Soil Formation in South Eastern Arunachal Pradesh of the Himalayan Region.

Abstract

Soil genesis in warm to hot per humid agro-ecological sub-region 16.3 with respect to altitude, geology, landform and vegetation was studied for Dilun block of Changlang dishict, Arunachal Pradesh using IRS P6, LISS IV and Cartosat-l images. Soil profiles were studied in major landforms viz.,low amplitudinal hill, inter hill valley, upper piedmont, lower piedmont, upland and flood plain for physiochemical properties. The soil at high altitude hills are fine textured varying silty clay loam to silty clay. The geology consisting of sandstone and shales along with abundant vegetation and high rainfall favoured illuviation and results in increase of clay with increase in depth and thus classified as Alfisols. In interhill valleys soils vary from coarse textured sandy loam to loamy sand, course gravel of cobbles and stones appear below 75 cm soil depth. Due to a depositional environment in this landscape soil development is almost insignificant and thus these soils are classified as Entisol. In piedmont, soils are well drained and coame textured varying from sandy loam to sandy clay loam. Soils in piedmonts are formed as a result of colluvial depositions and which depict formation of "Cambic" subsurface horizons and thus classified as Inceptisol. In uplands, soils vary from coarse (closer to piedmont) to heavy texture (closer to flood plains) and the soils are in general clay loam to loam in texture with uniform distribution of clay in the lower horizons. These soils also developed "Cambic" subsurface horizons and thus classified as Inceptisols. Similarly in flood plain, soil texture varies from silty clay to sandy clay loam. Soils of flood plain showed presence of gleyed horizons below 75 cm with mottles occurring from a depth of 50 cm below the surface. Some flood plains are old surfaces which are stable landforms (cultivated to tea) and developed problems of inherent nutrient deficit due to poor water holding capacity and non-uniformity in nutrient cycles and become harmful for wide spectrum of crops. In marshes and swamps, where, LD is not of much consequence, impeded drainage conditions render these soils unsuitable for most of the crops except rice. The OFP soils owing to high leaching and weathering conditions resulted in poor base saturation and CEC with LD layers occurring at a depth below 100 cm, generally not suitable for agricultural crops. These soils are suitable to grow tea and citrus. Moreover, LD occurring at a depth below 100 cm may not have any pedological significance on the land use systems including tea and citrus plantation. The study indicated that pedological information, which is related to Quaternary geology of Brahmaputra valley region, is very much essential for planning and management of all types of crops in the region.