Soil as Natural Resource: The abiotic environment or physical environment of the earth includes the non-living components, namely the air, water and soil. Soil is the outermost part of the earth’s crust on which we live, work and grow food crops.

Soil provides all mineral nutrients, anchorage and water needed for the growth and development of plants and animals. Plants grow on the soil. All animals are directly or indirectly dependent on plants for food. Thus plants and animals are both dependent on soil for nutrition. The man also uses soil for various other purposes, such as making bricks, pottery and porcelain.

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What is Soil?

Soil is the biologically active, porous medium in the uppermost layer of the earth’s crust. Soil is a complex mixture of inorganic mineral particles and humus. Humus is a dark and organic material containing dead and decayed plant and animal remains.

Fig: Soil

What is Healthy Soil?

Healthy soil is a mixture of different-sized particles and is rich in organic matter. It has a crumbly texture and plenty of air spaces. It allows a free flow of oxygen and water through the soil, making it easier for plant roots and soil organisms to work their way through. Organic matter improves absorption and water holding capacity leading to healthy root growth.

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Types of Soil

There are different types of soil such as clay soil, loam soil, sandy soil, black soil, red soil, silt soil, etc.

1. Sandy Soil: It is mainly made up of sand particles. This soil is light and porous. It has large pore spaces. So there is better aeration, but the water-retaining capacity is low. Rapid movement of water washes the minerals away to the lower layers where roots do not reach.

2. Clayey Soil: It has a large number of clay particles and very little sand. The pore spaces are small, and therefore, the movement of water to the lower level is very slow. Hence it has a good water-retaining capacity.
But this type of soil has very poor aeration, and roots do not get enough oxygen for respiration. The soil gets waterlogged, and it is disadvantageous for the growth of plants.

3. Loamy Soil: This type of soil has an equal proportion of sand and clay. It has enough air between soil particles, it can hold sufficient water, and it contains a lot of humus. It is the best soil for plant growth.

Types of Soil Found in India

The main types of soils found in India are as follows:

(a) Alluvial Soil
1. It is loamy in texture with a lot of humus. It is very fertile and good for crops like wheat and rice.
2. It Occurs in Haryana, Punjab, Orissa, Uttar Pradesh, Bihar, West Bengal, Tamil Nadu, and Andhra Pradesh.

(b) Black Soil
1. It is rich in iron and magnesium.
2. Clayey contains dead organic matter and water. Good for cotton and sugarcane.
3. It occurs in Maharashtra, parts of Andhra Pradesh, Madhya Pradesh, and Gujarat.

(c) Red Soil
1. It is red in colour due to the presence of iron oxide, rich in potash.
2. It is poor in humus but can be made fertile by adding manure or fertilizers.
3. It is found in interior Kerala and Tamil Nadu, South Karnataka, Andhra Pradesh, Orissa, and East Madhya Pradesh.

(d) Desert Soil
1. Desert soil is sandy and porous in nature. It cannot hold much water.
2. Crops can be grown if irrigated.
3. It is found in Rajasthan and some parts of Gujarat.

(e) Mountain Soil
1. It is very fertile due to the presence of huge quantities of humus.
2. It occurs in the Himalayan regions and northeast India.

(f) Laterite Soil
1. Laterite soil is rich in nutrients. This soil is acidic, poor in humus, infertile in nature.
2. Tea, coffee, and coconut grow well in this soil.
3. It is found in Tamil Nadu, Andhra Pradesh, Orissa, and Assam, where rainfall is heavy.

Formation of Soil

Rocks break up due to the action of wind, water, and sudden temperature changes. This slow and gradual process is called weathering. In the beginning, the large rocks are broken into smaller pieces by natural events like earthquakes. Broken pieces rub against each other and form very small particles. These small particles pile up on top of the parent rock to form soil.

The factors that cause weathering of rocks include wind, water, and temperature changes.

1. Wind: High-speed wind blowing in the mountains can cause loose rocks to slide down the slope of the mountain. They hit each other and break into smaller pieces. Rubbing against each other, these smaller pieces form finer particles. These fine particles are carried away by the blowing wind and deposited elsewhere as soil.

2. Water: Flowing water causes weathering the same way as wind. The continuous movement of flowing water causes the breaking down of rock particles into finer particles due to their abrasive effect.

3. Temperature Changes: During daylight, due to heat, the surface of the rocks expands more than the inside of the rock. At night when the temperature is low, the surface contracts more than the inner layers. Such non-uniform or unequal expansions and contractions cause the rock surface to break apart. The rocks develop cracks and eventually lead to weathering. Over a period of time, fine particles of soil are formed.

4. Parent Rock: It determines the colour, chemical properties, texture, minerals, content permeability, etc.

5. Relief: Altitude and slope determine the accumulation of soil.

6. Time: it determines the thickness of the soil profile.

7. Living Organisms: Living things cause biological weathering. Lichens that grow on rocks secrete acids that erode the rocky surface and form fine particles. In these fine particles, microbes, insects, and worms grow and die, forming more soil.

8. Roots of trees that grow through the crevices of rocks exert pressure on the rocks. This causes the cracks to expand, and weathering takes place.

9. The fine particles of rocks undergo decomposition by a number of processes such as hydrolysis, carbonation, hydration, oxidation, and reduction. Climatic conditions, vegetation, nature of the parent rock material, and time are important factors that affect both the form and rate of weathering.

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What is Soil Profile?

Soil profile can be defined as a vertical section of the soil from the surface down to the bedrock, showing different layers or horizons. The arrangement of the horizons constitutes the soil profile. It varies in different habitats. It can be as little as 10cms thick in immature soil and as deep as several meters in tropical soil.

The soil profile shows three main layers or horizons, one above the other.

Fig: Soil Profile

(a) ‘O’ Horizon: O horizon is the initial layer of the soil profile. It is also called the surface layer. It contains partly decayed organic matter, and the soil is loosely packed.

(b) ‘A’Horizon: ‘A’ horizon is also called the ‘ploughed layer’ in cultivated soil. A horizon is an uppermost layer, also known as the topsoil, and it shows the following features:

1. It is the darkest layer in colour.
2. It is soft and porous and has a good water-holding capacity.
3. It contains a lot of humus. Humus is the organic matter formed by the death of animals and the decay of plants.
4. It is the most fertile region of the soil and the best region for the growth of plants.
5. Roots of plants are present in this region. Roots of large trees grow further down into the second horizon.
6. Living organisms like insects, earthworms, bacteria and fungi are present in this layer.

(c) B Horizon: ‘B’ horizon is used to identify soil types. B horizon is located below the topsoil and is also known as the sub-soil. It shows the following features:

1. It is lighter in colour as compared to the topsoil.
2. It is composed of sand, silt and clay.
3. It serves as a reservoir of water.
4. It is harder and more compact than the topsoil.
5. It is rich in minerals and iron oxides.
6. Very little organic matter is found in this layer.
7. Roots of tall plants usually reach this layer.

(d) C Horizon: ‘C’ Horizon is often similar and consistent with the parent rock materials. It is the third layer located below the sub-soil. It consists of lumps of parent rock material that are partially weathered. They have rock pieces.

(e) Bedrock: Bedrock is found below the ‘C’ horizon and is made up of unweathered parent rock. It is also called the R horizon. It is not part of the soil profile. Additionally, bedrock provides the base for the other three horizons. It is very hard and cannot be dug up easily.

Composition of Soil

Soil is a mixture of inorganic and organic compounds. As soil is formed over a very long period of time, a number of physical and biological changes occur in the soil. Soil consists of air, water, humus, organic matter, organisms, etc.

Fig: Soil Composition

1. Inorganic Particles of Sand and Clay.

2. Humus: Humus is the organic matter in the soil produced by the decay of plant and animal remains. It is formed due to the activity of microorganisms like bacteria and fungi present in the soil. Humus makes the soil fertile and, therefore, more suitable for plant growth.

3. Water: The capacity of the soil to hold water depends upon its texture. Water is held in the space between soil particles due to capillary action. The root hairs of the plants absorb this capillary water with mineral salts dissolved in it. If water is less in the soil, the plants may wilt and die.

4. Air: Air is present in the spaces between the soil particles. The amount of air present in the soil depends upon the size of soil particles. Sandy soil with bigger particles has more air than other types of soil. Air being the source of oxygen is essential for the respiration of roots and other soil organisms like bacteria.

5. Inorganic Salts Dissolved in Water: Mineral salts dissolve in the soil water and make a very dilute solution. It is vital for plant growth.

6. Soil Organisms: Apart from bacteria, some fungi, blue-green algae, and a number of organisms such as earthworms, roundworms, insects like ants, centipedes, and millipedes are found in the soil.

Soil Erosion

Soil erosion is the removal of topsoil, usually by the action of wind, rain, or water and some human activities.

1. Water: The force of rainwater flowing along the hill slopes without vegetation carries away the fertile soil.
2. Wind: Wind carries away the exposed topsoil that is loose. This happens mostly in deserts.
3. Human Activities: Ploughing sometimes removes the natural vegetation and helps the rainwater or wind to remove the fertile topsoil.

What are the Causes of Soil Erosion?

1. Deforestation: Deforestation is the removal or cutting down of trees, and it exposes the soil and makes the soil loose. The root system of the plants binds the soil together and also helps in the percolation (seeping) of water downwards into the soil and prevents erosion. In the absence of plants, the topsoil is washed away by rainwater into the rivers, which get choked with silt. This results in floods. Deforestation is due to the increase in population, which requires more land for agriculture, housing, roads, and industries.

2. Poor Farming Methods: Ploughing loosens the soil and destroys its natural structure. Failure to replace humus after successive crops and burning the weeds reduces the water-holding properties of the soil. The soil thus dries easily and may be blown away by the wind. On slopes, such soil can be washed away by water.

3. Overgrazing: Sheep, goats, and other grazing animals graze the vegetation closely, leaving little plant cover on the soil. This results in barren lands. Barren lands do not hold water. The soil dries out quickly and may eventually be blown away by the wind.

4. Forest Fires: Forest fires, too, lead to soil erosion. After a fire, the vegetation is destroyed, and it results in erosion by wind and water.

Prevention of Soil Erosion/Soil Conservation

Soil conservation is the prevention of the loss of topsoil by erosion.

1. Afforestation: Planting trees to prevent erosion is called afforestation. The roots of plants or trees bind the soil. Hence planting helps to conserve soil.

2. Crop Rotation: The practice of growing different kinds of crops in a given area each season. For example, if wheat is grown in one season, pea or pulses are grown in the next season. This helps in reducing the loss of nutrients from the soil and maintains the fertility of the soil.

3. Terrace Farming: On the hill slopes, terrace farming should be practised. This reduces the steepness of the slopes and checks the flow of water carrying topsoil with it, thus reducing erosion.

4. Intercropping: Different crops are grown in alternate rows and are sown at different times to protect the soil from rain wash.

5. Rock Dam: Rocks are piled up to slow down the flow of water. This prevents gullies and further soil loss.

6. Land should not be left uncultivated or barren for long since roots hold the soil together and prevent erosion.

What are the Uses of Soil?

Below we have listed some of the uses of soil for your reference:

1. Soil is a rich source of minerals used in various industries, for example, iron, aluminium, manganese, etc.
2. Bricks, pottery, and porcelain are made from clay soil.
3. Rainwater that seeps through the soil layers gets stored underground. Man uses this groundwater through wells and borewells.
4. Soil provides habitats, and it is home to many of the organisms.
5. Soil is an important factor for plant growth.

Summary

Plants need soil for fixation, absorption of water, and minerals. Humans consume various plant parts and plant materials as food. Plants also provide us with other materials such as cotton, jute, wood, and medicines. Thus life on earth depends a lot on the soil. Healthy soil maintains a balance between how quickly water drains through the soil and how much water is retained. Hence the soil is never too wet or too dry.

There are different types of soil such as clay soil, loam soil, sandy soil, black soil, red soil, silt soil, etc. The soil consists of humus, sand and clay particles, air, water, etc. There are many layers of soil which are also called horizons, placed above the bedrock. We should not cut down the trees or leave the animals for overgrazing; this leads to soil erosion. We should conserve soil by planting more trees by following crop rotation and terrace farming.

FAQs

Q.1. What are the four types of soil?
Ans: The four types of soil are sand soil, loam soil, clay soil, black soil, etc.

Q.2. What are the 5 components of soil?
Ans: The 5 components of soil are air, water, humus, soil organisms, minerals, and salts.

Q.3. What is the best soil to use for construction?
Ans: Loam soil is the best soil to use for construction purposes.

Q.4. What are the uses of soil?
Ans: Soil is used to grow plants. These plants can be used as food, clothing, building materials, etc. Clay soil is used for making pottery, ceramics, etc.

Q.5. What are the 3 layers of soil?
Ans: The 3 main layers of soil are A horizon, B horizon, and C horizon.

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We hope this article on Soil as Natural Resource helps you in your preparation. Do drop in your queries in the comments section if you get stuck and we will get back to you at the earliest.