Question

Alkali soils/sodic soil have
(A). Very high permeability
(B). Salts dominated by bicarbonates, carbonates and silicate of sodium.
(C). pH greater than 8.5.
(D). Electrical conductivity greater than 4 dS/m.
(E). Exchangeable Sodium Percentage is greater than or equal to 15.

Choose the correct answer from the options given below:

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

Hint:

Remember the classic diagnostic limits for Sodic Soils:
- \(\text{pH} \gt 8.5\)
- \(\text{ESP} \ge 15 \%\)
- \(\text{EC} \lt 4\text{ dS/m}\)
- Soil structure: Dispersed/Poor permeability.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Alkali (sodic) soils are characterized by excessive levels of exchangeable sodium ions on the clay complex, which negatively impacts soil physical structure and chemical properties.

Step 3: Detailed Explanation:
Let us review the standard chemical and physical criteria for sodic (alkali) soils:
1.

pH (C): Sodic soils have a high pH, consistently

greater than 8.5 (often up to 10) due to the hydrolysis of sodium carbonate. Thus, (C) is correct.
2.

Exchangeable Sodium Percentage (ESP) (E): ESP is

greater than or equal to 15 %. Thus, (E) is correct.
3.

Electrical Conductivity (EC) (D): The EC of the saturated soil extract is

less than 4 dS/m (unlike saline soils, which have EC \(\ge\) 4 dS/m). Thus, (D) is incorrect.
4.

Permeability (A): High sodium concentrations cause dispersion of soil clay particles and organic matter. This collapses the soil structure, clogging macropores and resulting in

extremely poor permeability. Thus, (A) is incorrect.
5.

Dominant Salts (B): The soil contains soluble carbonates, bicarbonates, and silicates of sodium. Thus, (B) is correct.
Therefore, only (B), (C), and (E) are correct.

Step 4: Final Answer:
The correct option is 3, which corresponds to (B), (C) and (E) only.