The Process of Soil Formation
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Soil formation, or pedogenesis, is influenced by human activity, environmental factors, and various physical, chemical, and biological processes, primarily regulated by climate. Key processes involved in soil formation include addition, loss, translocation, and transformation of materials, which shape the soil profile through mechanisms like eluviation and different soil forming processes such as melanization, gleization, calcification, podzolization, and laterization. Each process contributes uniquely to soil characteristics, affecting drainage, nutrient content, acidity, and overall soil fertility.
The Process of Soil Formation
- 1. 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 of Horizon Formation in the Soil Profile Addition Water from rainfall. O2 & CO2 from the atmosphere. OM from decomposition of plants & animals residues. Eroded materials from sediments Nutrients or ions from rain water, atmosphere, etc. Energy from sunlight
- 4. Losses Water through evapotranspiration. Nitrogen by denitrification & volatilization. O2 & CO2 through oxidation of OM. Soil by erosion Water & nutrients by leaching. Energy by radiation.
- 5. Translocation (from one location to another) Salts that are dissolved in water. Nutrients that cycle in plants. Soil by animals, e.g.. Earthworms
- 6. Eluviation It is the mobilization and translocation of certain constituent’s viz. Clay, Fe2O3, Al2O3, SiO2, humus, CaCO3, 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 (A2 or E horizon).
- 8. Transformation Physical weathering that change size of rocks. Chemical weathering that change or produce various salts or nutrients. Formation of humus by decomposition of OM. Reactions of clay with OM.
- 9. 1. Melanization 2. Gleization 3. Calcification 4. Podzolization 5. Laterization
- 10. 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.
- 11. 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.
- 12. 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.
- 14. 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’.
- 15. Calcification It is the process of precipitation and accumulation of calcium carbonate (CaCO3) at the base of B- horizon. It is typical of grassland and occurs in areas of low precipitation. The accumulation of CaCO3 may result in the development of a calcic horizon. Calcium is readily soluble in acid soil water or when CO2 concentration is high in root zone.
- 17. 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, layer is acidic in nature.
- 19. 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.
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