Previous Year Question
Assertion (A): Black soils are suitable for cotton cultivation.
Reason (R): They are rich in humus.
Select the correct answer from the codes given below:
Both (A) and (R) are true and (R) is the correct explanation of (A).
Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(A) is true, but (R) is false.
(A) is false, but (R) is true.
Correct Answer: C
Detailed Solution
Black Soil, also called Regur or Vertisol, is highly suitable for cotton cultivation. It is therefore commonly known as Black Cotton Soil. Its suitability is mainly due to its high clay content and high water-holding capacity, which enable the soil to retain moisture for a long period during dry conditions.
Black soil shows characteristic swelling when wet and shrinkage with deep cracking when dry. This contributes to self-mulching and improves aeration of the soil. Its high cation-exchange capacity also helps in nutrient retention.
However, Reason (R) is false because black soil is not considered rich in humus or organic matter. ICAR descriptions indicate that black soils are generally low in organic carbon and available nitrogen, although bases such as calcium, magnesium and potassium may be relatively abundant.
Thus, its suitability for cotton is not due to richness in humus, but mainly due to its clayey texture, moisture-retention capacity and favourable physical properties.