Soil

• Soil is the top layer of continental crust made up of weathered rock particles and organic materials.
• Soils in India are a result of physical and human factors.
• Soil is a mixture of small rock particles/debris and organic materials/humus that support plant growth.
• Several factors influence soil formation, including parent material, relief/topography, climate, natural vegetation & biological factors, and time.

Soil types in India (Types of Soil)

• The first scientific classification of soil was done by Vasily Dokuchaev.  In India, the Indian Council of Agricultural Research (ICAR) has classified soils into 8 categories.
  • Alluvial Soil
  • Black Cotton Soil
  • Red Soil
  • Laterite Soil
  • Mountainous or Forest Soils
  • Arid or Desert Soil
  • Saline and Alkaline Soil
  • Peaty, and Marshy Soil/Bog Soil
• This classification scheme is based on constitutional characteristics – colour and the resource significance of the soils.

• The ICAR has also classified the Indian soils on the basis of their nature and character as per the United States Department of Agriculture (USDA) Soil Taxonomy.
  • Inceptisols (39.74%)
  • Entisols
  • Alfisols
  • Vertisols
  • Aridisols
  • Ultisols
  • Mollisols
  • Others

Alluvial Soils

• Alluvial soils are formed primarily from silt deposited by the Indo-Gangetic-Brahmaputra rivers and coastal wave action.
• The parent material of these soils is transported rocks from the Himalayas.
• Alluvial soils are the largest soil group in India, covering about 15 lakh sq km or 46% of the total area.
• They are highly productive and support more than 40% of India’s population by providing the most productive agricultural lands.

Characteristics of Alluvial Soils:

• Immature and weak profiles due to recent origin.
• Sandy and clayey soils, with loamy to sandy-loam in drier regions and clayey loam towards the delta.
• Pebbly and gravelly soils are rare, while kankar (calcareous concretions) beds may be present along river terraces.
• Porous due to loamy nature, providing good drainage for agriculture.
• Constantly replenished by recurrent floods.

Chemical properties of Alluvial Soils:

• Proportion of nitrogen is generally low.
• Adequate proportion of potash, phosphoric acid, and alkalies.
• Proportion of iron oxide and lime varies within a wide range.

Distribution of Alluvial Soils in India:

• Occur along the Indo-Gangetic-Brahmaputra plains, except in some places covered by desert sand.
• Also occur in deltas of Mahanadi, Godavari, Krishna, and Cauvery rivers (called deltaic alluvium or coastal alluvium).
• Found in Narmada, Tapi valleys, and northern parts of Gujarat.

Crops in Alluvial Soils:

• Mostly flat and regular soils, well-suited for agriculture.
• Ideal for irrigation, responding well to canal and well/tube-well irrigation.
• Suitable for growing rice, wheat, sugarcane, tobacco, cotton, jute, maize, oilseeds, vegetables, and fruits.

Geological divisions of alluvial soils

• Geologically, the alluvium of the Great plain of India is divided into newer or younger khadar and older bhangar soils.
• Bhabar:
  • 8-16 km wide belt along the Shiwalik foothills in Indo-Gangetic plain.
  • Porous due to deposition of pebbles and rock debris from alluvial fans.
  • Streams disappear in the region, marked by dry river courses except in the rainy season.
  • Not suitable for agriculture, only big trees thrive.
• Terai:
  • Narrow tract (15-30 km) to the south of Bhabar running parallel to it.
  • Swampy lowland with silty soils.
  • Underground streams from Bhabar re-emerge in this belt.
  • Rich in nitrogen and organic matter, deficient in phosphate.
  • Covered by tall grasses and forests, suitable for crops like wheat, rice, sugarcane, and jute.
  • Provides shelter to a variety of wildlife.
• Bhangar:
  • Older alluvium along the river beds forming terraces higher than the flood plain (about 30 meters above the flood level).
  • More clayey in composition, generally dark-colored.
  • Beds of lime nodules known as “Kankar” a few meters below the terrace.
• Khadar:
  • Composed of newer alluvium, forms the flood plains along the river banks.
  • Banks are flooded almost every year, resulting in new layer of alluvium deposition.
  • Sandy clays and loams, drier and leached, less calcareous and carbonaceous (less kankary).
  • Most fertile soils of the Ganges.

Alluvial regions with rainfall

• Above 100cm – Suitable for paddy
• B/w 50-100 cm – Suitable for wheat, sugarcane, tobacco, and cotton
• Below 50cm– Course grains (millets)

Black Soils

• Formation: weathering of basaltic rocks from fissure eruption during Cretaceous period
• Parent material: volcanic rocks from Deccan Plateau and Rajmahal trap; gneisses and schists in Tamil Nadu
• Climate: hot and dry regions of the Peninsula
• Extent: covers 15% of the area
• Color: black due to presence of titani-ferrous magnetic compounds in basalt.

Characteristics of Black Soils

• A typical black soil is highly argillaceous [Geology (of rocks or sediment) consisting of or containing clay] with a large clay factor, 62 percent or more.
• In general, black soils of uplands are of low fertility while those in the valleys are very fertile.
• The black soil is highly retentive of moisture. It swells greatly on accumulating moisture. Strenuous effort is required to work on such soil in rainy season as it gets very sticky.
• In summer, the moisture evaporates the soil shrinks and is seamed with broad and deep cracks. The lower layers can still retain moisture. The cracks permits oxygenation of the soil to sufficient depths and the soil has extraordinary fertility.
• When dry, it develops cracks and has blocky structure. (Self Ploughing Capacity)

Colour of Black Soils

• The black colour is due to the presence of a small proportion of titaniferous magnetite or iron and black constituents of the parent rock.
• In Tamil Nadu and parts of Andhra Pradesh, the black colour is derived from crystalline schists and basic gneisses.
• Various tints of the black colour such as deep black, medium black, shallow black , a mixture of red and black may be found in this group of soils.

Chemical Composition of Black Soils

• 10 percent of alumina,
• 9-10 percent of iron oxide,
• 6-8 percent of lime and magnesium carbonates,
• Potash is variable (less than 0.5 percent) and
• phosphates, nitrogen, and humus are low.
• Rich in iron and lime but deficient in humus, nitrogenous and phosphorous content.

Distribution of Black Soils

• It is found in the Deccan lava plateau region of India.
• Spread over 46 lakh sq km (16.6 percent of the total area) across Maharashtra, Madhya Pradesh, parts of Karnataka, Telangana, Andhra Pradesh, Gujarat, and Tamil Nadu.

Crops in Black Soils

• These soils are best suited for cotton crops. Hence these soils are called as regur and black cotton soils.
• Other major crops grown on the black soils include wheat, jowar, linseed, virginia tobacco, castor, sunflower, and millets.
• Rice and sugarcane are equally important where irrigation facilities are available.
• Large varieties of vegetables and fruits are also successfully grown on the black soils.
• This soil has been used for growing a variety of crops for centuries without adding fertilizers and manures, with little or no evidence of exhaustion.

Red Soil

• Soil developed on Archean granite
• Second largest soil type in the country
• Red colour due to presence of ferric oxides as thin coatings on soil particles
• Top layer of soil is red and horizon below is yellowish
• Occupies 18.5% of the area
• Texture ranges from sandy to clay and loamy
• Also known as the omnibus group

Characteristics of Red Soils:

• Rainfall is highly variable, leading to the development of three subtypes: Red & Yellow soil, Red Sandy Soil, and Red Alluvial Soil.
• Red & Yellow soil is found in areas with rainfall of around 200 cm, such as NE India (Nagaland, Mizoram, Manipur Hills) and parts of Malabar coast. Quick drainage is needed in these soils.
• Red Sandy Soil is found in drier plateaus like Karnataka, Tamil Nadu, Telangana, and Rayalseema, with rainfall ranging from 40-60 cm.
• Red Alluvial Soil is found along river valleys and is known for its good fertility.
• Well drained soil with sandy structure.
• Rich in iron and potash, but deficient in other minerals.

Chemical composition of Red Soils: 

• generally deficient in phosphate, lime, magnesia, humus, and nitrogen.

Distribution of Red Soils:

• Red Soils are mainly found in the Peninsula region of India, from Tamil Nadu in the south to Bundelkhand in the north and Raj Mahal in the east to Kathiawad in the west.

Significance:

• Once irrigated and added with humus, Red Soils can give high yields due to their rich mineral base.
• Red Soils are suitable for cultivation of crops such as rice, sugarcane, cotton, millets, and pulses.
• Red Alluvial Soils in the Kaveri and Vaigai basins are famous for paddy cultivation when well irrigated.
• Large regions of Karnataka and Kerala have developed Red Soil regions suitable for rubber and coffee plantation farming.

Laterite Soil

• Formation:
  • Laterite soil forms in regions where there is laterite rock or structure, which is rich in iron and aluminum content.
  • Alternating dry and wet periods are more suitable for the development of laterite soils.
• Characteristics of Laterite Soil:
  • Brown in color.
  • Composed essentially of a mixture of hydrated oxides of aluminum and iron.
  • Iron oxides are found in nodular form.
  • Rich in iron and aluminum, but poor in nitrogen, phosphorus, potash, lime, and magnesia.
  • Moderate humus and water-retaining capacities.
  • Bacterial activities are high, but heavy precipitation leads to leaching of humus, resulting in moderate to low humus content.
• Distribution of Laterite Soil:
  • Laterite soil is found in patches in the Western Ghats (Goa and Maharashtra).
  • It is also found in Belgam district of Karnataka and in the laterite plateau of Kerala.
  • In the state of Orissa, in the Eastern Ghats.
  • Amarkantak plateau region of Madhya Pradesh.
  • Panchmahal district of Gujarat.
  • Santhal Pargana divisions of Jharkhand.
• Significance:
  • Laterite soil is famous for crops like groundnut, cashew nut, etc.
  • Laterite soil of Karnataka is conducive for coffee, rubber, and spices farming.
• 

Forest Soil/ Mountain Soil

• Formation:
  • This soil is principally found on mountains with steeper slopes, high relief, and shallow profiles.
• Characteristics:
  • Thin layered soil with poorly developed profiles and horizons.
  • Fast drainage, making it vulnerable to soil erosion.
  • Rich in organic content, with adequate humus content, but deficient in other nutrients.
  • Loamy soil with sand, silt, and clay in mixed form.
• Distribution:
  • Generally found at altitudes over 900 meters.
  • Found in the Himalayas, Himalayan foothills, mountain slopes of Western Ghats, Nilgiri, Annamalai, and Cardamom hills.
• Significance:
  • Provides favorable air and water drainage for crops that require such conditions due to being on slopes.
  • Often used for rubber plantation, bamboo plantation, as well as tea, coffee, and fruit farming.
  • Large areas may also be used for shifting agriculture, where the soil fertility deteriorates after 2-3 years.
  • Silvi-pastoral farming (combination of forest and grasses) can be sustained due to limited scope for agriculture.
• 

Desert Soil

• Deposited by wind action
• Found in arid and semi-arid areas
• Regions include Rajasthan, West of the Aravallis, Northern Gujarat, Saurashtra, Kachchh, Western parts of Haryana, and southern part of Punjab
• Lacks moisture content
• Humus content is low
• Nitrogen is originally low but some is available in the form of nitrates
• Sandy with low organic matter
• Low living microorganisms
• Rich in iron contents
• Phosphorous content is nearly adequate
• Rich in lime and bases
• Low soluble salts and moisture
• Very low retaining capacity
• If irrigated, gives high agricultural return
• Suitable for less water-intensive crops like Bajra, pulses, fodder, and guar
• 

Saline and Alkaline Soil

• Alkali soil has a large content of NaCl
• The soil is infertile
• Also known as Reh, Usar, Kallar, Rakar, Thur, and Chopan
• Mainly found in Rajasthan, Haryana, Punjab, Uttar Pradesh, Bihar, and Maharashtra
• Contains sodium chloride and sodium sulphate
• Suitable for leguminous crops
• Natural formation includes dried up lakes of Rajasthan and Rann of Kuchchh
• Emerged in the Palaya basin (a clay basin in the midst of the desert)
• Anthropogenic formation in western UP and Punjab due to faulty agriculture
• Characteristics include lack of moisture, humus, and living microorganisms, resulting in almost absent humus formation.

Peaty, and Marshy Soil/Bog Soil

• Origination:
  • Formed in areas where adequate drainage is not possible
• Characteristics:
  • Dominance of clay and mud
  • High salinity
  • Rich in organic matter
  • Deficient in potash and phosphate
  • No organic activity due to excessive moisture content
• Distribution:
  • Delta regions of India, Alleppey (Kerala), Almora (Uttaranchal)
• Significance:
  • Suitable for jute and rice in Bengal delta
  • Suitable for spices, rubber, and big-sized rice in Malabar
  • Favorable for Mangrove forests
• 

Characteristics of Indian Soils

• Most Indian soils are old and mature.
• Soils of the peninsular plateau are much older than the soils of the great northern plain.
• Indian soils are largely deficient in nitrogen, mineral salts, humus, and other organic materials.
• Plains and valleys have thick layers of soils, while hilly and plateau areas have thin soil cover.
• Some soils like alluvial and black soils are fertile, while others such as laterite, desert, and alkaline soils lack fertility and do not yield good harvest.
• Indian soils have been used for cultivation for hundreds of years and have lost much of their fertility.

Problems of Indian Soils

• Soil erosion in the Himalayan region and Chambal Ravines
• Deficiency in fertility in Red, lateritic, and other soils
• Desertification in areas around the Thar desert and rain-shadow regions like parts of Karnataka and Telangana
• Waterlogging in the Punjab-Haryana plain
• Salinity and alkalinity in excessively irrigated regions of Punjab, Haryana, Karnataka, etc.
• Wasteland
• Overexploitation of soils due to an increase in population and rise in living standards
• Encroachment of agricultural land due to urban and transport development.