Maarg Manthan · Topic 16.7

Factors of Soil Formation in India

Geography › Indian Monsoon, Climate, Vegetation and Soils · Topic 16.7

Soil formation in India depends on parent material, relief, climate, natural vegetation and organisms, and time, together with human activity. Ancient crystalline rocks give red soils, Deccan basalt gives black soils, river deposits give alluvial soils, heavy rain with heat gives laterite, and arid climates give sandy, lime-rich desert soils. Peninsular soils are mostly sedentary, and the soils of the northern plains are transported.

6 min read · UPSC Prelims · Geography · Indian Monsoon, Climate, Vegetation and Soils

At a Glance

Parent material Granite, basalt, sediments, alluvium
Relief Steep slopes erode; plains accumulate
Climate Rain and temperature drive weathering
Vegetation Supplies humus
Time Alluvium immature; plateau soils mature
Exam link UPSC Prelims, Geography: Indian Monsoon, Climate, Vegetation and Soils

Where Does It Fit?

This is the seventh topic of the macro on the Indian monsoon, climate, vegetation and soils. The previous topic described soil texture and horizons, and this one explains why the soils of different parts of India differ. The last topic of the macro describes the major soil groups. Previous topic: Soil Types and Soil Profile. Next topic: Major Soil Groups of India.

How Does Parent Material Shape Indian Soils?

In short: the rock decides the colour, mineral content and texture of the soil that forms from it.

Parent material	Description	Resulting soil
Ancient crystalline and metamorphic rocks	Granites, gneisses and schists of the basement complex, rich in iron minerals, as in Archaean Rock System of India	Red soils; their colour comes from iron oxide
Cuddapah and Vindhyan rocks	Ancient sedimentary rocks, thick, with few metals	Calcareous and clayey soils
Gondwana rocks	Younger sedimentary rocks	Immature soils of uniform character but low fertility
Deccan basalt	Lava rich in iron, magnesium, aluminium and titanium, as in Dravidian and Aryan Rock Systems of India	Dark, fertile, moisture-retaining black soil or regur
Tertiary and Mesozoic sediments of the Himalaya and plains	Young, porous deposits	Alluvial soils, with little relation to the original rock

The soils of the Peninsula are generally coarse-grained, closely related to the underlying rock and less fertile, and are mostly sedentary soils, with limited transport and re-deposition. The soils of the Indo-Gangetic-Brahmaputra plains are made of deposits laid by rivers and wind. They are very deep and are called transported soils, or azonal because they do not reflect the local climate and vegetation, as in Indo-Gangetic-Brahmaputra Plain.

How Do Relief, Climate and Vegetation Act?

Relief: on steep slopes, such as the hills, plateau edges and the south-facing Himalayan slopes without forest, erosion is rapid and keeps soil thin, as in the ravines of the Chambal. On gentle slopes and plains, deposition builds deep soils. The river basins of the plateau also have deeper soils.
Climate: temperature and rainfall control the rate of weathering, leaching and the types of micro-organisms. The same rock can give different soils in different climates: granite gives laterite in the wet monsoon belt and ordinary red soil where it is drier, while in the arid Rajasthan both granite and sandstone give sandy soil. In arid and semi-arid areas, evaporation exceeds rainfall and lime accumulates, giving pedocal soils that are rich in calcium carbonate; where rainfall is heavy, leaching removes lime and silica and leaves iron and aluminium, giving pedalfer soils. In cold Himalayan climates, plant matter decays slowly and soils are acidic.
Natural vegetation and organisms: forests provide leaf litter and humus, so the forest soils are rich in organic matter. Grasslands add humus in the roots. Earthworms, termites, bacteria and fungi mix and decompose the organic matter. In arid regions with sparse plants, the soils are light-coloured and lack humus, as in Natural Vegetation of India.
Time: soils need a long time to develop horizons. The alluvial soils of the plains are young and have weak profiles, while those of the old plateau are more mature, as in Soil Types and Soil Profile.
Human activity: deforestation, ploughing on slopes, overgrazing, irrigation and fertiliser use change the soil by causing erosion, salinity and waterlogging.

Why Does Heavy Rain With Heat Make Laterite, and Why Does Erosion Matter?

In regions with high temperatures and torrential seasonal rain, as on the Western Ghats and in the north-east, heavy rain washes the nutrients, lime and silica down the profile by leaching, leaving a soil rich in iron and aluminium oxides, hard and red, called laterite. The dry spells harden it, which is why it is used for bricks. The five factors, together with time, are sometimes summarised in a formula by the soil scientist Hans Jenny: soil is a function of climate, organisms, relief, parent material and time.

Soil erosion works against soil formation. India is estimated to lose several billion tonnes of soil every year to water and wind erosion, most of it from sloping cultivated and degraded land, the ravines, the hill slopes and the arid zone, as in Soil Erosion – Water and Wind Erosion. Conservation measures such as terracing, contour ploughing, shelterbelts, afforestation and check dams, and the watershed development programmes, aim to keep soil in place. As an analytical point, soil formation takes centuries, while erosion works within a single monsoon, so the policy question is less about creating new soil than about not losing the soil that exists, especially on the hill slopes and in the semi-arid plateau where the soil layer is thin and the monsoon rain is heavy and intense.

Why Is This Topic Important?

Concept Factors and examples asked
Link Rocks to soils
Conservation Erosion control

What Came Next?

The last topic of the macro describes the major soil groups of India. Next topic: Major Soil Groups of India.

Key People and Terms

Parent material Rock or sediment from which soil forms
Sedentary soil Soil formed in place
Transported soil Soil carried by water or wind
Pedocal Lime-rich soil of dry areas
Pedalfer Iron and aluminium-rich soil of wet areas
Leaching Washing of nutrients downward

Exam Corner

Points to Remember

Granite gives red soil; basalt gives black soil.
Plateau soils are sedentary; plain soils are transported.
Arid climate gives lime-rich pedocal soil.
Heavy rain leaches and makes laterite.
Steep slopes have thin soils.

Do Not Confuse With

Pedocal and pedalfer Calcium-rich dry soil versus iron-aluminium wet soil
Sedentary and transported soils In place versus moved
Zonal and azonal soils Reflect climate versus do not

Memory Hook

Rock gives the colour, relief sets the depth, climate leaches or limes, plants add humus, time matures it.

Mains Angle

Questions link soils to rocks, relief and climate. These points add depth.

Rock Parent material control
Climate Leaching versus calcification
Loss Erosion outpaces formation

A Question You May Face

An original practice question, not a past paper question.

“Explain the factors responsible for the formation of different soils in India, with suitable examples.”

How to Answer

Parent material Red, black, alluvial.
Relief Slope and deposition.
Climate Laterite and desert soils.
Time and humans Maturity and erosion.

GS Relevance

Prelims: factors with examples, parent rocks and resulting soils, pedocal and pedalfer. GS Paper 1: soils of India; GS Paper 3: erosion and conservation.

Frequently Asked Questions

What are the factors of soil formation?

The main factors of soil formation are parent material, relief, climate, natural vegetation and organisms, and time, with human activity as an additional factor. They decide the colour, texture, depth and fertility of a soil, and they vary greatly across India.

How does parent rock influence soils in India?

The parent rock determines the colour, texture and minerals of the soil. Granites and gneisses give red soils, Deccan basalt gives black cotton soil, ancient sedimentary rocks give calcareous clayey soils, and the river deposits of the Himalayan region give the alluvial soils of the northern plains.

How does climate affect soil formation?

Temperature and rainfall control the rate of weathering and leaching and the organisms present. Heavy rainfall with heat leaches nutrients and leaves iron-rich laterite, while dry climates leave lime and salts in the soil, giving pedocal desert soils, and cold climates give acidic soils because of slow decay.

What is the difference between sedentary and transported soils?

Sedentary soils are formed in place from the underlying rock and are closely related to it, as in most of the Peninsula. Transported soils are made of material carried and deposited by rivers or wind, as in the deep alluvial soils of the Indo-Gangetic and Brahmaputra plains.

Why do steep slopes have thin soils?

On steep slopes, rain and gravity remove the weathered material faster than it can accumulate, so erosion keeps the soil thin. This is seen on hill slopes without forest cover and in ravines, while gentle slopes and plains allow deposition and the formation of deep soils.

PYQ Practice — Statement Analysis

1 Deccan basalt weathers to form black soil.

True

It is regur, rich in clay and moisture.

2 Alluvial soils of the Ganga plain are sedentary soils.

False

They are transported soils.

3 Heavy rainfall and high temperature promote laterite formation.