Question

Which of the following match(es) is correct ?
(A) Laterite soil - pH 7-8
(B) Black soil - has high amount of clay
(C) Alkali soil - pH 9
(D) Red soil - calcareous
Choose the correct answer from the options given below :

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

Hint:

- Laterite soils = Highly Acidic (pH < 5.5).
- Alkali soils = Highly Alkaline (pH > 8.5, typically around 9.0).
- Black soils = High clay content (Vertisols, clay > 40%).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Indian soils exhibit highly distinct physical and chemical properties depending on their mineralogy, climate, and parent material.
Key parameters like soil texture (clay content) and soil reaction (pH) are diagnostic features for classifying these soil groups.

Step 2: Detailed Explanation:
Let us evaluate the accuracy of each matched pair:
- (A) Laterite soil - pH 7-8:
Laterite soils are formed under high temperature and heavy rainfall conditions, which causes intense leaching of silica and basic cations.
As a result, these soils are highly acidic, typically having a pH of 4.5 to 5.5.
Thus, this match is incorrect.
- (B) Black soil - has high amount of clay:
Black cotton soils (Vertisols) are characterized by a very high clay content, typically ranging from 40% to 60% or even higher.
The dominant clay mineral is montmorillonite, which gives them high swelling-shrinking properties and high water retention.
Thus, this match is correct.
- (C) Alkali soil - pH 9:
Alkali (sodic) soils contain high amounts of exchangeable sodium, which undergoes hydrolysis to produce sodium hydroxide and sodium carbonate, raising the soil pH above 8.5 (frequently around 9.0 to 10.0).
Thus, this match is correct.
- (D) Red soil - calcareous:
Red soils are formed by the weathering of crystalline metamorphic rocks under semi-arid conditions.
They are generally acidic to neutral in reaction and are non-calcareous (lacking calcium carbonate accumulations), unlike kankar-rich alluvial soils.
Thus, this match is incorrect.
Therefore, only matches (B) and (C) are correct.

Step 3: Final Answer:
The correct option is (D), representing (B) and (C) only.