RAS question
With reference to NBSS&LUP soil classification for Rajasthan, which of the following soil orders is CORRECTLY described?
Correct answer: (B) Vertisols - dark cracking clays with high shrink-swell capacity, found in south-eastern Rajasthan.
In NBSS&LUP soil classification for Rajasthan, Vertisols are dark cracking clay soils with high shrink-swell capacity and occur in south-eastern Rajasthan.
Explanation
Vertisols fit the description because their defining feature is expanding clay: the NRCS describes them as soils with a high content of expanding clay minerals that change volume with moisture, shrink on drying, swell when wet, and develop deep, wide cracks during part of the year. That matches the Rajasthan explanation: these are dark cracking clay soils, linked to montmorillonite clay and known locally in the black cotton soil or Regur context. In Rajasthan, they are associated with the south-eastern Hadaoti belt, including Kota, Bundi and Jhalawar. The option is therefore correct on both the diagnostic soil behaviour and the regional distribution.
Why the other options are wrong
- (A) Aridisols are tied to arid, dry conditions and the western Rajasthan desert, so describing them as humid-tropical soils of southern Rajasthan reverses both climate and location.
- (C) Oxisols require long-term heavy rainfall and intense leaching with iron and aluminium oxides, which does not fit arid north-western Rajasthan.
- (D) Inceptisols are young soils with weak horizon development, but they are not confined to the Thar Desert and also occur in Rajasthan's Aravalli and eastern plain settings.
Concept
This tests soil taxonomy under Rajasthan physical geography, especially matching USDA/NBSS&LUP soil orders with diagnostic properties and regions. It recurs in RAS because soil order, climate, relief and agriculture are often tested together.