Question

Read the following statements about black soils
(A). These have dark colour.
(B). These have high clay content.
(C). These have low CEC.
(D). These are rich in organic matter and nitrogen.
(E). These are normally suitable for cultivation of cotton.
Choose the correct answer from the options given below:

• A. (A), (B), (D) and (E) only.
• B. (A), (B) and (E) only.
• C. (A), (B), (C) and (D) only.
• D. (B), (C) and (D) only.

Hint:

Black soils are characterised by a high content of ______Montmorillonite clay______, which behaves like a sponge (expanding when wet and shrinking/cracking when dry).
This high-clay mineralogy guarantees a ______high CEC______, directly contradicting statement (C).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Black soils (also known as Regur soils or Vertisols) are typical of the Deccan plateau in India.
They are formed by the weathering of basaltic lava rocks and possess highly distinct physical, chemical, and mineralogical characteristics.

Step 2: Detailed Explanation:
Let us evaluate each of the given statements:
- Statement (A): These have dark colour. This is correct. The dark color is primarily attributed to small quantities of titaniferous magnetite and clay-humus complexes.
- Statement (B): These have high clay content. This is correct. They generally contain $40\text{--}60\%$ clay, which is dominated by the smectite (montmorillonite) mineral group, giving them high shrink-swell properties.
- Statement (C): These have low CEC. This is incorrect. Because of the dominance of montmorillonite clay (which has a high surface area and charge), black soils possess a very ______high Cation Exchange Capacity (CEC)______, typically ranging from $40$ to $60\text{ cmol}(p^+)\text{ kg}^{-1}$.
- Statement (D): These are rich in organic matter and nitrogen. This is incorrect. Most Indian black soils are notoriously deficient in organic matter, nitrogen, and available phosphorus.
- Statement (E): These are normally suitable for cultivation of cotton. This is correct. Due to their excellent moisture retention capacity, they are ideal for rainfed cotton, earning them the name "Black Cotton Soils".
Thus, only statements (A), (B), and (E) are correct.

Step 3: Final Answer:
The correct combination is (A), (B), and (E) only, which corresponds to option (B).