Black soil — also called Regur soil or simply Cotton soil — is traditionally regarded as the ideal medium for growing cotton in India, which is why the answer is Black soil rich in clay and moisture.

Black soil forms from the weathering of volcanic basalt (lava) rocks of the Deccan Plateau. Because of its very fine clay content (rich in the mineral montmorillonite), it can absorb and hold large amounts of water. In the dry season it develops deep cracks that help aerate the soil, and it swells and becomes sticky when wet. This high moisture-retention capacity lets cotton — a crop with a long growing period and modest water needs — survive dry spells without frequent irrigation. The soil is also naturally rich in lime, calcium, magnesium, potash and iron, though it is generally poor in nitrogen and organic matter.

Why the other soils are unsuitable:

• Desert soil of the arid west is sandy, porous and drains water very quickly, so it cannot retain the moisture cotton needs.
• Alluvial soil laid down by Himalayan rivers is fertile and excellent for wheat, rice and sugarcane, but it is not specifically associated with cotton the way Regur soil is.
• Laterite soil of high-rainfall regions is heavily leached, acidic and low in fertility, making it better suited to plantation crops like tea, coffee and cashew than to cotton.