Fundamentals of Soil Science (1+1)

Specific Soil Forming Processes

B. SPECIFIC SOIL FORMING PROCESSES

The fundamental processes provide a framework for more specific processes like-
Podzolization (Russian, pod means under and zola means ash):

• It is the process of eluviation of oxide of iron and aluminium (sesqui oxides) and also humus under acidic condition (pH 4-5), removal of carbonates by organic acids formed by organic matter and illuviation of the silicon in surface horizon.
• Abudant organic matter, commonly found under forest, cold and humid climate are favourable for the formation of such soils.
• The eluiviated horizon assumes a bleached grey colour and is left in highly acid, siliceous condition and, the term podzol has been used for such soils.

Laterization (Latin, later-a brick):

• The term laterite is derived from the word later meaning brick or tile and was originally applied to a group of high clay Indian soils found in Malabar hills of Kerala, Tamil Nadu, Karnataka , Madya Pradesh and Maharashtra.
• Laterization is inverse process to that of podzolization i.e. the process that removes silica, instead of sesquioxides from the upper layers and thereby leaving sesquioxides to concentrate in the solum.
• The process operates under rain forests of tropical areas, warm and humid (tropical) climate and basic parent materials are favourable for such soils.
• It refers specifically to a particular cemented horizon in certain soils which when dried, become very hard, like a brick.
• Such soils (in tropics) when massively mixed with sesquioxides (iron and aluminium oxides) to an extent of 70 to 80 per cent of the total mass, are called laterites or latosols (Oxisols).

Salinization

• It is the process of accumulation of salts, such as sulphates and chlorides of calcium, magnesium, sodium and potassium in soils in the form of a salty (salic) horizon.
• The intensity and depth of accumulation vary with the amount of water available for leaching.
• It is quite common in arid and semi arid regions.
• It may also take place through capillary rise of saline ground water and by inundation with seawater in marine and coastal soils.
• Salt accumulation may also result from irrigation or seepage in areas of impeded drainage.

Desalinization

• It is the process of removal of excess soluble salts from horizons that contained enough soluble salts to impair the plant growth.
• Drainage is essential for desalinization.

Alkalization (Solonization) :

• The process by which soils with high exchangeable sodium and pH > 8.5 are formed; often sodium carbonate and sodium bicabonate are formed in extreme cases.
• The soil colloids become dispersed and tend to move downward. The dispersion results in poor physical condition of the soil.