Physicochemical properties of the soils associated with shifting cultivation in Northern Thailand with special reference to factors determining soil fertility

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.     

我国几种主要土壤胶体的NH4+吸附特征

本文讨论我国几种主要土壤胶体的NH₄⁺吸附特征。土壤胶体对NH₄⁺的吸附符合两种表面Langmuir方程。土壤胶体对NH₄⁺的结合能力强弱顺序是:黄棕壤>黑土、(土娄)土>红壤>砖红壤,而NH₄⁺的解吸率大小顺序与此相反。Langmuir吸附方程参数K₁与土壤胶体的粘粒矿物组成有关,并与土壤胶体对NH₄⁺的相对偏好性(A值)呈正相关。Langmuir参数(M₁+M₂)与土壤胶体的CEC呈正相关,去有机质(OM.)前后△K₁与△OM.呈反相关。去有机质可增加土壤胶体对NH₄⁺的偏好性。土壤胶体的NH₄⁺吸附和解吸特征决定于其组成和表面性质,并受有机无机复合作用的影响。永久电荷吸附位对NH₄⁺的偏好性较强,而可变电荷吸附位则较弱。     

Effect of Clay Minerals and Organic Matter on the Cation Exchange Capacity of Silt Fractions

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.     

Impacts of plantation forest management on soil organic matter quality

Purpose  

Light fraction soil organic matter is characterized by rapid mineralization due to the labile nature of its chemical constituents and to the lack of protection by soil colloids. The changes in the size of light fraction soil organic matter constituents are useful early indicators of management-related carbon (C) and nutrient changes. However, previous studies have not assessed the impacts of forest management practices on the chemical composition and sources of organic matter in the light fraction. The change in the chemistry of light fraction soil organic matter may significantly affect turnover rate of organic matter in the whole soil and soil fertility. The aim of this study was to assess how different forest management practices would affect the chemical composition of light fraction soil organic matter.     

新增耕地土壤物质组分特征及其培肥研究

为了解土地整理新增耕地土壤物质组成及土壤肥力状况,对新增耕地土壤矿物成分、化学成分、污染元素和土壤化学性质进行了分析,分析结果将为新增耕地土壤培肥提供依据.实验结果表明新增耕地土壤养分的有效氮、磷、钾及有机质比较缺乏,必须对其进行培肥.利用固体废物对新增耕地土壤进行培肥,其成本低,工艺简单,培肥效果良好.     

Studies on the Complexes of Montmorines with Urea and its Derivatives

It is considered that the study of the complex formation of soil colloids with urea and its derivatives is important not only to reveal the adsorption mechanisms of those compounds, but also to give valuable suggestions for the synthesis of organic fertilizers. Montmorine, on the other hand, is one of major clay constituents of soil colloids from arable soil in Japan, and that gives greater influence to the physical and chemical properties of the soils than other clay minerals do. The complex formation of montmorine with organic substances have been intensively studied by soil scientists, mineralogists and colloid scientists. From the data reported up to now, it is presumed that there are four different mechanisms in the complex formation of montmorine with organic substances. The first is a Van der Waals adsorption, the second the ion exchange reaction of adsorbed cations with organic molecules, the third the polar bonding of exchangeabe cations with polaar organic molecules, and the last the covalent bond of clays and organic substances. In the complex formation of montmorine with urea and its derivatives, two or more mechanisms are expected at a time, in accordance with their structural characters.     

水分非饱和条件下土壤矿物界面有毒有机物转化机制研究进展

土壤矿物作为土壤重要活性组分，可驱动土壤有毒有机物化学转化，降低污染风险。以往土壤矿物与有毒有机物界面行为研究主要集中于水环境或矿物悬浊液体系，然而实际环境中土壤及其矿物常处于干燥、湿润等水分非饱和状态。近年来，水分非饱和条件下土壤矿物界面有毒有机物转化及机制已成为研究热点，相关研究获得一系列新发现。低含水量铁锰矿物、黏土矿物和金属离子饱和黏土矿物能驱动多环芳烃、抗生素等疏水性有毒有机物化学转化。水分非饱和环境会减弱矿物界面水分子与有毒有机物竞争活性位点，并使矿物发生脱水、向高活性结构转变。此外，土壤矿物水分状态也会影响有毒有机物转化产物，水分非饱和环境更有利于持久性自由基和卤代二噁英等中间产物的形成和稳定。以往研究认为，电子转移反应是土壤矿物界面有毒有机物转化机制，随着检测技术与理论计算的发展，自由基催化和水解作用机制逐渐被发现，相关机制研究精准至矿物晶型和晶面层面。虽然水分非饱和条件下土壤矿物界面有毒有机物转化及机制已逐渐清晰，但其研究广度和深度有待进一步拓宽和加深。建议未来在实际水分非饱和土壤和矿物中开展有毒有机物转化研究，深入探究还原转化过程，研发原位反应装置及检测方法，尝试从微纳米尺度和分子水平解析有毒有机物在矿物界面转化机制。     

土壤矿物对有机质的吸附与固定机制研究进展

鉴于土壤有机质在生态系统及碳储存方面的重要性,关于土壤矿物对土壤有机质的吸附与固定机理方面的研究越来越受到了学术界的广泛关注。本文综述了近年来报道较多的土壤矿物对土壤有机质的吸附机制,以及主要影响因素。在众多矿物类型中,水合铁、铝氧化物及黏土矿物对有机质的吸附性较强,配体交换、络合、氢键、阳离子桥接、缩合及范德华力作用是土壤矿物与有机质之间的主要作用机制。土壤pH是影响矿物表面电荷及吸附位点的关键因素,进而影响矿物对有机质的吸附。土壤矿物表面的有机质含量对其继续吸附有机质具有一定的影响。吸附态有机质大多呈层状结构,越接近矿物表面的有机质与土壤矿物的结合越紧密。土壤有机质的稳定性受有机质与矿物间的作用力影响,一般而言,以化学键合吸附在矿物表面的有机质最稳定,其次为直接与矿物表面作用的电子"供体-受体"机制,范德华力和静电作用稳定性较差。近年来,随着分析设备和技术的进步,一些新的表征与探测方法(如热重分析、差示扫描量热法、傅里叶转换红外光谱、扫描电子显微镜、原子力显微镜、扫描透射X射线显微镜、中子散射技术等)被用于"矿物-有机质"结合机制的研究中,这些新手段毫无疑问会帮助更好地认识矿物与有机质间的作用机理。关于微生物在矿物吸附有机质、"矿物-有机质"复合体形成和演化过程中所起的作用,研究相对较少,但很明显这是至关重要的。     

粘粒矿物和有机质对土壤胶体比表面的影响

分别从黑土、黄绵土、黄棕壤、红壤和砖红壤提取<2nm的胶体,测定去有机质前后土壤胶体比表面;并用猪粪中提取的胡敏酸与上述5种土壤胶体相作用,由泥炭中提取的胡敏酸与蒙脱石、伊利石、高岭石相作用,测定其复合胶体的比表面;研究了粘粒矿物类型和胡敏酸对土壤胶体比表面的影响。结果表明,土壤胶体比表面大小与其所含主要粘粒矿物类型密切相关。5种土壤胶体比表面大小为:黑土>黄棕壤>黄绵土>红壤>砖红壤。砖红壤胶体去游离氧化铁后,胶体比表面明显降低;但黄棕壤胶体去游离氧化铁后比表面反而增加。有机质对土壤胶体比表面的影响因土壤类型不同而异,去除有机质后,黑土、黄绵土和黄棕壤胶体的比表面增加;而红壤、砖红壤胶体的比表面无明显变化。黑土和黄棕壤胶体与猪粪胡敏酸复合后,比表面降低;而砖红壤胶体与猪粪胡敏酸复合后反而增加。泥炭胡敏酸与蒙脱石、伊利石胶体复合后比表面降低;而高岭石却增加。     

Clay minerals from diallage in a warm and humid climate

In the course of chemical weathering, rockforming minerals release constituent ions changing into secondary minerals by alteration or recrystallization. Minerals formed in this way are primarily of colloidal nature, and are the most active portion in soils together with humus. The chemical weathering has dual meaning for soil fertility, that is, it provides soils with nutrients released and inorganic colloids formed, namely clay minerals. It has been well established that climate, vegetation, parent material, topography and time influence the formation of soils. Generally speaking, Japanese soils have developed under a warm and humid climate which causes leaching of released bases resulting in acid reactions, and a predominance of kaolin in soils. Accumulated information pertaining to Japanese soils, however, has disclosed that physical, chemical, and mineralogical properties of parent rocks are still obviously reflected in the clay minerals of soils.     

土壤团聚体中有机质研究进展

团聚体和有机质是保持土壤结构和肥力的基础,二者相互作用,不可分割,前者是后者存在的场所,后者是前者存在的胶结物质。在现有资料中,分别以团聚体和有机质为主要研究对象的报道较多,而团聚体中有机质性质的研究较少。本文从土壤有机质物理分组与化学分组相结合的角度,介绍国内外有关土壤团聚体中有机质的数量和特性及其对农业措施的响应方面的研究进展,内容包括团聚体分组、数量和稳定性,团聚体中的有机质的数量、未分组有机质的性质和腐殖物质组分的性质,颗粒分组中的有机质数量和性质,团聚体-密度联合分组中的有机质的数量和性质,不同土地利用方式和长期耕作施肥对团聚体中的有机质的影响等。以期推动不同粒级团聚体和不同HS组分相互作用及其对土壤固碳和肥力贡献研究工作的开展,为探索土壤有机质物理保护与化学保护之间的关系,揭示土壤固碳和培肥机理提供依据。     

Interaction of copper and zinc with allophane and organic matter in the B horizon of an Andosol

Andosols developed on basaltic material are naturally rich in metals. Organic matter and allophane, the key colloids of these soils, have a strong affinity for trace metals, but are intimately mixed so that speciation of trace metal is difficult to determine. We used three complementary approaches, namely physical fractionation, chemical extraction and potentiometric measurement, to distinguish them. Physical particle-size separations and chemical selective dissolution of allophanes and organic matter were combined to demonstrate relations between the occurrence of colloids and contents of Cu and Zn in an andic B horizon. About 22% of total soil Cu and 7% of total soil Zn were present in the < 5-μm fraction, associated with organic or amorphous mineral constituents. To support this association further, the affinity of soil colloids for Cu and Zn in a mimicked system was demonstrated. An Al-rich allophane was synthesized, and a portion of the organic matter was extracted from the clay fraction, and their reactivities towards Cu²⁺ or Zn²⁺ were studied by potentiometry. The two metallic cations displayed specific affinity towards allophane or soluble organic matter. Furthermore, the behaviour of copper and zinc in the ternary system, allophane + soluble organic matter + trace element, revealed a synergy in the surface complexation. The use of these three speciation approaches highlighted the linkage between metals and constituents, and showed how important the colloidal constituents are in the behaviour of Cu and Zn in Andosols.     

土壤微团聚体中矿物-有机复合体特征

以国家肥力网湖南祁阳红壤长期定位试验站的长期施有机肥和长期施化肥的土壤为研究对象,采用干筛法获得土壤微团聚体。利用同步辐射红外显微成像法研究土壤微团聚体中黏土矿物和有机官能团的原位分布图谱及其相关性。结果表明:土壤中黏土矿物(3 620 cm-1)和大分子有机物(脂肪,2 920 cm-1;蛋白质,1 650 cm-1;多糖,1 080 cm-1)呈高度异质性的分布规律。其中,黏土矿物和多糖有较为相似的分布模式;而黏土矿物和脂肪、蛋白类物质则呈现差异较大的分布模式。与长期施化肥处理的土壤微团聚体相比,长期施有机肥处理的土壤微团聚体中黏土矿物和大分子有机物呈现更高的分散性。此外,施有机肥和化肥处理土壤微团聚体样品中黏土矿物与有机官能团的决定系数(R2)均为:黏土矿物-脂肪黏土矿物-多糖黏土矿物-蛋白质,表明土壤微团聚体中黏土矿物和大分子有机物的亲和性有差异,且该差异不受长期施肥处理的影响。同步辐射微区域红外谱进一步表明,从土壤微团聚体外部到内部,黏土矿物的特征峰和大分子有机物的特征峰强度均逐渐增加。     

Clay mineralogy differs qualitatively in aggregate‐size classes: clay‐mineral‐based evidence for aggregate hierarchy in temperate soils

Clay minerals have a major role in soil aggregation because of their large specific surface area and surface charges, which stimulate interactions with other mineral particles and organic matter. Soils usually contain a mixture of clay minerals with contrasting surface properties. Although these differences should result in different abilities of clay minerals regarding aggregate formation and stabilization, the role of different clay minerals in aggregation has been seldom evaluated. In this study, we took advantage of the intrinsic mineral heterogeneity of a temperate Luvisol to compare the role of clay minerals in aggregation. First, grassland and tilled soil samples were separated in water into aggregate‐size classes based on the aggregate hierarchy model. Then, clay mineralogy and organic C in the aggregate‐size classes were analysed. Interstratified minerals containing swelling phases accumulated in aggregated fractions compared with free clay fractions under the two land‐uses. The accumulation increased with decreasing aggregate size from large macroaggregates (> 500 µm) to microaggregates (50–250 µm). Carbon content and carbon‐to‐nitrogen ratio followed the opposite trend. This fully supports the aggregate hierarchy model, which postulates an increasing importance of mineral reactivity in smaller aggregates than in larger aggregates in which the cohesion relies mostly on physical enmeshment by fungal hyphae or small roots. Consequently, differences in the proportion of the different 2:1 clay minerals in soils can influence their structure development. Further research on the links between clay mineralogy and aggregation can improve our understanding of mechanisms of soil resistance to erosion and organic matter stabilization.     

亚热带低丘区退化红壤肥力质量恢复性能的研究

试验和分析结果表明 ,退化红壤主要肥力因素的恢复与农用物质的投入和土壤本身理化性质均存在明显的关系。随着物质投入量的增加 ,土壤肥力质量的恢复也逐渐加快。在自然条件下 ,土壤肥力因素的恢复主要与土壤本身属性有关 ,在肥力恢复过程中 ,土壤有机质的增加量与土壤本身有机质含量呈抛物线关系 ,约当土壤有机质含量在 2 0 g/ kg时 ,增幅最大 ;在一定的含氮范围内 ,土壤氮素的增加与土壤全氮含量呈正相关 ;而速效钾的增加量与土壤本身速效钾含量呈反相关。土壤水稳定性团聚体的恢复与土壤粘粒含量及有机质含量呈正相关。试验结果表明 ,在合理的管理条件下 ,红壤肥力质量可以逐渐得到改善     

Adsorption of DNA on clay minerals and various colloidal particles from an Alfisol

Adsorption and desorption of salmon sperm DNA on four different colloidal fractions from Brown Soil and clay minerals were studied. The adsorption isotherms of DNA on the examined soil colloids and minerals conformed to the Langmuir equation. The amount of DNA adsorbed followed the order: montmorillonite?fine inorganic clay>fine organic clay>kaolinite>coarse inorganic clay>coarse organic clay. A marked decrease in the adsorption of DNA on organic clays and montmorillonite was observed with the increase of pH from 2.0 to 5.0. Negligible DNA was adsorbed by organic clays above pH 5.0. As for inorganic clays and kaolinite, a slow decrease in DNA adsorption was found with increasing pH from 2.0 to 9.0. The results implied that electrostatic interactions played a more important role in DNA adsorption on organic clays and montmorillonite. Magnesium ion was more efficient than sodium ion in promoting DNA adsorption on soil colloids and minerals. DNA molecules on soil colloids and minerals were desorbed by sequential washing with 10 mM Tris, 100 mM NaCl and 100 mM phosphate at pH 7.0. A percentage of 53.7-64.4% of adsorbed DNA on organic clays and montmorillonite was released, while only 10.7-15.2% of DNA on inorganic clays and kaolinite was desorbed by Tris and NaCl. The percent desorption of DNA from inorganic clays, organic clays, montmorillonite and kaolinite by phosphate was 39.7-42.2, 23.6-28.8, 29.7 and 11.4%, respectively. Data from this work indicated that fine clays dominate the amount of DNA adsorption and coarse clays play a more important role in the binding affinity of DNA in soil. Organic matter may not favor DNA adsorption in permanent-charge soil. The information obtained is of fundamental significance for the understanding of the ultimate fate of extracellular DNA in soil.     

抚仙湖流域典型农田土壤质量状况及烟草种植障碍因素

以云南抚仙湖北岸澄江市约1 130 hm²农田土壤为研究对象,通过调查分析土壤物理、化学性质,评价了研究区土壤质量状况,并进一步利用空间分析、相关分析与主成分分析对研究区烟草种植的主要土壤障碍因子进行了分析。结果表明:研究区土壤整体偏黏(平均黏粒含量496.7 g/kg)、偏碱(pH均值7.45)、有机质含量较高(均值28.55 g/kg)、大中微量营养元素有效态含量也整体偏高(水解性氮均值119.10 mg/kg、有效磷均值68.85 mg/kg、速效钾均值208.44 mg/kg、有效锰均值28.14 mg/kg),但各土壤性质在空间上变异较大。土壤基础地力、人为施肥管理、质地、酸碱性、有效锰是影响该地区土壤肥力的主要障碍因素,这些因素可通过有机质、速效钾、黏粒、pH、有效锰等指标进行评价,并指导烟草种植的土壤管理。烟草种植过程中应根据土壤性质、烟草养分需求,结合土壤养分空间变异采取相应的土壤改良措施。     

Soil adsorption complex of the meadow-chestnut soils at the Dzhanybek research station in the northern Caspian region

Data on the composition and properties of soil adsorption complex in the virgin and ameliorated meadow-chestnut soils in the northern Caspian region are generalized. It is shown that the experimental values of the effective CEC in the A1 horizon are lower than those calculated on the basis of data on the organic matter content and the content and mineral composition of fine fractions. We explain this discrepancy by the interactions between the organic matter and clay minerals resulting in the blocking of a part of the exchangeable positions. In the BC horizon, the experimental values of the effective CEC are twice as high as those calculated from the data on the amount of labile clay minerals in fine fractions. This can be explained by the presence of sorption centers on poorly crystallized illites and chlorites in the clay fraction and by the partial aggregation of clay material into coarser fractions that cannot be destroyed upon the separation of clay fractions by the Aidinyan procedure, which leads to the underestimation of the clay content.     

我国中亚热带缓丘区红粘土红壤肥力的演化Ⅱ.化学和生物学肥力的演化

本文着重探讨红粘土红壤化学和生物学肥力在利用过程中的演化特征,并通过聚类分析筛选出评价红壤化学和化学肥力演化的指标,并进行了相应的评价。结果表明：红粘土红壤的要草地及荒地系统由于长期受侵淋溶等退化过程的影响,土壤养分水平已跌至“保底”值．垦殖利用后,其化学肥力随着耕垦熟化过程不断提高,表现为土壤中各种速效养分及交换性Ｃａ、Ｍｇ含量均增加,而交换性Ａ１含量降低。同样,林草地系统红粘土红壤的生长学肥力     

Poorly crystalline mineral phases protect organic matter in acid subsoil horizons

Soil minerals are known to influence the biological stability of soil organic matter (SOM). Our study aimed to relate properties of the mineral matrix to its ability to protect organic C against decomposition in acid soils. We used the amount of hydroxyl ions released after exposure to NaF solution to establish a reactivity gradient spanning 12 subsoil horizons collected from 10 different locations. The subsoil horizons represent six soil orders and diverse geological parent materials. Phyllosilicates were characterized by X-ray diffraction and pedogenic oxides by selective dissolution procedures. The organic carbon (C) remaining after chemical removal of an oxidizable fraction of SOM with NaOCl solution was taken to represent a stable organic carbon pool. Stable organic carbon was confirmed as older than bulk organic carbon by a smaller radiocarbon (¹⁴C) content after oxidation in all 12 soils. The amount of stable organic C did not depend on clay content or the content of dithionite–citrate-extractable Fe. The combination of oxalate-extractable Fe and Al explained the greatest amount of variation in stable organic C (R² = 0.78). Our results suggest that in acid soils, organic matter is preferentially protected by interaction with poorly crystalline minerals represented by the oxalate-soluble Fe and Al fraction. This evidence suggests that ligand exchange between mineral surface hydroxyl groups and negatively charged organic functional groups is a quantitatively important mechanism in the stabilization of SOM in acid soils. The results imply a finite stabilization capacity of soil minerals for organic matter, limited by the area density of reactive surface sites.