OLDER ALLUVIUM- ITS ORIGIN, DISTRIBUTION, CHARACTERISTICS AND PRODUCTIVITY IN THE BRAHMAPUTRA VALLEY, ASSAM, INDIADiganta Goswami and Dulal C. Goswami
Older alluvium areas of Brahmaputra valley in Assam were identified using maps based on satellite images supplemented with ground truth verification. The major geomorphic units and their distributions were delineated on the map. Three representative locations were identified in the area namely Majuligarh, Negheriting and Makri from three agro climatic zones. Soil samples were collected horizon wise from three exposed pedons of each location. The morphological and physicochemical properties of older alluvium reveal its unique characteristics. Older alluvium soil profiles were very deep, well-drained and highly developed. These are believed to be formed during the Pleistocene time. The soils are dark yellowish brown to reddish brown in colour and finer in texture. Soils are sticky on wetting and hard when dry and compact. Surface soils vary considerably in organic matter (1.3-3.6%) which decreases with depth. Cation exchange capacity (3.2-5.6me/100g), exchangeable cations and base saturation are low. The soils are very strongly to extremely acidic (pH-4.0-4.9) in nature. Soils formed on older alluvium vary considerably with associated soil (Old flood plain) in characters like colour, texture, consistence, pH and profile development. Favourable climatic condition, acidic nature and high depth of the soil made the older alluvium area suitable for tea cultivation and other valuable trees. Thus, these soils have tremendous economic significance supporting a large number of tea gardens and lying well above the present flood level.
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