Practice question

Black soil of Deccan plateau, regur, formed by basalt weathering, possesses high clay content predominantly montmorillonite conferring superior moisture retention for months after monsoon, rich in calcium carbonate, potash, lime, yet poor nitrogen. Texture fine, cracks deep in summer facilitating self-ploughing. Cotton Gossypium requires long frost-free period, moderate water, black soil ideal as it retains moisture and supports deep taproot. Maharashtra Vidarbha and Marathwada cotton belts exemplify correlation, producing majority Indian cotton export due to regur fertility properties. Mastery of this rule helps candidates differentiate closely related categories and avoid common errors in diversity questions.