Hill Soil The landmass of Bangladesh comprises hill, terrace and floodplain areas. Hill soils occupy the Northern and Eastern Hills, which are about 12% of the country. Total land area covered under hill soils is about 18,171 sq km of which 92% is highland, 2% medium highland, 1% medium lowland and 5% homestead and water bodies. Hill soils occur mainly in Khagrachhari, Bandarban, Chittagong, Cox's Bazar, Habiganj and Maulvi Bazar districts. Small areas occur along the northern borders of Sherpur, Mymensingh, Sunamganj and Sylhet districts, in central and southeastern Sylhet and in the east of Brahmanbaria, Comilla and Feni districts.
The Northern and Eastern Hills are underlain by sandstone, siltstone and shale of Tertiary and Quaternary ages. The soils developed on these parent materials are brown in colour, usually loamy in texture and very strongly acidic in reaction. Landscape is steep and soils were mainly developed on steep slopes and some occur on more gentle slopes. Nature of parent materials strongly determine the texture of the soils. Shale results heavy silt loam or silty clay loam subsoil. Soils developed on sandstone have dominant textural class of sandy loams with occasional loamy sand or loam texture. Soils subject to erosion have topsoil with less clay content. The steepness of the landscape determines the depth of the soil. Soils are in general shallow in depth. The topsoil under tea plantation on gentle slope has the greatest thickness, while soils under forest have topsoil of usually 5 to 7.5 cm thick and consists of entirely of coalesced wormcasts. Soils developed at steep or very steep slopes of the hilly regions are susceptible to erosion (including landslips on some soils). Washout materials are deposited at the foot of the hills. Soils are permeable and due to presence of low clay content at the topsoil they have low water-holding capacity. Nutrients especially nitrogen is lost from the soils with runoff water.
The agricultural potential of hill soils is mainly low for field crops, but it ranges between low and high for tree crops. Deep soils on level or gently sloping land have the highest potential. Because of impracticality of irrigation, rainfed crop production is practised in most hill land. The main crops are: transplanted aman, broadcast aus, cowpea, aubergine, cucumber, okra, bitter gourd, sweet gourd, sweet potato, sugarcane, maize, cotton, pineapple, coriander leaf, and some other summer and winter vegetables. Although the land areas are not suitable for growing underground crops such as ginger and turmeric, these are also cultivated in limited areas without knowing the consequences of the practices. Shifting cultivation (jhum) is also practised by the Hill Tribes. rubber plantation has also been introduced in hilly areas of Bangladesh.
Naturally hill soils are prone to erosion. In addition to this, due to faulty agricultural practices in the hilly regions, the soils are at risk of severe degradation. Moreover, deforestation also created threat to local ecosystem. [Sirajul Hoque]