Soils in India: Formation And Types
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Soils in India: Formation & Types| Geography
Geography For Civil Services
In this article, we will study soil formation and its types in India. Soil is the thin top layer on the earth’s crust comprising mineral particles formed by the breakdown of rocks, decayed organic materials, living organisms, water, and air. The study of soils in their natural environment is called Pedology. Let's get Continue...
Soils in India: Introduction:
- Soil is the thin top layer on the earth’s crust comprising mineral particles formed by the breakdown of rocks, decayed organic materials, living organisms, water, and air.
- The study of soils in their natural environment is called Pedology.
- Pedogenesis is the natural process of soil formation that includes a variety of processes such as weathering, leaching, calcification, etc.
Soil formation in Indian Conditions:
Factors affecting the formation of soil:
- Parent Material
- Natural Vegetation
1. Parent material:
- The rocks from which soils are formed are called parent material.
- The parent material determines the coloration, mineral composition, and texture of the soil.
- when the surface rocks are exposed to the process of weathering (physical, chemical, and biological), the rocks are converted into fine grains and thus provide a base for the soil formation.
- It is the most important factor in places with steep slopes like the hilly regions, edges of plateaus, etc.
- Steep slope encourages soil erosion and hinders soil formation. Example: Chambal ravines,
- Whereas the areas of low relief experience deposition of soils. Example: Indo-Gangetic plain.
- The degree of the slope also largely determines the fertility of the soil.
- Main factors: Temperature and rainfall
- Determines the effectiveness of weathering of the parent rock and the type of micro-organism present in it.
- Two different parent materials may develop the same soil in the same type of climate and vice-versa.
- Hot summer and low rainfall develops black soil in some parts of Tamil Nadu irrespective of the parent rock.
- In Rajasthan, both granite and sandstone gives sandy soil under arid climate.
4. Natural vegetation:
- The growth of vegetation affects the formation and development of soil.
- The decayed leaf material adds much-needed humus to soil thereby increasing its fertility.
- The densely forested areas contain some of the best soils in India.
- Soil-formation is a long-term process
- All the other factors need time to form the soil
- After weathering – time decides maturity of soil
A vertical section (called Horizons) through different layers of the soil is called the soil profile.
- It is the part of topsoil.
- In this layer, organic matter incorporated with mineral matter, nutrients, water.
- The transition zone between Horizon A and Horizon C.
- Contains matter derived from below as well as from above.
- Has some organic matter but the mineral matter is noticeably weathered.
- is composed of the loose parent material.
- This layer is the first stage in the soil formation process and eventually forms the above two layers
- Underneath these three horizons is the rock which is also known as the parent rock or the bedrock.
Classification of soil:
- In ancient times soils used to be classified into two main groups
- Urvara (fertile)
- Later soils were classified on the basis of their inherent characteristics and external features such as texture, colour, the slope of the land, and moisture content in the soil.
On the basis of texture: sandy, clayey, silt and loam, etc.
On the basis of colour: Red, yellow, black, etc.
On the basis of genesis, colour, composition, and location:
- Alluvial soils
- Black soils
- Red and Yellow soils
- Laterite soils
- Arid soils
- Saline soils
- Peaty soils
- Forest soils
1. Alluvial soil:
Formed mainly due to silt deposited by Indo-Gangetic-Brahmaputra rivers.
- Largest soil group covering 40 percent of the total area of the country.
- The most productive agricultural lands.
- The soil is porous because of its loamy (equal proportion of sand and clay) nature.
- Provides good drainage and other conditions favorable for agriculture.
- low nitrogen
- Adequate Potash, phosphoric acid, and alkalies.
- The proportion of Iron oxide and lime vary within a wide range.
Distribution of Alluvial Soils in India:
- Indo-Gangetic-Brahmaputra plains, deltas of the Mahanadi, the Godavari, the Krishna, and the Cauvery, (called deltaic alluvium/coastal alluvium) here.
Crops in Alluvial Soils:
- Mostly flat and regular soils
- Best suited for agriculture
- Best suited for rice, wheat, sugarcane, tobacco, cotton, jute, maize, oilseeds, vegetables, and fruits.
Geological divisions of alluvial soils (covered in northern plains lecture)
2. Black soil:
- The parent material -volcanic rocks (Deccan Plateau).
- Region of high temperature and low rainfall.
- Typical to the dry and hot regions of the Peninsula.
- Highly argillaceous (consisting of or containing clay)
- Low fertility
- Highly retentive of moisture.
- Covers 16.6 percent of total geographical area of the country.
- They swell and become sticky when wet and shrink when dried.
- So, during the dry season, these soil develop wide cracks.
- Thus, there occurs a kind of ‘self ploughing’.
- Because of this character of slow absorption and loss of moisture, the black soil retains the moisture for a very long time, which helps the crops, to sustain even during the dry season.
The black color is due to the presence of a small proportion of iron and black constituents of the parent rock.
Chemical Composition of Black Soils:
- Rich in lime, iron, magnesia, and alumina.
- They also contain potash.
- But they lack in phosphorous, nitrogen and organic matter.
Distribution of Black Soils:
- Spread over (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:
- Best suited for cotton crop.
- Called regur and black cotton soils.
- Wheat, jowar, linseed, castor, sunflower, and millets.
- Large varieties of vegetables and fruits are also successfully grown on the black soils.
3. Red soil:
- The main parent rocks are crystalline and metamorphic rocks
- The texture varies from sand to clay, the majority being loams.
- On the uplands, the red soils are poor, gravelly, and porous. But in the lower areas, they are rich, deep dark, and fertile.
Chemical Composition of Red Soils:
- acidic mainly due to the nature of the parent rocks.
- poor in lime, magnesia, phosphates, nitrogen, and humus.
- rich in potash and potassium.
- The red colour is due to the presence of iron oxide.
Distribution of Red Soils:
- In areas of low rainfall in the eastern and
- The southern part of the Deccan Plateau.
- They occupy about (10.6 percent) of the total area of the country.
- Along the piedmont zone of the Western Ghat, long stretch of area is occupied by red loamy soil.
- Yellow and red soils are also found in parts of Orissa and Chattisgarh and in the southern parts of the middle Ganga plain.
Crops in Red Soils
- The red soils are mostly loamy and hence cannot retain water like the black soils.
- The red soils, with the proper use of fertilizers and irrigation techniques, give a good yield of cotton, wheat, rice, pulses, millets, tobacco, oilseeds, potatoes, and fruits.
4. Laterite soil:
- ‘Laterite’ means brick in Latin. They harden greatly on losing moisture.
- Laterite soils are mostly the end products of weathering.
- They are formed under conditions of high temperature and heavy rainfall with alternate wet and dry periods.
- Heavy rainfall promotes leaching (nutrients get washed away by water) of soil whereby lime and silica are leached away and a soil rich in oxides of iron and aluminum compounds is left behind.
- Laterite soils are red in colour due to little clay and more gravel of red sand-stones.
- Laterite soils are widely cut as bricks for use in house construction.
Chemical composition of Laterite:
- Rich in bauxite or ferric oxides.
- Poor in organic matter, nitrogen, phosphate, and calcium,
- While iron oxide and potash are in excess.
Crops in Laterite Soils:
- Laterite soils lack fertility due to intensive leaching so they are not suitable for cultivation
- But When manured and irrigated, some laterites are suitable for growing plantation crops like tea, coffee, rubber, cinchona, coconut, areca nut, etc.
- In some areas, these soils support grazing grounds and scrub forests.
Distribution of Laterite Soils:
- Laterite soils cover an area of 2.48 lakh sq km.
- Red laterite soils in Tamil Nadu, Andhra Pradesh, and Kerala are more suitable for tree crops like cashewnut.
- These soils have mainly developed in the higher areas of the Peninsular plateau.
- commonly found in Karnataka, Kerala, Tamil Nadu, Madhya Pradesh, and the hilly areas of Orissa and Assam.
5. Arid/ Desert soils:
- Consist of Aeolian sand (90 to 95 per cent) and clay (5 to 10 per cent).
- Covers 4.32% of total area of the country.
- Range from red to brown in colour.
- Generally sandy in structure and saline in nature.
Distribution of Arid – Desert Soils
- Occur in arid and semi-arid regions of Rajasthan, Punjab and Haryana lying between the Indus and the Aravalis
- Sandy soils without clay are also common in coastal regions of Odisha, Tamil Nadu and Kerala.
Chemical properties of Arid Soils
- poor in organic matter
- Due to the dry climate, high temperature, and accelerated evaporation, they lack moisture and humus.
- Nitrogen is insufficient and the phosphate content is normal.
Crops of Arid – Desert Soils
- In large areas, only the drought resistant and salt tolerant crops such as barley, cotton, millets, maize and pulses are grown.
6. Saline soil:
- Also known as Usara soils.
- Contain a larger proportion of sodium, potassium and magnesium.
- Infertile and do not support any vegetative growth.
- They contain more salts, largely because of dry climate and poor drainage.
- Their structure ranges from sandy to loamy.
Distribution of Saline – Alkaline Soils
- Occupy 68,000 sq km of area
- Found in canal irrigated areas.
- Parts of Andhra Pradesh, Telangana, Karnataka, Bihar, Uttar Pradesh, Haryana, Punjab , Rajasthan and Maharashtra.
- The accumulation of these salts makes the soil infertile and renders it unfit for agriculture.
- Vast areas comprising the estuaries of the Narmada, the Tapi, the Mahi and the Sabarmati have become infertile.
7. Peaty soil:
- Soils with large amount of organic matter and considerable amount of soluble salts.
- The most humid regions have this type of soil.
- They are black, heavy and highly acidic.
Distribution of Peaty – Marshy Soils:
- Kottayam and Alappuzha districts of Kerala where it is called Kari.
- In the coastal areas of Odisha and Tamil Nadu, Sunderbans of West Bengal, in Bihar and Almora district of Uttarakhand.
Chemical Properties of Peaty – Marshy Soils:
- They are deficient in potash and phosphate.
Crops of Peaty – Marshy Soils
- Most of the peaty soils are underwater during the rainy season but as soon the rains cease, they are put under paddy cultivation.
8. Forest soil:
- Occupy 8.67% of the total land area of India.
- Mainly heterogeneous soils found on the hill slopes covered by forests.
- The soils vary in structure and texture depending on the mountain environment where they are formed.
Chemical properties of Forest Soils:
- Very rich in humus.
- Deficient in potash, phosphorus, and lime.
- Require good deal of fertilizers for high yields.
Distribution of Forest – Mountain Soils:
- In the Himalayan region, mainly found in valleys, north-facing slopes.
- Occur in Western and Eastern Ghats also.
Crops in Forest – Mountain Soils:
- They are suitable for plantations of tea, coffee, spices, and tropical fruits in the peninsular forest region.
- Wheat, maize, barley are grown in the Himalayan forest region (J & K, Himachal Pradesh, and Uttarakhand).