Notes on Soils, Structure and Physiography of India

Soils of India

“Soil is the mixture of rock debris and organic materials which develop on the Earth’s surface. The major factor affecting soil formation are relief, parent material, climate, vegetation and life forms”

Layers of Soil (Soil Profile)

Soil consists of three layers which are called Horizons.

Horizon A – It is the topmost zone, where organic materials have got incorporated with the mineral matter, nutrients and water which are helpful for plant’s growth.
Horizon B – It is a transition zone between horizon A and C. It contains matter derived from horizon A as well as C.
Horizon C – It is composed of loose parent material. It is the first stage in the soil formation.

Note – Below these 3 horizons, parent rock or the bedrock is present.

Classification of Soils

Alluvial

Location: Northern plains and river valleys. Also found in peninsular region; in deltas of East coast and river valleys.

Color: Light grey to Ash Grey

Key Points:

These are depositional soils,transported and deposited byrivers and streams
This soil is extensively fertile
Rich in Potash and poor in Phosphorus
Types of Alluvial soil
Khadar – New alluvial soil, deposited by floods annually.
Bhangar – old alluvial soil, deposited away from the flood plains.
Both Khadar and Bhangar contains Kankars

Black Soil

Location: Deccan Plateau (Maharashtra, Gujarat, Andhra, MP and some parts of Tamil Nadu)

Color: Black -Also known as Regur Soils.

Key Points:

This soil swells and becomes sticky when wet and shrink when dried. So, during dry season, these soils develop cracks. Thus, there is a mechanism of “Self-Ploughing”
Suitable for Cotton plantation
Rich in lime, iron, magnesia and alumina, but lack in Phosphorus, Nitrogen and organic matter.

Red and Yellow Soils

Location: Eastern and Southern Part of Deccan Plateau Also found in Odisha and Chhattisgarh and southern part of Ganga Plain

Color: It is red when in crystalline form and yellow when hydrated.

Key Points:

Fine grained red and yellow soil is fertile while coarse grained soil is not fertile.
Poor in Nitrogen, Phosphorus and Humus

Laterite Soil

Location: Areas of High temperature and High rainfall. Southern India, West Bengal, Odisha, Some parts of Maharashtra and Assam.

Color: Reddish to Yellow.

Key Points:

Not suitable for cultivation; because it lacks organic matter, Nitrogen, phosphate and Calcium while Iron oxide and Potash are in excess.
It is made cultivable by application of manures and fertilizers.
In Tamil Nadu, Andhra and Kerala, this soil is suitable for Cashew nut cultivation.

Arid Soils

Location: Western Parts of Rajasthan.

Color: Red to Brown.

Key Points:

Sandy in structure and Saline in Nature.
Lacks moisture and humus due to dry climate, high temperature and evaporation
Lowers horizons of the soil are occupied by Kankars because of increasing Calcium content downwards.

Saline Soils

Location: Western Gujarat, Deltas of Eastern coast and Sunderban areas of West Bengal.

Color: White, Brown (when nitrates are in excess).

Key Points:

Sea water invasion in the deltas promotes the occurrence of Saline soils.
Contains high amount of Sodium, Magnesium and Potassium.
Infertile; and does not support any vegetation growth.
Gypsum is added to reduce the salinity of soil.

Peaty Soils

Location: Areas of heavy rainfall and high humidity. Northern Bihar, Southern Uttarakhand, Coastal areas of West Bengal, Odisha and Tamil Nadu.

Color: Black -Suitable for vegetation growth due to high amount of organic matter.

Soil Erosion

It is defined as the removal of upper layer of soil. It is caused by various agents like water, ice, snow, wind, Plants, animals and humans.

Generally, the rate of removal of layer of soil is same as the rate of addition of particles but sometimes, this balance is disturbed by the action of natural of human factors, leading to soil erosion.
Wind erosion is significant in arid and semi-arid regions
In region with high rainfall and steep slopes, water erosion is significant

Cause of Soil Erosion

Wind
Water
Overgrazing
Deforestation

Soil Conservation

Afforestation – Planting new trees and plants. It will reduce soil erosion because plants and trees keep soils bound in locks of root.
Crop rotation – Between harvesting of a crop and planting of other, farmers grow grass or other crops to prevent soil from being vulnerable to external agents like wind, water etc.
Terrace farming – Farming is done by cutting steps on slopes of hills. This slows down the flow of water and soil removed from one step is deposited on next step.
Building dams – Protects the crops from floods.

Structure and Physiography of India

Physiography is the other name for “Physical Geography”. Physiography of an area is an outcome of structure, process and stage of development of that area.

Physiography of India

The land of India shows various macro variations viz; In North, it consists of a series of

mountain ranges, peaks, valleys etc. In south it consists of flat land (plateaus), steep

pieces of land (Scarps), rocks etc. Based on these micro variations, India is divided into

following physiographic divisions –

Northern and North-Eastern mountains
Northern Plain
Peninsular Plateau
Indian desert
Coastal Plains
Islands

Northern and North-Eastern Mountains

The North and North-Eastern Mountains consists of Himalayas and North-Eastern Hills. It runs in West-East direction from Indus to Brahmaputra

Features:

These are geologically young and structurally fold mountains. (Fold mountains are formed when two or more tectonic plates collide)
These are one of the highest mountain ranges in the world.
These are one of the most rugged mountain barriers of the world. These are not only physical barrier but also climatic, drainage and cultural divide.

The Himalayas consists of three parallel ranges –

Great or Inner Himalayas
Himachal or Lesser Himalayas
Shiwalik or Outer Himalayas

On the basis of relief and alignment of ranges, the Himalayas can be divided into following sub-divisions –

Kashmir or Northwestern Himalayas
Himachal and Uttarakhand Himalayas
Darjeeling and Sikkim Himalayas
Arunachal Himalayas
Eastern Hills and Mountains

Kashmir or Northwestern Himalayas

The North-Eastern part of Kashmir Himalayas is a cold desert, which lies between the Greater Himalayas and the Karakoram ranges.

Important ranges are:

Karakoram
Ladakh
Zaskar
Pir Panjal

Important glaciers – Baltoro and Siachen

Important Passes are:

Zoji La on the Great Himalayas
Banihal on Pir Panjal
Photu La on Zaskar
Khardung La on Ladakh.

Fresh Water Lake – Dal and Wular

Salt water lakes – Pangong Tso and Tso Moriri

Srinagar is located on the banks of Jhelum River

Himachal and Uttarakhand Himalayas

This part lies between the Ravi in the West and the Kali in the East.
All the three ranges of Himalayas are prominent in this section – Great Himalayas, Lesser Himalayas (locally known as Dhauladhar in HP and Nagtibha in Uttarakhand) and Shiwaliks
The great Himalayan range is mostly inhabited by nomadic group – Bhotias
This region is drained by the Indus and the Ganga
Other rivers in this region – Ravi, Beas, Sutlej, Yamuna and Ghaghara
Distinguishing features of this region – “Shiwalik” and “Dun Formations”

Dun Formation – These are longitudinal valleys formed as a result of folding when Eurasian Plate and Indian Plate collided. These are formed between Lesser Himalayas and Shiwaliks.

Some important Duns located in this region – Chandigarh-Kalka Dun, Harike Dun, Nalagarh Dun and Dehradun. (Dehradun is the largest of all Duns)
“Valley of Flowers” is also situated in the region

The Kashmir Himalayas are famous for Karewa formations which are useful for cultivation of Zafran, a local variety of saffron.

Darjeeling and Sikkim Himalayas

This region is surrounded by Nepal Himalayas in the West and Bhutan Himalayas in the East.
It is a region of high mountain peaks like Kanchenjunga and deep valleys.
Important river – Tista
Higher reaches of this region are inhabited by Lepcha tribes while the southern part has a mixed population of Nepalis, Bengalis and Tribals.
Weather and physical conditions of this region is suitable for tea plantation. Moderate slope, Thick soil cover with high organic content, Well distributed rainfall, Mild winters
One of the distinguishing features of this region is “Duar Formation”.

Duar Formation – These are the alluvial floodplains in the Eastern and North-Eastern region of India. It lies between south of foothills of Himalayas and North of Brahmaputra basin

Arunachal Himalayas

It extends from East of the Bhutan Himalayas to the Diphu Pass in the East
Important mountain peaks – Kangtu and Namcha Barwa
Important rivers – Kameng, Subansiri, Dibang, Dihang and Lohit
This region is inhabited by a number of ethnic tribal community namely- Monpa, Abor, Mishmi, Nyishi, Nagas
Jhum/Shifting/Slash and Burn cultivation is prominent in this region.

Jhum Cultivation – It is a traditional farming method where first the land is cleared, burned and then cultivated for a limited number of years.

Rivers in this region are perennial with high rate of fall having highest hydro- electric power potential in the country. Barak is an important river of Manipur and Mizoram

Eastern Hills and Mountains

These ranges have relatively low heights. These are known by different local names –

In North – Patkai Bum (Arunachal Pradesh), Naga hills, Manipur hills
In South – Mizo hills, Lushai Hills (Mizoram and Manipur)

Most of these ranges are separated from each other by numerous small rivers. In Manipur, “Loktak” lake surrounded by mountains from all sides is present

The Northern Plains

Formation – These plains are formed by the alluvial deposits brought by the rivers – Indus, Ganga and Brahmaputra. These plains are divided into three major zones – The Bhabhar, The Tarai and The Alluvial Plains.

Bhabhar

It is a narrow belt ranging between 8-10 km parallel to Shiwalik foothills
Streams and rivers coming from the mountains deposit heavy rocks in this region.

Tarai

It is located South of Bhabhar with a width of 10-20 km
Most of the streams and rivers re-emerge without any properly demarcated channel, creating marshy and swampy conditions.
This region has a luxurious growth of natural vegetation.

Alluvial Plains

It is located South of Tarai
It is a belt consisting of old and new alluvial deposits known as Bhangar and Khadar respectively.
This region has depositional landform such as sand bars, Meanders, ox-bow Lakes and braided channels.

Sandbars – Area of sand, gravel or fine sediments that sits above water

Meanders – Series of regular curves in the channel of river

Oxbow lakes – U-Shaped lake that forms when a wide meander of river cuts off

Braided Channels – Consists of a network of river channels separated by small islands

Points to be Noted

Rivers of this region form some of the largest deltas of the world. For ex – Sundarbans delta.
Haryana and Delhi form a water divide between Indus and Ganga.
Brahmaputra river flows from North-East to South-West direction before it takes 900 southwards turn at Dhubri before entering into Bangladesh.

The Peninsular Plateau

It is an irregular triangle at a height of 150m above the river plains.
Delhi ridge in the North-West, Rajmahal hills in the East, Gir Range in the West and Cardamom hills in the South constitute the boundaries of peninsular plateau.
However, its extension is found in North-East in the form of Shillong and Karbi Anglong plateau.

It consists of various Patland plateaus –

Hazaribagh Plateau
Palamau Plateau
Ranchi Plateau
Malwa Plateau
Coimbatore Plateau
Karnataka Plateau

Physiographic features of this region -

Tors – Large freely standing rock.
Block Mountains – Formed when two tectonic plates move away and middle block moves upwards.
Rift Valley – Lowland region formed when Earth’s tectonic plates move apart
Spurs – It is a long, gently sloping “tongue” of that runs down from a hill to ground.
Bare Rocky Structures.
Dykes – Sheet of rock formed in a fracture of pre-existing rock body.

The North-Western part of the plateau consists of Ravines and Gorges. For ex – Ravines of Chambal, Bhind and Morena

Ravines – erosional landform formed as a feature of constant erosion by rivers and streams.
Gorges – Narrow valley with steep and rocky walls located between hills or mountains.

On the basis of prominent features, the peninsular plateau is divided into three parts-

Deccan plateau
Central highlands
North-Eastern Plateau

Deccan Plateau

It is bordered by Eastern Ghats in the East, Western Ghats in the West and Satpura, Maikal and Mahadeo hills in the North.

Western Ghats

Height ranges from 900-1600m
These are continuous chains of mountains
Most of the peninsular river originates here
Soil is highly fertile

Eastern Ghats

Height ranges from 600-900m
Discontinuous and highly eroded by rivers such as Godavari, Krishna etc.
No river originates here
Soil is less fertile

Points to be noted

Western ghats are locally known by different names –

Sahyadri – Maharashtra
Nilgiri – Karnataka and Tamil Nadu
Anaimalai and Cardamom hills in Kerala

Highest peak of peninsular plateau, Anaimudi, is located on the Anaimalai hills of Western Ghats.

Central Highlands

It lies to the North of Deccan Plateau and is bounded by Aravalli hills in the West and Satpura range in the South.
Elevation above sea level – 600-900m
Mountains in this region are relict, highly denuded and form discontinuous ranges.
Banas is the only significant tributary of river Chambal that originates from Aravalli.

North-Eastern Plateau

It is an extension of main peninsular plateau.
Formation – Due to the force exerted by the Northeastward movement of the Indian plate at the time of Himalayan origin, a huge fault was created between the Rajmahal hills and the Meghalaya plateau. Later this fault got filled up by the deposition brought by rivers.
Meghalaya Plateau is divided into 3 regions – Garo, Khasi and Jaintia hills.
Meghalaya Plateau has a highly eroded surface because it receives maximum rainfall from the South-West monsoon.

The Indian Desert (Marusthal)

The Great Indian Desert lies North-West of the Aravalli hills.
It is a land of undulating topography dotted with longitudinal dunes and barchans.

Dunes – landform composed of wind or water driven sand. It takes the form of a hill or a ridge

Barchans – Crescent shaped sand dunes produced by the action of winds

On the basis of orientation, it is divided into two parts – Northern part is sloping towards the Sindh and southern towards the Rann of Kutch.
The climate is arid with low vegetation cover.
Low rainfall – Below 150mm per year
This region has some prominent features like mushroom rocks, shifting dunes and oasis.
Most rivers are ephemeral; Luni River is significant.

Oasis – Fertile land in a desert where the water table approaches the surface

Mushroom Rocks – Naturally occurring rocks whose shape resembles a mushroom

The coastal Plains

India is divided into two coastal plains –
Eastern coastal plains
Western coastal plains

Eastern Coastal Plains

It is divided into two stretches – North (Northern Circar) and South (Coromandel Coast)
It lies between Bay of Bengal and Eastern ghats
Deltas are formed
Broader
Level surface

Western Coastal Plains

It is divided into 3 sections: Southern – Malabar coast; Central – Karavali or Karana; Northern – Konkan
It lies between Arabian sea and Western Ghats
Deltas are not formed
Narrow
Intersected by mountain ridges

Points to be Noted

Malabar coast has kayals (backwaters) which is used for fishing and inland navigation.
Nehru trophy Vallamkali (Boat Race) is held every year in Punnamada Kayal in Kerala.

The Islands

There are two major islands groups in India – Bay of Bengal and Arabian Sea.

Bay of Bengal Islands Group

These are located between 60N-140N and 920E-940E
The group is divided into two broad categories – Andaman in North and Nicobar in South
Andaman and Nicobar are separated by Ten Degree Channel.
These islands lie close to equator and thus have equatorial climate.
These islands have thick forest cover due to heavy convectional rainfall.
Barren Islands, the only active volcano in India is also situated in the Nicobar Islands.

Arabian Sea Islands Group

These are located between 80N-120N and 710E-740E longitude.
The islands of this group include Lakshadweep and Minicoy.
Entire island group is built of coral deposit
Minicoy is the largest island
The entire group of islands is divided by Eleventh Degree channel, North of which is the Amini island and to the South, it is Cannanore islands.