Soil is the topmost layer of the earth’s crust, mainly consisting of small rock particles and humus, which can support the growth of plants. It is a complex mixture of rock debris and organic material developing on the surface of the earth. It is formed mainly by the weathering or decomposition of the upper crust of the earth.
The major factors which affect soil formation are parent rock material, relief, climate, natural vegetation, microorganisms, land use particles, time, and other life forms. Mineral particles, humus, water, and air are the main components of soil.
India is a vast country having varied relief features, landforms, climatic conditions, and vegetation types. In the ancient period, soils were classified into two main categories: Urvara (fertile soil) and Usara (sterile soil). During the last century, several attempts had been made to classify the soils. Russian geologist V. V. Dokuchaev made the first scientific classification of soil in 1886.
Soils can be classified based on inherent characteristics and external factors like texture, structure, colour, pH value, moisture content, porosity, and slope of the land. If the soil is classified based on texture, it is sandy, clayey, silty, and loam, whereas classified based on colour, soil can be red, yellow, black, etc.
In India, based on the genesis, colour, composition, and location, the Indian Council of Agriculture Research (ICAR) has classified the soil into eight categories:
- Alluvial Soil.
- Black Soil,
- Red and Yellow Soil.
- Laterite Soil.
- Mountainous or Forest Soil.
- Desert or Arid Soil.
- Saline and Alkaline Soil.
- Peaty and Marshy Soil.
1. Alluvial Soils
Alluvial soils are formed due to the erosional and deposition activities of rivers and streams. These are the most fertile soils, covering the North Indian plains and the drainage basins of Peninsular India. Alluvial soil deposits in the Greater plains of India are derived mainly from the debris brought down from the Himalayas.
The texture of alluvial soils varies from sandy to silty-loam, whereas colour varies from light grey to ash grey. These soils have a well-developed and mature profile in levelled areas, whereas, in undulating areas, they have an immature and weak profile. The soil is porous, which provides good drainage. Alluvial Soil has an adequate proportion of Potash, Phosphoric acid, lime, alkalines, and organic matter, but it is deficient in Nitrogen.
Alluvial deposits mainly occur in the Satluj-Ganga-Brahmaputra Plains. These deposits also occur in the Eastern & Western coastal plains, mainly in the valley of Narmada & Tapi and the deltas of Mahanadi, Krishna, and Cauvery rivers.
The alluvial soil of the Great Plains of India can be divided into two parts: Khadar (new alluvial soil) and Bhanger (older alluvial soil).
- The Khadar soil is composed of newer alluvium enriched in fresh silt deposits and occupies the flood plains of rivers. These soils are low-lying and inundated by floods during the rainy season. With every flood in the river, a new layer of aluminum is deposited.
- The Bhangar soil is the older alluvium that lies above the flood level. As it contains calcium carbonate nodules (Kankars), the soil texture varies from loamy soil to clayey-loam. The Bhangar soil is generally well-drained and suited for wheat, maize, rice, sugarcane, pulses, oilseeds, fruits, and vegetables.
2. Black Soil (Regur Soil)
Black Soil is also known as Regur soil or Cotton soil because it is best suited for cotton cultivation. These soils are formed due to the weathering of the basaltic rocks that emerged during fissure eruptions of the Cretaceous period. The parent material for most black soils is the volcanic rocks of cretaceous lava.
The black colour of this soil is due to the presence of Titaniferous Magnetite (compound of Fe and Mg) found in the basalt. Blach soil has a clayey texture, and its colour varies from deep black to light black. These soils are rich in iron, magnesium, lime, calcium, potash, aluminum, but it’s deficient in nitrogen, phosphorous, and humus. Black soils are mature soils and have a high water-retaining capacity. During the rainy season, they swell greatly and become sticky on accumulating moisture.
Black soil is extremely compact & tenacious when wet, while, when dry, it develops wide cracks. If the soil is wet, it becomes difficult to plough the field. These soils are suited for cotton, rice, sugarcane, castor, pulses, vegetable, and citrus fruits.
Black Soil is found in the Deccan lava plateau, stretching over Gujarat, parts of Rajasthan, and western Madhya Pradesh. Maharashtra, Karnataka, Tamil Nadu, north-western Andhra Pradesh, Chhattisgarh, and Jharkhand.
3. Red and Yellow Soils
Red soils developed on the Archaean granite. The colour of this soil is red because of the presence of ferric oxide (Iron Oxide). Generally, the top layer is red, and the horizon below is yellowish in colour. In hydrated form, the soil appears to be yellow, hence, also known as yellow soil.
Red soil is porous, well-drained, and has a friable structure. The texture varies from sandy to clay and loam. The red soil is rich in potash and iron but deficient in lime, magnesia, phosphate, nitrogen, and humus. In places where water is available for irrigation, this soil is suitable for cultivating cotton, wheat, pulses, millets, and oilseeds.
Red soil deposits are found mainly over the Penisula from Tamil Nadu in the south to Bundelkhand in the north and Kaithaiwad & Kutch in the west to Rajmahal in the east. These soils are also found in the tracts of western Maharashtra, Andhra Pradesh, Odisha, Chhattisgarh, Jharkhand, Uttar Pradesh, and Rajasthan.
4. Laterite Soils
Laterite soils are found in regions under alternative wet and dry conditions. The alternative wet and dry season leads to the leaching away of the siliceous and alkalis matter from the rocks leading to the formation of laterite soil. The soil becomes soft when it’s wet, while, on drying, it becomes hard and cloddy.
Laterite Soil is Brown in colour. These soils are rich in iron and aluminum but deficient in potash, phosphorous, lime, nitrogen, and organic matter. This soil hardens rapidly and irreversibly on exposure to the air, which leads to its use for brick making. Laterite Soils are low fertile and have moderate water-retaining capacity. These are suitable for growing tea, coffee, groundnuts, and cashew nuts.
Laterite soils developed mainly in the highland area of the plateau. The soils in the higher areas are more acidic than those in the low-lying areas. These soils are found in the Western and Eastern Ghats hills, Vidhayan & Satpura hills, Odisha, Chhattisgarh, Jharkhand, West Bengal, Rajmahal Hills, North Cachar Hills in Assam, and Garo Hills of Meghalaya.
5. Mountainous and Forest Soils
Mountain soils are found on mountains with high relief, steeper slopes, and shallow profiles. These soils differ from region to region, depending upon the climate. Due to fast drainage, mountain soils are vulnerable to soil erosion.
In texture and structure, the Mountain soil varies from silt-loam to loam. The soil has a dark brown colour. The soil profile is less developed and generally immature. These soils are acidic in nature because of the presence of organic matter. They have low humus content and are deficient in potash, phosphorous, and lime.
Mountains soils are found mainly in the valley and hill slopes of the Himalayas, mountain slopes of Vidhayan, Satpura, Western Ghats, Nilgiri, Annamalai, and Cardamom hills.
6. Desert Soils (Arid Soil)
Desert soils are deposited mainly by wind action and developed under arid and semi-arid conditions. High temperature and wind erosion are responsible for the formation of this soil.
The Desert soils are light in colour, and their texture varies from sandy to gravelly. These soils contain a high percentage of soluble salt content and an adequate proportion of phosphorous but have low organic matter, low moisture content, low nitrogen, and varying percentages of calcium carbonate. Their water retaining capacity is also low. If this soil is irrigated, it may give a high agricultural return. These soils are devoted to bajra, pulses, fodder, gaur, and less water-requiring crops.
These soils are mainly found in arid and semi-arid areas, such as west of Aravallis, Rajasthan, northern Gujarat, Saurashtra, Kutch, south-western parts of Punjab, and western parts of Haryana.
7. Saline and Alkaline Soils
Saline soils have a high percentage of Sodium Chloride (NaCl) and Sodium Sulphate. These soils are generally found in arid and semi-arid regions, where high temperature and low rainfall is causing intense evaporation. In these soils, due to capillary action, the saline and alkaline efflorescence appears as a layer of white salt on the surface.
Saline/Alkaline soils are known by different names, such as reh, kallar, rakar, thru, Karl, usar, and chopan. The texture of these soils varies from sandy to sandy-loam. These soils have a low water-bearing capacity and are deficient in nitrogen, and calcium.
These are found mainly in Rajasthan, Punjab, Haryana, Uttar Pradesh, Bihar, and Maharashtra. These soils are infertile; however, they can reclaim by improving drainage, leaching salts, applying gypsum or lime, using acidifying fertilizers, and cultivating salt-resistant crops like dhaincha, barseem, and other leguminous crops.
8. Peaty and Marshy Soils
Peaty soils originate in heavy rainfall areas where adequate drainage is not available. During the rainy season, they are generally submerged. These soils are developed in hot and humid conditions as a result of an accumulation of organic matter.
Peaty soils are acidic in nature because of the presence of organic matter. These soils are highly saline and rich in organic matter but deficient in potash, phosphorous, and nitrogen. Rice is an acidic-tolerant crop, which can be grown in such soils.
Peaty and marshy soils are found mainly in deltas of Mahanadi, Godavari, Krishna, Cauvery, Sunderban delta, and parts of Kerala, Rann of Kutch.
Other Types of Soil
Submontane soils are found in the Tarai region of the sub-montane, stretching in the form of a narrow belt from Jammu & Kashmir to Assam. These soils are formed due to the deposition of eroded material from the Shiwaliks and the Lesser Himalayas. It is fertile soil and supports the growth of forests.
Karewas are the lacustrine deposits found in the Valley of Kashmir and Bhadarwah Valley of Doda district of Jammu. These deposits are composed of fine silt, clay, sand, and bouldery gravel. Karewas are flat-topped mounds that border the Valley of Kashmir on all sides. According to geologists, the entire Kashmir Valley was under the water during the Pleistocene Period. Subsequently, the Baramullah Geoge was created due to endogenic forces, and the lake was drained through this George. The deposits left in this process are called Karewas.
The Karewas are suitable for the cultivation of Saffron, walnut, apple, almond, and orchards. Karewas of Kulgam, Palampur, and Pulwama are well-known for their production of superior-quality Saffron.
The highest peaks of Karakoram, Zaskar, Ladakh, and the Greater Himalayas are covered by ice and glaciers. The soil of these areas is immature, generally without soil erosion. It remains frozen and unsuitable for the cultivation of crops.