SOIL

IMPORTANT TERMS

Soil: - Soil is a natural resource that is essential for life. Soil is essential for the growth of land plants. It is a shelter for many organisms.

Weathering: - Soil is formed when rocks are broken down by the action of wind, water, temperature and humidity. This process is called weathering.

Humus: - The decaying dead matters in soil is called humus.

Soil profile: - A vertical section through different layers of the soil is called soil profile.

Soil erosion: - Soil erosion is removal of land surface by agents like floods, wind, overgrazing etc.

Soil Pollution: - Soil Pollution is contamination of soil due to excess use of chemicals like fertilizers and pesticides.

Afforestation: - Afforestation is planting of tree in new land (in an area where there was no previous tree cover).

Reforestation: - Reforestation is the natural or intentional planting of tree on the land where deforestation occurred earlier.

Deforestation: - Deforestation is the permanent removal of forests in order to make the land available for other uses.

 

SOIL

Soil is a natural resource that is essential for life. It contains minerals, organic matter, air and water. All living organisms depend on soil. Soil is shelter of many organisms like bacteria, algae, fungi, insects, and worms.

FORMATION OF SOIL

It is a two-step process: -

A. Weathering of rocks takes place. Rock is broken down into small particles.

Soil is formed by weathering of rocks. Weathering is the breakdown of rocks by the action of air, water, temperature and humidity. Soil formation is a very slow process. It occurs all the time. Millions of years is required to form soil:

B. These small particles mix with decomposed organic matters and form soil.

The dead organic matters are decomposed by microbes. The decomposed organic matters form a dark and spongy product called humus which mixes with soil.

SOIL PROFILE

A vertical section through different layers of the soil is called the soil profile. It shows three distinct layers of the soil.

A-horizon: Upper most layer of soil is called topsoil or A-horizon. It is soft, porous and holds more water than the other layers. It is rich in humus and minerals. The humus makes soil fertile. Plants get most of the nutrients and water from this layer. It is also a home of many living organisms like rodents, snakes, moles, worms etc.

 

B-horizon: Second most layer from the top. It is consist of sand, silt and clay. It is more compact and harder than soil. It contains very little organic matter. It is rich in minerals

 

C-horizon: It is consist of small pieces of original rock broken due to weathering. It is made up of small lumps of rocks with cracks and crevices. Bedrock is found below the C-horizon.

 

CLASSIFICATION OF SOIL

The soil is classified on the basis of the proportion of particles of various sizes into following types:

 

Sandy Soil:  This kind of soil contains greater proportion of big particles. It has poor water holding capacity. Sand particles are quite large, so there are large spaces between them. These spaces are filled with air. Water can drain quickly through the spaces between the sand particles. So, sandy soil has high percolation rate of water and poor water holding capacity.

 

Loamy Soil: Loamy soil is a mixture of sand, clay and humus. It has the right water holding capacity for the growth of plants. It holds enough air for respiration of microbes, insects and roots of plant.

 

Clay soil: Clay particles, being much smaller, pack tightly together, leaving little space for air. Unlike sandy soil, water can be held in the tiny gaps between the particles of clay. So clay soil has high water holding capacity and less percolation rate of water.

 

SOIL EROSION

 

The removal of topsoil (upper layer) from a region by water and wind is called soil erosion. Humus present in the soil is eroded by soil erosion, thus it affects the fertility of soil. Deforestation, Overgrazing, Frequent flooding of rivers, Forest Fires, Poor farming methods are the causes of soil erosion.

Prevention of Soil Erosion

(a) Afforestation: Large scale planting. (b) Avoiding overgrazing of grass lands. (c) Use of step farming in hill regions. (d) Constructing embankment or gabions at river banks.

SOIL POLLUTION

The contamination of soil due to excess use of chemicals and harmful waste products like fertilizers, pesticides, industry waste is called soil pollution. Soil pollution deteriorates fertility of soil. Following are the causes of soil pollution:

Excessive use of chemical fertilizers and pesticides, Dumping of waste material, Acid rain, usage of Polythene and plastic bags.

Prevention of Soil Pollution

a. Excess use of chemical should be avoided. Use manures instead.

b. Industrial waste should be treated before release into soil.

c. Use of polythene and plastic bag should be banned.

PERCOLATION RATE

Passage of water from the surface into soil is called percolation. Amount of water drained through soil in unit time is known as percolation rate of water in soil.
Percolation rate is calculated by using the following formula:

Percolation rate (mL/min) = amount of water (mL) /percolation time (min)

SOIL AND CROP

Various crops can grow well in different kinds of soil due to its different characteristics.

Sandy soil: Groundnut and millet

Loamy soil: Pulses and maize

Clayey soil: Paddy and gram

Clayey loam: Wheat and other cereals

INTERESTING FACTS

• Each layer of soil is different in texture, colour and chemical composition.
• A-horizon is dark in colour and rich in humus.
• B-horizon has less humus but has more minerals.
• Earthworm is called the "Friend of farmers"
• Clayey soil is used in making of toys.
• Clayey soil is good for growing paddy.
• Terrace farming in hilly areas is effective in preventing soil erosion.
• Gravel, Sand, Silt, and Clay are the soil particles in descending order of size of particles.