Soil of India

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Soil is the uppermost layer of the Earth’s crust, formed by the weathering of rocks and organic material decomposition. It supports plant growth and is a vital natural resource for agriculture, forests, and human settlement.

 

India, being a land of diverse geological structure, relief, climate, and vegetation, has developed various soil types. These soils vary in texture, colour, fertility, and moisture-retention capacity.

 

Factors of Soil Formation

 

Soil formation (or pedogenesis) is a slow and continuous process influenced by various natural factors. The five main factors of soil formation were first proposed by Hans Jenny, a Swiss soil scientist.

 

Formula:
S = f (Cl, O, R, P, T)
Where: S = Soil, Cl = Climate, O = Organisms, R = Relief (topography), P = Parent material, T = Time.

 

Parent Material

 

• The original rock from which the soil is formed.
• Determines mineral content, texture, structure, and chemical composition of the soil.
• Example: Basalt rock forms black soil in the Deccan region.

 

Climate

 

• Temperature and Precipitation affect the rate of weathering and humus formation.
• It is probably the most important factor that can shape the formation of Soil.

 

Organisms (Flora and Fauna)

 

• Microorganisms like bacteria, fungi, and earthworms help in decomposition and humus formation.
• Vegetation type influences organic matter content in the soil.
• Human activities (agriculture, deforestation) also impact soil quality.

 

Relief (Topography)

 

• Slope and aspect are two topographical features that affect soil formation.
• Flat areas: deeper soils with more moisture and organic material.

 

Time

 

• Time is the fifth factor in soil formation. Soil formation is a slow geological process.
• Older soils are usually deeper and more developed.
• Over time, soils become mature, showing distinct horizons (O, A, B, C layers).

 

Factors that Slow Down Soil Formation

 

Soil formation is a gradual process that can take hundreds to thousands of years. Several natural and human-induced factors can significantly slow down the rate of soil formation, making soil a non-renewable resource over human timescale.

 

• Low rainfall and Dry climate.
• Cold temperature.
• High water table.
• High lime content in parent material.
• High quartz content in parent material.
• High clay content in parent material.
• Hard rock parent material.
• Steep slop and Lack of vegetation.
• Human Activities (Unsustainable Practices).

 

Soil Classification on the basis of Factors of Soil formation

 

Based on the factors of soil formation, soil classified into three types;

 

• Zonal Soil: Zonal Soils are mature soils that have developed over a long period of time under the influence of climate and vegetation. These soils exhibit well-developed soil horizons (layers) and are in equilibrium with the climate and natural vegetation of their region. They reflect the climatic zones where they are formed and are thus termed ‘zonal.’ Example- Podzol soil, Chernozem soil etc.

 

• Intra Zonal Soil: Intrazonal soils are soils whose development is strongly influenced by local factors such as relief, parent rock, and groundwater, rather than by climate and vegetation. These soils have well-developed profiles, but their formation is controlled by a dominant local condition, such as poor drainage, salinity, or calcium content. Example- Saline and Alkaline, Peaty and Marshy Soils etc.

 

• Azonal Soil: Azonal soils are immature soils that have not yet developed well-defined soil horizons due to insufficient time or constant deposition of new material. They are typically formed from transported material like alluvium or sand. Example- Alluvial soil, Coastal soil, Sandy soil, Loess soil etc.

 

Characteristics of Soil

 

Soil is the uppermost layer of the Earth’s crust that supports plant life. It is a complex mixture of minerals, organic matter, air, and water. Its characteristics vary by region depending on parent rock, climate, vegetation, and time.

 

Soil Texture

 

• Refers to the proportion of sand, silt, and clay particles.
• Determines porosity, permeability, and water retention capacity.
• Soils can be sandy, loamy, silty, or clayey in texture.
  • Sandy soil: It consists mostly of sand-sized particles and has very low water-holding capacity. This soil is found abundantly in arid and semi-arid regions.
  • Clayey soil: This soil is rich in minerals, but poor in aeration and drainage. It holds high water retention capacity, making it heavy and sticky when wet.
  • Loamy soil: Loamy soil is a well-balanced mixture of sand, silt, and clay. It is fertile, well-drained, and moisture-retentive, often called ‘farmer’s best friend.'

 

Soil Structure

 

• It refers to the arrangement of soil particles.
• Structure influences aeration, drainage, and root growth.
• It can be granular, blocky, platy, or prismatic.

 

Soil Colour

 

• Soil colour indicates organic content, mineral composition, and moisture condition.
• Black soil: rich in organic matter or volcanic origin.
• Red soil: presence of iron oxides.
• Yellow or Lateritic soil: leaching of nutrients.

 

pH Level (Acidity/Alkalinity)

 

• Soils may be acidic, neutral, or alkaline.
• Ideal agricultural soil: pH 6.5 to 7.5
• Affects availability of nutrients and microbial activity.
• A strong alkaline has a pH value of 8 or more.
• Natural soils have pH value of 7.
• Acidic soil has pH value below 7.

 

Soil Profile

 

A soil profile is a vertical section of the soil that shows different layers or horizons from the surface down to the bedrock. Each layer varies in color, texture, composition, and thickness, and reveals the processes of soil formation and weathering. The soil is divided into five main horizons, usually denoted by the letters: O, A, E, B, C, and R.

 

O Horizon (Organic Layer)

 

• It is the topmost layer of the soil profile and rich in organic matter.
• Composed of dead leaves, twigs, decomposed materials etc.
• Found in forest and wetland soils
• This layer is helping in formation of humus
• Color: Dark brown to black.

 

A Horizon (Topsoil)

 

• A horizon is a part of Topsoil and called as Surface soil.
• Contains humus mixed with minerals.
• Dark in color due to organic content.
• Rich in nutrients and most fertile layer. This layer is most suitable layer for agriculture.

 

E Horizon (Eluviation Layer)

 

• Present below A and above B horizon (often absent in Indian soils).
• Zone of leaching or eluviation (washing out of minerals like clay, iron, aluminium).
• Light in color and low in nutrients.
• Common in forest soils and high rainfall areas.

 

B Horizon (Subsoil)

 

• Zone of accumulation (also called illuviation layer).
• Contains minerals leached from upper horizons (like iron, aluminium, clay)
• Denser and harder than A horizon.
• Less fertile but stores moisture
• Color: Brownish or reddish

 

C Horizon (Parent Material)

 

• Consists of partially weathered rock fragments.
• It is the layer of unbroken rocks.
• Source of minerals for the upper layers
• This layer helps understand origin of soil.

 

R Horizon (Bedrock)

 

• This layer denotes the layer of partially weathered bedrock at the base of the soil profile.
• It is not a layer of Soil; it is the layer of parent rock.
• It is located below the C horizon and it is also called Saprolite.

 

Key Facts to remember

 

• Eluviation - Removal of minerals (from E horizon).
• Illuviation - Deposition of minerals (in B horizon).
• Humus - Dark organic material in A horizon.
• Regolith - Loose material above bedrock.
• ‘Solum’ is consisting of A and B horizons.
• Munsell colour system is used to determine soil colour.
• The arrangement of layers of soil is known as the soil profile.

 

Classification of Indian Soil

 

The soils of India show great diversity due to variation in climate, topography, vegetation, parent rock, and age. Indian Council of Agricultural Research (ICAR) classifies Indian soils into 8 major types:

 

1. Alluvial Soil

 

Alluvial soil is one of the most important and widespread soils in India, covering about 40% of the total land area. It is formed by the deposition of sediments brought down by rivers from the Himalayas and other highlands.

 

This soil is fertile and ideal for agriculture, especially in the Indo-Gangetic-Brahmaputra plains and coastal river valleys.

 

• Alluvial soil known as the Transport soil or Migrated soil.
• Alluvial soil of Ganga plains is mainly Azonal.
• Generally, the soil of the northern plain in India has been formed by aggradation.

 

Origin and Formation

 

• Formed by fluvial deposition of silt, clay, sand, and gravel by rivers.
• The Himalayan rivers (Ganga, Yamuna, Brahmaputra) and peninsular rivers (Mahanadi, Godavari, Krishna) contribute to its formation.
• Replenished every year during floods; hence, renewable in nature.

 

Geographic Distribution

 

• Northern Plains: Punjab, Haryana, Uttar Pradesh, Bihar, West Bengal, Assam.
• Coastal Plains: Odisha, Tamil Nadu, Andhra Pradesh.
• River Deltas: Ganga-Brahmaputra, Mahanadi, Godavari, Krishna.

 

Types of Alluvial Soil

 

• Khadar (New alluvium): Found in low-lying floodplains, closer to river channels. It is more fertile, rich in organic matter and suitable for intensive agriculture.

 

• Bhangar (Old Alluvium): Found in upland areas, away from riverbanks. It is older, harder, clayey, often with calcareous nodules (called kankar) and less fertile than Khadar but still agriculturally useful.

 

Crops Grown in Alluvial Soil

 

• Staple crops: Rice, Wheat, Maize, Barley etc.
• Cash crops: Sugarcane, Jute, Cotton, Tabacco etc.
• Pulses, Oilseeds, Vegetables, Fruits etc.
• West Bengal, Punjab, and Uttar Pradesh benefit the most agriculturally from this soil.

 

2. Black Soil (Regur Soil)

 

Black soil is one of the most important soils of the Deccan Plateau. It is locally called Regur and is popularly known as ‘Cotton Soil’ due to its high suitability for cotton cultivation. It is dark in color, clayey in texture, and rich in minerals like iron and lime.

 

• The parent material for the most of the Black soil are the Volcanic rocks.
• Black cotton soil belongs to the Chernozem soil group.
• Water holding capacity is the highest in Black soil.
• Black soil is also known as Self-ploughed soil.

 

Origin and Formation

 

• Formed by the weathering of basaltic lava rocks.
• The parent rock of Black soil is Basalt. (In Tamil Nadu, the parent rock of Black soil is gneisses and schist).
• Mainly found in the Deccan Trap region.
• Developed under semi-arid climate and moderate rainfall.
• Volcanic origin makes it rich in minerals like iron and magnesium.

 

Geographic Distribution

 

• Black soil or the Lava soil are found in Malwa Plateau.
• Spread over 5.46 lakh sq. km (16.6% of the total area) across Maharashtra, Madhya Pradesh, parts of Karnataka, Telengana, Andhra Pradesh, Gujarat, and Tamil Nadu.

 

Types of Black Soil

 

• Shallow Black Soil: Low water retention
• Medium Black Soil: Moderately fertile
• Deep Black Soil: High moisture capacity

 

Crops Grown in Black Soil

 

• Black soil is best suitable for Cotton crop; hence this soil is called as Regur soil and Black Cotton soil.
• Other major crops grown in black soil includes Wheat, Jowar, Tobacco, Sunflower, Sugarcane, Pulses, Oilseeds, Citrus fruits etc.
• India is a leading cotton producer, largely due to this soil.

 

3. Red Soil

 

Red soil gets its characteristic reddish color due to the presence of iron oxides. It is one of the oldest soils in India, formed by weathering of crystalline igneous rocks like granite and gneiss. This soil is widespread in southern, eastern, and central parts of India.

 

• Red soil is having high phosphorus fixing capacity, because of the presence of Kaolinite.
• Red soil of West Bengal is known as Rahr.
• Largest soil group in Peninsular India is red soil.

 

Origin and Formation

 

• Formed by prolonged weathering of ancient metamorphic and igneous rocks.
• The red colour is due to diffusion of iron in crystalline rocks (ferric oxide content).
• It develops in areas of low rainfall, high temperature, and good drainage; typical of tropical and subtropical regions.

 

Distribution of Red Soil in India

 

• Red soil occupies the second largest area about 18.5% of the total reporting area.
• Along the piedmont zone of the Western Ghats, long stretch of area is occupied by red loamy soil. Yellow and red soils are also found in the parts of Odisha and Chhattisgarh and in the southern parts of the middle Ganga plain.
• Red soil is the dominant soil in Tamil Nadu, Rayalaseema (AP), and Chotonagpur Plateau.

 

Crops Grown in Red Soil

 

• The Red soil is mostly Loamy soil; hence it cannot retain water like the Black soil.
• Though it less fertile, but with proper irrigation and fertilization, red soils support a variety of crops: Paddy, Millets, Groundnut, Pulses, Cotton, Tobacco, Oilseeds etc.

 

4. Laterite Soil

 

The term ‘Laterite’ comes from the Latin word ‘Later’, meaning brick. This soil becomes hard like a brick when dry and is commonly found in areas with heavy rainfall and high temperature. It is formed due to intense leaching and is rich in iron and aluminium but poor in fertility.

 

• Laterite Soil also known as Pink Soil.
• Laterite Soil in India are rich in iron.

 

Origin and Formation

 

• Laterite soil is a result of leaching, which occurs in tropical and subtropical climates with heavy rainfall.
• The alternate wet and dry seasons cause the minerals to dissolve and drain away, especially silica.
• These soils are acidic in nature and poor in organic matter, nitrogen, phosphate, and calcium.
• Laterite soils are red in Colour due to little clay and more gravel of red sand-stones.
• Laterite soils are mostly the end products of Weathering.
• Pat land of Chotonagpur plateau is covered by Laterite soil.

 

Distribution of Laterite Soil in India

 

• Laterite soil is found in regions with high rainfall and temperature, especially in:
  • Western Ghats (Maharashtra, Goa, Karnataka, Kerala).
  • Eastern Ghats (Odisha, Andhra Pradesh, Tamil Nadu)- Laterite soils are predominant in Malabar coastal region.
  • Chhattisgarh and Jharkhand (in patches).
  • North-Eastern states like Assam and Meghalaya.
  • In West Bengal laterite soils are found in Bankura, Birbhum, and Purulia.

 

Crops Grown in Laterite Soil

 

• Due to intense leaching, laterite soil is not very fertile. However, with proper irrigation and use of fertilisers, it supports the cultivation of: Tea, Coffee, Cashew Nuts, Rubber, Tapioca, Pineapple, Coconut, Plantation crops in general etc.

 

5. Forest/ Mountain Soil

 

Forest soil, also known as Mountain Soil, is found mainly in hilly and mountainous regions of India. These soils are formed under the influence of thick forest cover, cold climate, and steep slopes. Their nature and fertility vary with altitude and vegetation type.

 

• Indian Forest soil is compared to Podzol soil of the World.

 

Origin and Formation

 

• Formed by the weathering of rocks under forested and mountainous regions.
• Mechanical weathering due to frost, snow, and steep gradients plays a major role.
• High amounts of organic matter get added due to continuous decomposition of forest vegetation.
• The soil remains undisturbed and rich in humus, especially in areas with dense forest cover.
• These soils occupy about 2.85 lakh sq. km or 8.67% of the total land area of India.

 

Distribution of Forest Soil in India

 

• Forest or mountain soil is found mainly in:
  • Western and Eastern Himalayas- Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Sikkim, Arunachal Pradesh.
  • North-Eastern Hills- Nagaland, Mizoram, Manipur, Meghalaya.
  • Parts of Western Ghats, Nilgiri Hills, and Eastern Ghats (in upper slopes).
• The nature of forest soil changes with altitude:
  • In lower altitudes, it is brown forest soil, rich in organic content.
  • In higher altitudes, it becomes podzolic (acidic and low in nutrients).

 

Crops Grown in Forest Soil

 

• The fertility of forest soil is not uniform. In many places, it is rich in humus, but lacking in minerals like phosphorus and potassium.
• However, in regions where the soil is deep and well-managed, it supports cultivation of: Tea, Coffee, Spices, Maize, barley, wheat, Apples, and other temperate fruits.

 

6. Arid/ Desert Soil

 

Arid soil, also known as Desert Soil, is found in the dry and semi-dry regions of India. This type of soil forms in areas with low rainfall, high temperature, and strong winds. It is mostly sandy, loose, and low in fertility, but it can be made cultivable through proper irrigation and soil treatment.

 

• Arid soil is generally Sandy in texture and Saline in nature.

 

Origin and Formation

 

• Formed in arid and semi-arid regions due to the weathering of rocks under extreme dryness and high temperatures.
• Winds constantly shift and deposit sand, creating sandy dunes and loose textures.
• Lack of rainfall leads to low organic content and accumulation of salts, making the soil alkaline in nature.
• Sometimes, soil horizons contain calcium carbonate layers called kankar, which limit water penetration.

 

Distribution of Arid Soil in India

 

Arid soil is mainly found in:

 

• Rajasthan - Thar Desert.
• Gujarat - Kutch region.
• Punjab and Haryana - Western dry zones.
• Southern Haryana and Western Madhya Pradesh.

 

Crops Grown in Arid Soil

 

• Although naturally low in fertility, arid soil can support agriculture through canal irrigation and soil improvement techniques. Example: Indira Gandhi Canal has transformed parts of western Rajasthan.
• Common crops grown: Millets, Pulses, Barley, Guar, Mustard, Cumin, Fodder crops etc.

 

7. Saline/ Alkaline Soil

 

Saline and Alkaline soils are often found in dry, poorly drained regions or areas with excessive irrigation and evaporation. These soils are commonly known as Reh, Usar, Kallar, and Thur in different parts of India. Their high content of soluble salts, sodium, and sometimes calcium carbonate makes them unfit for normal cultivation unless properly treated.

 

• Saline soil is found in Estuary of Narmada.
• Maximum Alkaline soil is found in Uttar Pradesh, Gujarat etc.
• Rajasthan has the largest inland Saline wetland.

 

Origin and Formation

 

Formed mainly due to:

 

• Poor drainage and capillary rise of groundwater.
• Over-irrigation in canal-command areas
• Weathering of rocks with high salt content
• In coastal areas, sea water intrusion also contributes to salinity

 

Distribution of Saline/Alkaline Soil in India

 

These soils are widespread in:

 

• Punjab, Haryana, Uttar Pradesh- especially in canal-irrigated zones
• Rajasthan- particularly in arid western parts
• Gujarat- Rann of Kutch and coastal belts
• Maharashtra, Bihar, West Bengal- scattered patches
• Andhra Pradesh and Tamil Nadu- coastal saline patches

 

Crops Grown in Saline/Alkaline Soil

 

• Naturally, these soils are not suitable for agriculture due to high salt and sodium content. However, with proper reclamation techniques like: Leaching, Gypsum application, Drainage improvement, and organic manuring.
• Common crops after reclamation: Sugar beet, Sesame (Til) etc.

 

Peaty/ Marshy Soil

 

Peaty and Marshy soil is found in waterlogged, swampy, and humid areas, where the organic matter does not decompose fully. Over time, thick layers of partially decayed vegetation accumulate, forming soil rich in humus and organic acids, but poor in essential minerals.

 

These soils are usually dark brown or black, acidic in nature, and often found in regions with heavy rainfall and poor drainage.

 

• In Kerala, the Peaty/Marshy soil is known as ‘Kari.’
• Small areas of Peaty soils occur in Uttaranchal.

 

Origin and Formation

 

• Formed in wet, humid, and marshy environments where water remains stagnant for long periods.
• Continuous accumulation of organic matter from dead plants, leaves, and mosses builds up over time.
• Due to lack of oxygen in waterlogged conditions, the organic matter doesn’t decompose fully, creating a thick layer of peat.
• The soil becomes acidic and nutrient-deficient, especially low in phosphate and potash.

 

Distribution of Peaty/Marshy Soil in India

 

This soil type is mostly found in:

 

• Sundarbans (West Bengal) – the largest tidal swamp in India
• Kuttanad region of Kerala – known for farming below sea level
• Coastal Odisha and Bihar – in depressions and marshy tracts
• Parts of Tamil Nadu, Assam, and Meghalaya – in low-lying wetlands and marshes

 

Crops Grown in Peaty/Marshy Soil

 

• Despite being acidic and nutrient-poor, these soils are rich in humus and can be made productive with lime and proper drainage.
• Crops grown include: Rice, Jute, Taro, Water chestnut, lotus roots, and other aquatic crops in wetlands

 

Soil Erosion in India

 

Soil erosion is the removal or wearing away of the topsoil by natural forces like wind, water, or human activities such as deforestation and overgrazing. Since the topsoil contains most of the nutrients needed for plant growth, its loss affects agriculture, biodiversity, and ecological balance.

 

India faces severe soil erosion, especially in the Himalayan region, the Western Ghats, and plateau areas due to a combination of climate, poor land practices, and population pressure.

 

Causes of Soil Erosion

 

1.     Water Erosion

 

• Caused by heavy rainfall, floods, and run-off from slopes.
• Most common in hilly regions, river valleys, and unprotected agricultural fields.
• It forms gullies, rills, and sheet erosion.

 

2.     Wind Erosion

 

• Happens in dry and semi-arid areas like Rajasthan, Gujarat, and Haryana.
• Wind blows away loose topsoil, especially from sandy lands with no vegetation cover.

 

3.     Deforestation

 

• Cutting down trees reduces the binding force of roots, making the soil loose and easily eroded by wind or water.

 

4.     Overgrazing

 

• In areas where animals graze heavily, the vegetative cover is lost, leading to exposure of soil to erosion.

 

5.     Faulty Agricultural Practices

 

• Ploughing up and down the slope, monoculture farming, excessive irrigation, and overuse of chemicals contribute to erosion.

 

Types of Soil Erosion

 

1.     Sheet Erosion

 

• When the top is removed, it is known as Sheet erosion.
• It takes place on the level lands after a heavy shower. It is much harmful since it removes the finer and more fertile top soil.
• Sheet erosion is the least visible form of land erosion.

 

2.     Rill Erosion

 

• Rill erosion is a type of erosion that results in small, yet well-defined streams.
• It happens when water from rainfall does not soak into the soil, but runs across it instead. The rills or small channels (often only 30cm deep) are caused when water running across the surface of the ground gathers in a natural depression in the soil, and erosion is concentrated as the water flows through the depression.

 

3.     Gully Erosion

 

• When rills increase in size, they become gullies.
• Especially seen in Chambal valley (MP), it is called Badlands.
• Gully erosion is a high destructive soil erosion.
• In West Bengal, Gully erosion shows in Kopai River in Birbhum.

 

Effects of Soil Erosion

 

• Loss of fertile topsoil affects agriculture and crop yield.
• Silting of rivers and reservoirs, reducing their storage capacity.
• Leads to floods and droughts due to imbalance in water cycle.
• Causes desertification, especially in western India.
• Landslides and habitat destruction in hilly regions.

 

Measures to Control Soil Erosion

 

• Afforestation and Reforestation: Planting trees and maintaining forest cover helps bind the soil and reduce run-off.
• Terracing and Contour Ploughing: In hilly areas, ploughing along contour lines reduces water flow and checks erosion.
• Strip Cropping and Crop Rotation: Growing crops in alternating strips and rotating crops improves soil health and reduces erosion.
• Controlled Grazing: Rotational grazing and restricting cattle to specific areas preserve vegetative cover.
• Building Check Dams and Bunds: Small barriers built across streams slow down the water flow and promote water absorption in the soil.
• Desert Development Programme: Launched by the Government of India to control desertification in Rajasthan, Gujarat, and Haryana.

 

Key Facts to remember:

 

• Major regions of Badlands Topography in India: Chambal valley, Mahanadi valley, Upper Son valley, Tapi valley, Shiwalik, Bhabhar regions of western Himalayas, Western Ganga in Uttar Pradesh etc.
• Major Causes of Water logging in India: Seepage of water form canals, Faulty onfarm water management, Lack of drainage, Interception of natural drainage, Indiscriminate cultivation in bed of drainage channel, Inundation of marine delta cycles, Inundation in coastal areas during cyclonic storms etc.
• Main causes of soil damage in Punjab and Haryana is Salinity and Water logging.
• In a desert region, soil erosion can be checked by afforestation or tree plantation.
• Black gram crop grown to increase the fertility of soil.
• Fertility of soil can be improved by adding living earthworms.
• ‘Fallowing’ practices is adopted for restoring the fertility of soil.
• Maad soil found in the southern part of Uttar Pradesh (Bundelkhand and Baghelkhand region).