Soil Environment

Soil Environment sum of factors affecting the condition of soils, including physical surroundings, climate and influences of living organisms. Due to interaction of soil with their environment a particular environment is created in individual soils. Bangladesh possesses diverse nature of soils because it has a wide range of environmental conditions. These are parent material, climate, relief, drainage, vegetation, and age.

There are 18 kinds of parent materials consisting mainly of river alluvium, hill rocks, clays and piedmont alluviums. These provide a wide range of soil textures and variable contents of easily weatherable minerals. climate is the most important factor in relation to the rate of mineral weathering and soil formation. The high temperature (mean annual temperature is 25'C) and plentiful moisture (mean annual rainfall is about 2300 mm) supply in Bangladesh provide almost ideal conditions for mineral weathering and biological activity. Differences in cliate within the country is not important but differences in annual rainfall between drier western and wetter eastern areas affect the amount of water passing through the soil and causing leaching of clay and chemicals, and these influence soil formation as well as soil environments.

Relief is of various kinds, such as the steep slopes of hill areas, extensive level areas on the barind tract, and the broad ridges and basins of floodplain areas. Drainage varies from very rapid to very poor. There are different types of vegetation under dry land forest, mangrove forest and reed swamps, as well as between these soils and cultivated soils, specially where cultivation has created an impervious topsoil layer. Age is important because of the great rapidity with which soil formation can take place under Bangladesh's environmental conditions. For instance, significant differences can be detected on the Brahmaputra-Jamuna floodplains between soils less than about 10-25 years old and those up to about 200 years old (since the Brahmaputra moved from its parent channel).

Environmental diversity in the country occurs not only at national and regional levels, but also occurs at the upazila and village levels. In fact, small-scale complexity of soil and hydrological conditions is an important characteristic of Bangladesh environment. Besides, considerable year to year variability in moisture, temperature and flood regimes create major problems for soil environment. Depth and duration of flooding significantly affect soil environment. Reduced and anaerobic conditions exist in flooded soils whereas oxidised and aerobic conditions prevailing in non-flooded soils result diversity in soil properties and kinds of crops to be grown.

Use of chemical fertilisers has doubled since the early 1980s due to intensification of cropping, introduction of high yielding varieties and expansion of irrigated areas. However, improper use of fertiliser is also creating second generation problems in the production system. Moreover, a large number of cattle etc and human population and their unplanned way of living in a small country like Bangladesh deserves more attention to the dynamics of its soil environment. Because here lies the potential sources of atmospheric as well as soil pollution by different industrial and city-wastes and emissions, biomass burning, deforestation, excessive use of chemical fertilisers and impacts of some toxic laden materials. Moreover, soil erosion is now a serious problem in the madhupur tract and in the hill regions in the east. The use of good topsoil for brick manufacture has now become a general practice, as a result of which there will be a decline in crop productivity in many areas of the country. [Md Harunor Rashid Khan]