Acid Soil  type of soil in which the quantity of free H+ ions is higher than that of alkali or alkaline earth cations. The pH is therefore less than 7.0. However, the term 'neutral' is generally used for a soil with pH between 6.6 and 7.3. Acid soils therefore have a pH less than 6.6. This means that it is more acidic, which results from the presence of exchangeable hydrogen and aluminium ions. The salt contents of this soil are composed predominantly of aluminium sulphate and ferrous sulphate. The sources of hydrogen cations in soil solution could be from acidic parent materials, plant roots, humus, carbon dioxide, alumino-silicate, iron pyrites, use of ammonium fertilisers and sulphur too.

Most of the soils of Bangladesh are low to medium acid in reaction, due to the predominance of high rainfall areas and leaching. There are mainly three groups of acid soils found in Bangladesh, such as: acid basin clay, acid sulphate soil and brown hill soil. [Md Khurshid Alam]