CLAY MINERALOGY OF RED AND LATERITIC SOILS OF NORTH KARNATAKA
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Date
1996
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University of Agricultural Sciences, Bangalore
Abstract
Clay mineralogy of four red and three lateritic soils from north Karnataka were studied with an objective to understand the relative abundance of clay minerals and their transformations in these soils.Both red and lateritic soil clays exhibited greater CEC (18.4 to 55.4 Cmol Kg-1 except Jamboti. Specific surface of clays closely followed the trend of CEC and ranged from 126 to 343 m2g-1 The molar ratio of Si02/R203 ranged from 1.95 to 2.33 and Si02/Al203 ranged from 2.06 to 2.52. Both these ratios were not distinctly different among the clays of two soil groups. The amorphous ferri-aluminosilicate content ranged from 8.24 to 14.26 per cent in these clays. The molar Si02/Al203 ratio of the constituents of the clays extracted by boiling in 0.5N NaOH followed by CBD was in the range of 1.33 to 2.87. The FeOOH component was in the range of 21.60 to 47.97 per centCommon to all soils the presence of a peak around 2.5nm ascribable to interstratified mica-smectite/vermiculite. Discrete vermiculite was present in Ranebennur and Kulageri pedons. Kaolinite content was more in lateritic pedons compared to red soils. Mica is present in all the pedons to varying degrees. The first order peak of mica showed shoulders on the low angle side and broadening on Mg-saturation and glycerol solvation indicate that the mica is undergoing weathering. The data on chemical composition, CEC, specific surface and X-ray diffraction of clay fraction it can be stated that interstratified mica-smectite/vermiculite, mica, smectite and vermiculite, kaolinite are the minerals identified in these soils. Quartz is present in all the pedons to a small extent, as evidenced by peak at 0.426nm and 0.333nm.The probable of pathway of weathering and transformation is mica on weathering has transformed to interstratified mica- smectite/vermiculite —> smectite/vermiculite —> kaolinite.
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No. of references 101