Different Soil Types in India

• Soil is a natural body found on the Earth’s surface, comprising solids, liquids, and gases, and is characterized by distinguishable layers known as horizons.
• Soil formation is influenced by factors such as parent material, climate, time, and biodiversity, including human activities.
• Pedology, the study of soils in their natural environment, explores processes like pedogenesis, which involves weathering, leaching, and calcification.
• India’s diverse relief features, landforms, climates, and vegetation types have led to the development of various soil types.
• Indian agriculture heavily relies on soil quality and extent due to the country’s agricultural predominance.
• Climate, natural vegetation, and rocks significantly influence soil nature in a region.
• Types of soil in India include alluvial, laterite, red, black, desert, and mountain soils.
• Soils vary in their mineral makeup, composed of small particles resulting from weathered rock fragments.
• Soil particles vary in size, shape, and chemical composition, categorized into sand, silt, and clay based on particle size.

Soil Types: Sandy, Clayey & Loamy

• Sandy soil contains mostly large particles, resulting in quick drainage and aeration, leading to light coloration and dryness.
• Clayey soil, with predominantly fine particles, holds water tightly between particles, resulting in poor aeration and heaviness due to water retention.
• Loamy soil, a mix of sand, clay, and silt particles, along with humus, offers optimal water retention and aeration, making it ideal for plant growth.
• Silt, found in river beds, has particle sizes between sand and clay and contributes to the composition of loamy soil.
• Clayey and loamy soils are suitable for cereals like wheat and gram due to their water retention properties.
• Paddy cultivation requires soils rich in clay and organic matter for water retention.
• Lentils and pulses thrive in loamy soils that allow for easy water drainage.
• Cotton cultivation benefits from sandy loam or loamy soils that drain well and provide ample aeration.

Soil Profile (Soil Horizon)

• The uppermost layer of soil, known as the A-horizon or topsoil, is typically dark in color due to its richness in humus and minerals.
• Humus in this layer enhances soil fertility by providing essential nutrients for plant growth.
• The topsoil is soft, porous, and capable of retaining more water compared to lower layers.
• Beneath the topsoil lies the B-horizon or middle layer, which contains fewer humus but more minerals.
• This layer is generally denser and more compact than the topsoil.
• The lowest layer, the C-horizon, is composed of small rock fragments with cracks, providing a base for the upper layers.

O Horizon

• Layers dominated by organic material.

C Horizon or Parent rock

• This layer accumulates weathered parent material, particularly from sedimentary deposits.
• It tends to accumulate more soluble compounds, especially inorganic material, compared to other layers in the soil profile.

R Horizon or Bedrock

• Unlike the above layers, R horizons largely comprise continuous masses of hard rock.

Factors that influence soil formation in Indian Conditions

Parent Material

• Parent materials, the rocks from which soils originate, dictate soil characteristics such as coloration, mineral composition, and texture in most cases.
• However, the resulting soil may or may not exhibit identical physical properties to the parent rock.
• Climatic conditions trigger chemical changes that further influence soil properties.
• Weathering processes transform surface rocks into fine grains, laying the foundation for soil formation.
• In India, parent materials are typically categorized into:
  • Ancient crystalline and metamorphic rocks: They are the Oldest rocks (pre-Cambrian era) (formed due to solidification of molten magma about 4 billion years ago). They are basically granites, gneisses and schists. These rocks are rich in ferromagnetic materials and give rise to red soils on weathering.
  • Cuddapah and Vindhyan rocks: They are ancient sedimentary rocks (4000 m thick). On weathering they give calcareous (containing calcium carbonate) and argillaceous (consisting of or containing clay) soils.
  • Gondwana rocks: These rocks are also sedimentary in nature, and they are much younger. On weathering, they give rise to comparatively less mature soils.
  • Deccan basalts: A volcanic outburst over a vast area of Peninsular India gave rise to Deccan Traps. Basalts are rich in titanium, magnetite, aluminium and magnesium. Consequently, the weathering of these rocks has given rise to soils of darker colour. The soil is fertile with high moisture holding capacity and is popularly known as regur or black cotton soil.
  • Tertiary and Mesozoic sedimentary rocks of extra peninsular India, referred to as the Rock System: Rocks of extra peninsular (plains and Himalayas) India have given rise to soils with high porosity.These soils are generally immature recent and sub recent rocks, result in alluvial soils on weathering.

Relief

• Relief plays a crucial role in soil formation, particularly in areas with steep slopes such as hilly regions and plateau edges.
• Barren slopes are prone to soil erosion, impeding soil formation; notable examples include the Chambal ravines and the steep southern slopes of the higher reaches of the Himalayas with minimal forest cover.
• Regions with low relief or gentle slopes typically undergo deposition processes, resulting in the development of deep soils; a prime example is the Indo-Gangetic plain.
• River basins within plateaus often exhibit deep soil layers, presenting exceptions to the general plateau terrain.

Climate

• Temperature and rainfall emerge as pivotal factors influencing soil formation processes.
• They impact the efficiency of weathering on parent materials, water infiltration rates, and the microbial composition within soil.
• Under similar climatic conditions, distinct parent materials may yield identical soil types, while the same parent material might result in different soil types across varying climates.
• Crystalline granites, for instance, generate laterite soil in moist monsoonal regions and non-laterite soil in drier areas.
• Black soil formation, characteristic of hot summers and low rainfall, occurs in parts of Tamil Nadu irrespective of parent rock.
• In Rajasthan, both granite and sandstone contribute to sandy soil formation in arid climates.
• Arid and semi-arid regions experience excessive evaporation compared to precipitation, leading to light-colored soils with minimal humus content.
• Rajasthan and adjacent arid zones exhibit lime-accumulating soils due to evaporative conditions, classified as pedocal soils rich in calcium carbonate.
• In the cold Himalayan climates, slow vegetation decay results in acidic soils.

Natural Vegetation

• Natural vegetation serves as a reflection of both relief and climate conditions.
• Soil formation and development significantly benefit from the presence and growth of vegetation.
• Decay of leaf litter contributes essential humus to soil, enhancing its fertility.
• Regions with dense forest cover often boast some of India’s highest-quality soils.
• A strong correlation exists between the types of vegetation and soil found in India.

Major Soil Groups of India

The Indian Council of Agricultural Research (ICAR) divided the Indian soils into eight major groups.

1. Alluvial Soils
2. Black Soils
3. Red Soils
4. Lateritic Soils
5. Forest and Mountain Soils
6. Arid and Desert Soils
7. Saline and Alkaline Soils
8. Peaty and Marshy Soils

Alluvial Soils

• Alluvial soils are formed by sediment deposition from rivers, known for their richness in humus and high fertility.
• Found in the Great Northern Plain, lower valleys of Narmada and Tapti, and Northern Gujarat, they are renewed annually and are vital for Indian agriculture.
• Alluvial soils primarily result from silt deposition by rivers like the Indo-Gangetic-Brahmaputra, covering a significant portion of India’s land area.
• They are immature with weak profiles due to recent origins and mainly consist of loamy soil, with sandy and clayey variations.
• Kankar beds, containing calcareous concretions, are present in some regions, contributing to soil porosity and good drainage.
• Constant replenishment from floods enriches these soils, though nitrogen content tends to be low.
• Adequate proportions of potash, phosphoric acid, and lime support agricultural productivity.
• Variations in iron oxide and lime content are observed across different regions.
• Alluvial soils are widespread across the Indo-Gangetic-Brahmaputra plains and delta regions of rivers like the Mahanadi, Godavari, Krishna, and Cauvery.
• Additionally found in the Narmada, Tapti valleys, and parts of Gujarat, they are well-suited for irrigation and support various crops such as rice, wheat, sugarcane, and cotton.
• Geologically, the alluvium of the Great Indian plain is categorized into newer Khadar and older Bhangar soils.

Black Soils

• Black soils, also known as regur or black cotton soils due to cotton cultivation, cover approximately 5.46 lakh sq km or 16.6% of India’s total geographical area.
• These soils are believed to have originated from lava solidification during volcanic activity in the Deccan Plateau.
• Rich in clay, with over 62% clay content, black soils also contain significant amounts of alumina, iron oxide, lime, and magnesium carbonates, while phosphates, nitrogen, and humus levels are low.
• Found predominantly in the dry and hot regions of the Indian Peninsula, particularly Maharashtra, Madhya Pradesh, Karnataka, Telangana, Andhra Pradesh, Gujarat, and Tamil Nadu.
• Black soils exhibit high moisture retention and swell significantly upon moisture accumulation, forming deep cracks during dry seasons.
• The black color of these soils is attributed to titaniferous magnetite or iron and black constituents from the parent rock.
• Crystalline schists and basic gneisses contribute to the black coloration in certain regions like Tamil Nadu and parts of Andhra Pradesh.
• Ideal for cotton cultivation, black soils also support crops like wheat, jowar, linseed, tobacco, castor, sunflower, millets, rice, and sugarcane where irrigation facilities are available.

Red Soils

• Red soils, along with their minor groups, constitute one of India’s largest soil groups.
• Formed primarily from weathering of ancient crystalline and metamorphic rocks like acid granites, gneisses, and quartzites.
• The red color of these soils, which can vary into shades of brown, chocolate, yellow, grey, or black, is attributed more to wide diffusion than to high iron content.
• Occupying approximately 3.5 lakh sq km, or 10.6% of India’s total geographical area, red soils are found in regions like south Bihar, West Bengal’s Birbhum and Bankura districts, parts of Uttar Pradesh, Rajasthan’s Aravallis, Assam, Nagaland, Manipur, Mizoram, Tripura, and Meghalaya.
• Texture ranges from sand to clay, with most being loams; they are acidic due to their parent rocks’ nature, with fair alkali content.
• Poor in lime, magnesia, phosphates, nitrogen, and humus, red soils are relatively rich in potash and potassium.
• Occurring mostly in low rainfall regions, they are widespread in almost the entire Tamil Nadu region.
• Compared to black soils, red soils, being mostly loamy, have less water retention capability.

Lateritic Soils

• The term “laterite,” derived from Latin meaning “brick,” was initially used by Buchanan in 1810 to describe a clayey rock observed in Malabar, but Farmer later restricted its usage to soils composed predominantly of iron, aluminum, titanium, and manganese oxides.
• Laterite soils form under conditions of high temperature and heavy rainfall, prevalent in South Maharashtra, the Western Ghats in Kerala and Karnataka, parts of the Eastern Ghats, Assam, Tamil Nadu, Karnataka, and western West Bengal, particularly in Birbhum district.
• These soils are typically infertile and represent the end products of weathering processes.
• Formation involves heavy rainfall inducing leaching, leading to the removal of lime and silica, leaving behind a soil rich in iron and aluminum oxides.
• The red color of laterite soils results from low clay content and the presence of gravel from red sandstones, while they are rich in bauxite or ferric oxides.
• Laterite soils are deficient in lime, magnesia, potash, and nitrogen, although phosphate content may be high in the form of iron phosphate.
• In wetter regions, higher humus content may be present.
• Covering an area of 2.48 lakh sq km, laterite soils lack fertility due to intensive leaching but can support plantation crops like tea, coffee, rubber, coconut, and arecanut when manured and irrigated.
• They may also be utilized for grazing grounds and scrub forests.
• Found on Western Ghats summits at 1000 to 1500 m, laterite and lateritic soils serve as valuable building materials due to their durability resulting from extensive weathering.

Forest and Mountain Soils

• Forest soils occupy approximately 2.85 lakh sq km or 8.67% of India’s total land area.
• Primarily heterogeneous, these soils are typically found on forest-covered hill slopes, exhibiting significant variation even within close proximity.
• In the Himalayan region, forest soils are prevalent in valleys, less steep slopes, and north-facing slopes.
• Forest soils are also present in the Western and Eastern Ghats.
• Rich in humus content, forest soils are deficient in potash, phosphorus, and lime.
• Suitable for plantation crops like tea, coffee, spices, and tropical fruits in the peninsular forest region.
• In the Himalayan forest region, crops such as wheat, maize, barley, and temperate fruits are cultivated.

Arid and Desert Soils

• Sandy soils in Rajasthan, Haryana, and South Punjab have become saline and unsuitable for cultivation due to insufficient rainwater wash.
• Despite this, modern irrigation allows for cultivation in these regions.
• Covering an area of 1.42 lakh sq km, these soils contain varying percentages of soluble salts, calcium carbonate, and are low in organic matter.
• In certain areas, the subsoil contains significantly higher calcium content compared to the topsoil.
• Cultivation in desert soils primarily involves drought-resistant and salt-tolerant crops like barley, rape, cotton, wheat, millets, maize, and pulses.
• Desert soils consist predominantly of aeolian sand (90 to 95%) and clay (5 to 10%).
• These soils occur in arid and semi-arid regions of Rajasthan, Punjab, and Haryana, with sandy soils without clay being common in coastal regions of Odisha, Tamil Nadu, and Kerala.
• Generally poor in organic matter, some desert soils exhibit alkaline properties with varying degrees of soluble salts such as calcium carbonate.
• While nitrogen content is initially low, phosphates and nitrates contribute to fertility wherever moisture is available.

Saline and Alkaline Soils

• Saline and Alkaline Soils are prevalent in Andhra Pradesh and Karnataka, as well as in drier regions of Bihar, Uttar Pradesh, Haryana, Punjab, Rajasthan, and Maharashtra, covering an area of 68,000 sq km.
• These soils are prone to saline and alkaline efflorescence, known by various names such as reh, kallar, usar, thur, rakar, karl, and chopan.
• Undecomposed rock and mineral fragments release sodium, magnesium, calcium salts, and sulphurous acid upon weathering, leading to soil infertility.
• Approximately 1.25 million hectares of land in Uttar Pradesh and 1.21 million hectares in Punjab have been affected by Usar.
• Gujarat’s Gulf of Khambhat area is impacted by salt-laden deposits carried by sea tides.
• In Saline and Alkaline Soils, the topsoil is impregnated with saline and alkaline efflorescences.
• In regions with low water tables, salts percolate into the subsoil, while areas with good drainage see salts washed away by flowing water. Poor drainage leads to salt accumulation in topsoil after water evaporation.
• In regions with high subsoil water tables, injurious salts are transferred from below via capillary action during dry season evaporation.
• Found in canal irrigated areas and regions with high subsoil water tables, affecting parts of Andhra Pradesh, Telangana, Karnataka, Bihar, Uttar Pradesh, Haryana, Punjab, Rajasthan, and Maharashtra due to improper or excessive irrigation.

Peaty and Marshy Soils

• Peaty and Marshy Soils originate in humid regions due to the accumulation of significant amounts of organic matter.
• These soils contain considerable amounts of soluble salts and 10-40% organic matter.
• Found in regions like Kottayam and Alappuzha districts of Kerala, where it is known as Kari, as well as in coastal areas of Orissa and Tamil Nadu, Sunderbans of West Bengal, Bihar, and Almora district of Uttaranchal.
• Peaty soils are black, heavy, and highly acidic, often submerged underwater during the rainy season but utilized for paddy cultivation once rains cease.
• Typically deficient in potash and phosphate, these soils are characterized by a large amount of organic matter and considerable soluble salts.
• Most commonly found in the humid regions, these soils are primarily used for paddy cultivation in areas like Kottayam and Alappuzha districts of Kerala.

Indian Soils at a Glance