Soil Forming Processes - 2 | Agriculture Optional Notes for UPSC PDF Download

Gleization

• The term "glei" originates from the Russian language, referring to blue, grey, or green clay. Gleization is a soil formation process that leads to the development of a glei horizon (or gley horizon) in the lower part of the soil profile above the parent material. This occurs due to poor drainage conditions, characterized by a lack of oxygen and waterlogged conditions, resulting in the formation of hydromorphic soils.
• Gleization is not solely dependent on climate, such as high rainfall typical of humid regions, but is primarily influenced by drainage conditions.
• The poor drainage conditions are a consequence of several factors:
  • Lower topographic positions, such as depressions where water stands continuously at or near the surface.
  • The presence of impervious soil parent material.
  • Inadequate aeration.
• In these waterlogged conditions, iron compounds undergo reduction to become soluble ferrous forms. This reduction of iron is mainly a biological process that requires both organic matter and microorganisms capable of anaerobic respiration. This process results in increased solubility of calcium (Ca), magnesium (Mg), iron (Fe), and manganese (Mn). Most of the iron exists in the form of ferrous (Fe++) organo-complexes in solution or as a mixed precipitate of ferric and ferrous hydroxides.
• The outcome of this process is the formation of a characteristic bluish to grayish horizon in the soil profile, often exhibiting mottling with yellow and/or reddish-brown colors.

Salinization

Salinization is the process by which salts, including calcium, magnesium, sodium, and potassium sulfates and chlorides, accumulate in soils, forming a salty horizon (referred to as a salic horizon). This phenomenon is quite common in arid and semi-arid regions. Salts may also accumulate due to the capillary rise of saline groundwater or inundation with seawater in coastal and marine soils. Additionally, salt accumulation can result from irrigation or seepage in areas with poor drainage.

Desalinization

Desalinization is the process of removing excess soluble salts from soil horizons or the entire soil profile, especially when the salt content is high enough to hinder plant growth. This removal is achieved through leaching, typically by ponding water and enhancing drainage conditions by implementing artificial drainage systems.

Solonization or Alkalization

Solonization, or alkalization, is the process in which sodium ions accumulate on the exchange complex of clay particles, leading to the formation of sodic soils, known as Solonetz. In this process, all cations present in the solution engage in a reversible reaction with the exchange sites on clay and organic matter particles.
The reaction can be represented as:

Solodization or Dealkalization

Solodization, or dealkalization, is the process of removing sodium ions (Na+) from the exchange sites in the soil. This process often leads to the dispersion of clay particles, where dispersion occurs as the sodium ions become hydrated. However, much of this dispersion can be mitigated by concentrating calcium (Ca++) and/or magnesium (Mg++) ions in the water used for leaching. These Ca and Mg ions can replace the sodium on the exchange complex, and as a result, the sodium salts are leached out of the soil.

Pedoturbation

Pedoturbation is a process that involves the mixing of soil, and it can occur in various ways:

• Faunal Pedoturbation: This type of pedoturbation is characterized by the mixing of soil by animals. Animals like ants, earthworms, moles, rodents, and even human activity can contribute to the mixing of soil.
• Floral Pedoturbation: In this type, the mixing of soil is a result of plant activity. For example, tree tipping can lead to the formation of pits and mounds in the soil.
• Argillic Pedoturbation: This form of pedoturbation involves the mixing of materials within the soil profile due to the churning process caused by the expansion and contraction of clay-rich soils, as commonly seen in deep Black Cotton Soils.