Match List–I (Clay Minerals) with List–II (Cation Exchange Capacity in cmol(+) kg⁻¹):

Correct option is D

Cation Exchange Capacity (CEC) varies depending on the structure and charge of the clay minerals:

1.      Vermiculite → (iv) 150–160 cmol(+) kg⁻¹

• Highest CEC due to high surface charge and expanding structure.

2.      Smectite → (iii) 100–120 cmol(+) kg⁻¹

• High CEC because of interlayer expansion and high surface area.

3.      Illite → (ii) 20–40 cmol(+) kg⁻¹

• Moderate CEC, with limited exchange due to potassium fixation.

4.      Kaolinite → (i) 5–25 cmol(+) kg⁻¹

• Lowest CEC as it is a non-expanding clay with minimal charge.

Information Booster:

1.      Cation Exchange Capacity (CEC):

• It refers to the ability of soil or clay minerals to retain and exchange positively charged ions (cations).
• Higher CEC means greater nutrient-holding capacity.

2.      Vermiculite:

• It has the highest CEC among the listed minerals due to its expanding lattice structure.
• Used in horticulture and soil conditioning.

3.      Smectite:

• It has a high CEC due to its high surface area and ability to absorb water.
• Montmorillonite, a type of smectite, is used in soil amendments.

4.      Illite:

• Has a moderate CEC due to potassium-rich structure that prevents full expansion.
• Commonly found in sedimentary rocks and weathered soils.

5.      Kaolinite:

• Has the lowest CEC since it lacks an interlayer space for cation exchange.
• Predominantly found in tropical soils and used in ceramics and paper industries.

6.      Importance of CEC in Agriculture:

• Higher CEC means better nutrient retention and soil fertility.
• Soils with low CEC require frequent fertilizer application.

Additional Information:

·         Vermiculite: Used in potting mixes, improves aeration and water retention.

·         Smectite: Expands significantly when wet, making it important in industrial applications like drilling muds.

·         Illite: Often found in weathered soils and is a transition between high and low CEC clays.

·         Kaolinite: Highly stable and resistant to weathering, making it suitable for ceramics and cosmetics.

·         CEC is influenced by:

• Soil pH: Higher pH generally increases CEC.
• Organic Matter: More organic matter increases CEC due to functional groups.
• Clay Type: Expanding clays like smectite have higher CEC than non-expanding ones like kaolinite.

·         Application in Soil Management:

• High CEC soils hold nutrients better, reducing the need for fertilizers.
• Low CEC soils require more frequent fertilization to sustain crop productivity.