SOIL FORMING PROCESSES (Pedogenic processes)

 A. Fundamental soil-forming processes

(1) Humification

(2) Eluviation and illuviation

B. Specific soil-forming processes

(1) Podsolisation

(2) Laterisation

(3) Calcification

(4) Gleization

(5) Salinization

(6) Desalinization

(7) Solonization (Alkalization)

(8) Solidization (dealkalization)

(9) Pedoturbation

 A. Fundamental soil-forming processes

1. Humification:

is the process of decomposition of organic matter and synthesis of new organic substances. It is the process of transformation of raw organic matter into the formation of a surface humus layer, called O- horizon.

2. Eluviation and illuaviation

Eluviation is the process of removal of constituents by percolation from the upper layers to lower layers. This layer of loss is called eluvial and designated as the E-horizon. The eluviated producers move down and become deposited in the lower horizon which is termed as the illuvial or B-horizon. The eluviation produces textural differences.

B. Specific soil-forming processes

(1) Podsolisation

It is a type of eluviation in which humus and sesquioxides become mobile, leach out from upper horizons and become deposited in the lower horizons. This process is favoured by cool and wet climate. It requires a high content of organic matter and low alkali in the parent material.

(2) Laterisation

In this process, silica is removed while iron and alumina remain behind in the upper layers. Laterisation is favoured by the rapid decomposition of parent rocks under climates with high temperature and sufficient moisture for intense leachings, such as found in the tropics. The soil formed in this process is acidic in nature.

(3) Calcification

In this process, there is usually an accumulation of calcium carbonate in the profile. This process is favoured by scanty rainfall and alkali in the parent material.

(4) Gleization

The term glei is of Russian origin, which means blue, grey or green clay. The gleization is a process of soil formation resulting in the development of a glei (or gley horizon) in the lower part of the soil profile above the parent material due to poor drainage condition (lack of oxygen) and where waterlogged conditions prevail.

(5) Salinization

Salinization is the process of accumulation of salts, such as sulphates and chlorides of calcium, magnesium, sodium and potassium, in soils in the form of salty (salic) horizons. It is quite common in arid and semi-arid regions.

(6) Desalinization

It is the removal by leaching of excess soluble salts from horizons or soil profile by ponding water and improving the drainage conditions by installing an artificial drainage network.

(7) Solonization (Alkalization)

The process involves the accumulation of sodium ions on the exchange complex of the clay, resulting in the formation of sodic soils (solonetz).

(8) Dealkalization

The process refers to the removal of Na+ from the exchange sites. This process involves the dispersion of clay.

(9) Pedoturbation

Another process that may be operative in soils is pedoturbation. It is the process of mixing the soil.