Soil pH

Soil pH a unique physico-chemical property of soil that signifies whether a soil is acidic, neutral or alkaline in reaction. Chemically, pH can be defined as the negative logarithm of the hydrogen ion activity of soil solution expressed in moles per litre. Soils having pH below 6.6 are acid and above 7.3 are alkaline. Any soil whose pH is close to 7(6.6-7.3) is considered neutral.

Most alluvium in Bangladesh is near neutral to moderately alkaline in reaction when first deposited. Ganges and Lower Meghna deposits are calcareous in addition. The Black Terai Soils are medium to strongly acid in the upper layers but less acid in the substratum. The topsoil of the Non-calcareous Brown Floodplain Soils is mainly medium to strongly acid but the subsoil is medium acid to neutral. Most topsoil of the Calcareous Brown Floodplain Soils is neutral to moderately alkaline; so is the Non-calcareous Alluvium Soils. Grey Floodplain Soils are moderately acid to moderately alkaline. Calcareous Dark Grey Floodplain Soils are near neutral when wet and become strongly acid when dry. acid basin clays are strongly to extremely acid. peat also becomes medium to strongly acid if allowed to dry out. acid sulphate soils become toxically acid if allowed to dry out. Grey Piedmont Soils are medium to strongly acid, so is the Grey Terrace and Valley Soils when dry. Deep and Shallow Red-brown Terrace Soils, Brown Mottled Terrace soils and brown hill soils are strongly acid throughout. Small patches of alkaline soils have been encountered only in the western part of the Ganges River Floodplain, mainly in the Jessore region where the floodplain deposits may be several thousand years old. [Rameswar Mondal]