Morphological and physicochemical properties as an indicator to profile development were studied in a soil chronosequence in West Bengal. Among the different morphological properties, the soil colour clearly brought out the differences in soil development with age. The colour becomes redder with increasing age and its quantitative index (Hurst index) showed the highest value in soils of Archaean age, intermediate in Pleistocene age and the lowest in soils of Holocene age. The illuviation of clay with the formation of clay cutans in subsoils was observed in the soils of Archaean and Pleistocene period during field morphological studies. Among the physicochemical properties, soil pH and organic carbon failed to follow any particular trend with age. The cation exchange capacity showed no noticeable variation in soils of different ages, but the CEC/clay ratio decreased in subsurface horizons with increasing age of soils. The studies on vertical distribution of different forms of iron and their ratios on soils of different geologic ages revealed that the amount of Fet and Fed increased with depth. The ratio of Fed minus Feot Fet increased and Feo/Fed decreased with age indicating the transformation of iron into “less active” forms in older soils.
Soil chronosequence, profile development, colour index, illuviation of clay, forms of iron and redness rating
