Soil Phase

Soil Phase division at the level of soil series when the natural phenomena (erosion, colluviation, action of animals and plants) or acts of man modify, sometimes temporarily, the nature, arrangement and dynamics of the surface horizons of a series. It gives to the reader information on the characteristics of the soil that can modify the conditions of the growth of plants, or the working of the soil, but that does not necessarily have genetic significance. Soil phases, in an international context, have been proposed to subdivide third level classes depending on land features which are significant to use, and management of land. These imply limiting factors related to surface and subsurface features of the land and across the boundaries of distinct soil units. Anthraquic, duripan, fragipan, gelundic, gilgai, inundic, lithic, petric, petrocalcic, petroferric, petrogypsic, phreatic, palcic, rudic, saline and sodic are used as phases in the soil map of the world.

However, in Bangladesh, a soil phase is a subdivision of a soil series. They are differentiated within a soil series in order to make subdivision of practical importance for landuse, crop suitability, potential productivity or management requirements. The most significant practical difference between soils in the same series are in the depth of seasonal flooding, hazard of flood or storm surge, damage to crops, time of drainage (early, normal or late) in the dry season, smooth or irregular relief, soil depth, soil slope, dry soil salinity, erosion etc. For example, five phases have been recognised in the Gopalpur series: Gopalpur Highland, Gopalpur Medium Highland, Gopalpur Medium Lowland, Gopalpur Medium Lowland flood hazard and Gopalpur Medium Lowland (river) erosion hazard. For soil fertility trials on the field may be required to recognise phases with narrower limits than described. [Aminul Islam]