Question

Which of the following statements are correct statements?

(a) Montmorillonite dominated soils are well-drained.

(b) Soils with high Cation Exchange Capacity (CEC) store more cationic nutrients.

(c) Kalinit dominated soils are better drained.

(d) Soils with high Cation Exchange Capacity (CEC) store more anionic nutrients.

1. (a) and (b) only
2. (b) and (c) only
3. (c) and (d) only
4. (a) and (d) only

Answer 1

Correct Answer - Option 2 : (b) and (c) only

The correct answer is (b) and (c) only.

• Cation exchange capacity (CEC) is the total capacity of a soil to hold exchangeable cations.
  • It influences the soil’s ability to hold onto essential nutrients and provides a buffer against soil acidification.
  • Soils with a higher clay fraction tend to have a higher CEC.
  • Organic matter has a very high CEC.
  • Sandy soils rely heavily on the high CEC of organic matter for the retention of nutrients in the topsoil. Hence, statement (b) is correct.
• Kaolinite
  • It is a clay mineral, with the chemical composition Al2Si2O5(OH)4.
  • Kaolinite has a low shrink-swell capacity and a low cation-exchange capacity. 
  • It is a soft, earthy, usually white, mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicate minerals like feldspar and they are better drained. Hence, statement (c) is correct.
• Montmorillonite dominated soils:
  • ​Montmorillonite belongs to the smectite family and is composed of two silica-based tetrahedral sheets with water molecules within the interlayer sheets and are easily available for incoming contaminants.