Chemical species of Al in a gypsum-treated Kitakami Andosol

To examine the possibility that the Al₁₃ polymer ([A10₄Al₁₂(OH)24(H₂0)₁₂]⁷⁺) could be formed in soils after gypsum application, an analytical method using a cation exchange resin and ²⁷Al nuclear magnetic resonance (NMR) spectroscopy was applied to gypsum-treated Kitakami Andosol (fine, mixed, mesic, Andic Dystrochrept). The NMR spectra of the cation exchange resins which retained artificially synthesized hydroxy-AI, showed two broad peaks at 0 and 63 ppm. These results indicated that monomer and/or dimer Al and Al¹³ polymers adsorbed on the cation exchange resin could be detected with ²⁷Al NMR. The amount of polymer Al increased by gypsum application in the Kitakami soil. The NMR spectrum of this resin showed only one peak at 0 ppm indicating that the polymer Al formed in the gypsum treated Kitakami soil was not the Al¹³ polymer.     

Effect of liming on organically complexed aluminum of nonallophanic Andosols from northeastern Japan

Aluminum–humus complexes are believed to be highly stable under natural conditions in nonallophanic Andosols. However, it has been shown that the aluminum complexed with humus is easily released by acidic buffer solutions and possibly controls the aluminum solubility of these soils. Thus, it is highly probable that Al–humus complexes are easily influenced by rather simple chemical treatments. We examined the effects of liming (CaCO₃ treatment) on Al–humus complexes of A and B horizons from Andosols. It was observed that liming reduced the Al release rates from soil samples with pH 3.5 acetate buffer solution and the amounts of the KCl-extractable Al, suggesting the formation of precipitation from easily exchangeable Al. A much larger decrease with liming was also obtained for 0.1 M sodium pyrophosphate-extractable Al (decrease rates of 7–52%) and 0.5 M CuCl₂-extractable Al (decrease rates of 9–43%). These results strongly indicate that liming reduces significant amounts of organically complexed Al as well as the exchangeable Al. The increase in the cation exchange capacity of soils at pH 7 after liming further suggested that the carboxyl group of humus complexed with Al was partly liberated from the Al complexation and became to develop negative charges.     

Gypsum applications to aggregated saline—sodic clay topsoils

Gypsum application was highly efficient as a treatment for reducing amounts of exchangeable sodium and inhibiting clay dispersion in highly structured saline-sodic clay topsoils. Phosphogypsum, applied to the surfaces of aggregates in soil columns treated with simulated rainfall, was dissolved efficiently by frequent intermittent ‘rainfall’. The calcium released by dissolution displaced sodium on the exchange complex within soil aggregates ranging from 7.5 mm to 45 mm in diameter. Of the applied calcium, 64–74% was transferred to ion exchange sites; however, almost one-third of this adsorbed calcium displaced exchangeable magnesium. Comparison of three gypsum treatments, phosphogypsum, rock gypsum, and a saturated gypsum solution (representing a top dressing of highly soluble gypsum), showed that the effectiveness of calcium uptake on the exchange complex followed the order: rock gypsum < saturated solution < phosphogypsum, but differences were small. Application of phosphogypsum caused a 90% reduction in the total amount of dispersed clay released in column leachates, and decreased the maximum clay concentration in the effluents by at least 80%, when compared to soils leached without gypsum treatment.     

Organo-metallic complexes in an Andosol: a comparative study with a Cambisol and Podzol

Current soil-forming processes were studied in a nonallophanic Andosol from the Vosges mountains (north-eastern France). For this purpose, we conducted comparative studies on the organo-metallic fraction dynamics of selected profiles of an Andosol and other typical soils from this region, Cambisol and Podzol. These soils are derived from old volcanic rocks under mesic soil temperature and udic soil moisture regimes. The Andosol profile displayed the characteristics of nonallophanic Andosols: large accumulation of humus, active Al mostly complexed with humus, and low pH. Special attention was given to physical and microbial stability of these organo-metallic associations, respectively by disaggregation tests and incubation experiments. The results indicated that these associations showed a strong resistance against disaggregation by water and against biodegradation. Moreover, the very low concentration of DOC, Al and Fe in soil solutions collected by zero-tension lysimeters, coupled with very low amounts of water-dispersed clays obtained after dispersion tests, suggested that no significant translocations of these components occurred in this Andosol profile. Low mobility together with a strong resistance against mineralization may account for the large accumulation of carbon in this Andosol.     

Changes in Chemical Structure and Biological Activity of L-DOPA as Influenced by an Andosol and Its Components

Velvetbean ( Mucuna pruriens ) has been reported to release 3-(3',4'-dihydroxyphenyl)-L-alanine (L-DOPA) as an allelochemical that inhibits the growth of other plants, although the inhibitory activity depends on the soil type and it is extremely reduced in Andosols. To clarify the effects of Andosols and their components on the chemical structure and plant-growth-inhibitory activity of L-DOPA, an L-DOPA solution was reacted with an Andosol and its components (weathered pumice and purified allophane), and the resultant solution was subjected to ¹H nuclear magnetic resonance and ultraviolet-visible spectral analyses, and plant-growth-inhibitory activity tests. When the L-DOPA solution was added to the soil components, the concentration of L-DOPA in the solution decreased by adsorption and transformation (polymerization) reactions. The adsorption mechanism included a ligand exchange reaction. The rate of L-DOPA transformation was faster at higher pH values. The soil components displayed a catalytic activity and accelerated the transformation of L-DOPA. Similar transformation occurred when light was irradiated. At pH values higher than 4.0, the transformed products from L-DOPA consisted of humic substances-like heterogeneous components, whereas specific components with low molecular weight were included when L-DOPA was transformed at a pH value of 9.7 or higher. The plant-growth-inhibitory activity of L-DOPA was extremely weakened when L-DOPA was adsorbed on or transformed (polymerized) by soil components. Therefore, in soils with high abilities of adsorption and transformation of L-DOPA such as in Andosols, it was likely that the L-DOPA concentration in the soil solution decreased quickly by adsorption and transformation reactions and the allelopathic activity of L-DOPA was lost.     

Horizontal distribution of main hydroxyanthraquinones in soil

Six hydroxyanthraquinones (chrysophanol, chrysotalunin, microcarpin, physcion, 7,7′-biphyscion, and hinakurin) present in the samples of 26 surface soils were quantitatively analyzed, and the contents of HAQs in soil types were compared. The soil samples had been collected from 19 Umbric Andosols and seven Distric Cambisols, and the Andosols were further subdivided into those with allophanic soil materials (exchange acidity (y ₁<5 mL 100 g^-l) and nonallophanic soil materials (y _l≧5 mL 100 g^-l). The following results were obtained. (1) It was determined quantitatively for the first time that chrysotalunin was the major hydroxyanthraquinone in many soils. (2) The amounts of major dime ric hydroxyanthraquinones (chrysotalunin, 7,7′-biphyscion, and microcarpin) in non-allophanic soil materials were significantly larger than those in allophanic soil materials. As the contents of chrysotalunin in Andosols were positively correlated with y _l, which was reported to be positively correlated with aluminum toxicity and exchangeable aluminum in soil, it is suggested that toxic aluminum may be involved in the production of soil hydroxyanthraquinones.     

不同改良剂对酸性土壤的修复效应

为明确不同改良剂对酸性植烟土壤的修复效应,采用盆栽试验,分析了施用丰收延酸性土壤改良剂、金叶酸性土壤改良剂及石灰后土壤pH、水解性酸、潜性酸及土壤交换性能的动态变化。结果表明:施用改良剂可提高土壤pH 3.01%~24.11%,降低土壤水解性酸16.08%~50.46%、交换性Al 3+51.80%~64.27%、交换性H+含量84.12%~93.56%,提高土壤交换性盐基总量45.18%~46.16%、阳离子交换量0.33%~20.10%、盐基饱和度21.35%~49.78%。施用土壤改良剂后,土壤pH先升高后下降,至移栽60天后趋于稳定;土壤水解性酸在烤烟移栽后30~90天差异较小,至移栽后120天略有增加。施用石灰的土壤交换性氢、交换性铝一直下降,但施用丰收延、金叶酸性土壤改良剂的土壤交换性铝下降至烟苗移栽后120天略有增加,土壤交换性氢上升至烟苗移栽后120天大幅度下降。施用土壤改良剂后,土壤交换性盐基总量、阳离子交换量、盐基饱和度一直提高,但变化幅度较小。不同土壤改良剂的材料来源及组成成分不同,其对酸性土壤的恢复效果也不同,以施用石灰的效果最好。     

Contribution of SO3 to the acid neutralizing capacity of Andosols exposed to strong volcanogenic acid and SO2 deposition

Soil response to acid and sulphur inputs is influenced largely by the soil's physico‐chemical properties. We studied the effects of such depositions in two types of Andosols exposed to volcanogenic emission (Masaya, Nicaragua), namely Eutric Andosols rich in allophanic constituents, and Vitric Andosols rich in volcanic glass. Small mineral reserves and large contents of secondary short‐range ordered minerals indicate a more advanced weathering of the Eutric than the Vitric Andosols. Strong correlations between soil specific surface and oxalate‐extractable Al, Si and Fe contents highlight the predominant contribution of short‐range ordered minerals to surface area. Both types of Andosols showed a decrease in pH upon acid input. Sulphur deposition increased the soil's S content to 5470 mg S kg^?1. However, the acid neutralizing capacity of the soil solid phase (ANC_s) was not significantly affected by the acid and S inputs. Non‐exchangeable (mineral reserve) and exchangeable cations and total contents of sulphur and phosphorus dictate most of the ANC_s variation. In the Vitric Andosols, mineral reserves contributed up to 97% to these four additive pools, whereas the exchangeable cations accounted for 1–4%. In the Eutric Andosols, the contribution of mineral reserves was less (71–92%), but the exchangeable cation content was greater (1–20%), whereas the contribution of sulphur and phosphorus was significant at 1–15% and 2–7%, respectively. The main process involved in H⁺ consumption is mineral weathering in Vitric Andosols and ion exchange in Eutric Andosols.     

Acidiphily in pteridophytes: Assessment of the role of root cation‐exchange properties

The soil preference with respect to soil acidity of Asplenium scolopendrium L., Dryopteris filix‐mas (L.) Schott, Pteridium aquilinum (L.) Kuhn as well as of subspecies of the Asplenium trichomanes L. and Polypodium vulgare L. complexes were studied in relation to root cation‐exchange properties. Data were collected for substrate acidity, soil exchangeable cations, and root cation‐exchange capacity. Acidiphilous pteridophytes were characterized by low cation‐exchange capacities. It is unlikely that cation‐exchange properties protect plants from potentially harmful cations such as aluminium or hydrogen, which are abundant under acid soil conditions, through immobilization. It is postulated that cation‐exchange properties are a secondary adaptation to soil acidity, in addition to major adaptations which determine the apparent soil preference. Possibly, a limited variation in cation‐exchange capacity as a function of soil conditions could prevent harmful interactions of soil exchangeable cations with the cation‐exchange sites, such as displacement of cell wall calcium by aluminium or hydrogen ions in acid soils.     

Degradation and remediation of soils polluted with oil-field wastewater

The changes in the properties of gray forest soils and leached chernozems under the impact of contamination with highly saline oil-field wastewater were studied in a model experiment. It was shown that the soil contamination results in the development of technogenic salinization and alkalization leading to worsening of the major soil properties. The salinization of the soils with oil-field wastewater transformed the soil exchange complex: the cation exchange capacity decreased, and the exchangeable sodium percentage increased to up to 25% of the CEC upon the wastewater infiltration and up to 60% of the CEC upon the continuous soil saturation with the wastewater independently of the soil type. The content of exchangeable magnesium also increased due to the phenomenon of super-equivalent exchange. Despite the saturation of the soil adsorption complex with sodium, no development of the soil alkalization took place in the presence of the high concentration of soluble salts. However, the soil alkalization was observed upon the soil washing from soluble salts. The gypsum application to the washed soils lowered the exchangeable sodium concentration to acceptable values and normalized the soil reaction. The gypsum application without the preliminary washing of the soils from soluble salts was of low efficiency; even after six months, the content of exchangeable sodium remained very high. The subsequent soil washing resulted in the removal of the soluble salts but did not affect the degree of the soil alkalization.     

Modelling cation exchange in columns of disturbed and undisturbed subsoil

Cation exchange is often studied with disturbed and dried soils, but the applicability of the results to undisturbed soils is not straightforward. We investigated the value of exchange coefficients obtained from standard procedures for predicting cation exchange in soil. Columns of undisturbed and disturbed subsoil of a Luvisol (SBt horizon) were leached under saturated conditions with 0.4, 4, 20, 41, 102 and 205 mm BaCl₂ at a Darcy velocity of 1400 mm day^?1. The model PHREEQC was used to calculate one‐dimensional transport, inorganic complexation and multiple cation exchange. Two model variants were tested: m1 (exchangeable cations obtained by percolation with NH₄Cl) and m2 (exchangeable cations obtained by shaking the soil with BaCl₂). The exchange coefficients (Gaines–Thomas formalism) were calculated from the ion activities in solution and exchangeable cations obtained by NH₄Cl percolation (m1) or shaking with BaCl₂ (m2). Variant m1 predicted cation exchange of the disturbed (homogenized) soil for the entire BaCl₂ concentration range, whereas variant m2 resulted in a two‐fold overestimation of desorbed K for all experiments, which was related to large amounts of K released from the soil by shaking with BaCl₂. In experiments with undisturbed soil, variant m1 predicted the concentrations of Mg, Ca, K, and Na in the solution phase and the sum of cations released from exchange sites. However, variant m2 predicted changes in ion concentrations and exchangeable cations somewhat less well. This study suggests that the amounts of exchangeable cations and exchange coefficients obtained from experiments with homogenized soil by percolation are useful to predict cation concentrations in column experiments with undisturbed soils.     

有机肥替代化学氮肥提升红壤抗酸化能力

  【目的】  长期过量施用化学氮肥加剧了红壤区农田土壤酸化,严重制约着该区域农业的可持续发展。施用石灰和有机肥是防治红壤酸化的主要措施,我们研究了有机无机肥配合提高红壤抗酸化能力的作用与机理。  【方法】  本研究基于2009年在湖南祁阳中国农业科学院红壤站开展的有机肥替代化学氮肥长期定位试验,其中4个处理分别为单施化肥(由于酸化严重,于2018年底添加石灰改良)、有机肥替代化肥氮20%、40%和60%,供试有机肥为猪粪。采集2018和2020年的土壤样品,分析各施肥处理红壤pH、交换性酸铝、阳离子交换量、有机质、酸缓冲能力等指标的变化及相互关系。  【结果】  至2018年,单施化肥处理较试验之初土壤pH降低了0.48个单位,交换性酸、铝分别增加了2.74和1.06 cmol/kg;添加石灰改良后,土壤pH升高了0.58个单位,交换性酸、铝分别降低了2.62和1.45 cmol/kg。有机肥替代化肥氮40%和60%处理均可有效防治红壤酸化,其中以替代60%处理效果最佳;至2020年60%有机替代处理土壤pH较初始值提高了0.78个单位,交换性酸和交换性铝分别降低了1.10和1.25 cmol/kg。有机肥替代化肥氮40%和60%处理较单施化肥处理显著提高了土壤阳离子交换量,而石灰改良前后土壤阳离子交换量无显著变化。土壤酸缓冲曲线表明,土壤交换性铝含量随着pH的降低而显著升高,单施化肥、有机肥替代化肥氮20%、40%和60%处理的斜率分别为2.71、2.42、1.93和0.16;土壤交换性铝对pH响应斜率与土壤pH、交换性镁、阳离子交换量、交换性钾、有机质含量呈极显著或显著负相关关系。  【结论】  有机肥替代40%以上化学氮肥既能防治红壤酸化,又能提升红壤抗酸化能力。土壤阳离子交换量和有机质可能是导致土壤交换性铝对pH响应差异的主要因素,即阳离子交换量和有机质含量高的土壤pH降低1个单位时,交换性铝增幅较小,但其作用机理还有待进一步研究。     

Chemistry of soil aluminum

Abstract

Better understanding of soil aluminum has had dramatic effects on the interpretation of many aspects of soil chemistry. Aluminum is a Group III element, metallic in nature, and exhibits both ionic and cuvaient bonding. It is the most plentiful of all metallic cations of the earth's crust. It is released from octahedral coordination with oxygen in minerals by weathering processes. Once released, the trivalent Al ion assumes octahedral coordination with six OH₂ groups each of which dissociates a H ion in sequence as pH increases. The resulting hydroxy‐Al ions are absorbed to the cation exchange capacity of the soil. Here they polymerize on charged surfaces and in the interlayers of the clay minerals obstructing both the contraction of the clay lattice and the exchange of cations. Soluble Al is toxic to most plants, and reacts readily with soluble phosphates converting them to relatively insoluble and plant‐unavailable forms. Adsorbed and polymerized aluminum affects actual lime requirements of soils by its acidic nature and indicated lime requirements by its effect on the buffers of the lime requirement test. The level of exchangeable Al has been suggested as an Index of lime requirement of acid soils, but this may be an adequate Index for liming only on highly weathered soils.     

Exchange-induced dissolution of gypsum and the reclamation of sodic soils

A study was undertaken to define the dissolution kinetics of gypsum in the presence of ion exchange resins and to study sodic soil reclamation in laboratory soil columns.
Gypsum pellets were prepared at 1.5 MPa pressure and the time course of their dissolution followed by measuring the electrical conductivity of the solution. Dissolution experiments were carried out in distilled water with and without Na- and Cl-saturated exchange resins or a combination of the two. The results indicate that in the presence of resin the reaction is first order as calcium and/or sulphate are removed from solution by the resin driving the reaction to completion. In water alone the reaction follows second-order kinetics and depends on the rate of mixing as the reaction is transport controlled.
The effect of gypsum placement (uniformly mixed with the entire soil, mixed with the top third of the soil, applied to the soil surface or applied as a saturated gypsum solution) on the efficiency of exchangeable sodium removal, leaching of soluble salts and soil hydraulic conductivity was studied. In addition, the effect of various flow rates on reclamation efficiency was investigated.
The amount of leachate required for reclamation was found to be dependent on gypsum placement, tending to decrease in the order mixed < top third mixed < saturated gypsum solution < gypsum surface application < water. Soil hydraulic conductivity was much higher in the mixed gypsum column than in the gypsum applied on the surface; a result of the higher effective gypsum solubility. Sodic soil electrical conductivity in the presence of solid-phase gypsum is linearly related to the total amount of exchangeable sodium expressed in mol dm⁻³.     

工业副产品改良土壤酸度和铝毒的潜力

It is imperative to choose some low cost, available and effective ameliorants to correct soil acidity in southern China for sustainable agriculture. The present investigation dealt with the possible role of industrial byproducts, i. e., coal fly ash (CFA), alkaline slag (AS), red mud (RM) and phosphogypsum (PG) in correcting acidity and aluminum (Al) toxicity of soils under tea plantation using an indoor incubation experiment. Results indicated that CFA, AS and RM increased soil pH, while PG decreased the pHs of an Ultisol and an Alfisol. The increment of soil pH followed the order of RM > AS > CFA. All the industrial byproducts invariably decreased exchangeable Al and hence increased exchangeable Ca, Mg, K and Na and effective cation exchange capacity. RM, AS and lime decreased total soluble Al, exchangeable Al and organically bound Al. Formation and retention of hydroxyl-Al polymers were the principal mechanism through which Al phytotoxicity was alleviated by application of these amendments. In addition, the heavy metal contents in the four industrial byproducts constituted a limited environmental hazard in a short time at the rates normally used in agriculture. Therefore, the short-term use of the byproducts, especially AS and RM, as amendments for soil acidity and Al toxicity in acid soils may be a potential alternative to the traditional use of mined gypsum and lime.     

Efficiency of gypsum application to acid Andosols estimated using aluminum release rates and plant root growth

Abstract

A great deal of information on the efficiency of gypsum or phosphogypsum to ameliorate acidity in highly weathered soils is available, but only limited information is available on the efficiency in acid Andosols, which possess large amounts of active aluminum (Al). We examined the effectiveness of gypsum application to non-allophanic Andosols (one humus-rich A horizon and two B horizons poor in humus) using extractable soil Al analyses (batch and continuous extraction methods) and a cultivation test using burdock (Arctium lappa). With gypsum amendment, pH(H₂O) values of the soil decreased from 4.5–4.7 to 4.2–4.4, whereas the treatment made almost no difference to the values of pH(KCl). Total active Al (acid oxalate-extractable Al) was hardly affected by gypsum for all samples. Potassium chloride-extractable Al definitely decreased with the addition of gypsum in all soils; however, the decrease was small (0.1–1.4 cmol_c kg^?1) and the values still exceeded “the threshold of 2 cmol_c kg^?1” for inducing Al toxicity in sensitive plants (4.4–8.6 cmol_c Al kg^?1). The change in Al solubility with gypsum application represented by Al release rates from soils using continuous extraction methods with a dilute acetate buffer solution (10^?3 mol L^?1, pH 3.5) differed greatly among the soil samples: The release rate of one of the B horizon samples decreased by 71%, certainly showing the insolubilization of Al compounds, whereas the release rates of the A horizon sample showed almost no change. These changes in Al solubility were well correlated with the plant root growth. Root growth was improved with gypsum in the B horizon sample, whereas improvement was not observed in the A horizon soil. The decrease in the rate of Al release of another B horizon soil with gypsum treatment was smaller (by 20–34%), possibly because of lower pH values after gypsum application (pH[H₂O] of 4.2–4.3). In the B horizon soil, root growth improved only slightly. Thus, the effectiveness of gypsum application to acid Andosols appeared to be largely influenced by soil humus contents and slight differences in soil pH values, and corresponded to a decrease in Al release rates using the continuous extraction method.     

Porosity and soil water properties of Caribbean volcanic ash soils

Abstract. Volcanic ash soils are generally recognized as soils with excellent and stable physical properties. Here we characterized the porosity and water properties of volcanic ash Andosols and Nitisols from Guadeloupe in contrasting banana systems: (1) perennial crop without mechanization, (2) mechanized and regularly replanted crop. Desiccation from 1 kPa to 1550 kPa moisture tension leads to significant shrinkage in the Andosol, representing a 50% reduction of the void space. The clayey Nitisol exhibited limited shrinkage. Soil clods from the mechanized plots had a significantly smaller macroporosity than that from perennial plots. The soil hydraulic conductivity was also drastically reduced in the compacted layers of the mechanized plots. However, Nitisols appeared to be less affected than Andosols. Laboratory compression tests showed that both soils were susceptible to compaction at soil moisture close to field capacity. The shrinkage properties of the Andosol were due to microaggregation of non-crystalline components upon drying. The relative stability of the macroporosity in the Nitisol was probably related to the presence of stable microaggregates made of halloysite and iron oxide. Two major processes promote soil structure degradation in the Andosol under mechanized banana cropping, surface desiccation and soil compaction. They are both induced by repeated tillage after clearing.     

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.     

武陵山地植烟土壤酸度特征及影响因素——以湖南省湘西自治州为例

为了解多年种植烤烟的山地土壤酸度特征,研究了湘西自治州的土壤酸度指标特征及其关系以及植烟年限和土壤类型、有机质、黏粒对土壤酸度的影响。结果表明:(1)植烟年限对土壤酸度的影响大于土壤类型;随植烟年限增加,土壤pH下降,潜性酸度增加,黄棕壤土的交换性盐基、阳离子交换量和盐基饱和度下降。(2)土壤pH与交换性酸为幂函数关系,交换性铝是土壤交换性酸的主体,土壤交换性酸强度随交换性铝及其相对比例的增加而增加。(3)土壤pH与交换性盐基、阳离子交换量、盐基饱和度为二次曲线关系,当pH6时,随土壤pH增加,交换性盐基和阳离子交换量下降,盐基饱和度增加;当pH6时,随土壤pH增加,交换性盐基和阳离子交换量增加,盐基饱和度变幅小。(4)土壤交换性盐基离子主要是交换性钙,其次是交换性镁;对土壤pH影响较大的盐基离子是交换性钙。(5)有机质和黏粒主要影响土壤pH、阳离子交换量、交换性盐基和交换性钙。     

Adsorption of herbicidally active degradate 2-(2,4-dichloro-3-methylphenoxy)propanoic acid on an andosol

The adsorption of 2-(2,4-dichloro-3-methylphenoxy)propanoic acid (DMPA) on the surface horizon of a humus-rich Andosol was examined. To investigate the mechanisms of adsorption, chemically treated Andosols, such as organic matter removed Andosol, organic matter and active metals removed Andosol, and clay minerals of the Andosol, were prepared. Furthermore, humic acid was extracted from the Andosol. The mechanisms of the DMPA adsorption were identified by using those untreated and chemically treated Andosols and the humic acid. The amount of DMPA adsorbed increased with decreasing equilibrium pH value. Active surface hydroxyl groups were identified as the most important soil functional group in DMPA adsorption. The predominant mechanism of DMPA adsorption on the Andosol is a ligand-exchange reaction, in which an active surface hydroxyl on Al and/or Fe is replaced by a carboxylic group of DMPA. A comparative study revealed that the amount of DMPA adsorbed was slightly greater than that of (2,4-dichlorophenoxy)acetic acid (2,4-D), especially at equilibrium pH values below 5. This is because the octanol-water partition coefficient (log Kow) of DMPA in the equilibrium pH range is higher than that of 2,4-D, and SOM participates in the adsorption process through a hydrophobic interaction.