Short Notes on Calcareous Soils

This article provides a short note on calcareous soils.

Zonal soils of arid regions usually contain sufficient amount of lime (CaCO₃) at some horizons of the soil profile. When the zone of lime accumulation coincides with the depth of high root concentration, it may be an important factor in plant nutrition.

Many soils are formed from limestone or marl parent materials. Such soils are typically calcareous throughout the profile. Calcareous soils encompass special problems that seem associated with the alkali soils.

Soils containing sufficient amount of lime (CaCO₃), and often magnesium carbonate (MgCO₃), show alkaline pH due to the hydrolysis of lime as follows:

The OH^– ions cause alkalinity, HCO₃^– behaving as a weak acid – HCO₃^– = H⁺ + CO₃^2-. The pH of calcareous soils is usually above 7.0 and may be as high as 8.5. This variation is due to partial pressure of CO₂ being high and formation of un-dissociated carbonic acid, so that hydrolysis of CaCO₃ is reduced.

The lowering of partial pressure of CO₂ on dilution of soil suspension raises the pH of calcareous soils. The carbonates of calcium and magnesium participate directly in some reactions, controlling the solubility of phosphate and iron.

The availability of iron reduces by the following chemical reactions:

Soils high in lime are frequently productive for many ordinary field crops, including most forage crops, corn cotton, sugar beets, potatoes and tomatoes.