Clay Mineralogical Composition of Some Soils in Myanmar

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 potentiality, 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 fraction was weighed to calculate the particle-size distribution 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 between 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) . 96 Nguyen Q.H. et al.

TABLE 2. Particle-size distribution and texture of soils

Mineral identification minerals other than layer silicate minerals were iden- The XRD patterns of the<2ƒÊm clay fraction of all tified by the peaks at 0.418, 0.484, 0.425 and 0.334, and samples are illustrated in Fig. 2 and the approximate around 0.32nm, respectively. The contents in the clay relative mineral contents in the<2ƒÊm clay fraction of fraction of goethite, gibbsite and feldspars were rela- them are given in Table 3. Mica was identified by the tively low, normally lower than 5%, while that of quartz presence of the 0.99-1.00nm peak along with its higher- was high and ranged from 7 to 28%. order reflections at 0.499-0.500 and 0.334nm. The presence of kaolinite was ascertained by the peaks at Clay mineralogical characterization of soils 0.716-0.719 and 0.357nm which disappeared by heating As shown in Table 3, the mineralogical composition at 550•Ž in the K-saturated specimen. Mica and kao- in the clay fraction of soils was related to physiography linite were detected in the clay fraction of all samples as an integration of the topography, parent material and with greatly variable contents ranging from trace to 72% soil type. Three soils (Heho-1, Heho-2 and Aungban) for mica and from 13 to 70% for kaolinite. Chlorite distributed in the hilly region of Shan State (Southern) which is normally identified by the peaks at 1.42, 0.708, and classified as Red earths and yellow earths were 0.472 and 0.354nm with their persistence after heating characterized by predominance of kaolinite having the at 550•Ž was hardly detected in all samples. contents of 57 to 70%, with some amounts of chlorite- Vermiculite was identified by the decrease in the vermiculiteintergrade (7 to 13%) and minor amounts of intensity of the 1.42-1.45nm peak with the correspond- mica (until 5%). The high kaolinite content of these soils ing increase in the intensity of the 0.99-1.00nm peak by was consistent with the results reported for ferralitic K-saturation and air-drying and contributed to 2 to 34% soils in the midland and mountainous regions of Viet- of the total mineral content in the clay fraction of some nam by Dao (1987) and Ho et al. (2000).Myanmar and samples. Smectite was noticed by the broad peak around Vietnam belong to the tropical to subtropical monsoon 1.80nm in the Mg-saturated and glycerol-solvated spec- climate. Under such conditions, weathering of rocks imen with the content in the clay fraction ranging from and minerals strongly takes place with leaching-away 4 to 30% in half of the samples. The mica/vermiculite/ of some basic cations and SiO2, and kaolinite is formed smectite•`mica/smectite mixed-layer mineral (abbreviated as a predominant layer-silicate clay mineral by allitiza- as Mx thereafter) was noticed on the XRD pattern by tion in soils in the hilly/mountainous regions. the poorly defined diffraction effect between 1.0 and Four soils from the inland valley in Mandalay Di- 2.0nm in the Mg-saturated and glycerol-solvated spec- vision were characterized by predominance of 2:1-type imen and by the increase in the intensity of the 1.00nm expansible minerals such as vermiculite, smectite and peak after K-saturation and air-drying (Egashira, 1988). Mx; the kaolinite content (13 to 27%) was low in Mx was observed in some samples and the content in comparison with that of the soils in the hilly region the clay fraction varied from trace to 47%. Chlorite- while the mica content (5 to 17%) was somewhat higher. vermiculite intergrade is a mineral that does not collapse In the respective soil types, however, vermiculite was readily when K-saturation but its 1.42nm reflection observed for samples Tatkon-1 and Tatkon-2 classified becomes diffuse and shifts toward 1.00nm after heating as Light forest soils but not for samples Meiktila-1 and at 300 and 550•Ž. This mineral was detected in most Meiktila-2 classified as Yellow brown dry forest and samples with a considerable amount from 6 to 40% in indaing, whereas Mx was detected for the latter but not the clay fraction. for the former. Both vermiculite and Mx are transfor- Goethite, gibbsite, quartz, and feldspars which are mation products of mica, and transformation of mica Clay Mineralogical Composition of Myanmar Soils 97

Heho-1 Heho-2

Aungban Oktwin

Tatkon-1 Tatkon-2

Meiktila-1 Meiktila-2

FIG. 2. The XRD patterns of the<2ƒÊm clay fraction . Spacing is in nm. Treatments: a, Mg-saturation and glycerol-solvation; b , Mg-saturation and air-drying; c, K-saturation and air-drying; d, K-saturation and heating at 300•Ž; e , K-saturation and heating at 550•Ž.

occurs accompanied by reduction of the layer charge the nature of the original mica, it was considered and cation exchange of K by Ca or Mg in the sequence that the homogeneous distribution pattern of the layer of mica•¨vermiculite or Mx•¨smectite. charge in the mica particles brought about transforma- The reason for such transformation difference be- tion of mica into vermiculite for samples Tatkon-1 and tween the two soil types might be ascribed to the Tatkon-2 and that the heterogeneous distribution pattern difference in the nature of the original mica or in of the layer charge in the mica particles brought about the transformation environment of mica. Concerning transformation of mica into Mx for samples Meiktila-1 98 Nguyen Q.H. et al.

Madaya-1 Madaya-2

Hmawbi-1 Hmawbi-2

Hmawbi-3 Hmawbi-4

FIG. 2. The XRD patterns of the<2ƒÊm clay fraction (continued).

TABLE 3. Approximate relative mineral contents (%) in the<2ƒÊm clay fraction

Abbreviations: Mc, mica; Ch, chlorite; Vt, vermiculite; St, smectite; Mx, mica/vermiculite/smectite•`mica/smectite mixed-layer mineral; Ch-Vt, chlorite-vermiculite intergrade; Kt, kaolinite; Gt, goethite; Gb, gibbsite; Qr, quartz; Fd, feldspars. tr., trace. Clay Mineralogical Composition of Myanmar Soils 99 and Meiktila-2. As for the transformation environt, native reduced and oxidized conditions. Kaolinite is a the homogeneous reduction of layer charge in the mica predominant mineral in ferralitic soils suffered from particles would be favorable to transformation into severe weathering, as described already. vermiculite, whereas the heterogeneous reduction of layer charge be favorable to transformation into Mx. Assessment to inherent potentiality of soils Samples Madaya-1 and Madaya-2 representing soils Inherent potentiality of soils could be roughly on the meander floodplain of the Ayeyarwady River assessed by the clay content (amount in clay minerals) system in Mandalay Division were characterized by (Table 2) and the clay mineralogical composition (type predominance of mica having the contents of 51 and in clay minerals) (Table 3) of them. Three soils (Heho-1, 72%, respectively, with some amounts of kaolinite (16 Heho-2 and Aungban) from the hilly region were and 14%). In addition, appreciable amounts of 2:1-type dominated by kaolinite which is inactive in terms of expansible minerals, mainly smectite, were identified for retention of nutrients and water. Therefore, their inher- sample Madaya-1. The presence of 2:1-type expansible ent potentiality was evaluated to be low and was minerals with the low mica content compared to sample affected by the clay content in soil. Samples Tatkon-1 Madaya-2 suggests that 2:1-type expansible minerals in and Meiktila-2 from the inland valley contained major sample Madaya-1 have been transformed from m amounts of 2:1-type expansible minerals coupled with and supports the vertic nature of Dark compact s. the moderate to high clay contents and were evaluated The high mica content of samples Madaya-1d to be of the intermediate to high level of inherent Madaya-2 asserts that mica is a predominant clay potentiality. The very low clay content of samples mineral in lowland soils derived from alluvial sediments Tatkon-2 and Meiktila-1, irrespective of major amounts transported by large rivers originating from the moun- of 2:1-type expansible minerals in the clay fraction, tainous regions of central Asia composed of metamor- suggests their low level of inherent potentiality. phic rocks. This is the case for lowland soils in Laos Among the soils from the meander floodplain of the (Egashira et al., 1997), Bangladesh (Egashira et al., Ayeyarwady River system, sample Madaya-1 was eval- 2004) and Vietnam (Nguyen and Egashira, 2005). uated to be in the high level of inherent potentiality Sample Oktwin in Bago Division, representing soils due to the high clay content and considerable amounts on the meander floodplain of the Sittang River and of 2:1-type expansible minerals, and sample Madaya-2 classified as Meadow alluvial soils, was characterized was to be in the intermediate level of inherent poten- by domination of kaolinite (46%) over mica (18%) and tiality based on the intermediate clay content and pre- vermiculite (12%). Smectite and chlorite-vermiculite dominance of mica. Mica is a predominant clay mineral intergrade were also detected but with small amounts for both samples Madaya-1 and Madaya-2 and may of 4 and 6%, respectively. Irrespective of the same serve as a source of K to crops. However, the high clay topography of meander floodplain, the clay mineralog- content coupled with considerable amounts of 2:1-type ical composition of sample Oktwin was different from expansible minerals in sample Madaya-1 may cause those of samples Madaya-1 and Madaya-2, probably inconvenience to tillage practice. In addition, the high due to the difference in origin of the parent material. inherent potentiality of a soil affects adversely growth Four soils of samples Hmawbi-1 through Hmawbi-4, and yield of paddy rice under the unfavorable weather representing soils on the deltaic plain of the Ayeyarwady condition (Egashira et al., 1992). River system in Yangon Division, were characterized by Samples Hmawbi-2 and Hmawbi-3 from the deltaic different clay mineralogical compositions depending on plain of the Ayeyarwady River system were dominated the elevation, parent material and soil type. Sample by chlorite-vermiculite intergrade and kaolinite. This Hmawbi-1 showed the clay mineralogical composition mineralogical suite along with the intermediate clay comparable with that of sample Oktwin, except presence content suggeststhe low to intermediate level of inherent of Mx and a little larger kaolinite for sample Hmawbi-1. potentiality for them. Samples Hmawbi-1, Hmawbi-4 Both samples Hmawbi-1 and Oktwin are classified as and Oktwin were classified to be of the low level of Meadow alluvial soils and distributed on the depression inherent potentiality due to the low active-mineral con- where land has been waterlogged by surface water and tent (Hmawbi-1) and to the low clay and active-mineral subjected to cultivation of paddy rice for long time. contents (Hmawbi-4 and Oktwin). Sample Hmawbi-4, in spite of designation to the deltaic plain of the Ayeyarwady River system, is located on the CONCLUSIONS gently slopping site and showed the clay mineralogical composition characteristic to both Meadow alluvial Surface soils from hilly region in Shan State (South- soils (fair in the mica content) and soils on the hilly em), inland valley and meander floodplain in Mandaly region (high in the kaolinite content). Samples Hmawbi- Division, and deltaic plain in Bago and Yangon Divi- 2 and Hmawbi-3 were characterized by dominance of sions of Myanmar had a large variability in the particle- chlorite-vermiculite intergrade (32 and 40%) and kao- size distribution that was not well related to the topog- linite (34 and 30%) with small amounts of mica (4 and raphy, parent material and soil type. However, the clay 2%). Chlorite-vermiculite intergrade has been probably mineralogical composition of these soils showed a good formed by chloritization of vermiculite under the alter- relationship to physiography as a total of them. Soils 100 Nguyen Q.H. et al. on the hilly region was characterized by domination of EGASHIRA,K., ARAMAKI,K., YOSHIMASA,M., TAKEDA,A. and YAMA- kaolinite over other minerals in the clay fraction, where- SAKI,S. (2004) Rare earth elements and clay minerals of soils of as soils from the inland valley, meander floodplain and the floodplainsof three major rivers in Bangladesh.Geoderma, 120, 7-15. deltaic plain were dominated by mica, its transformation EGASHIRA,K., FUJII, K., YAMASAKI,S. and VIRAKORNPHANICH,P. products such as vermiculite, smectite and mixed-layer (1997) Rare earth element and clay minerals of paddy soils from mineral, or chlorite-vermiculite intergrade as a chloriti- the central region of the Mekong River, Laos. 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