Clay mineralogy in some sugarcane growing black red and red Laterite soils of Telangana

The study was carried out to characterise and classify the sugarcane growing soils of Medak district of Telangana State. The selected red soils (Pedon 8, 10, 11, 13 and 14) were developed on weathered granite-gneiss parent material at gently sloping lands, red laterite soils (Pedon 2, 3, 4, 5 and 6) developed on weathered granite-gneiss over hard laterite parent material at gently sloping lands whereas the black soils (Pedon 1, 7, 9 and 12) were formed at nearly level and plain topography on granitic gneiss parent material mixed with calcareous murram. The silt clay ratio was found to be less than 0.5 in black and red laterite soils pedons indicating the moderate weathering, whereas in red soils Pedon silt clay ratio ranged from 0.19 to 0.82 indicating the moderate to high weathering. The dominance of Smectite type clay was also confirmed by the CEC / clay ratio. The CEC /clay ratios of these black soils were high (0.58 to 0.86). It indicates the presence of smectitic type of clay minerals. The CEC /clay ratios of these red soils were medium to high in range (0.43 to 0.77) which is indicates the mixed or illItic mineralogy, where the presence of secondary clay minerals such as kaolinite, Illite and montmorillonite are more or less in equal range. The CEC /clay ratios of the red laterite soils were low to medium in range (0.16 to 0.46), indicating the presence of secondary clay mineral such as kaolinite. Direct conversion of mica to kaolinite might be one of the causes for the synthesis of kaolinite.