Red and yellow soils, and laterite soils

Detail

Where these soils fit in the ICAR classification

• ICAR (Indian Council of Agricultural Research) groups Indian soils into eight major groups. Four of them matter most for farming: alluvial, black, red and lateritic soils [2].
• Red and yellow soil and laterite soil are the two main soils of the Peninsular plateau that form on old, hard rock. They differ mainly in how much rain falls on that rock.

Red and yellow soil: formation

• Red and yellow soil is soil that forms when old crystalline rock breaks down in low-rainfall areas. It is red or yellow because of the iron it holds.
• Parent rock: it forms on crystalline igneous rocks (such as granite, which cooled from molten magma) and on metamorphic rocks (rocks changed by heat and pressure, such as gneiss).
• How it forms:
• Low rain means only mild weathering (the slow breaking down of rock where it lies).
• Iron from the rock spreads through the soil.

• The soil turns red.

• Another source traces it to weathered metamorphic rocks [2].

Red and yellow soil: why it is red or yellow

• Red colour: iron spreads through the crystalline and metamorphic rocks (diffusion of iron).
• Yellow colour: the same soil looks yellow where the iron is hydrated (joined with water).
• So the change in colour comes from the state of the iron, not from a different parent rock.

Red and yellow soil: where it is found

• Core area: the low-rainfall parts of the eastern and southern Deccan plateau.
• Other areas:
• Odisha and Chhattisgarh
• the southern parts of the middle Ganga plain

• the piedmont zone of the Western Ghats (piedmont: the strip of land at the foot of a mountain range)

• Large areas: Tamil Nadu, Karnataka, Telangana and Jharkhand.

• Another list of states: Tamil Nadu, Karnataka, north-east Andhra Pradesh, eastern Madhya Pradesh, Bihar, West Bengal and Rajasthan [2].

Red and yellow soil: properties and crops

• Texture: light and porous (full of tiny air spaces, so water drains fast). It is also friable (crumbles easily) [2].
• Nutrients: poor in nitrogen, phosphorus and humus (humus: dark organic matter from rotted plants and animals). It is also low in lime [2].
• Fertility: fine-grained red soils become fertile when fertiliser and irrigation are added. Coarse, upland red soils stay poor.
• Crops: ragi, groundnut, millets, pulses and tobacco.

Laterite soil: meaning and formation

• Laterite comes from the Latin word later = brick. It is a deep, acidic soil left behind after heavy rain washes most minerals out of the rock. NCERT's puzzle calls it the "intensively leached soil of the monsoon climate".
• Climate: tropical and subtropical areas with high rainfall and alternate wet and dry seasons [2].
• How it forms (cause → process → result):
• Cause: very heavy seasonal rain and high heat.
• Process: leaching happens. Leaching means rainwater sinks through the soil and carries dissolved minerals down and away. Silica and bases (calcium, magnesium, potassium) are washed out [2].
• Result: iron and aluminium oxides stay behind. This gives the soil its red to reddish-yellow colour [2].

Laterite soil: properties

• Depth: deep to very deep.
• Acidity: acidic, with pH below 6.0 (pH: a scale of how acidic or alkaline a soil is; 7 is neutral).
• Nutrients: generally poor in plant nutrients, because leaching has removed them.
• Humus depends on the plant cover:
• under thick forest: rich in humus (leaves keep falling and rotting).

• under sparse plants and in semi-arid areas: poor in humus.

• Erosion: it is easily washed away on slopes once the plant cover is removed.

• Hardens in air: wet laterite is soft. Exposed to air and sun, it sets hard like brick. It is cut into building blocks in Malabar (Kerala), Goa and the Konkan coast.

Laterite soil: where it is found

• Main areas: the southern states, the Western Ghats of Maharashtra, Odisha, parts of West Bengal and the north-east.
• Other states with laterite: eastern Andhra Pradesh, Karnataka, Kerala, Madhya Pradesh, Odisha, Assam and parts of Maharashtra [2].
• Geo-heritage site: the laterite near Angadipuram (PWD rest house premises, Malappuram district, Kerala) is a declared geo-heritage site / National Geological Monument. The Geological Survey of India (GSI) or the state government is responsible for protecting it [3].
• On 6 October 2023, GSI held a Swachhata (cleanliness) campaign at the Angadipuram laterite. It was one of 15 geo-heritage sites covered in the drive [4].

Laterite soil: crops and conservation

• Tea and coffee: with soil conservation (terracing, contour planting, mulching), laterite in the hills of Karnataka, Kerala and Tamil Nadu grows tea and coffee.
• Cashew: red laterite in Tamil Nadu, Andhra Pradesh and Kerala suits cashew.
• Acidity and low nutrients: farmers add manure and fertiliser to raise output.

Red and yellow soil vs laterite soil

Feature	Red and yellow soil	Laterite soil
Rainfall	Low	High, with alternate wet and dry seasons
Main process	Weathering of crystalline rock; iron spreads through the soil	Intense leaching; silica and bases washed out
What gives colour	Iron (red), hydrated iron (yellow)	Iron and aluminium oxides left behind
Texture	Light, porous, friable	Deep to very deep; hardens when exposed to air
pH	Not specially acidic	Acidic (below 6.0)
Fertility	Poor in N, P and humus; good with fertiliser and irrigation	Poor in nutrients; humus-rich only under forest
Typical crops	Ragi, groundnut, millets, pulses, tobacco	Tea, coffee (hills); cashew (red laterite)
Main areas	Eastern and southern Deccan, Odisha, Chhattisgarh, Western Ghats piedmont	Southern states, Western Ghats of Maharashtra, Odisha, West Bengal, north-east
Special use	—	Building bricks (Malabar, Goa, Konkan)

Prelims Hooks

• Red colour comes from diffusion of iron in crystalline and metamorphic rocks. Yellow shows where the iron is hydrated.
• Red and yellow soil forms in low-rainfall areas. Laterite forms in high-rainfall areas with alternate wet and dry seasons. This is a common trap.
• "Laterite" comes from the Latin later = brick. It hardens in air and is cut into building blocks.
• Laterite forms by leaching: silica and bases are removed and iron and aluminium oxides stay behind.
• Laterite is acidic (pH < 6.0). It is humus-rich under forest and humus-poor under sparse vegetation.
• Crop–soil pairs: cashew – red laterite (TN, AP, Kerala); tea/coffee – laterite hills (Karnataka, Kerala, TN); ragi/groundnut – red soil.
• The Angadipuram laterite (Malappuram, Kerala) is a GSI National Geological Monument [3].
• ICAR has 8 soil groups. The 4 most important for farming are alluvial, black, red and laterite [2].
• Red soil is found in the piedmont zone of the Western Ghats and in the southern middle Ganga plain, not only on the Deccan.

Mains Points

• Distribution follows rainfall over the same old rock: both soils form on the Peninsular crystalline rocks. Red soils form where rain is low and weathering is mild. Laterite forms where heavy monsoon rain causes intense leaching, as in the Western Ghats, Kerala and the north-east. This shows how climate decides soil type (GS-I).
• Farming limits and solutions: both soils lack N, P and humus, and laterite is also acidic. They need liming, organic manure, balanced fertiliser and irrigation. Soil testing under the Soil Health Card scheme (2015) helps match fertiliser to these soils (GS-III).
• Degradation risk: laterite on slopes erodes fast once forest is cleared. Plantations need terracing, contour bunds and cover crops to stay productive in Karnataka, Kerala and Tamil Nadu (GS-III, conservation).
• Economic value beyond farming: laterite blocks are cheap local building material along the Malabar–Goa–Konkan coast. Iron- and aluminium-rich laterite links to mineral resources. Quarrying, though, damages the land, so sites like Angadipuram are protected as geo-heritage [3][4].