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1.
Different types of cation exchange capacity (CEC) and related chemical properties were determined in the main genetic horizons of meadow-chestnut soils in the mesodepressions at the Dzhanybek Research Station of the Institute of Forestry of the Russian Academy of Sciences. In the A horizon, the CEC is mainly due to the organic matter from the clay and coarse fractions, which provides 36% of the soil CEC, and to labile silicates and other clay minerals of the clay fraction. In the Bt horizon, the CEC is mainly provided by the labile minerals of the clay fraction and organic matter of the clay and coarse fractions. The standard soil CEC was found to be significantly higher than the sum of the exchangeable cations in the A horizon and slightly lower than the sum of the exchangeable cations in the Bt and Bca2 horizons. This difference can be related to the fact that the NH4+ ion, which is selectively adsorbed by clay minerals, is used as a displacing cation during the determination of the exchangeable bases, while the Ba2+ ion, which is more selectively adsorbed by organic matter, is used during the determination of the standard CEC. In all the genetic horizons, the experimentally determined value of the standard CEC almost coincides with the CEC value obtained by summing the standard CECs of the different particle-size fractions with account for their contents; hence, this parameter is additive in nature.  相似文献   

2.
Towada Ando soils consisted of five soils—Towada-a (1,000 years old), Towada-b (2,000 years old), Chuseri (4,000 years old), Nanbu (8,600 years old), and Ninokura soils (10,000 years Amorphous clay materials of these soils taken at different localities were studied by the combined use of selective dissolution and differential infrared spectroscopy, X-ray analysis, electron microscopy, etc.

The main clay minerals of Towada-a soils, present-day soils, were montmorillonite-vermic-ulite chloritic intergrades and opaline silica, or these minerals and allophane in the humus horizons, and allophane in the non-humus ones. Towada-b soils overlain by the Towada-a soils showed the clay mineralogical constituents similar to those of Towada-a soils. However, allophane was one of the main clay minerals in all the humus horizons as well as non-humus ones. The main clay minerals of Chuseri soils were allophane and layer silicates consisting chiefly of chloritic intergrades and chlorite in the humus horizons, and allophane in the non-humus ones. Opaline silica was present in minor amounts in the humus horizons of Chuseri soils, but nearly absent in Nanbu and Ninokura soils.

There were remarkable differences in the clay mineralogical composition of Nanbu and Ninokura soils with differences of their environmental conditions. Allophane and imogolite Were dominant in the clay fractions of both humus and non-humus horizons of very shallowly buried Nanbu soil which was subjected to the strong leaching process. Allophane was the main clay mineral of deeply buried Nanbu and Ninokura soils which showed the absence of notable accumulation of bases and silica. On the contrary, halloysite with a small amount of siliceous amorphous material appeared in very deeply buried Nanbu and Ninokura soils where bases and silica were distinctly accumulated. The amounts of halloysite in the clay fractions were larger in the humus horizons than non-humus ones, and in Ninokura soil than Nanbu soil.

Soil age, soil organic matter, and depositional overburden of tephras were observed to be conspicuous among various factors relating to the weathering of amorphous clay materials in Towada Ando soils.  相似文献   

3.
Agricultural, environmental and ecological modeling requires soil cation exchange capacity (CEC) that is difficult to measure. Pedotransfer functions (PTFs) are thus routinely applied to predict CEC from easily measured physicochemical properties (e.g., texture, soil organic matter, pH). This study developed the support vector machines (SVM)‐based PTFs to predict soil CEC based on 208 soil samples collected from A and B horizons in Qingdao City, Shandong Province, China. The database was randomly split into calibration and validation datasets in proportions of 3:1 using the bootstrap method. The optimal SVM parameters were searched by applying the genetic algorithm (GA). The performance of SVM models was compared to those of multiple stepwise regression (MSR) and artificial neural network (ANN) models. Results show that the accuracy of CEC predicted by SVM improves considerably over those predicted by MSR and ANN. The performance of SVM for B horizon (R2 = 0.85) is slightly better than that for A horizon (R2 = 0.81). The SVM is a powerful approach in the simulation of nonlinear relationship between CEC and physicochemical properties of widely distributed samples from different soil horizons. Sensitivity analysis was also conducted to explore the influence of each input parameter on the CEC predictions by SVM. The clay content is the most sensitive parameter, followed by soil organic matter and pH, while sand content has the weakest influence. This suggests that clay is the most important predictor for predicting CEC of both soil horizons.  相似文献   

4.
Abstract

A method to determine the contents of imogolite and Al-rich allophane (Sil Al ? 1 : 2) in volcanic ash soils was presented. The method is based on the (1) assessment of the presence of Al-rich allophane in clays by successsive extraction with dithionite-citrate and oxalate-oxalic acid, (2) trimethylsilylation of soil clay with a mixture of hexamethyldisiloxane, HCl, and isopropyl alcohol, and determination of the content of monomeric Si based on the trimethylsilyl derivative of monomeric orthosilicate anion by gas / liquid chromatography, (3) determination of the total content of imogolite and Al-rich allophane based on the content of monomeric Si from imogolite, (4) determination of the imogolite content by Thermogravimetry (TG )-Differential Thermal Analysis (DTA) based on the weight loss due to endothermic dehydroxylation with maximum values at ca. 386°C, (5) calculation of the Al-rich allophane content by subtracting the imogolite content from the total content of these minerals, and (6) evaluation of the imogolite and Al-rich allophane content of soil by multiplying clay content of soil and the two mineral content of clay. The trimethylsilylation analysis was found to be reproducible, and the estimated total amounts of two minerals in clays by this method were adequately approximated to those evaluated from the amount of Si (= Sio) extracted with oxalate-oxalic acid after extraction with dithionite-citrate. The variation in the abmldance of two minerals in the soil horizons of volcanic ash soils from the San'in region indicated that this method is suitable for the profile-study of volcanic ash soils.  相似文献   

5.
The clay mineralogy of 22 samples of the Ap horizons of Ando soils was determined by a combination of methods. Of these samples, 15 did and 7 did not contain allophane and imogolite. Opaline silica was found in 4 samples, whereas aluminum—humus complexes, iron oxides and layer silicates were found in all samples. The presence of allophane and imogolite and the absence of opaline silica in a few Ap horizons was related to mixing of A1 horizons and subsoils by cultivation and to lower supplies of organic matter relative to the amounts of aluminum released from volcanic ash by weathering. The contents of 2:1 and 2:1:1 layer silicates and their intergrades were larger in soils in which quartz predominated in fine fractions. It was inferred that aluminum bound with humus and in allophane-like constituents, rather than aluminum in allophane and imogolite, is important in reactions with phosphate and fluoride.  相似文献   

6.
The macromorphology, micromorphology and chemical nature of illuvial material in podzol B horizons and subsoils can be explained by contributions from two different migrating species: (a) a positively-charged mixed Al2O3-Fe2O3-SiO2-H2O sol incorporating minor amounts of adsorbed organic matter and silicate clay, and (b) negatively charged organic sols and solutions, carrying minor amounts of Al, Fe and clay. These species can also be generated within B horizons of high root activity. An alternative theory, that requires allophane to be formed in situ in the B horizon by microbial decomposition of precipitated organic complexes, fails to predict the observed distribution of allophane.  相似文献   

7.
The organic matter in soils may be stabilized by its interactions with minerals. We have studied such interactions in a Haplic Alisol under forest in which clay and organic matter have migrated from an eluvial A horizon to accumulate in an illuvial B horizon. We have tried to trace the fate of organic matter in these horizons (Ah and Bvt) by determining clay mineralogy, carbon and nitrogen content, hydrolysable amino acids, lignin signature by alkaline CuO oxidation and carbon species by 13C CPMAS NMR of bulk soils and particle‐size fractions. In both horizons, most of the organic matter was present in O–alkyl and methylene structures, each contributing one‐third to the bulk organic matter. In the Ah horizon the ratios of carbon‐to‐nitrogen, and yields for lignin and hydrolysable amino acids decreased as the particle‐size class decreased, but side‐chain oxidation of lignin compounds increased with decreasing particle size. In contrast to previous observations, the proportions of O–alkyl carbon increased as particle size decreased, constituting a major proportion of the organic carbon in the clay‐size fractions from both the Ah and Bvt horizons (≥ 38%), while proportions of methylene carbon decreased. Illite was the dominant mineral in the fraction ≤ 6 μm, whereas the mobile fine clay fraction (<0.2 μm) was rich in smectites – minerals with large surface areas. Our results support the hypothesis that potentially labile organic matter, such as O–alkyl carbon typically present in polysaccharides, may be stabilized against further degradation in organomineral complexes.  相似文献   

8.
In soil carbon dynamics, the role of physicochemical interactions between organic matter and minerals is not well understood nor quantified. This paper examines the interactions between soil organic matter and poorly crystalline aluminosilicates in a volcanic ash soil on La Réunion in the southern tropics. The soil examined is a profile composed of a surface soil (L-Ao-E-Bh) overlying four buried horizons (horizons 2Bw, 3Bw, 4Bw, 5Bw) that have all developed from successive tephra deposits. Non-destructive spectroscopy (XRD, FTIR and NMR of Si and Al) showed that the mineralogical composition varies from one buried horizon to another. Further, we show that buried horizons characterized by large amounts of crystalline minerals (feldspars, gibbsite) have the least capacity to store organic matter and the fastest carbon turnover. In contrast, buried horizons containing much poorly crystalline material (proto-imogolite and proto-imogolite allophane, denoted LP-ITM) store large amounts of organic matter which turns over very slowly. To understand the mechanism of interactions between LP-ITM and organic matter better, we focused on a horizon formed exclusively of LP-ITM. We demonstrate, using Δ14C and δ13C values, that even though LP-ITM is extraordinarily effective at stabilizing organic matter, C linked to LP-ITM is still in dynamic equilibrium with its environment and cycles slowly. Based on Δ14C values, we estimated the residence time of organic C as ∼ 163 000 years for the most stabilized subhorizon, a value that is comparable to that for organic carbon stabilized in Hawaiian volcanic soils. However, this calculation is likely to be biased by the presence of microcharcoal. We characterized the organo-mineral binding between organic matter and LP-ITM by 27Al NMR, and found that the organic matter is not only chelated to LP-ITM, but it may also limit the polymerization of mineral phases to a stage between proto-imogolite and proto-imogolite allophane. Our results demonstrate the important role of poorly crystalline minerals in the storage of organic C, and show that mineral and organic compounds have to be studied simultaneously to understand the dynamics of organic C in the soil.  相似文献   

9.
Abstract

Characteristics of Brown Forest soils developed under different bio-climatic conditions from low to high eleyations in the Kinki District were studied with special reference to their pedogenetic processes. The Brown Forest soils at high elevations were characterized by a lower bulk density, higher capacities to adsorb organic matter, phosphate, and moisture, which were correlated with the ratio of the amorphous content to the clay content (the value of the ratio of (Feo + Alo)/clay), as compared to those at low elevations. Considering the fact that the value of the (Feo + Alo)/clay ratio was not correlated with the volcanic glass index, the formation of an amorphous fraction at high elevations was considered to proceed according to the following mechanism.

Low temperature at high elevations (above 700 m) may retard the crystallization of oxide minerals. The amorphous oxides with variable positive charge thus formed may adsorb organic matter, confering a darker color and high moisture and high phosphate retention capacities to the subsoil. Adsorbed organic matter stabilizes these amorphous oxides, thus enhancing the amorphous properties and inhibiting crystallization. A1 translocation due to the weak podzolization may contribute to the increase of the content of amorphous materials.

Characterization of the B horizons in forest soils in Japan, in terms of the values of the ratios of (Feo + Alo)/clay, (Fed-Feo)/Fet, and Alo/Ald, (CEC -ECEQ/CEC and STPT-ZPC, suggested that forest soils might be classified into four groups.  相似文献   

10.
The cation exchange capacity (CEC) and specific surface properties were investigated in four particle‐size fractions < 50 μm from three loess (one Kastanozem and two Phaeozems), a holocene (Fluvisol) and a basalt soil (Nitisol) before and after destruction of organic matter. Particle‐size fractions were separated by sedimentation after chemical and physical dispersion of the soil samples. Illite, amorphous minerals, mixed layers, smectite and kaolinite were the predominant clay minerals. They were detected in all size fractions. The CEC increased with increasing organic matter contents and this effect was more pronounced in coarser fractions. The organic matter content per unit surface area was two or three times larger in coarse silt than in clay, irrespective of the soil type.  相似文献   

11.
黄土高原小流域土壤阳离子交换量分布特征及影响因子   总被引：10，自引：2，他引：8  
通过对黄土高原陕北地区3个小流域(朱家沟、纸坊沟和泥河沟)27个采样点的54个土壤样品分析,应用统计方法讨论土壤阳离子交换量的分布特征和影响因子。结果表明:(1)在3个所选定的典型小流域中,土壤CEC呈现明显的地带性,从北到南,CEC值显著升高。(2)在同一流域,CEC垂直地带变化基本表现为随高度降低而增大;而在同一剖面中,表层土壤CEC值总是高于下层。通过相关性分析和逐步回归检验,得出在粘土矿物类型基本相同的前提条件下,影响CEC值变化的主要因素有pH值、土壤黏粒含量和有机质含量,粉粒含量的影响较小,而砂粒含量则与CEC表现出显著负相关。  相似文献   

12.
C.W. Childs  R.L. Parfitt  R. Lee 《Geoderma》1983,29(2):139-155
Chemical and mineralogical data are presented for three Spodosols (podzols) and a related Inceptisol (yellow-brown loam). Allophane with an Al/Si atomic ratio close to two is identified in the B horizons of all four soils, and minor amounts of imogolite are present in association with allophane in all but one soil where small-particle gibbsite occurs. Parent materials for these soils are essentially non-vitric. Allophane (Al/Si = 2) has been estimated quantitatively in all soils using oxalate-extractable Si (Si0) and is selected clay fractions using both Si0 and infrared spectroscopy. Maximum concentrations of allophane (Al/Si = 2) range from 5% to 18% of fine earth (< 2 mm) fractions and all occur in B horizons. Fe0 values are low relative to Al0 values except for the upper horizons of the Inceptisol. Al0 values peak in B horizons and the ratio pyrophosphate-extractable Al to Al0 decreases from about 1 in A and upper B horizons to 0.1–0.4 in lower B horizons.An interpretation of the data is consistent with recent proposals that the movement of Al in podzolisation is due primarily to the formation of inorganic complexes with Si. Chemical criteria for spodic horizons should be consistent with the total illuviation of Al and Fe (and perhaps Si), rather than just the organic-bound fraction of Al and Fe in these horizons as indicated by amounts in extractants such as pyrophosphate.  相似文献   

13.
A contrasting occurrence of clay minerals was found within a soil profile which was derived from volcanic materials in the suburbs of Fukuoka-city, Northern Kyushu. The soil profile is located on an isolated terrace, and the morphological characteristics of the soil correspond exactly to Andosols, so-called Kuroboku soils or Humic Allophane soils.

The clay fraction of upper horizons of the soil consists largely of alumina-rich gel-like materials, gibbsite, and layer silicates such as chlorite and chloritevermiculite intergrades, while that of lower horizons is composed of allophane and gibbsite or halloysite. There was no positive indication of allophane in the upper horizons. Corresponding with the clay mineralogical composition, quartz is abundant in the fine sand fraction of the upper horizons, while the mineral is very scarce or none in the lower horizons, suggesting a close relation between the petrological nature of parent volcanic materials and the mineralogical composition of weathering products. The dominant clay mineral in the volcanic 1.10il might be dependent on the petrological nature of parent materials, and allophane is mostly formed from andesitic materials, and alumina-rich gel-like materials and layer silicates have come from quartz andesitic materials. Allophane would transform to gibbsite or halloysite according to weathering conditions, and aluminarich gel-like materials change to gibbsite under a well-drained condition.

The soil materials have been so greatly weathered that some horizons contain gibbsite of even more than 40 per cent or halloysite over 70 per cent. The morphology and mineralogy are quite similar to so-cailed “non-volcanic Kuroboku soils.”  相似文献   

14.
水溶性有机碳在各种粘土底土中的吸附：土壤性质的影响   总被引：3，自引：0，他引：3  
Clay-rich subsoils are added to sandy soils to improve crop yield and increase organic carbon (C) sequestration; however, little is known about the influence of clay subsoil properties on organic C sorption and desorption. Batch sorption experiments were conducted with nine clay subsoils with a range of properties. The clay subsoils were shaken for 16 h at 4 oC with water-extractable organic C (WEOC, 1 224 g C L-1) from mature wheat residue at a soil to extract ratio of 1:10. After removal of the supernatant, the residual pellet was shaken with deionised water to determine organic C desorption. The WEOC sorption was positively correlated with smectite and illite contents, cation exchange capacity (CEC) and total organic C, but negatively correlated with kaolinite content. Desorption of WEOC expressed as a percentage of WEOC sorbed was negatively correlated with smectite and illite contents, CEC, total and exchangeable calcium (Ca) concentrations and clay content, but positively correlated with kaolinite content. The relative importance of these properties varied among soil types. The soils with a high WEOC sorption capacity had medium CEC and their dominant clay minerals were smectite and illite. In contrast, kaolinite was the dominant clay mineral in the soils with a low WEOC sorption capacity and low-to-medium CEC. However, most soils had properties which could increase WEOC sorption as well as those that could decrease WEOC sorption. The relative importance of properties increasing or decreasing WEOC sorption varied with soils. The soils with high desorption had a low total Ca concentration, low-to-medium CEC and low clay content, whereas the soils with low desorption were characterised by medium-to-high CEC and smectite and illite were the dominant clay minerals. We conclude that WEOC sorption and desorption depend not on a single property but rather a combination of several properties of the subsoils in this study.  相似文献   

15.
About the sorption of dissolved organic matter to forest soils This investigation characterizes the major forest soils of the temperate climatic zones (leptosols, vertisols, cambisols, luvisols, podzols, stagnosols, gleysols) as sorbents for dissolved organic matter (DOM). Sorption isotherms were obtained for 135 soil horizons from 36 profiles. When solutions containing no DOC were added, the release of dissolved organic carbon (DOC) was highest for horizons rich in organic C (A and Bh horizons). In subsoil horizons DOC release was much lower. Most of the investigated top soils (A and E horizons) and Bh, Bg, and C horizons showed a weak DOC sorption. This was caused by low contents of sorbents (clay and sesquioxides) and/or high contents of organic C. Organic C seems to reduce the DOC sorption by occupying binding sites. Subsoils rich in clay and sesquioxides like Bs, Bt, and Bw horizons showed a strong retention of DOC. Under the aerobic conditions of the experiments, some of the subsoils of stagnosols and gleysols also showed a strong sorption of DOC. However, in sorption experiments conducted after an anaerobic incubation, the DOC sorption decreased significantly.  相似文献   

16.
A soil's reflectance spectrum in the visible and near infrared is rich in information. It is an integrative property of the soil that measures its colour, the abundance of iron oxides, clay minerals and carbonates, the amount of water and organic matter and its particle size. We explored the merit of discriminating between soil horizons, of which we had 13 654 samples, and soil orders from the Australian Soil Classification, of which we had samples from 1697 profiles with designated horizons, by analysing quantitatively their diffuse reflectance spectra in the visible‐near infrared (vis–NIR) range (350–2500 nm). We re‐sampled the spectra to 10‐nm intervals and converted them to logarithms of deviations from their convex hulls. We then transformed them to canonical variates, which we display as scatter diagrams in low‐order canonical planes. The minerals, colour and organic constituents thought to be responsible for their discrimination are identified. Each spectrum was re‐examined and allocated to the group whose centroid was nearest in the canonical space. Topsoil horizons (A, A2 and transitional AB and AC horizons) were distinguishable from subsoils (B, C and transitional BC horizons). Vertosols, Ferrosols, Podosols (Podzols), Organosols, Calcarosols, Rudosols, Sodosols, Hydrosols, Kandosols and Kurosols were in general well separated from other soil orders and were assigned to their own orders such that 80% or more were correctly allocated. These orders possess characteristics that are easily distinguished by vis–NIR spectroscopy. Re‐allocations to other orders were interpretable and could be related to identifying features of the ASC classification. Our results show that spectra distinguish soil horizons and soil type. They suggest that vis–NIR spectroscopy could make an important contribution to the definition and identification of classes in an effective system of soil classification.  相似文献   

17.
为了解我国亚热带地区山地草甸土性态的变化和成土特点,从福建、浙江、江西、安徽、湖南和贵州等省采集了20个代表性山地草甸土剖面,详细观察了土壤剖面形态特征,分析了土壤颗粒组成、有机质、阳离子交换量(CEC)、酸度、氧化铁形态和黏土矿物类型等指标,并从诊断分类的角度探讨了它们在中国土壤系统分类中的地位。结果表明:这一地区的山地草甸土表层有机质积累均非常明显,颜色普遍呈黑色和深褐色,土壤酸化明显,土壤氧化铁游离度多在40%以下,土壤CEC较高。但研究也发现,不同样点之间土壤的土体厚度、剖面构型、黏化状况、有机质垂直分布、氧化铁含量、矿物类型及其诊断层和诊断特性均有较大的差异。土体构型大致有Ah-C、Ah-Bw-C、Ah-Bt-C和Ah-G-C等4类。根据中国土壤系统分类的诊断标准,可把研究的20个剖面归并为均腐土、潜育土、淋溶土、雏形土和新成土等5个土纲,下续分为6个亚纲、10个土类和15个亚类。研究认为,在地理发生分类中笼统地把这些土壤归为一个土类存在边界不明确等问题。  相似文献   

18.
In thin sections of a cemented Bs horizon, allophane is present as isotropic, or weakly anisotropic, transparent, yellow, commonly fluorescent gel deposits, which line or fill voids, cement sand and silt, and form pseudomorphs of root structures. Atomic ratios of Si: Al range from 1: 2.2 to 1: 3.7 in pale deposits, but drop to 1: 8.8 in regions of organic staining. Fe: Al atomic ratios in transparent deposits range from near zero to 0.4. The local uniformity of the gels indicates that the allophane, with associated iron oxides, is deposited from solution, and is not formed in situ from a precipitated organic complex, or by weathering of minerals in situ. Mineralogical evidence indicates that the origin of the allophane is related to intense acidic weathering of plagioclase and biotites in the Eg and Bhg horizons. A fibrous morphology indicative of imogolite is seen under the scanning electron microscope only in critical point dried specimens. It is proposed that the cracked coatings characteristic of cemented Bs horizons can be interpreted as allophanic deposits, associated with varying amounts of clay and iron oxide, and impregnated with varying amounts of fulvic acids. Such deposits cannot be taken as evidence for the migration of Al and Fe as organic complexes.  相似文献   

19.
Abstract

The charge properties of three soils developed on granulite and serpentinite were investigated. These soils contain large amounts of organic matter, free iron oxide, and clay, and are therefore a good medium for measuring the interactions between those components. Cation‐ and anion‐exchange capacities (CEC and AEC) were measured in percolation experiments with and without ammonium acetate buffer pretreatment, using various electrolyte concentrations. The measurements were repeated after removal of sesquioxides and/or organic matter. In addition, potentiometric titrations were carried out to determine the ‘point of zero salt effect’ of each sample. Untreated samples showed a mutual blocking of positive charge on sesquioxides and negative charge on organic matter, leading to decreased CEC and negligible AEC values. Because the AEC is fully blocked, the natural soils do not have a ‘point of zero net charge’ (PZNC), and the apparent ‘points of zero salt effect’ (PZSE) obtained in potentiometric batch titrations are artifacts. Positive charge appeared only after the removal of organic matter. Percolation with acetate buffer strongly increased the measured CEC in samples containing organic complexes. After removal of organic matter, a slight buffer effect remained. This is attributed to the release of sesquioxides from organic complexes and clay surfaces by preferent binding to the acetate anion.  相似文献   

20.
Abstract

Recently agricultural activity in the mountainous area of northern Thailand has increased and problems relating to soil fertility have arisen. In order to gain basic information about the soil properties associated with shifting cultivation, physicochemical properties of the surface soils (0–10 cm) and subsoils (30–40 cm) were investigated in selected villages in the area. The physicochemical properties of the soils studied are summarized as follows: 1) The soils were rich in organic matter, content of which ranged from 11.4 to 63.3 g C kg?1 in the surface soil. 2) The pH(H2O) of the soils mostly ranged from 5 to 7 and soil acidity was more pronounced in the deeper horizons. In the surface soils, exchangeable Ca and Mg were generally dominant, whereas exchangeable Al was often predominant in the subsoils. 3) Most of the soils showed a medium to fine texture with more than 30% clay. The clay mineral composition was characterized by various degrees of mixture of kaolin minerals and clay mica with, in some cases, a certain amount of 2:1-2:1:1 intergrades. 4) According to the ion adsorption curves, most of the B horizon soils were characterized by the predominance of permanent negative charges. On the other hand, organic matter contributed to the increase of variable negative charges in the surface soils. The content of organic matter and the percentage of the clay fraction were essential for determining the CEC of the soils of the surface 10 and 30–40 cm depths, respectively. Under the field conditions, the composition of exchangeable cations largely reflected the soil acidity. In addition, the content of organic matter also showed a significant correlation with that of available N in the surface soils. Thus, soil acidity both in the surface soils and subsoils, organic matter content in the surface soils, and clay content in the subsoils were considered to be the main factors that affected soil chemical fertility in the area.  相似文献   

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