Landscape - Soil Relationships and Pedogenic Evaluation of Soils in Ghiladhari Watershed of the Brahmaputra Valley of Assam

Geomorphology plays a major role in regulating the process that dictates the distribution of soils on the geomorphic units. The relationship between landscape and soil was studied in the Ghiladhari watershed of the Northern Brahmaputra valley of Assam. Image interpretation of IRS-1C data led to the recognition of six different landscape units in the studied area which include structural hill (SH), upper piedmont plain (UPP), lower piedmont plain (LPP), upper alluvial plain (UAP), lower alluvial plain (LAP) and old flood plain (OFP). Soils from unstable geomorphic surfaces viz. shoulders showed A-C profiles, while soils developed on other relatively stable geomorphic surfaces had well developed A-Bw-C profile development. Topography along with nature of parent material and time was found to be responsible for the pedogenic differences in the soils developed on different landscapes. Field morphology rating system using relative horizon distinctness (RHD) and relative profile development (RPD) rating values were used to assess the pedological evaluation of the soils. Based on the RHD and RPD values, the studied soils could be arranged as: LAP>UAP>OFP>LPP>UPP>SH. The study established a well defined relationship between geomorphic surfaces and development of soils. Concatenation of soils on these landform units was the result of surface and subsurface movement of materials.