RAS question
Red soils in Rajasthan are found mainly in which districts, and what gives them their characteristic colour?
Correct answer: (B) Dungarpur, Banswara, Chittorgarh, Udaipur; iron oxide (Fe₂O₃).
In Rajasthan, red soils are found mainly in Dungarpur, Banswara, Chittorgarh and Udaipur, and their red colour comes from diffused iron oxide (Fe2O3) in crystalline and metamorphic rocks.
Explanation
Red soils in Rajasthan are concentrated in the southern districts of Dungarpur, Banswara, Chittorgarh and Udaipur. Their distribution and parent material are important clues: these soils form through tropical weathering of gneisses and schists, which are ancient crystalline and metamorphic rocks. Their colour is not caused by a surface stain or organic matter; it comes from diffused iron oxide in the rocks, with Fe2O3 or haematite acting as the colouring agent. These soils are well drained, generally poor in nitrogen and phosphorus, and become suitable for crops such as maize, jowar, groundnut and cotton when irrigated.
Why the other options are wrong
- (A) Bikaner and Jaisalmer point to western Rajasthan's arid, sandy soils, where calcium carbonate kankar is associated with desert soils rather than the iron-oxide redness of southern red soils.
- (C) Kota, Bundi and Jhalawar belong to the black cotton soil belt, whose dark colour is linked to titaniferous magnetite and humus, not manganese oxide.
- (D) Sikar, Jhunjhunu and Churu have semi-arid sandy-loam conditions with low humus, so humus accumulation cannot explain a red-soil zone there.
Concept
This question tests your understanding of soil classification in Rajasthan by linking distribution, parent rock and colour chemistry. The theme recurs in RAS because district distribution and soil properties connect physical geography directly with agriculture.