Basic Processes of Soil Formation
During soil formation, the unconsolidated weathered material under goes many changes. These changes are brought about by variations in the four-basic soil forming processes. These four basic processes often referred as soil forming or Pedogenic processes. They are responsible of soil formation under all kind of environments. These processes are
Inputs of materials to the developing soil profile from outside sources are considered additions. For example, fallen plant leaves, twigs, dust, animal dung, salts or silica dissolved in groundwater and deposited near or at the soil surface when rising water evaporates.
Materials are lost from soil profile by leaching to groundwater, erosion of surface material, or other forms of removal. Leaching causes the loss of water and dissolved substances such as salts or silica, weathered from parent materials. Grazing of animals or harvest by people can remove large amounts of both organic matter and nutrient element.
It involves the physical or chemical modification of soil constituents i.e. some materials are broken down and others are synthesized. For example, weathering of primary minerals results in disintegration and alteration of various kinds of silicate clays. As primary minerals decompose, the decomposition products recombine to form new minerals which include additional type of silicate clays and hydroxides of iron and aluminum. The decomposition of organic residues gives rise to organic acids, humus and other products
It involves the movement of inorganic and organic material laterally within a horizon or vertically from one horizon up or down to another. Water, either percolating down with gravity or rising up by capillary action is the most common translocation agent. The material moved within the profile includes dispersed clay particles, dissolved salts and dissolved organic substances.
Soil organisms also play a major role in translocation of soil material e.g. Incorporation of surface organic matter into A and B horizons by certain earth worms, transport of B and C horizon to the surface by termites and rodents.
Fig. 1: Sketch of a typical soil profile showing different master horizon.
Syed Shabbar Hussain Shah
Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan
M +92 304 6020238 E [email protected]