Soil Resources in India

The soils are formed by disintegration and denudation of rocks under specific natural conditions. The natural forces responsible for soil formation are water, wind, vegetation, animals and temperature variations. These forces lead to weathering of the rocks and formation of soil. This process of formation of soil is called pedogenesis.

The factors responsible for soil formation are following:

1. Parent rock material
2. Relief
3. Climate
4. Vegetation
5. Animals
6. Insects
7. Man

The soil is composed of inorganic and organic components.

1. Inorganic components: Following are the inorganic components of soil:
   1. Silica — is present in the soil in the form of small crystalline grains, the main constituent of sand.
   2. Clay — is a mixture of silicates and many other minerals such as iron, calcium, sodium, potassium and aluminium.
   3. Chalk (Calcium Carbonate) — provides the most essential elements for plant growth which is calcium.
2. Organic components: Organic matter is formed by the decomposition of plant remains, animal waste and dead animals. The ultimate form of organic matter is humus.

The major soils of India are:

1. Alluvial Soils
2. Black Soils
3. Red Soils
4. Laterite and Lateritic Soils

Alluvial soils are very fertile because of following reasons:

1. It is rich in minerals like iron, magnesia, alumina, potash and lime. It is also rich in organic matter and humus.
2. It is loamy.
3. It has sufficient depth.
4. It is renewed annually / replenished by floods.
5. It is transported soil which brings along lots of minerals, alluvium and silt.
6. It is non-porous and water retentive if all the minerals are present.

Black soils are formed from solidification of basic lava spread over large areas of Deccan Plateau during volcanic activity. Therefore, they are essentially formed by weathering of Deccan Trap. Black soils are formed in situ i.e., formed where they are found.

No, black soil does not undergo leaching. Black soil retains moisture and becomes sticky when wet. Due to this property, black soil does not undergo leaching.

The other names for black soil are Regur Soil and Black Cotton Soil.

The two characteristic features of black soil are:

1. The black soil retains moisture and becomes sticky when wet.
2. It releases moisture during dry period.

Red soils are generally low in nutrients and have poor water-holding capacity. They lack lime, magnesia, phosphate, nitrogen and humus. This makes red soils unsuitable for agriculture.

Leaching is defined as the loss of soluble nutrients or substances and colloids from the top layer of soil by percolation or runoff due to heavy rainfall.

Laterite soils are leached soils.

Alluvial soils are widely distributed over the Ganga Basin.

Alluvial soil is the most widely transported soil as they are carried by the rivers.

Laterite soil is found suitable for growing coffee in India.

Laterite soils are found on the summits of Eastern Ghats.

The mountain soils are heterogeneous in nature, and their character changes with mountainous environment and altitude.

The properties of desert soils are:

1. Low organic matter — Desert soils tend to have a low concentration of organic matter, as the dry conditions make it difficult for decomposing organisms to thrive.
2. Low nutrient levels — Desert soils are often low in nutrients, particularly nitrogen and phosphorus, due to the limited availability of organic matter and the high rates of evaporation that occur in these regions.
3. High salt content — Desert soils may have a high concentration of salt due to the dry conditions, which can cause salt to accumulate in the soil.
4. Poor water-holding capacity — Desert soils tend to be well-drained and have a low water-holding capacity due to the low levels of organic matter and the high evaporation rates in these regions.

Laterite soils are formed due to atmospheric weathering of rocks under conditions of high temperature and heavy rainfall with alternate wet and dry periods. They are formed strictly under monsoon conditions. They are the residual soils formed by leaching due to tropical rains.

The laterite soils are formed in area of high temperature and heavy rainfall. High temperature and heavy rainfall leads to leaching of Laterite soils. In addition, laterite soil tends to be well-drained, which means it does not retain water well. As it does not become sticky and wet, this also leads to its leaching.

The removal of topsoil by different agents of weathering like wind, running water, human activities, plants and animals is known as soil erosion.

The different types of soil erosion are:

1. Splash erosion
2. Sheet erosion
3. Gully erosion/ Rill erosion

Soil conservation means the efforts made to prevent or reduce the loss of soil due to soil erosion and prevention of reduced fertility of soil caused by over-use, acidification, salinisation or other types of soil contamination.

Two ways in which one can reduce soil erosion are:

1. Through afforestation by increasing area under forests and stopping indiscriminate felling of trees.
2. By checking overgrazing in grasslands

Topsoil — The uppermost fertile layer of soil, which is used for cultivation is called Topsoil.

In situ — It means 'at its original place'. It refers to anything which is formed where it is found. For example the black soil is formed in situ.

Bangar — The older alluvium is called as Bangar soil. They are darker in colour. They contain kankar, pebbles and gravels.

Khadar — The newer alluvium is called Khadar soil. They contain fine sand and clay. They are pale brown in colour. They are replenished by the floods.

Humus — The organic matter which is found in the soil is called Humus. It is formed by decaying remains of plants and animals

1. Red soils are generally low in nutrients and have poor water-holding capacity. They lack lime, magnesia, phosphate, nitrogen and humus. This makes red soils unsuitable for cultivation.
2. Laterite soils are used as building material because they harden like iron when exposed to air.
3. Black soils are black in colour because they are formed from weathered lava rocks like black crystalline schists and basic gneisses.
4. The Alluvial soils of the coastal regions are formed due to the deposition of sediments brought mainly from the Deccan Trap region. The Deccan Trap region is volcanic in origin so the sediments are black in colour. This imparts black colour to the Alluvial soils of Coastal region.

1. Black soil
2. Deltaic alluvium
3. 6 m

Magnesium Carbonates

Weathering of ancient crystalline rocks

Potash

Chambal ravines

Maharashtra

Laterite soil

The summits of Western ghats

Alluvial soil

Laterite soil

Black soil