RAS question
Black soil (Regur soil) is ideal for cotton cultivation. It is formed from the weathering of which type of rock?
Correct answer: (B) Basaltic lava (Deccan Trap).
Black soil, also called regur or black cotton soil, is formed from the weathering of basaltic lava flows of the Deccan Trap region.
Explanation
Black soil is linked to its parent rock material: NCERT identifies it as typical of the Deccan trap (Basalt) region and made up of lava flows. That is why basaltic lava, not older crystalline or sedimentary rocks, is the correct source. The same soil is also called regur or black cotton soil because it is ideal for cotton. Its fine, clayey material gives it a strong capacity to hold moisture, and it is rich in iron, lime, calcium, magnesium and alumina but poor in phosphorus and nitrogen. Those properties explain both parts of the question: its origin in weathered Deccan Trap basalt and its suitability for cotton cultivation.
Why the other options are wrong
- (A) Granite and gneiss are not the parent material identified for regur soil; the question points to the Deccan Trap basaltic lava origin of black cotton soil.
- (C) Quartzite and slate do not explain black soil's Deccan Trap association or its formation from lava flows.
- (D) Sandstone and limestone are not source rocks for black soil, which NCERT places in the basaltic Deccan Trap region.
Concept
This tests the Indian geography link between soil type, parent rock and crop suitability. It recurs in RAS because black soil is a standard example where geology, soil properties and agriculture meet in one fact pattern.