Question

_______ and _______ types of clay minerals are dominant in acid soils

• A. Kaolinite and Illite
• B. Illite and Nontronite
• C. Kaolinite and Montmorillonite
• D. Montmorillonite and Nontronite

Hint:

Acid soils are dominated by low-CEC (cation exchange capacity), non-expanding clays (Kaolinite), which limits their nutrient-retention capacity compared to alkaline soils.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Soil pH influences the weathering, stability, and dominant types of silicate clay minerals present in different soil profiles.

Step 2: Detailed Explanation:
- Acid soils (such as those in humid tropical or highly leached forest zones) are subject to intense chemical weathering and leaching of basic cations (\(Ca^{2+}, Mg^{2+}, K^{+}\)).
- This weathering breaks down expanding 2:1 type clays (like montmorillonite).
- Under these acidic, highly leached conditions, the dominant clay minerals remaining are the stable, non-expanding 1:1 type clay Kaolinite and the non-expanding 2:1 type clay Illite (hydrous mica).
- Montmorillonite and nontronite are expanding clay minerals dominant in neutral-to-alkaline soils with high base saturation (like Vertisols).

Step 3: Final Answer:
Kaolinite and Illite are the dominant clay minerals in acid soils.