Table of contents | |
Introduction | |
Fundamental Soil forming Processes | |
Specific Soil Forming Processes | |
Laterization |
Humification is a complex process in which raw organic matter is transformed into humus. This process involves various organisms. It begins with the breakdown of simple compounds like sugars and starches, followed by the decomposition of proteins and cellulose. Finally, even highly resistant compounds like tannins are broken down, resulting in the formation of dark-colored humus.
Eluviation refers to the mobilization and movement of specific constituents, including clay, Fe2O3, Al2O3, SiO2, humus, CaCO3, and other salts, from one part of the soil to another. This process involves the washing out of these constituents. It occurs as percolating water moves from the upper layers to the lower layers, carrying the constituents with it. Eluviation leads to differences in soil texture, and the horizon created by this process is known as the eluvial horizon (A2 or E horizon). The extent of translocation depends on the relative mobility of elements and the depth of percolation.
Illuviation is the process by which soil materials that were removed from the eluvial horizon (the horizon where materials are washed out) are deposited in a lower layer or horizon that has the property of stabilizing the translocated clay materials. The horizons formed by illuviation are known as illuvial horizons, typically labeled as B-horizons, with Bt horizons being a common example. This process creates a textural contrast between the eluvial (E) and illuvial (Bt) horizons, often resulting in a higher fine clay to total clay ratio in the Bt horizon.
Horizonation is the process of differentiating the soil into distinct horizons as you move deeper into the soil. This differentiation occurs due to fundamental processes like humification, eluviation, and illuviation.
The basic pedologic processes provide a framework for later operation of more specific processes
Calcification is the process of calcium carbonate (CaCO3) precipitation and its accumulation in a specific part of the soil profile. This accumulation of CaCO3 can lead to the formation of a calcic horizon. Calcium is easily soluble in soil water with high acidity or when there is a high concentration of CO2 in the root zone.
The process of precipitation after mobilization under these conditions is called calcification and the resulting illuviated horizon of carbonates is designated as Bk horizon (Bca).
It is the reverse of calcification that is the process of removal of CaCO3 or calcium ions from the soil by leaching
Podzolization is a soil formation process that leads to the development of Podzols and Podzolic soils. In contrast to calcification, which concentrates calcium in the lower part of the B horizon, podzolization involves the leaching of calcium carbonates from the entire soil profile. This process not only removes calcium but also other basic elements, resulting in an overall increase in soil acidity. Essentially, podzolization is characterized by the acid leaching of the soil.
The process operates under favorable combination of the following environments:
Iron and aluminum movement leads to the A horizon taking on a bleached, grey, or ashy appearance. The term "Podzols" was coined by Russians, combining "pod" meaning under and "zola" meaning ash-like, to describe soils with an ash-like horizon appearing below the surface horizon.
In conclusion, Podzolization is a soil formation process that occurs in cold and humid climates dominated by coniferous vegetation with acid-forming properties. This process results in the mobilization and leaching of humus and sesquioxides from upper horizons, which are then deposited in lower horizons.
The term "laterite" originated from the word "later," meaning brick or tile. Initially, it was used to describe a group of highly clayey Indian soils found in the Malabar hills of Kerala, Tamil Nadu, Karnataka, and Maharashtra.
Specifically, it refers to a particular cemented horizon in certain soils that, when dried, becomes as hard as a brick. In tropical regions, when these soils are significantly saturated with sesquioxides (iron and aluminum oxides), making up about 70 to 80 percent of the total mass, they are referred to as laterites or latosols (Oxisols). The soil formation process associated with this is called Laterization or Latozation.
Laterization is the process that removes silica from the upper soil layers instead of sesquioxides, leading to the concentration of sesquioxides in the soil profile.
This process occurs under specific conditions:
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