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Mineralogical Composition of Soils from Urir Char; a Tiny Offshore Island of Bangladesh

M.S. HUSSAIN
Department of Soil, Water and Environment, University of Dhaka, Dhaka 1000

Z. H. KHAN
Department of Soil, Water and Environment, University of Dhaka, Dhaka 1000

M. IBRAHIM
Department of Soil, Water and Environment, University of Dhaka, Dhaka 1000

Abstract/ Executive Summary:

Mineralogical composition of three surface soils from Urir Char − an environmentally vulnerable small offshore island of Bangladesh − was determined by X-ray diffraction analysis. In the bulk soils layer silicates and quartz were the dominant minerals while the quantity of feldspars was around ten percent. Quantity of weatherable minerals was very high in the soils. Illite was the dominant mineral in the clay fraction of the soils. The second dominant clay mineral was smectite which comprised around one-fourth of the clay fraction closely followed by chlorite with a small quantity of kaolinite mineral. Soil vermiculite and mixed layer minerals were absent in these soils. These soils had a mixed mineralogical composition with a high cation exchange capacity and percent base saturation. Texturally the soils were silty loam. Exchangeable Ca++/ Mg++ ratio was less than unity. Magnesium solonization was considered as the dominant pedogenic process along with gleization. There was problem of salinity as the elevation of land was around one meter above the mean sea level. Natural calamities like tropical cyclones and tidal surges were highly devastating as the island was completely washed with sea water.

Keywords: Urir char, Offshore island, Clay mineralogy, Soil properties

Location: Urir Char − an environmentally vulnerable small offshore island of Bangladesh

Start Date: 00-00-2013

End Date: 00-00-2013

Program Area: Crop-Soil-Water Management

Commodity: Land degradation

Objectives:

1. The present paper attempts to report information on some basic soil properties and the bulk and clay mineralogical composition of some selected soils from Urir Char.

Methodology:

Three surface soil samples (0-15 cm depth) from three selected locations of the oldest parts of the island, where rice cultivation is being practised, were collected for mineralogical investigations. The locations of the soil sampling sites have been recorded using a GPS and marked in a sketch map of Urir Char. Soils in the older part of this island where cambic horizon have developed have been characterized as Inceptisols, mostly Endoaquepts. The collected soil samples were physically and chemically analysed following standard methods. The mineralogical analysis of the soils was carried out in the laboratory of the Institute of Applied Geology, University of Natural Resources and Applied Life Sciences (BOKU), Vienna, Austria. The mineralogical composition of bulk soil sample (< 2mm) as well as separated clay (< 2μm) fractions were determined. 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 (45kV, 40mA) from 2° to 70° 2θ. The measuring time was 1 sec. in step-scan mode with a step size of 0.02°. Semi -quantitative mineral composition of the soil samples was estimated. The clay mineralogical studies were performed by removing organic materials by oxidation with H₂O₂ and iron oxides by citrate –dithionite- bicarbonate method. Clay fraction was separated by sedimentation method and the separated clay was saturated with Mg++ and K+ ions using 1 M MgCl₂ and KCl solutions. The oriented clay samples on ceramic plates were scanned with a Philips 1710 X-ray diffractometer (XRD) with Ni filtered Cu- Kα radiation (at 45 kV, 40 mA) at a scanning speed of 2° 2θ per minute from 2° to 40° 2θ. The identification of clay minerals was generally based on the standard methods. Semi-quantitative estimations of minerals were carried out using the corrected intensities of characteristic X-ray peaks.

Source of Information: J. Asiat. Soc. Bangladesh, Sci. 39(1): 95-104, June 2013

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The mineralogical composition indicates that the soil materials of the Urir Char island were mainly allogenic and their transformation process appears to be in the initial stage only. Occurrence of high quantity of weatherable minerals also indicates the occurrence of weak weathering and a considerably high nutrient reserve.

Knowledge Management: Journal