Maarg Manthan · Topic 16.6

Soil Types and Soil Profile

Geography › Indian Monsoon, Climate, Vegetation and Soils · Topic 16.6

Soil is the thin upper layer of the Earth's crust made of weathered rock particles mixed with organic matter, water and air. By texture it is sandy, clayey or loamy, depending on the proportion of coarse and fine particles, and loam is best for crops. A soil profile is a vertical section through its horizons, labelled O, A, E, B, C and R, from the organic top layer down to bedrock.

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

At a Glance

Best soil for crops Loam: sand, silt, clay and humus
Topsoil A horizon; most humus
Subsoil B horizon; accumulates leached minerals
Parent rock C horizon, then bedrock R
Study Pedology
Exam link UPSC Prelims, Geography: Indian Monsoon, Climate, Vegetation and Soils

Where Does It Fit?

This is the sixth topic of the macro on the Indian monsoon, climate, vegetation and soils. The previous topic described the natural vegetation, and this one begins the study of soils with their texture and layers. The next topic covers the factors that form the soils of India. Previous topic: Natural Vegetation of India. Next topic: Factors of Soil Formation in India.

What Is Soil and How Is It Classified by Texture?

In short: soil is weathered rock plus humus, and its feel and fertility depend on the size of its particles.

Soil is the thin top layer of the Earth’s crust made of rock particles mixed with organic matter. Pedology is the study of soils in their natural setting, and pedogenesis is the process of soil formation, which includes weathering, leaching and calcification. Soils are classified by the size of particles.

Type	Particles	Properties	Crops
Sandy soil	Mostly large particles	Light, well aerated, drains fast, dry; poor in nutrients	Cotton and millets in sandy loam; drought-resistant crops
Clayey soil	Mostly fine particles	Heavy, holds water, poor in air	Paddy, which needs a soil that retains water
Loamy soil	A mix of sand, silt and clay with humus	The best soil: good water retention and drainage; fertile	Wheat, gram, pulses such as lentil, cotton in sandy loam

Silt, the particles of intermediate size, is deposited by rivers. Humus is the dark, decomposed organic matter that makes soil fertile. Clay and loam are good at retaining water and so suit wheat and gram; lentils and other pulses need loams that drain easily; cotton needs sandy loam or loam that is well aerated; and paddy needs clayey soil rich in organic matter. The main soil groups of India are described in Major Soil Groups of India.

What Are the Layers of a Soil Profile?

Horizon	Name	Features
O	Organic layer	Fallen leaves, twigs and other litter, undecomposed or partly decomposed; on top of mineral soil, in forests
A	Topsoil	Dark, rich in humus and soil life, soft and porous, with the highest content of organic matter mixed with minerals; where roots and most nutrients are
E	Eluvial layer	A light-coloured layer, from which clay, iron and aluminium have been leached; sand and silt with resistant quartz remain; found in older, well-developed soils
B	Subsoil	Harder and more compact, with less humus; collects the minerals leached from above by illuviation, such as clay, iron and aluminium
C	Weathered parent material	Small lumps of rock with cracks, partly broken-up rock from which the soil forms
R	Bedrock	Unweathered, continuous hard rock; soils formed in place resemble it

The soil horizons form as water moves materials down through the profile. Eluviation is the removal of material from a layer by water moving down, and illuviation is the deposition of that material in a lower layer. A young soil has a thin profile with weakly developed horizons, as the alluvial soils of the Ganga plain do, and an old soil has a deep and well-differentiated profile. In warm, wet regions leaching is strong and the topsoil may lose nutrients, as in laterite soils, whereas in dry regions salts and lime accumulate in the subsoil.

Why Does Soil Matter and What Is Its Condition?

Foundation of food: soil supports plant growth, stores water and carbon, and filters water. It takes hundreds of years to form a centimetre of topsoil, so it is effectively a non-renewable resource.
Degradation: erosion, loss of organic carbon, salinity, waterlogging, nutrient imbalance and desertification affect large areas. ISRO’s atlas of desertification and land degradation estimated that nearly 98 million hectares, about 30 per cent of the country, were degraded in 2018–19, and India has pledged to restore 26 million hectares of degraded land by 2030, as in Soil Erosion – Water and Wind Erosion.
Nutrient imbalance: heavy use of subsidised nitrogen fertiliser, urea, over phosphorus and potash has distorted the nutrient balance in Punjab, Haryana and Uttar Pradesh.
Policy: the Soil Health Card scheme, launched in 2015, provides farmers with the nutrient status of their fields and recommendations, and the PM-PRANAM scheme approved in 2023 rewards states for reducing the use of chemical fertilisers.

As an analytical point, India’s soils are diverse, but the pressure on them is similar everywhere: they are cropped continuously, irrigated with poor drainage and fertilised in an unbalanced way, so soil health, and not only water, is going to be the limiting factor for agricultural growth.

Why Is This Topic Important?

Foundation Basis for all soil topics
Concepts Horizons and texture asked
Policy Soil health schemes

What Came Next?

The next topic describes the factors that form the soils of India. Next topic: Factors of Soil Formation in India.

Key People and Terms

Pedology Study of soils
Humus Decomposed organic matter
Loam Mixed sand, silt and clay soil
Eluviation Removal of material from a layer
Illuviation Deposition in a lower layer
Horizon Layer in a soil profile

Exam Corner

Points to Remember

Loam is the best soil for crops.
A is topsoil; B is subsoil; C is parent material.
Paddy likes clayey soil.
The E horizon is leached.
The Soil Health Card began in 2015.

Do Not Confuse With

Eluviation and illuviation Removal versus accumulation
Topsoil and subsoil A horizon versus B horizon
Humus and soil Organic matter versus the whole mixture

Memory Hook

O is litter, A is rich, E is washed, B collects, C is cracked rock, R is rock.

Mains Angle

Questions ask about soil layers and degradation. These points add depth.

Layers Profile and processes
Fertility Humus and texture
Policy Soil health

A Question You May Face

An original practice question, not a past paper question.

“Describe the soil profile and explain why loam is considered the best soil for agriculture. Discuss the problem of soil degradation in India.”

How to Answer

Texture Sand, clay, loam.
Profile Horizons.
Degradation Erosion, salinity, imbalance.
Policy Soil Health Card.

GS Relevance

Prelims: sand, clay and loam, crops suited to each, horizons A B C, terms such as eluviation. GS Paper 1: soils; GS Paper 3: agriculture and soil health.

Frequently Asked Questions

What is a soil profile?

A soil profile is a vertical section through the soil showing its layers, called horizons, which differ in colour, texture and composition. The main soil horizons are the organic O layer, the A horizon or topsoil, the E layer of leaching, the B horizon or subsoil, the C horizon of weathered rock and the R horizon of bedrock.

Why is loam the best soil for crops?

Loam is a mixture of sand, silt and clay with humus. It holds enough water for the plants but drains well, has air spaces for roots and contains nutrients, so it suits most crops such as wheat, gram, pulses and cotton, while sandy and clayey soils are either too dry or too wet.

What is the difference between eluviation and illuviation?

Eluviation is the removal of clay, iron, aluminium and organic matter from an upper soil horizon by downward-moving water, which leaves a leached layer. Illuviation is the deposition of these materials in the horizon below, usually the B horizon, which makes the subsoil richer in clay and minerals.

What is humus?

Humus is the dark, stable organic matter in the soil formed by the decomposition of plant and animal remains. It gives the topsoil its dark colour, improves its structure and water-holding capacity, and supplies nutrients, which is why the A horizon is the most fertile layer.

What is the Soil Health Card scheme?

The Soil Health Card scheme, launched in 2015, provides farmers with a card that shows the nutrient status of their soil, and gives recommendations on the amount of fertilisers and soil amendments. Its purpose is to encourage balanced fertiliser use and improve soil health and productivity.

PYQ Practice — Statement Analysis

1 The A horizon is the topsoil rich in humus.

True

It is dark, soft and fertile.

2 Sandy soil retains more water than clayey soil.

False

Clayey soil retains more water.

3 Paddy grows best in clayey soil that retains water.