Mineralogy of Vertisols of the Pedhi Watershed of Maharashtra

摘要

In the adjacent east upland of the Purna Valley, namely in the Pedhi Watershed of Maharashtra, Vertisols occur on both microhigh (MH) and microlow (ML) positions. The watershed is characterized by a tropustic moisture regime and a hyperthermic temperature regime. The distance between the MH and ML positions is approximately 6 km and the elevation difference is 0.5 - 5 m. The soils of the MH positions are strongly alkaline (sodic) and those of ML are mildly alkaline (non-sodic). Formation of sodic Vertisols in MH alongside non-sodic Vertisols in ML positions is a unique phenomenon. The present study was undertaken to provide the qualitative and quantitative difference in minerals between soils of the MH and ML positions. The mineralogical composition of the silt fractions of both type of soils is similar. However, it differ in the clay fractions. The soils are mainly dominated by fairly well crystallized smectite in the coarse and fine clay fractions. The soils of MH however contain more amount of pedogenie carbonate and chlorite than soils of the ML positions. This suggests that the humid climate prevailed during last geological period in the study area. Thereafter climatic change towards the arid restricted the further leaching of soils. Due to microtopographic difference distribution of water across the landscape was modified and facilitated greater penetration of rain water in ML position than the MH. Thus the arid environment in MH position helped in the formation of more amount of pedogenic carbonate than ML position that resulted in higher pH, ESP and SAR and also in the more amount of pedogenic chlorite by hydroxy-interlayering of smectites at high pH conditions. The formation of pedogenic carbonate, pedogenic chlorite and presence of fairly well crystallized smectite indicate that the weathering of primary minerals was minimal under arid environment of late Holocene.