Assertion (A): The soils of the Deccan Plateau, locally known as Regur or black cotton soils, exhibit high fertility and exceptional moisture-retention capacity. Reason (R): These soils are formed in situ from the weathering of ancient basaltic lava flows of the Deccan Traps and are rich in iron, lime, and magnesium, while being deficient in nitrogen and phosphorus.

💡 Solution & Explanation

Both assertion and reason are true, and the reason accurately explains the genesis and nutrient composition of black cotton soils. Weathering of Deccan basalt volcanic rocks under semi-arid tropical climates produces clay-rich soils that swell when wet and shrink when dry, creating deep cracks that facilitate self-ploughing. These soils are exceptionally suited for cotton cultivation without heavy irrigation. Laterite soils form under different climatic regimes with high leaching.