Fundamentals of Soil Science (1+1)

Introduction

• A soil forming process may be defined as a complex or sequence of events including both complicated reactions and simple rearrangement of matter which intimately affect the soil.
• These processes are also known as soil building processes or pedogenic processes.

The basic soil forming processes involved in soil formation (Simonson, 1959) includes the following.

• Gains or Additions of water, mostly as rainfall, organic and mineral matter to the soil.
• Losses of the above materials from the soil.
• Transformation of mineral and organic substances within the soil.
• Translocation or the movement of soil materials from one point to another within the soil. It is usually divided into two aspects.
• Movement in solution (leaching)
  
• Movement in suspension (eluviation) of clay, organic matter and hydrous oxides

A. Fundamental Soil Forming Processes
Humification:

• It is the process of transformation or decomposition of raw organic matter in to humus.
• In this process the soluble organic substances regroup themselves in to large molecules by polymerization and become poorly soluble.
• The characteristics are influenced by the nature of vegetation residue and the way it becomes decomposed and synthesized in to new organic compounds.

Eluviation (Latin, ex or e,out and lavere, to wash ):

• Eluviation means washing out. It is the process of removal of constituents in suspension or solution (Clay, Fe₂O₃, Al₂O₃, SiO₂, humus, CaCO₃, other salts etc) by the percolating water from the upper to lower layers. The Eluviation process involves mobilization and translocation of mobile soil constituents resulting in textural differences. Translocation depends upon relative mobility of elements and depth of percolation.
• The horizon formed by the process of eluviation is termed as eluvial horizon (A₂ or E horizon).

Illuviation ( Latin- il, in, and lavere, to wash):

• The process of deposition of soil materials (removed from the eluvial horizon) in the lower layer is termed as Illuviation.
• This is the region of maximum accumlation of materials such as iron and aluminium oxides and silicate clays.
• The horizon formed by this process is termed as illuvial horizon (B-horizon, especially Bt).
• The process leads to horizon of gains and textural contrast between E and Bt horizons.