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Bulk and Clay Mineral Composition of Some Benchmark Soils of Bangladesh and Their Implications in Soil Classification and Management

Z. H. Khan
Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh

M. S. Hussain
Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh

F. Ottner
Institute of Applied Geology, University of Natural Resources and Applied Life Sciences, Peter-Jordan Str. 70, 1190 Vienna, Austria

Abstract/ Executive Summary:

Bulk and clay mineralogical composition of some benchmark soils of the floodplains and the Pleistocene terraces of Bangladesh were studied. The terrace soils are characterized by high quartz content followed by layer silicates, plagioclase and K-feldspars, while the floodplain soils have relatively low quartz and high layer silicate minerals. In the clay fraction of the soils developed on Pleistocene terraces kaolinite is the dominant mineral closely followed by illite, soil vermiculite (18Å vermiculite) and some unspecified interstratified minerals. Chlorite and smectite are characteristically absent in the clay fraction of these soils. The clay traction of the soils on the floodplains shows mixed mineralogical composition consisting mainly of illite. kaolinite and soil vermiculite with traces of interstratified minerals. A small quantity of smectite and chlorite occurs in the clay fraction of these soils. Most minerals in the clay traction of the floodplain soils might have had inherited from alluvial parent materials with very little in situ mineral transformation. Implications of clay mineral composition in the classification and management of the soils have been discussed.

Keywords: Benchmark soil, Clay mineralogy

Location: All over Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Land development productivity

Objectives:

The objective of this study was to identify the minerals in bulk and clay samples of nine selected benchmark soils of Bangladesh.

Methodology:

For this investigation nine benchmark soil series (two from the Pleistocene terraces and seven from various floodplains) of Bangladesh was selected. The names of Soil series are Amnura, Lauta, Gangachara, Nilkamal, Ramgati, Pritimpasha, Salta, Harta and Taras. The parent material, physiography, geographic location and classification of these soil series are presented. Morphological description of these soil series along with some chemical properties were presented by Hussain et al. (2005). Pits were dug at the typical sites of representative soil series and samples were collected from two depth ranges from each pedon. A total of 18 soil samples were collected and analyzed in the clay mineralogical laboratory of the Institute of Applied Geology University of Natural Resources and Applied Life Sciences (BOKU), Vienna, Austria for physicochemical and mineralogical investigations. Some selected physicochemical properties of the soils are presented. For bulk mineral analysis soil samples were prepared according to the "backload procedure" and analysed in a Philips X-ray-diffractometer (PW 1710, a long fine focus tube) with Ni filtered Cu-Kα radiation (45 kV, 40 mA) from 2° to 70° 28. The measuring time was 1 sec. in step-scan mode and the step size was 0.02°. Semi-quantitative mineral composition of the soil samples was estimated using the method described by Schultz (1964). Minerals in the clay fraction were identified by X-ray diffraction (XRD) using a Philips X-ray-diffractometer. Before separation of clay fraction carbonates, organic matter and free iron oxides were removed according to the method of Mehra and Jackson (1960) and Wilson (1989). The XRD patterns of oriented clay samples were taken after the following treatments: (I) Mg-saturated and air-dried, (2) K-saturated and air-dried, (3) Mg-saturated and ethylene glycol solvation, (4) K-saturated and ethylene glycol solvation, (5) K-saturated and dimethylsulfoxide (DMSO) solvation and (6) heating to 300 and 550°C for at least 2 hours. The identification of clay minerals was generally based on the methods outlined by Thorez (1975), Brindley and Brown (1980). Moore and Reynolds (1997) and Wilson (1989). Semi-quantitative estimations were carried out using the corrected intensities of characteristic X-ray peaks (Riedrnilller 1978).

Source of Information: J. Asiat. Soc. Bangladesh. Sci. 37( I ): 23-34. June 2011

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Application of muriate of potash may be problematic as K may be fixed in these soils. Satla and Harta soils - the two Histosols - have very high organic matter content. Since these two soils also have considerable amount of expanding lattice minerals there is possibility of the formation of clay - humus complexes. All other soils having low organic matter content might showed organic matter depletion problem - a serious problem in the tropical region. Hussain (1998) reported that clay mineral composition in Bangladesh soils exerts little adverse effect on their management. Accordingly mixed mineralogy classes were the most numerous and, by far, cover the largest area of agricultural land in this country. The clay traction of the soils on the floodplains shows mixed mineralogical composition consisting mainly of illite. kaolinite and soil vermiculite with traces of interstratified minerals. A small quantity of smectite and chlorite occurs in the clay fraction of these soils. Most minerals in the clay traction of the floodplain soils might have inherited from alluvial parent materials with very little in situ mineral transformation. Implications of clay mineral composition in the classification and management of the soils was discussed.

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