Clay Mineralogical Composition of Some Soils in Myanmar
Total Page：16
File Type：pdf, Size：1020Kb
Clay Science 13, 93-100 (2006) CLAY MINERALOGICAL COMPOSITION OF SOME SOILS IN MYANMAR NGUYENQUANG HAIa, KAZUHIKOEGASHIRAb, AYE AYE THANa and SAYAKAHAYASHIc aDepartmentof Plant Resources, GraduateSchool of Bioresourceand BioenvironmentalSciences, Kyushu University, Fukuoka812-8581, Japan bDepartmentof Plant Resources, Faculty of Agriculture,Kyushu University, Fukuoka 812-8581, Japan Departmentof Bioresourceand Bioenvironment,School of Agriculture, KyushuUniversity, Fukuoka 812-8581, c Japan (ReceivedJanuary 22, 2007.Accepted February 13, 2007) ABSTRACT Fourteen surface soil samples were collected from hilly region in Shan State (Southern) , inland valley and meander floodplain in Mandalay Division, and deltaic plain in Bago and Yangon Divisions of Myanmar and subjected to clay mineral analysis. The clay mineralogical composition of the soils was found to have a good relationship with physiography as a total of the topography , parent material and soil type. Soils on the hilly region in Shan State (Southern) were characterized by the high kaolinite content in the clay fraction, whereas soils on the meander floodplain of the Ayeyarwady River system were dominated by mica. 2:1-type expansible minerals (vermiculite , smectite, and mica/vermiculite/ smectite•`mica/smectite mixed-layer mineral) considered as the transformation products of mica were predominant in soils on the inland valley in Mandalay Division. Soils on the deltaic plain of the Ayeyarwady River system and on the meander floodplain of the Sittang River were characterized by major amounts of kaolinite with considerable amounts of chlorite-vermiculite intergrade or some amounts of mica. Inherent potentiality of the soils was assessed based on the type and amount of clay minerals. The assessment showed a large variability in the inherent potentiality of the soils , which is useful to effective management of soil for crop production. Key words: Clay mineralogical composition, Particle-size distribution , Physiography, Inherent poten- tiality, Myanmar INTRODUCTION in order to intensify soil production capacity for pro- moting crop production in Myanmar. Union of Myanmar is situated in the western end of Clay minerals mostly comprise phyllosilicatesor layer Southeast Asia, within 9•‹58•Œ to 28•‹31•ŒN latitude and silicates which are characterized by layer structure and 92•‹09•Œ to 101•‹10•ŒE longitude ranges. The total land area layer charge and fulfill a function through large surface of Myanmar is around 680 thousands km2. The central area and high cation-exchange capacity. Clay minerals and lower parts of the country are plains surrounded by play an important role in determining physical and hilly regions with altitudes varying from 915 to 2,134m chemical properties and inherent potentiality of a soil. in the western, northern and eastern parts (Ministry of A good understanding on the existing clay minerals of Agriculture and Irrigation, 2000). The whole country of a specified soil can help for scientists not only to Myanmar belongs to the tropical to subtropical mon- diagnose the genetic processesof the soil and to classify soon climate with three seasons: hot (middle February it but also to manage the soil effectivelyand to propose to middle May), rainy (middle May to middle October) , measures for improving or keeping soil productivity. and dry-cold (middle October to middle February) . The purposes of the present study are: (1) to examine Agricultural land in Myanmar is around 11million clay minerals in some Myanmar soils; (2) to characterize ha, occupying 16% of the total land area, and crop the clay mineralogical composition of the soils in ref- production is still in an improving level (Egashira and erence to physiography; and (3) to assess inherent po- Than, 2006). Study on the fundamental properties of tentiality of the soils based on the type and amount of soils, including clay mineralogy, is helpful or inevitable clay minerals. 94 Nguyen Q.H. et al. TABLE 1. General information on soil samples 1)Estimated based on the book published by Ministry of Agriculture and Irrigation (2004). MATERIALS AND METHODS at the deltaic plain in Yangon Division. Samples Madaya-1 and Madaya-2 were derived from alluvival Soils sediment. Sample Hmawbi-1 was collected from the General information on soil samples used in the depression where land has been waterlogged by surface study is given in Table 1, and their sampling sites water and subjected to cultivation of paddy rice for long are shown on the administrative map of Myanmar in time. Samples Hmawbi-2 and Hmawbi-3 were collected Fig. 1. Total 14 surface soil samples were colled from the flat land saturated by underground water in from hilly region in Shan State (Southern), inland valley the rainy season. Sample Hmawbi-4 was collected from and meander floodplain in Mandalay Division, and the gently slopping land developed to orchard. Sample deltaic plain in Bago and Yangon Divisions of Myan- Oktwin was collected from the depression in Bago mar. Three samples derived from limestone (He1, Division where land has been flooded by both runoff Heho-2 and Aungban) were taken from the hilly- water from the hilly area and overflowing water from gion in Shan State (Southern). Samples Tatkon-1, the Sittang River in the rainy season. As a result, this Tatkon-2, Meiktila-1 and Meiktila-2 in Mandalay- soil was derived from a mixture of the colluvial sediment vision are distributed in the inland valley surrounded (limestone-derived sediment) and the recent river sedi- by the hilly region composed of limestone; they ment (alluvium). All of these soils have been subjected estimated to originate from the limestone-derived se- to cultivation of rice, wheat, vegetables, cash crops, and ment. fruit trees. Six samples belong to the plain region of the Ayeyar- Soil samples were taken at a depth within 0-15cm wady (the former name is Irrawaddy) River system, from soil surface, air-dried and gently ground to pass of which two samples (Madaya-1 and Madaya-2) were through a 2-mm sieve. Clay mineral analysis was done taken at the meander floodplain in Mandalay Division at the Laboratory of Soil Science, Kyushu University, and four samples (Hmawbi-1 through Hmawbi-4) were Japan. Clay Mineralogical Composition of Myanmar Soils 95 repeated sedimentation and siphoning, followed by sep- aration of the 20-200 and 200-2,000ƒÊm sand fractions by wet-sieving. After oven-drying at 105•Ž, each frac- tion was weighed to calculate the particle-size distribu- tion of a soil. Clay mineral analysis The<2ƒÊm clay fraction wholly separated from the fine soil was used to examine the clay mineralogical composition by the X-ray diffraction (XRD) method. Duplicate clay sols containing 50mg clay each were taken in 10-mL glass tubes and then washed twice with 8mL of an equal mixture of 1M NaCl and 1M NaCH3COO (pH 5.0) by centrifugation to lower the pH. Of the duplicate sets, one was saturated with K and the other with Mg by washing 3 times with 8mL of 1 M KCl and 0.5M MgCl2, respectively. The excess salt was removed by washing once with 8mL of water and the clay in the tube was thoroughly suspended with 1 mL of water. An aliquot of 0.4mL of the clay sol was dropped on to a glass slide (28•~48mm) covering two- thirds of its area, air-dried and X-rayed (parallel powder mount). The XRD analysis was made with the air-dried and glycerol-solvated specimens for the Mg-saturated clay and air-dried and heated (at 300•Ž and 550•Ž for 2 h) specimens for the K-saturated clay. The XRD anal- ysis was conducted using a Rigaku diffractometer with Ni-filtered CuKƒ¿ radiation at 40kV and 20mA and at a scanning speed of 2•‹2ƒÆmin-1 with a scanning step of 0.02•‹ and a continuous scanning mode over a range of 3 to 30•‹2ƒÆ. Relative mineral contents in the clay fraction were semi-quantitatively estimated on the basis of the XRD peak intensities. In the present estimation, the peak height was used as the peak intensity by assuming the relative proportions of the minerals of a sample normalized to 100% and the same proportionality be- tween the peak intensity and the content for each mineral. RESULTS AND DISCUSSION Particle-size distribution The particle-size distribution and texture of soils are FIG. 1. Soil sampling sites on the administrative map of Myanmar . given in Table 2. The particle-size distribution varied from soil to soil, and the variation was not well explained by the factors such as topography, parent Particle-size analysis material or soil type. It was different even among the Organic matter was first decomposed by the treatment soils under the same physiology, like samples Heho-1, with hot 7% H2O2. After dispersion by the sonic wave Heho-2 and Aungban, suggesting the influence by micro- treatment and deflocculation by adjustment of the pH relief of the locations. Among the soils from inland of the suspension to 10 by addition of a small amount valley in Mandalay Division, the clay content was higher of 1M NaOH, the soil suspension was stood in a 1- for the soil distributed far from the stream (Tatkon-1) L sedimention cylinder for a prescribed time followed than for the soil near the stream (Tatkon-2) and for the by siphoning-out of the clay fraction. The soil sample soil situated at the depression (Meiktila-2) than for the was then subjected to repetition of sonification- soil at the higher location (Meiktila-1). According to sedimentation-siphoning with intermittent pH adjust- the IUSS system, soils had the light clay or coarser ment to separate the whole<2ƒÊm clay fraction. The texture. Only sample Madaya-1 had a texture of heavy whole 2-20ƒÊm silt fraction was then separated by clay characterized for Dark compact soils (Vertisols) .