Soil-forming Factors – Geomorphic Processes

There are various factors that influence the formation of soils. For example, the parent material’s role as a basis for soil formation can be discussed as one of the soil forming factors as it is one of the most important factors in the ecological system.

Parent material, which consists of mineral and organic materials, provides physical conditions and chemical reactions for soil to form. Topography and organisms’ activities also affect its development

Five basic factors control the formation of soils: (i) Parent material; (ii) topography; (iii) climate; (iv) Biological activity; (v) time

Parent Material

Parent material is a passive control factor in soil formation. Parent materials can be any in-situ or on-site weathered rock debris (residual soils) or transported deposits (transported soils).

Soil formation depends upon the texture (sizes of debris) and structure (disposition of individual grains/particles of debris) as well as the mineral and chemical composition of the rock debris/deposits.

Topography

Topography like parent materials is another passive control factor.

The influence of topography is felt through the amount of exposure of a surface covered by parent materials to sunlight and the amount of surface and sub-surface drainage over and through the parent materials.

Climate

The climatic elements involved in soil development are:

• moisture in terms of its intensity, frequency and duration of precipitation – evaporation and humidity;
• Temperature in terms of seasonal and diurnal variations.

Removal of silica from the soil is known as desilication. In dry climates, because of high temperature, evaporation exceeds precipitation and hence ground water is brought up to the surface by capillary action and in the process the water evaporates leaving behind salts in the soil.

Biological Activity

The vegetative cover and organisms that occupy the parent materials from the beginning and also at later stages help in adding organic matter, moisture retention, nitrogen etc.

Dead plants provide humus, the finely divided organic matter of the soil. Some organic acids which form during humification aid in decomposing the minerals of the soil parent materials.

Intensity of bacterial activity shows up differences between soils of cold and warm climates. Humus accumulates in cold climates as bacterial growth is slow.

Further, bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants. This process is known as nitrogen fixation.

Time

Time is the controlling factor for soil formation. It is the key factor in developing mature soils. If time is lost, favorable environment can be restored after hundreds of years but the soil formation process itself cannot be restored.

Cycling of sediments and re-establishment of vegetation can take place in few hundred years after pre-disturbance but soil formation process is never restored.

A soil becomes mature when all soil-forming processes act for a sufficiently long time developing a profile.