Processes involved in soil formation

• What is Soil Formation?
• Processes Involved in Soil Formation
1. Eluviation
2. Melanization
3. Gleization
4. Calcification
5. Podzolization
6. Laterization

1. Processes Involved in Soil Formation Characterized by Climate

2. What is Soil Formation? Soil formation or  pedogenesis, is the combined effect of human impact on environment, physical, chemical and biological processes working on soil parent material . Climate regulates soil formation. Soils are more developed in areas with higher rainfall and more warmth. The rate of chemical weathering increases by 2-3 times when the temperature increases by 10 degree Celsius.

3. Processes Involved in Soil Formation Eluviation Melanization Gleization Calcification Podzolization Laterization

4. Eluviation It is the mobilization and translocation of certain constituent’s viz. Clay, Fe 2 O 3 , Al 2 O 3 , SiO 2 , humus, CaCO 3 , other salts etc. from one point of soil body to another. It is the process of removal of constituents in suspension or solution by the percolating water from the upper to lower layers. The horizon formed by the process of eluviation is termed as eluvial horizon (A 2 or E horizon).

5. Melanization Melanization is the development of dark, humus-rich coatings on ped faces and mineral grains, rendering the horizon a dark brown or black. This process is very common in the regions of low humidity where humus is formed from the organic matter .

6. Due to melanization the black humus along with water is mixed in the A- horizon which becomes dark coloured. The degree to which a soil becomes melanized is a function of the rate and duration of humus production.

7. Gleization The term ‘ glei ’ is of Russian origin which means blue, grey or green clay. 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.

8. The process is not particularly dependent on climate (high rainfall as in humid regions) but often on drainage conditions. Under reducing conditions, Due to ferrous compounds, the soil colour becomes blue-grey or grey, and The rate of decomposition of organic matter is very low. These together result into the accumulation of a sticky, compact layer of blue-grey or grey colour at the bottom of B- horizon. This process is called ‘gleization’ and the soil is called ‘glays’.

9. Calcification It is the process of precipitation and accumulation of calcium carbonate (CaCO 3 ) at the base of B- horizon. It is typical of grassland and occurs in areas of low precipitation. The accumulation of CaCO 3 may result in the development of a calcic horizon. Calcium is readily soluble in acid soil water or when CO 2 concentration is high in root zone.

10. Podzolization It is a process of soil formation resulting in the formation of Podzols and Podzolic soils which are highly acidic and infertile. It is the negative of calcification. Conifers produce leaf litter contains:- high lignin and low nutrient (Ca) contents, rich in phenolic compounds which inhibit microbial activities, l ayer is acidic in nature.

11. The process operates under the following conditions: i) Climate : A cold and humid climate is most favourable for podzolization. ii) Parent material : Siliceous (Sandy) material helps in easy percolation of water. iii) Vegetation : Acid producing vegetation such as coniferous pines. iv ) Leaching and Translocation of Sesquioxide : Sesquioxide and organic clay complexes, which are soluble and move with the percolating water to the lower horizons . The humus and Sesquioxide become mobile and leached out from the upper horizons and deposited in the lower horizon.

12. Laterization 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 impregnated with aluminium and iron sesquioxides to extent of 70 to 80% of the total mass, are called laterites. The soil forming process is called Laterization. Under high temperature regimes and high rainfall in the tropics, the silicate minerals are very unstable . These sesquioxides of the parent minerals are resistant to decomposition. It leaves a residue of primary laterite.

13. The process operates under the following conditions. i) Climate - Unlike podzolization, the process of laterization operates most favourable in warm and humid (tropical) climate with 2000 to 2500 mm rainfall and continuous high temperature ( 25°C) throughout the year. ii) Natural vegetation - The rain forests of tropical areas are favourable for the process. iii) Parent Material - Basic parent materials, having sufficient iron bearing ferromagnesian minerals, which on weathering release iron, are congenial for the development of laterites.

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