase of Soils Developed over Schists as a Function of Land Use

ABSTRACT

Land use may modify certain soil properties while soil physicochemical characteristics can influence metal partitioning in soils. Therefore, the total content and various forms of aluminum (Al) in solid phase of schist-developed topsoils (0–20 cm) in NW Spain under different land uses (i.e., forest, pasture, and cultivation) were evaluated to identify the Al-bearing phases. Aluminum fractionation was performed, using a six-step sequential extraction procedure with ammonium acetate, hydroxylamine hydrochloride, ammonium oxalate in darkness, hydrogen peroxide, ammonium oxalate under ultraviolet radiation, and acid digestion. Mean concentrations of total Al were similar in the soils under three land uses. Mean percentage of the various Al forms in all soils were in the following order: residual fraction > amorphous compounds > crystalline compounds > water-soluble/exchangeable/specifically adsorbed > bound to oxidizable organic matter > manganese oxides. The forest soils contained considerably higher contribution of amorphous compounds (16.3%) to total Al concentration compared with the soils under other two uses (mean about 9%). Maximum mean concentration of exchangeable Al was also observed in forest soils (mean 8.8% of total Al vs. about 4% in pasture soils and cultivated soils); this is attributed to lower pH and higher organic matter content of the forest soils. Thus, this study revealed the impact of land use on the Al-bearing phases and, hence, in its bioavailability to plants.     

Fractionation of extractable aluminum in acid soils: A review and a proposed procedure

Abstract

Different forms of soil aluminum (Al) are involved in the retention of anions and cations, phytotoxicity of Al in acid soils, CEC reduction and soil physical properties such as aggregate stability and water infiltration. Therefore it is desirable to quantify the different forms of Al in soil especially acidic soils. A rationale was developed from a literature survey to identify the following fractions of Al: (a) exchangeable quantified by 1M KC1 extraction; (b) organic bound quantified by 0.1M CuCl₂ + 0.5M KCl extraction; (c) sorhed Al extractable with 1M NE₄OAc at pH 4.0; (d) amorphous Al oxide and hydroxide and amorphous aluminosilicates (if present) extractable with 0.2M ammonium oxalate at pH 3.0; and (e) interlayered Al extractable with 0. 33M sodium citrate at pH 7.3. Pools (a), (b), and (c) are extracted sequentially. Amorphous Al oxide and hydroxide (pool d) is calculated from ammonium oxalate extractable Al minus (a + b + c). Interlayered Al is calculated from sodium citrate extractable Al minus ammonium oxalate extractable Al. The latter two extractions are done on separate subsamples of soils. From preliminary studies and data for 13 soil samples it is suggested that this fractionation of soil Al is more meaningful than that obtained by the KCl ‐> K₄P₂O₇ ‐> ammonium oxalate > citrate‐bicarbonate‐dithionite extraction sequence.     

Extractability and Transformation of Copper and Zinc Added to Tropical Savanna Soil under Long-Term Pasture

The extractability and slow reactions of copper (Cu) and zinc (Zn) in a weathered savanna soil under Brachiaria decumbens, Digitaria smutsii, and Stylosanthes guianensis pastures were determined in a laboratory incubation study using a sequential extraction to remove operationally defined fractions of the metals, consisting of exchangeable, organically bound, precipitate [occluded in aluminum (Al) and iron (Fe) oxides], and residual metal fractions. The soils from the pasture fields were spiked with 100 mg Cu kg^–1 soil and 200 mg Zn kg^–1 soil for 24 weeks. Copper and Zn extractable with 1 N potassium nitrate (KNO₃) solution decreased exponentially with time but reached a steady state after 2–3 weeks. The concentrations of Cu and Zn exchangeable with potassium (K) were greater in the Digitaria smutsii field soil than Brachiaria decumbens and Stylosanthes guianensis field soils. The exchangeability of added Cu and Zn (indexed Mⁿ⁺ _(exch)) with time was described by a simple exponential decay equation: Mⁿ⁺ _(exch) = αe^βt, where α is a constant, β is a coefficient that defines the rate of transformation of added Cu and Zn from the exchangeable to nonexchangeable pools, and t is time. The β values for Cu (0.040–0.076 mg kg^–1 d^–1) were almost 10 times greater than those of Zn (0.005–0.007 mg kg^–1 d^–1). Sequential extraction of added Cu and Zn indicated that between 26 and 30% of the total Cu and between 19 and 30% of the total Zn were associated with organic matter. Similarly, between 35 and 38% of total Cu and between 47 and 60% of total Zn were associated with Fe, Al, and manganese (Mn) oxides. The differential capacity of the pasture fields to transform added Cu and Zn from exchangeable and labile form to nonlabile and nonexchangeable form appears to be governed by organic matter (OM), pH, and active Fe ratio in the pasture field soils.     

Equilibria of weak acids and organic Al complexes explain activity of H+ and Al3+ in a salt extract of exchangeable cations

Two sequential extractions with unbuffered 0.1 m BaCl₂ were done to study the release of salt-exchangeable H⁺ and Al from mineral horizons of five Podzols and a Cambisol. Released Al was found to have a charge close to 3+ in all horizons and in both extractions. This finding was supported by the near-equality of the titrated exchangeable acidity (EA_T) and the sum of exchangeable acids (EA = H_e + 3Al_e, calculated from the pH and Al concentration of the extract). The ratio between EA of the second and the first extraction was over 0.50 in the Bs2 and C horizons and smaller in the other horizons. H⁺ was assumed to be in equilibrium with weak acid groups, and the modified Henderson–Hasselbach equation, pK_HH = pH ? n log (α/(1 ? α)), was used to explain pH of the extract. The degree of dissociation (α) was calculated as the ratio between effective and potential cation exchange capacity. Value of the empirical constant n was found to be near unity in most horizons. When the monoprotic acid dissociation was assumed in all horizons, pK_HH had the same value in both extractions. For Al³⁺, two equilibrium models were evaluated, describing (i) complexation reactions of Al³⁺ with soil organic matter, and (ii) equilibrium with Al(OH)₃. Apparent equilibrium constants were written as (i) pK_o = xpH ? pAl³⁺, and (ii) log Q_gibbs= log Al³⁺ ? 3log H^+. The two extractions gave an average reaction stoichiometry x close to 2 in all horizons. Results suggest that an equilibrium with organic Al complexes can be used to express dissolved Al³⁺, aluminium being apparently bound to bidentate sites. The value of log Q_gibbs was below the solubility of gibbsite (log K_gibbs = 8.04) in many horizons. In addition, log Q_gibbs of the second extraction was greater than that of the first extraction in all horizons except the C horizon. This indicates that equilibrium with Al(OH)₃ cannot explain dissolved Al³⁺ in the soils. We propose that the models of pK_HH and pK_o can be used to simulate exchangeable H⁺ and Al³⁺ in soil acidification models.     

Distribution of Aluminum Fractionation in the Acidic Rhizosphere Soils of Masson Pine (Pinus massoniana Lamb)

The modified Tessier’s sequential extraction procedure and rhizobox cultivation were employed to investigate the distribution of aluminum (Al) fractions in the acidic rhizosphere soil of Masson pine (Pinus massoniana lamb) seedlings. The results showed that the Al in soils was fractionated into five operationally defined fractions. Three sets of soil samples used in the rhizoboxes were collected from the three forest sites in the southeast of China: Sichuan, Zhejian, and Jiangsu. At the end of 100-day cultivation, the rhizosphere Al fractions for the original or bulk soils were in the order of residual > iron-manganese (Fe-Mn) oxides > organic > carbonate > exchangeable. However, in rhizosphere soil, the Al fraction follows the order of residual > organic > Fe-Mn oxides > carbonate > exchangeable. On average, the rhizosphere experienced significant increase in organically bound Al and slight decrease in exchangeable Al contents, but had decreases in contents for the other three Al fractions compared to the nonrhizosphere. The correlation analysis indicated that the Al contents accumulated in roots were significantly and positively correlated with exchangeable Al contents in the rhizosphere, and also characterized by the major portion of organically bound Al, which exhibited a bioavailable transformation of Al fractions. Results indicated that decreases in both redox potential and soil pH, as well as increase in dissolved organic carbon (DOC), were observed in the rhizosphere. Exchangeable Al and organic Al fractions were dependent mainly on soil pH (hydrogen ion concentration) and DOC, accordingly. Decreasing rhizosphere pH from 5.93 to 3.42 accelerated the secretion of organic carbon. These data are helpful for understanding the mobility and bioavailability of Al fractions in the acidic rhizosphere soils of Masson pine.     

Changes in aluminum pools of andisols due to soil acidification

Abstract

Aluminum concentrations in soil solutions are not only controlled by inorganic clay minerals but also by organically bound aluminum. The objective of this study was to determine which pools contribute to Al dissolution. Soil samples were taken at various distances from tree trunks and at various depths at the Rolling Land Laboratory (RLL), Hachioji, Tokyo. Selective dissolution techniques were used to analyze the changes in pools of solid-phase aluminum. Soil pH values around Hinoki cypresses were in the aluminum buffer range. Exchangeable aluminum contents in soils under Hinoki cypresses were 104 mmol_c kg-^?1 on the average. This value was similar to that of the cation exchange capacity (CEC) of Andisols at RLL at a soil pH of 4. The relationship between the soil pH and exchangeable, organically bound, and amorphous aluminum pools showed that dissolved aluminum ions in the soil solution were primarily derived from the amorphous Al pool. Dissolved aluminum ions were substituted with base cations of soils, resulting in the increase of the content of exchangeable Al and/or the formation of complexes with organic matter which increased the proportion of organically bound Al pools. Increase in the proportion of organically bound Al pools indicated the importance of complexation with soil organic matter for controlling the aluminum concentration in the soil solution.     

Forms and buffering potential of aluminum in tropical and subtropical acid soils cultivated with Pinus taeda L

Purpose

Several interactions between Al and the solid phase of soil influence Al buffering in soil solution. This work evaluated soils cultivated with Pinus taeda L. to determine Al forms in organic and mineral horizons using various extraction methods and to relate acidity with clay mineralogy.

Materials and methods

Organic and mineral horizons of 10 soil profiles (up to 2.1 m deep) in southern Brazil were sampled. Organic horizons were separated into fresh, aged, and fermented/humified litter. The following Al extraction methods were utilized: 0.5 mol L^?1 pH 2.8 CuCl₂–Al complexed in organic matter; 1.0 mol L^?1 KCl–exchangeable Al; water–Al soluble in soil solution; HF concentrated?+?HNO₃ concentrated?+?H₂O₂ 30% (v/v)–total Al. Six sequential extractions were carried out to isolate different forms of amorphous minerals that can buffer Al on soil solution: 0.05 and 0.1 mol L^?1 sodium pyrophosphate; 0.1 and 0.2 mol L^?1 ammonium oxalate; 0.25 and 0.5 mol L^?1 NaOH. Samples of clay were also analyzed by XRD.

Results and discussion

There was a clear effect of litter age on increasing total Al concentration. In the aged litter and fermented and/or humified litter, levels of total Al were 1.4 to 3.8 and 1.5 to 7.8 times greater than in fresh litter, respectively. The CuCl₂ method had higher Al extraction capacity than the KCl method for litter. The lowest Al–pyrophosphate values were observed in the Oxisol, which also had a predominance of gibbsite and the lowest levels of Al–KCl and Al–CuCl₂. There was an inverse relationship between degree of soil weathering and soluble and exchangeable Al in soils. Available Al increased with higher Si proportion in minerals of the clay fraction (2:1?>?1:1?>?0:1).

Conclusions

The worst scenario was soils with the combination of high soluble and exchangeable Al levels and high concentrations of amorphous forms of Al minerals. The best predictors of Al accumulation in the youngest litter horizon were extractions of amorphous minerals with pyrophosphate and NaOH. These extractors are normally used to predict the level of Al buffering in soils. Organic matter had less influence on Al dynamics in soils.

     

A re‐examination of exchangeable acidity as extracted by potassium chloride and potassium fluoride

Abstract

In order to better understand some of the factors likely to affect measurements of KC1 extractable acidity, experiments were conducted using synthetic solutions and extracts from a wide range of contrasting soils. The reagents used for measuring exchangeable acidity (i.e., KC1 and KF) were also examined to evaluate the effects of chemical impurities on acidity measurements. Two commonly used titrimetric methods were adapted and tested to determine the accuracy and precision of acidity measurements. The exchangeable acidity of soil extracts was investigated by extraction methods, extractant concentration, and extractant volume. Results from the soil extract experiments indicated that continuous shaking has no significant effect on acidity measurements. Filtration, however, is critical, especially for acidic organic‐rich soils, since aluminum (Al) ions can be lost during centrifugation. Extractant concentration and volume had variable effects on the acidity measurements for individual soils. In general, the modified Yuan's method is preferable to the modified Thomas’ method for estimating exchangeable Al. To ensure successful determination of exchangeable acidity, we recommend using a wider KCl:soil ratio (>15:1, v/w) for organic soils with low base saturation and allophanic Andisols. In sum, potassium chloride and potassium fluoride extraction for estimating exchangeable acidity is applicable for most soils.     

Assessment of Cadmium Distribution in Some Australian Krasnozems by Sequential Extraction

A sequential extraction procedure was used to investigate the influence of long-term phosphate fertilization on the distribution of cadmium throughout the major components of krasnozemic soils in the potato growing district located to the East of Ballarat, Victoria, Australia. The soil fractions investigated consisted of the water soluble, exchangeable, weakly bound to metal oxides, strongly bound to metal oxides, bound to organic material and residual. Other soil parameters, such as pH_H2O, pH_CaCl2, electrolytical conductivity and total organic material were investigated. The concentrations of Ca, Mg, Fe, Mn and Zn in each soil fraction were also measured. The total concentration of cadmium in the farmed soils had increased from the background level of 100.5 μg/kg to an average of 210 μg/kg. The proportion of cadmium available or potentially available for plant uptake was very low. On average, 89% of the cadmium in the farmed soils had been adsorbed by amorphous metal oxides and organic material, or was associated with silicates, and is therefore unavailable for plant uptake. The metal oxides adsorbed the highest proportion of cadmium.     

Measuring reactive metal in soil: a comparison of multi‐element isotopic dilution and chemical extraction

The isotopically exchangeable metal pool (E‐value) of zinc (Zn), cadmium (Cd) and lead (Pb) were simultaneously measured, using stable isotope dilution, in soils contaminated by Pb/Zn mining activities and varying in properties likely to affect metal reactivity, including pH, organic matter content, metal concentration and land use. E‐values were compared with single and sequential extraction schemes. Results showed a wide range of metal reactivity (approximately 1–100% of total) depending on the extent of contamination and on the prevailing soil conditions. Across the range of soils, the E‐values showed no consistent correspondence to any single chemical extraction procedure (EDTA, DTPA and HNO₃) although there was reasonable agreement with the extractants 0.05 m EDTA and 0.43 m HNO₃ in acidic organic soils. Extraction with 0.005 m DTPA substantially under‐estimated the isotopically exchangeable metal content. E‐values corresponded reasonably well with the exchangeable metal (fraction 1 (F1) of the sequential extraction procedure) in calcareous soils but relatively poorly and inconsistently with F1–F2, F1–F3 or F1–F4 in acidic‐neutral soils. Operational aspects associated with determination of multi‐element E‐values are discussed.     

Impact of Calcareous Amendments on Rye Production and the Exchange Complex in a Palexerult in Northwestern Spain

A Typic Palexerult from northern Spain was subjected to acidity correction field tests over a period of 2 years. The experimental crop was a local rye variety and the amendments included gypsum, dolomite, limestone, and sugar foam waste, all at a 6000 kg ha^–1 rate as calcium carbonate (CaCO₃). General analyses were integrated with specific tests for soluble and easily exchangeable aluminum (Al) forms (Al-CaCl₂) in addition to potassium chloride (KCl)–, barium chloride (BaCl₂)–, and copper chloride (CuCl₂)–extracted Al and adsorbed and amorphous Al. Two types of multiple linear regression models for production each year were established; some encompassed all studied variables and others the six Al forms only. As shown here, Al-KCl, Al-CaCl₂, base saturation, and exchangeable Ca were the individual variables most strongly correlated with production, with R ² = 0.865, within the topmost 12 cm. A principal component analysis exposed a substantial share of pH-dependent charge in organic matter on the cation exchange capacity of the soil.     

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.     

长期酸化对红壤中活性固相铝库大小及亏损程度的影响

用连续分级提取和反复多次酸提取方法研究了长期土壤酸化对红壤固相铝库中铝含量及亏损程度的影响。研究结果表明:嵊县红壤的活性铝库大于永春红壤和屯溪红壤;因永春红壤和屯溪红壤的酸化程度大于嵊县红壤,前两者的有机铝库和无机铝库都比嵊县红壤的亏损,因此反复酸提取过程中铝的释放量也比嵊县红壤少;当高强度酸输入土壤后,弱键合的有机络合态铝可快速活化并亏损,剩余铝库因活性小而释放速率减小,但长期酸化过程中,动力学控制的低活性铝库的活化可能对铝的溶解量仍有重要贡献。     

Extraction of mobile element fractions in forest soils using ammonium nitrate and ammonium chloride

The extraction of earth alkaline and alkali metals (Ca, Mg, K, Na), heavy metals (Mn, Fe, Cu, Zn, Cd, Pb) and Al by 1 M NH₄NO₃ and 0.5 M NH₄Cl was compared for soil samples (texture: silt loam, clay loam) with a wide range of pH(CaCl₂) and organic carbon (OC) from a forest area in W Germany. For each of these elements, close and highly significant correlations could be observed between the results from both methods in organic and mineral soil horizons. The contents of the base cations were almost convertible one‐to‐one. However, for all heavy metals NH₄Cl extracted clearly larger amounts, which was mainly due to their tendency to form soluble chloro complexes with chloride ions from the NH₄Cl solution. This tendency is very distinct in the case of Cd, Pb, and Fe, but also influences the results of Mn and Zn. In the case of Cd and Mn, and to a lower degree also in the case of Pb, Fe, and Zn, the effect of the chloro complexes shows a significant pH dependency. Especially for Cd, but also for Pb, Fe, Mn, Zn, the agreement between both methods increased, when pH(CaCl₂) values and/or contents of OC were taken into account. In comparison to NH₄Cl, NH₄NO₃ proved to be chemically less reactive and, thus, more suitable for the extraction of comparable fractions of mobile heavy metals. Since both methods lead to similar and closely correlated results with regard to base cations and Al, the use of NH₄NO₃ is also recommended for the extraction of mobile/exchangeable alkali, earth alkaline, and Al ions in soils and for the estimation of their contribution to the effective cation‐exchange capacity (CEC). Consequently, we suggest to determine the mobile/exchangeable fraction of all elements using the NH₄NO₃ method. However, the applicability of the NH₄NO₃ method to other soils still needs to be investigated.     

Fractionation of Cu, Pb, Cr, and Zn in a Soil Column Amended with an Anaerobic Municipal Sewage Sludge

The objective of this study was to investigate the changes in the chemical partitioning of Cu, Pb, Cr and Zn within a column of soil incubated with an anaerobic sewage sludge (ANSS) for 2.5 months. The soil was irrigated during the incubation period. A sequential extraction method was used to fractionate these metals into exchangeable, weakly adsorbed, organic, Al oxide, Fe–Mn oxide, and residual, respectively. ANSS was applied at a loading rate of 69 Mg ha^?1. The soil is a Dystric Cambisol with low pH (<3.8), low CEC [<10 cmol(+) kg^?1 below the first 4 cm depth], and low base saturation (<7%). The addition of the ANSS caused a decrease in concentrations of Cu, Pb, and Cr in the A1 horizon, and an increase in the concentrations with depth. Below the A1 horizon, concentrations of Cu increased uniformly (~1 mg cm^?1), and the greatest increases were observed in the residual, Fe–Mn oxides, and weakly adsorbed fractions. Maximum increases in Pb occurred at 4–9 cm of depth (1.6 mg cm^?1), and mainly affected the weakly adsorbed fraction. Chromium essentially accumulated at the limit between the A2 and the Bw horizons (1.1–1.5 mg cm^?1) as residual and organic bound forms, probably through particulate transport. Zinc mainly accumulated in the A1 horizon (2.9 mg cm^?1) as exchangeable Zn. At depth, Zn increments were predominantly observed in the residual fraction. The results of this study thus demonstrate the redistribution of contaminants into different chemical pools and soil layers after sludge amendment.     

Soil podzolization induced by reforestation as shown by sequential and kinetic extractions of Fe and Al

The impact of 60‐year‐old reforestation on soil evolution was studied by following the evolution of Fe and Al distribution as an indicator of early podzolization. We determined the distribution of Al and Fe in soils by combining sequential and kinetic extractions. We extracted the soil sequentially with: 1 mol litre^?1 sodium acetate at pH 5.5 (stage 1); twice with 0.1 mol litre^?1 sodium pyrophosphate at pH 10 (stage 2 and 2b); and with 1 mol litre^?1 hydroxylamine in 4.3 mol litre^?1 acetic acid solution at 90°C (stage 3). For each, we drew a kinetic‐extraction curve. We show that no re‐adsorption, precipitation or complexation with dissolved organic matter occurred for the reaction times recommended in this procedure, that is 6 hours for stage 1, 1.5 hours for stage 2 and 2b and 3 hours for stage 3. For a given extraction, the kinetic curves have the same shape for all samples, that is their behaviour is similar for a given reagent. Sequential extraction can therefore be used to compare the speciation of metals in different samples taken from the same soil. In addition, 60 years after reforestation by beech, a decrease of 12 and 17% is noted in the total Fe and Al contents, respectively, in the 0–10 cm layer, accompanied by a re‐distribution of these elements within the different soil compartments: a decrease of the Fe and Al bound to oxy‐hydroxide in favour of organic complexes and more soluble forms. Sequential extraction is therefore a good indicator of the first pedogenetic modifications induced by human intervention through reforestation.     

几种土壤交换性酸测定方法的效果比较

为真实地反映酸性土壤交换性酸含量水平,探讨了KCl淋溶法、BaCl_2淋溶法、NaAc淋溶法、KCl-三乙醇胺(Triethanolamine,TEA)提取法和BaCl_2-TEA提取法对紫色土、黄壤、红壤和砖红壤4种土壤的交换性酸测定效果。结果表明:5种方法测得的土壤交换性酸大小关系为:BaCl_2-TEA提取法KCl-TEA提取法NaAc淋溶法BaCl_2淋溶法KCl淋溶法。BaCl_2淋溶法能较为真实地反映出土壤交换性酸水平,其次为KCl淋溶法。受土壤有机酸和铝氧化物的影响,NaAc淋溶法、KCl-TEA提取法和BaCl_2-TEA提取法测得的土壤交换性酸含量偏高。但由于尚无标准方法对测定结果进行验证,因此,还需进一步对土壤交换性酸测定方法及其影响因素开展研究。