Question

Which one of the following standard sets of values for pH, EC, and ESP respectively for saline-alkaline soils is correct?

• A. \(> 8.5, 15\)
• B. \(< 8.5, < 4.0\text{ dSm}^{-1}\text{ and } < 15\)
• C. \(> 8.5, > 4.0\text{ dSm}^{-1}\text{ and } < 15\)
• D. \( 4.0\text{ dSm}^{-1}\text{ and } > 15\)

Hint:

Saline-Alkali soil criteria: $EC > 4.0\text{ dS/m}$, $ESP > 15\%$, $\text{pH} < 8.5$ (or $\approx 8.5$).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The US Salinity Laboratory (USSL) criteria classify salt-affected soils into Saline, Sodic (Alkali), and Saline-Sodic (Saline-Alkaline) based on pH, Electrical Conductivity ($EC$), and Exchangeable Sodium Percentage ($ESP$).
Key Formula or Approach:
\[ \text{Saline-Sodic Soil: } EC > 4.0\text{ dS/m}, \quad ESP > 15\%, \quad \text{pH} \le 8.5 \text{ (or } \approx 8.5\text{)} \]

Step 2: Detailed Explanation:
According to USSL diagnostics:
1. Saline Soils: \(EC > 4.0\text{ dS/m}\), \(ESP < 15\%\), \(\text{pH} < 8.5\).
2. Sodic (Alkali) Soils: \(EC < 4.0\text{ dS/m}\), \(ESP > 15\%\), \(\text{pH} > 8.5\).
3. Saline-Alkali Saline-Sodic Soils: \(EC > 4.0\text{ dS/m}\), \(ESP > 15\%\), and \(\text{pH} < 8.5\) (or variable near 8.5 due to excess neutral soluble salts buffering the pH).

Step 3: Final Answer:
Thus, the correct set of values is \( 4.0\text{ dSm}^{-1}\text{ and } > 15\), corresponding to option (D).