Soils of India: Classification of Soil

Alluvial Soil:

• Distribution: Alluvial soils are widespread in the northern plains and river valleys of India, covering about 40% of the total land area. They are also found in the deltas of the east coast and in the river valleys of the Peninsular region.
• Origin: These soils are mainly derived from the debris brought down from the Himalayas by rivers like the Ganga, Brahmaputra, and others. They are also created by coastal wave action.
• Characteristics:
  • Color and Texture: The color of alluvial soil varies from light grey to ash grey. They vary in nature from sandy loam to clay.
  • Chemical Composition: Alluvial soils are rich in potash but poor in phosphorus. They are low in nitrogen but have sufficient levels of potash, phosphoric acid, and alkalies. Iron oxide and lime content can vary.
• Types:
  • In the Upper and Middle Ganga plains, two different types of alluvial soils have developed – Khadar and Bhangar. Khadar is the new alluvium found in the flood plains of rivers, enriched with fresh silt deposits every year. Bhangar is the old alluvium, deposited away from the flood plains.
  • Alluvial soils in the lower and middle Ganga plains and the Brahmaputra valley are more loamy and clayey.
• Chemical Properties: Alluvial soils are highly fertile and suitable for agriculture. They are rich in humus, lime, and organic matter.
• Crops: Alluvial soils are intensely cultivated and support a variety of crops including wheat, rice, maize, sugarcane, pulses, oilseeds, and more. They are particularly well-suited for rice cultivation.
• Geological Divisions: The alluvium in India’s Great Plain is divided into newer khadar and older bhangar soils, which have different characteristics and fertility levels.
• Regions and Rainfall: Alluvial soils are found throughout the Indo-Gangetic-Brahmaputra plains, except for areas covered in desert sand. They are also found in deltas like Mahanadi, Godavari, Krishna, and Cauvery. Regions with different levels of rainfall are suitable for different crops grown in alluvial soils.

Red Soil

• Also Known As: The “omnibus group.”
• Coverage: About 18.5% of the total land area of India.
• Location: Found in regions of low rainfall, particularly in the eastern and southern parts of the Deccan Plateau. Along the piedmont zone of the Western Ghats, a long stretch of area is occupied by red loamy soil. It is also present in parts of Odisha, Chattisgarh, and the southern parts of the Middle Ganga Plain.
• Color: Red due to the presence of iron in crystalline and metamorphic rocks. Appears yellow when hydrated.
• Fertility: Fine-grained red and yellow soil is usually fertile, while coarse-grained soil is less fertile.
• Nutrient Content: Generally deficient in nitrogen, phosphorus, and humus.
• Crops: Wheat, cotton, oilseeds, millets, tobacco, and pulses are mainly cultivated in red and yellow soil.
• Formation: Develops on Archean granite and covers a significant portion of India.
• Characteristics:
  • Vary based on rainfall, with some types suitable for quick drainage.
  • Rich in iron and potash but deficient in other minerals.
• Chemical Composition:
  • Generally low in phosphate, lime, magnesia, humus, and nitrogen.
• Distribution:
  • Found in the Peninsula from Tamil Nadu to Bundelkhand, Raj Mahal to Kathiawad.
• Crops Grown:
  • Supports rice, sugarcane, cotton, millet, and pulses. Kaveri and Vaigai basins are famous for red alluvium and are suitable for paddy.
• Features:
  • Porous, friable structure.
  • Absence of lime, kankar (impure calcium carbonate).
• Deficiencies:
  • Deficient in lime, phosphate, manganese, nitrogen, humus, and potash.
• Color and Texture:
  • Color: Red because of Ferric oxide. The lower layer is reddish-yellow or yellow.
  • Texture: Sandy to clay and loamy.
• Crops Cultivated: Wheat, cotton, pulses, tobacco, oilseeds, potatoes, etc. are cultivated in red soil.

Black Soil (Regur Soil):Soils of India: Classification of Soil

• Definition: Black soil is also known as “Regur Soil” or the “Black Cotton Soil.” It covers about 15% of the total land area of India.
• Distribution: It covers most of the Deccan Plateau, including parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh, and some parts of Tamil Nadu. In the upper reaches of the Godavari and Krishna rivers, and the north-western part of the Deccan Plateau, the black soil is very deep.
• Characteristics:
  • Color: The color of these soils varies from deep black to grey.
  • Texture: Black soils are generally clayey, deep, and impermeable. They swell greatly and become sticky when wet in the rainy season. In the dry season, the moisture evaporates, the soil shrinks, and develops wide cracks.
  • Composition: Black soils are rich in iron, lime, aluminium, magnesium, and also contain potassium. However, they are deficient in nitrogen, phosphorus, and organic matter.
• Formation: These soils are formed from the weathering of basaltic rocks that emerged during fissure eruptions in the Cretaceous period. They are typical in dry and hot regions.
• Chemical Composition: Black soils are rich in iron and lime but lack humus, nitrogen, and phosphorus.
• Crops: Black soil is ideal for cotton cultivation, hence it is also called “regur” and “black cotton soil.” It is also suitable for wheat, jowar, linseed, tobacco, castor, sunflower, millets, rice, sugarcane, vegetables, and fruits.
• Unique Features:
  • Self-plowing is a characteristic of black soil as it develops wide cracks when dried.
  • High water-retaining capacity.
  • Swells and becomes sticky when wet, and shrinks when dried.
• Color and Texture: Deep black to light black in color, and clayey in texture.
• Importance: Black soil is considered mature soil, with high fertility and good water retention, making it crucial for agriculture in the region.
• Suitability for Crops: Cotton, pulses, millets, castor, tobacco, sugarcane, citrus fruits, linseed, etc., are mainly cultivated in black soil due to its fertility and water retention properties.

Desert Soil / Arid Soils:

• Definition: Also known as arid soil, desert soil accounts for over 4.42% of India’s total land area.
• Color: The color of desert soil ranges from red to brown.
• Texture: Sandy to gravelly, with low moisture content and low water-retaining capacity.
• Salinity: Desert soils are saline in nature, and in certain regions, the salt content is high enough to obtain common salt by evaporating water.
• Nutrient Content: Normal phosphate content but deficient in nitrogen.
• Formation of ‘Kankar’ Layers: Due to increased calcium content in the lower horizons of the soil, kankar layers are formed. These layers restrict the penetration of water, but when water is made available through irrigation, soil moisture becomes readily available for sustainable plant growth.
• Distribution: Primarily found in arid and semi-arid regions, including Rajasthan, West of the Aravallis, Northern Gujarat, Saurashtra, Kachchh, Western parts of Haryana, and southern Punjab.
• Characteristics:
  • Lacks moisture, with low humus content, low organic matter, and a low population of living microorganisms.
  • Rich in iron, nearly adequate phosphorus, and high lime content.
  • Low soluble salts and low moisture retention capacity.
• Agricultural Potential: If irrigated, desert soil can yield high agricultural returns. Suitable for less water-intensive crops like bajra, pulses, fodder, and guar.
• Distribution Areas:
  • Western Rajasthan, the Rann of Kachchh.
  • Patches in southern Haryana and southern Punjab.
• Conditions: Seen under arid and semi-arid conditions, deposited mainly by wind activities.
• Key Points:
  • High salt content, lack of moisture and humus.
  • Impure calcium carbonate content is high, which restricts water infiltration.
  • Insufficient nitrogen and normal phosphate content.
• Texture and Color: Sandy texture, with a color ranging from red to brown.

Laterite Soil:Soils of India: Classification of Soil

• Definition: Laterite soil is named after the Latin word “later,” meaning brick. It is a type of soil that accounts for about 3.7% of the total area of India.
• Formation: It forms in regions with a monsoon climate, characterized by seasonal rainfall. With rain, lime and silica are leached away, leaving behind soil rich in iron oxide and aluminum.
• Characteristics:
  • Brown in color, composed of hydrated oxides of aluminum and iron.
  • Rich in iron and aluminum but deficient in organic matter, nitrogen, phosphate, and calcium.
  • Responds well to manures and fertilizers despite its low fertility.
• Distribution in India:
  • Found in Karnataka, Tamil Nadu, Kerala, Madhya Pradesh, and hilly regions of Assam and Odisha.
  • Specific areas include patches in the Western Ghats, Belgaum district of Karnataka, laterite plateau of Kerala, parts of Orissa in the Eastern Ghats, Amarkantak plateau region of Madhya Pradesh, Panchmahal district in Gujarat, and Santhal Pargana divisions of Jharkhand.
• Significance:
  • Well-suited for growing crops like groundnuts and cashew nuts.
  • Karnataka’s laterite soil is used for cultivating coffee, rubber, and spices.
• Other Information:
  • Laterite soil hardens rapidly and irreversibly on exposure to air, making it suitable for use as building bricks in southern India.
  • It becomes soft when wet and hard when dried, and is formed as a result of high leaching.
  • Due to high temperature and rainfall, organic matter is quickly removed by bacteria and taken up by plants, leading to low humus content.
  • Rich in iron and aluminum, deficient in nitrogen, potash, potassium, lime, and humus.
  • Red in color due to iron oxide.
  • Suitable for cultivating rice, ragi, sugarcane, and cashew nuts.
    

Mountain Soil:

Definition and Characteristics:

• Found in forest regions with sufficient rainfall.
• Texture depends on mountain environment, coarse-grained in upper slopes, loamy and silty on valley sides.
• In snowbound Himalayan areas, acidic with low humus; fertile in lower valleys.
• Also known as forest soil.

Distribution:

• Primarily found on mountains with steep slopes, high relief, and shallow profiles.
• Occurs at altitudes above 900 meters.
• Found in the Himalayas, Himalayan foothills, Western Ghats, Nilgiri, Annamalai, and Cardamom hills.

Characteristics:

• Thin layers, poorly developed profiles and horizons.
• Vulnerable to soil erosion.
• Rich in organic content (adequate humus but deficient in other nutrients).
• Loamy composition when sand, silt, and clay are mixed.

Significance:

• Beneficial for crops needing good air and water drainage due to slope location.
• Commonly used for rubber, bamboo, tea, coffee, and fruit plantations.
• Some areas practice shifting agriculture, but soil fertility may decline after 2-3 years.
• Supports silvi-pastoral farming, combining forest and grassland for animal husbandry, due to limited agricultural opportunities.

Peaty and Marshy Soils:

• Location: Found in regions of heavy rainfall and high humidity, such as southern Uttarakhand, northern Bihar, and coastal areas of West Bengal, Odisha, and Tamil Nadu.
• Characteristics:
  • Rich in humus and organic matter.
  • Generally heavy and black in color, sometimes alkaline.
• Marshy Soil Characteristics:
  • Originates in areas with poor drainage, rich in organic matter but high in salinity, deficient in potash and phosphate.
  • Heavy due to clay and mud dominance.
  • High moisture content, significant salt content, making it infertile.
  • Excessive moisture inhibits organic activity.
• Distribution:
  • Characteristic of delta regions in India, including the Bengal delta, Alleppey (Kerala), and Almora (Uttaranchal).
• Significance:
  • Suitable for jute and rice cultivation in the Bengal delta, used for spices, rubber, and large-sized rice in the Malabar region.
  • Favorable for mangrove forests.
• Peaty/Marshy Soil Characteristics:
  • Areas of heavy rainfall and high humidity.
  • Low growth of vegetation.
  • High quantity of dead organic matter/humus, making the soil alkaline.
  • Heavy soil with black color.
• Use:
  • Found in areas with high water tables, suitable for wetland agriculture, rice, and aquatic crops.

Saline and Alkaline Soils:

• Composition: These soils have high percentages of sodium, magnesium, and potassium, making them infertile. The high salt content is mainly due to the dry climate and poor drainage.
• Texture: The texture of these soils ranges from sandy to loamy.
• Location: Saline and alkaline soils are found in arid and semi-arid areas, as well as in waterlogged and swampy regions. They are mostly found in western Gujarat, deltas of the eastern coast, and in the Sundarbans areas of West Bengal. In the Rann of Kutch, salt particles are brought by the south-western monsoon and deposited as a crust. Seawater near deltas also increases the salinity of the soil.
• Deficiencies: These soils are deficient in calcium and nitrogen.
• Reclamation: Saline and alkaline soils can be reclaimed by improving drainage, applying gypsum or lime, and cultivating salt-resistant crops like berseem and dhaincha.
• Names: These soils are also known as Reh, Usar, Kallar, Rakar, Thur, and Chopan.
• Suitability for Crops: They are suitable for leguminous crops.
• Formation: Saline and alkaline soils can form naturally, such as in dried-up lakes of Rajasthan and the Rann of Kutch. They can also form due to anthropogenic factors like faulty agriculture in western Uttar Pradesh and Punjab.