Soil formation

• Soil formation is a slow, stepwise process and it takes thousands of years to form a layer of soil just a few centimeters thick.
• It is a result of continuous breaking down of rocks by a process called weathering.

Weathering:

• Weathering is the disintegration of rocks on the Earth's surface caused by exposure to natural forces such as wind, water, frost, roots of plants, etc.
• Weathering is of two types:

1. Physical weathering
2. Chemical weathering

Physical Weathering:

• In this process, rocks are broken down into smaller pieces.
• It is a mechanical process and does not involve any change in the characteristics of the original rock.
• It may be caused by temperature differences, frost, growing roots of plants, movement of animals, etc.

Chemical Weathering:

• It is a process in which existing minerals are broken down into new mineral components.
• In this process, the chemical nature of the rock gets changed. Water is one of the main agents of chemical weathering.
• The process of weathering can be divided into three stages:

Stage I

• Huge pieces of parent rock begin to break up near the surface, which can take place due to physical or chemical changes.

Stage II

• Smaller rocks continue to undergo weathering making the upper layer full of very fine rock particles.

• Bacteria and other micro-organisms break down plant or animal remains to form humus.
• This makes the soil very fertile, rich in organic material and in several minerals vital to plant growth.

Stage III

• Minerals and salts seep into the ground along with water to complete the formation of soil and make it favorable for plant growth.

Three stages of the process of weathering

Factors Affecting Soil Formation:

• There are a number of factors which affect soil formation, namely,

1. Climate
2. Characteristics of the parent rock
3. Slope of land

Climate:

• Climatic factors or weathering forces such as temperature, rain, wind, etc., play an important role in loosening and breaking up rocks (physical weathering).
• Water in rock crevices expands when it freezes, causing the rocks to crack.
• Rocks are also worn down by wind.
• Soil formation is fastest in hot, moist climates and slowest in cold, dry climates.
• In the warm and wet tropics, bacterial activity is high, thoroughly decomposing dead plant and animal matter.
• As desert regions have very little vegetation and animal life, limited decaying material is available for the soil.
• The lack of rainfall leads to the formation of coarse-textured soil in arid regions.
• In areas having severe winters, bacterial activity is very slow causing dead plant and animal matter to build up.
• Thus, the rate of soil formation and the type of soil formed depends on the climate of a place.

Characteristics of the parent rock:

• The composition of the parent rock also determines the kind of soil formed.

For example, if the parent rock is rich in calcium, the soil formed by its weathering would also be rich in calcium.

Slope of l and:

• The physical features of a place also play an important role in the formation of soil.
• Hilly areas generally have a thin layer of soil, because running water and wind tend to take away the soil down the slope.
• On flat plains, soil remains relatively undisturbed leading to the formation of a thick layer.