Acidic Soils Related Concept for Agricultural Exam

Acidic Soils

Soils having PH less than 6 are categorised as acid soils. These soils can be defined as those having PH less than 5.5 in 1:1 soil water extract.
More precisely a soil which is acid in reaction throughout the root zone are called as acid soils.
Such types of soils have more H+ concentration than OH- in the soil solution.

Why Soils are Acidic:

There are various factors which influence formation of acid soils.

Parant Material:

Rocks like granite and rhyolite are acid rocks and on disintegration and {Agrilearner} decomposition of these rocks results in accumulation of acid soil material.


In heavy rainfall areas continuous leaching process removes most of CaCO3 and gypsum from soil giving rise to increased soil acidity.

Organic Matter:

The carboxylic, enolic and phenolic groups present in organic matter debris {Agrilearner} dissociate releasing H+ thus contributes towards soil acidity.

Root Biomass and Soil Organism:

Respiration by plant roots and soil micro organisms are major contributing factors to soil acidity .(Agrilearner) CO2 liberated during respiration reacts with water to produce carbolic acid which in turn breaks down to release H+.

CO2 + H2O—-> H2CO3 + H+

On the other hand when plants exchange cations with external medium they give an equivalent number of H+ and thus contribute to soil acidity.

Soil Acidic Reaction:

Contribution of H+ in formation of acid soils.

  1. CO2 from decomposition organic matter
    CO2 + HOH à HCO3 + H+


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