Clay Research
Year : 2005, Volume : 24, Issue : 1
First page : ( 45) Last page : ( 61)
Print ISSN : 0255-7193.

Mineralogy of Some Rice Growing Soils of West Bengal

Nayak D.C., Sarkar Dipak

National Bureau of Soil Survey & Land Use Planning (ICAR), Regional Centre, Sector-II, Block-DK, Salt Lake, Kolkata - 700091.

Abstract

The mineralogical studies of clay and silt fractions of four rice growing soil series (Ballartop, Belar, Nalpur and Jagdishpur) of West Bengal were done to identify the dominant minerals present in the silt and clay fractions and also for understanding the transformation of different mineral components under varying degree of waterlogging/flooding situations. Ballartop and Belar soils are poorly drained and affected by moderate to severe waterlogging whereas Nalpur and Jagadishpur soils are imperfectly drained and are affected by slight waterlogging hazards. Morphological data indicate that the soils of poorly drained (Ballartop and Belar) are more grayish in colour (lower hue and chroma) than Nalpur and Jagadishpur soils, which have less waterlogging problems. Surface soils are strongly to moderately acidic (pH 4.7 to 5.4) and have medium organic carbon. The clay content is moderate to high and CEC ranges from 5.4 to 40.1 cmol (p) kg⁻¹. Mineralogical analysis of clay fraction indicates that soils are dominated by mica (illite) (35 to 79%) followed by kaolin (10 to 30%) and chlorite (2 to 19%). Smectite is present mainly in Belar and Ballartop soils, which ranges from 5 to 30% and the presence of interstratified mixed minerals are also observed. The mineralogical composition of silt fraction shows that mica (illite is the dominant (42 to 30%) followed by kaolin (5 to 19%), chlorite (3 to 15%), potash feldspar (3 to 6%), plagioclase feldspar (1 to 4%) and quartz (1 to 18%). The mineralogy class of Ballartop, Nalpur, Jagadishpur series is “illitic” and that of Belar series is “mixed”. Vermiculite and smectite are very slightly chloritised. The low degree of chloritisation of soil clays does not commensurate with the ferrolysis process in rice soils of West Bengal.

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