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Mineralogical Characterization of Clay Fraction of Some Ganges Floodplain Soils

Iftekhar U. Ahmed
Soil Resource Development Institute, Mrittika Bhaban, Krishi Khamar Sarak, Dhaka-1215

S. Akhter
Soil Resource Development Institute, Mrittika Bhaban, Krishi Khamar Sarak, Dhaka-1215

Mainul Ahsan
Soil Resource Development Institute, Mrittika Bhaban, Krishi Khamar Sarak, Dhaka-1215

Abstract/ Executive Summary:

Top soils of five different series developed on Gangetic alluvium were studied to investigate the clay mineralogical composition. X-ray diffraction technique was employed to identify and quantify the minerals. The XRD patterns were obtained with Ni-filtered Cu Ka radiation at a scanning speed of 2 '28 min and content of minerals were estimated by XRD peak intensities at parallel powder mount. Mica was dominant clay mineral (36-55%) in all soils under study. Although high content of smectite was found in Ghior (2) and lshwardi soils (26 and 15%, respectively), it was minor in other three cases which might be because of disappearance of smectite from top soils. Appreciable amount of primary minerals like quartz and feldspars have also been observed in the clay fraction of the soils.

Keywords: Soil, Ganges floodplain soils, Mineralogical soil

Location: Jhenaidaha Upazila, Jhenaidaha district, Narail Upazila, Narail district and Jessore Upazila, Jessore district, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Land management

Objectives:

To determination of clay mineral soils along with their quantification in the soils of Ganges river floodplain for detail characterization of those soils.

Methodology:

The soil samples were collected from the south-west region of Bangladesh between 89°ll.97d & 89°31.6171 east and 23°01.7211 & 23°33.3241 north located in Jhenaidaha Upazila (sub-district) under Jhenaidaha district, Narail Upazila under Narail district and in Jessore Upazila under Jessore district. Five soil samples belonging to 4 soil series from different locations of Ganges river floodplain were selected for the study. 10g of air dry soil was treated with 30 % H₂ 0₂ heated for about 2h to decompose organic matter. Excess H₂0₂ was removed by centrifugation by washing 3 times with water. 3M NaCl was added each time to prevent deflocculation of clay particles and the supernatant was discarded by decantation. The pH of the soil suspension was adjusted to 10 by addition of 1 N NaOH. Clay fraction (< 2 µm) was separated by repeated sedimentation- siphoning method (Moslehuddin et al. 1998). Identificati on a nd estimation of mineralogical composition were carried out by X-ray diffraction (XRD). The separated clay fraction was treated by 1M KCl and 0.5N MgCl₂ respectively to made K+ and Mg+ saturated clay and washed them with ethanol to remove excess salts. Suitable amount (0.4 ml) of sol was dropped on a glass slide covering two third of its area, air dried, and X-rayed (parallel powder mount). In addition to the air-dried specimen, the Mg saturated clay was X-rayed after saturation with glycerol; and K-saturated clay after heating at 300°C and 550°C for two hours. The XRD pattern were obtained using Shimadzu XRD6000 diffractometer with Ni-filtered CuKa radiation at 40 kV and 30mA and at a scanning speed of 2.0°/min over a range of 3-35°28. Ip /Iq = Kp.q Wp/wq, Where Ip and Iq are the intensities of the P and Q components in XRD, Wp and Wq are the weight proportion of P and Q components and Kp.q, a constant value, is the intensity- weight coefficient of P and Q components. Reflections of the Mg saturated and glycerol solvent specimen were mainly used to calculate contents of different minerals.

Source of Information: Bangladesh J. Soil Sci. 30(1-2): 71-78, 2004, ISSN 0253-5440

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

These primary minerals found in nature usually dominant in silt and sand fractions but clay fraction also have appreciable amount of these minerals. Small amount of Goethite (iron oxides) estimated in the present study as iron oxides was not removed from soils by sodium dithionite treatment. In the frame of this study, identification and approximate quantification of minerals only from top soils were considered and emphasis was given to methods of the experiment. To document weathering sequences of minerals of floodplain soils and the factors governing the processes, more detailed studies along with morphological study are needed. Although high content of smectite was found in Ghior (2) and lshwardi soils (26 and 15%, respectively), it was minor in other three cases which might be because of disappearance of smectite from top soils. Appreciable amount of primary minerals like quartz and feldspars have also been observed in the clay fraction of the soils.

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