Soils of India – UPSC Geography Guide

Soil Formation

Soil formation is a beautiful process. It takes hundreds to thousands of years for the formation of soil. The factors involved in the formation of soil are:

• Parent rocks
• Climate
• Vegetation
• Animals
• Micro organisms

Parent rocks refer to the original rocks from which the soil is formed. If the original rock is basalt, the soil formed is Black soil. If the he original rock is ancient crystalline metamorphic rock, the soil formed is Red soil. If the original rock is laterite, the soil formed is Lateritic soil.

Now these rocks are subjected to weathering. It means softening and breaking down of rocks. This happens due to the influence of Climate. Every day due to the heat of the sun, the temperature rises and the rocks expand. And at night time the rocks contract. Now due to regular expansion and contraction of rocks, they break up into small sediments. Sometimes the rocks break down because they are in contact with water. Lime and silica in the soil reacts with water and they are extracted out of the rocks. The rocks finally become weak and they break. When the leaves from the tree complete their cycle, they fall down and decompose and finally become one with the soil. The animals excrete when they die, and they too decompose and become one with the soil. The dead remains of plants and animals is known as humus. It adds to the fertility of the soil and makes it sticky. Earthworms, ants, termites, microscopic organisms mix up in the soil, significantly affecting soil formation.

Types of Soil

Let’s learn about the eight different types of soils.

• Alluvial Soil
• Black Soil
• Red Soil
• Laterite Soil
• Mountain Soil
• Arid Soil
• Peat Soil
• Saline and Alkaline Soil

Alluvial Soil – This soil occupies 40% of the land area in India. Alluvial soil is formed by the depositional work of the rivers, and that is why they are known as riverine soil. These soils are found in the river basins and the deltas. River basin refers to an area covered by the main river and it’s tributaries. Delta refers to the triangular shaped land between the distributaries of different rivers. The color of the Alluvial soil can be gray, light brown or yellowish. This soil is very rich in chemicals like potash, phosphoric acid, lime, and carbon compounds. At the same time, they are deficient in nitrogen and humus. Humus refers to the dead remains of plants and animals which decompose. Alluvial soil is rich in clay, and if the clay content is more, water retaining ability of the soil is also high. This is ideal for the growth of crops like sugar cane, paddy, wheat, and other cereal and pulse crops. Due to its high fertility, regions of alluvial soils are intensively cultivated and densely populated. The entire northern plains are made up of these soils, and they are known as inland alluvium. It extends from Sindh in Pakistan up to Bangladesh. These soils are also predominant in deltas, known as deltaic alluvium. It is found in the deltas formed by the rivers such as Ganga, Brahmaputra, i.e. Sundarbans delta. Other important rivers forming delta are Mahanadi, Godavari, Krishna, Kaveri. In all these deltas we will find deposition of alluvial soil. Alluvial soil is also found in the coastal plains of the country.

On the basis of its age, Alluvial soils is of two types – Khadar and Bhangar. Khadar is light in color and is composed of newer deposits, whereas Bhangar refers to the older alluvium and is composed of lime nodules known as Kankars, and it has a clayey composition. Khadar is more fertile than Bhangar soils because new layers are deposited year after year during monsoon. Crops can be grown on old alluvium soil also, but that is after using manure. Soils in the drier areas are more alkaline and can be more productive after proper treatment and irrigation. In the upper reaches of the river valleys, the soils are coarse. Such soils are predominant in the Piedmont plains. It refers to an area of land formed or lying at the foot of a mountain or mountain range. In the lower reaches of the River Valley, the soil particles become smaller and more uniform. It is suitable for the growth of large variety of Rabi as well as Kharif crops, i.e. winter as well as the monsoon crops. In the lower Ganga-Brahmaputra valley, they are useful for jute cultivation. Alluvial Soil is found in the states of Punjab, Haryana, Uttar Pradesh, Bihar, West Bengal, and Brahmaputra valley of Assam, and also in the coastal plains of India.

Black Soil – This soil is formed by the weathering of basal rocks. This soil is the residual soil because it is formed at the place of its origin over the underlying rocks. It is dark in color and it is suitable for cotton cultivation. So it is also known as the Regur Soil or the Black Cotton Soil. The Regur Soils are concentrated over the Deccan lava trap which includes parts of Maharashtra, Gujarat, Madhya Pradesh, Telangana, Andhra Pradesh, Karnataka. We can find Regur Soil even in some parts of Rajasthan. This soil has a high proportion of LIMCa – p i.e. Lime, Iron, Magnesium, Calcium Carbonate, and Potash. And it is deficient in NO – p, i.e. Nitrogen, Organic matter, and Phosphorus.

Red Soil – Red Soil is formed from ancient crystalline metamorphic rocks of the peninsular plateau. Under prolonged weathering by rainfall, these rocks break up to form these soils. The soils differ from place to place. They are red in color as they contain large amount of iron oxides. At several places their color slightly changes as they appear brown or gray. It looks yellow when it occurs in a hydrated form. This soil is mainly found on the plateau regions of the peninsular India. Red Soil covers the states of Karnataka, Kerala, Tamil Nadu, Andhra Pradesh, Telangana, Orissa, Chhattisgarh, Jharkhand, and the northeastern states. If we look at it carefully, they practically encircle the entire Black Soil region on all sides. They extend northward in the West, and along the Konkan coast of Maharashtra. If we look at the characteristics of Red Soil, it is porous and has high percentage of Iron Oxides. It is generally shallow and its pH value range from 6.6 to 8. It is poor in Nitrogen, Phosphorus, Potassium and Organic matter. It is not fertile, but responds to fertilizers. It needs irrigation support for cultivation. It contains soluble salts in small quantities.

Laterite Soil – Laterite Soil is formed by the weathering of lateritic rocks. It is found in regions of heavy rainfall with alternating wet and dry periods. Due to heavy rainfall, lime and silica are leached out of the rocks, i.e. they are extracted out of the rocks, leaving behind high content of Iron Oxides and Aluminum. Finally, what is left out, disintegrates, i.e. it is subjected to weathering, and what we get is like Lateritic soil. Now these soils are of two types – Upland Laterites and Lowland Laterites, based on their location. This soil is red in color with a high content of Iron Oxides. It is poor in Nitrogen, Lime, and rich in Iron. It is of a coarse texture, soft, as well as friable. Friable, i.e. the soil is loose. It is loose because it has very low content of clay, whereas, we have seen that Alluvial Soil and Black Soil have high content of clay. Laterite Soils have low fertility because of high acidity and low moisture retention. Manuring and other activities are required to make them suitable for growing crops. Now crops that are grown on lower elevations are mainly paddy. Whereas the crops that are grown on higher elevations are rubber, cinchona, and tea plantations.

Arid Soils – Arid Soils are derived from the disintegration of adjacent rocks and are largely blown from coastal regions and Indus Valley. Arid soils are characteristically developed in western Rajasthan, which exhibit characteristic arid topography. Arid soils range from red to brown in color. They are generally sandy to gravelly in texture and have a high percentage of soluble salts. These soils are saline in nature. In some areas, the salt content is so high that common salt is obtained by evaporating the saline water. Due to the dry climate, high temperature, and accelerated evaporation, they lack moisture as well as Humus. These soils are deficient in Nitrogen and Humus. The Phosphate and Iron content is normal, which is good for the soil. These soils are rich in minerals, but the main limitation is lack of water. The soils exhibit poorly developed horizons. Plants are widely spaced and chemical weathering in these regions is limited. Lower horizons of soils are occupied by Kankar layer, because of the increasing Calcium content downwards. Now the Kankar layer formation in the bottom horizon restrict the infiltration of water. When irrigation is made available the soil moisture is readily available for a sustainable plant growth. So we can say that the layer of Calcium plays a very important role in retaining the water.

Mountain Soil – Mountain Soils are found in the valleys and hill slopes. These soils occupy about 8% of the total land area of India. They are formed due to mechanical weathering caused by snow, rain, and temperature variations. Soil formation is quite slow in mountainous areas. This is because of the low temperatures. So Mountainous soils are comparatively thin and are badly anchored. These soils are generally shallow in depth and that is why they are known as Immature Soil, because the soil formation is not complete. These soils are heterogeneous in nature, and their character changes with parent rocks and climate. These soils are very rich in humus, but are deficient in Potash, Nitrogen, Phosphorus, and Lime. The slopes are used for horticulture and plantation crops like tea, coffee, spices, apple, peach, etc. Rice and wheat are grown in valleys. Potatoes are grown in mostly all areas. These mountain soils are found in hilly regions of Jammu and Kashmir, Sikkim, Assam and Arunachal Pradesh.

Peat Soil – These soils are locally called Kari in Kottayam and Alleppey districts of Kerala. These soils are marshy soils, and are a result of water logging and anaerobic conditions. This leads to partial decomposition of organic matter. They are found in areas of heavy rainfall, high humidity, where there is a good growth of vegetation. It occurs widely in the narrow part of Bihar, the southern part of the Uttaranchal, and the coastal areas of West Bengal, Odisha and Tamil Nadu. These soils are normally heavy and black in color. These soils are characterized by a rich humus and organic content. There is a presence of Iron and varying amount of organic matter. The organic matter in these soils may even go up to 40%. These soils are generally acidic in nature, but in many places they are alkaline also. These soils are generally submerged during the rainy season, and are utilized for the cultivation of rice, because rice as a crop in the initial stage requires standing water.

Saline and Alkaline Soils – Saline Soils usually have a surface crust of white salts. Especially in the season when the net movement of soil moisture is upward. Salts, dissolved in the soil water, moves up to the surface. There they are left as a crust when the water evaporates. There are many undecomposed rock and mineral fragments which over weathering liberate Sodium, Magnesium, Calcium Salts and Sulfurous acid. Some of the salts are transported in solution by the rivers which percolate in the sub soils of the plains. In canal irrigated areas and in areas of high subsoil water, the salts are transferred from below to the top soil by the capillary action. That is, they rise up along the gap as a result of evaporation in dry season. The accumulation of these salts make the soil infertile and renders it unfit for agriculture. Alkaline soils are clay soils with high pH value. The pH value is more than 8.5, with a poor soil structure and a low infiltration. They have a hard calcareous layer of .5 to 1 meter depth. So if a layer of Calcium develops in the subsoil, it does not allow the penetration of water. So in such areas the ground water level is badly affected. In such soils, agriculture is possible but only after treating the soil.

This summarizes the details of all the different types of soils in India.