Previous Year Question

Correct answer: (b) Fissure volcanic rock

The black cotton soil of India has primarily developed through the weathering of basaltic volcanic rocks of the Deccan Trap.

• Volcanic eruptions in Peninsular India did not occur from a single central vent. Basaltic lava emerged through long cracks or fissures in the Earth’s crust.

• The highly fluid lava spread over extensive areas in successive sheets. The solidification of these lava layers produced the Deccan Trap formation.

• Long-term physical and chemical weathering of these basaltic rocks produced an extremely fine and clayey black soil, also known as regur soil.

• Its major distribution covers the plateaus of Maharashtra, Saurashtra, Malwa, Madhya Pradesh and Chhattisgarh. It also extends towards the Godavari and Krishna valleys.

Important characteristics of black soil

• It contains a high proportion of fine clay particles.

• It has a very high moisture-retaining capacity.

• It swells and becomes sticky when wet, while it shrinks and develops wide, deep cracks when dry.

• These cracks improve aeration and bring lower soil material towards the surface. Therefore, it is also described as a self-ploughing soil.

• It is relatively rich in calcium carbonate, magnesium, potash and lime but is generally deficient in phosphorus.

• Its high moisture-retaining capacity makes it particularly suitable for cotton cultivation, giving it the name black cotton soil.

Why are the other options incorrect?

• Brown forest soil is itself a soil type, not the volcanic parent rock of black soil.

• The weathering of granite and schist is commonly associated with the formation of red and yellow soils in Peninsular India.

• Shale and limestone may serve as parent material for some local soils, but they are not the principal parent material of the extensive black cotton soils of the Deccan region.