Question

Which of the following conditions define saline soil?
(EC= Electrical conductivity of saturation extract and ESP = Exchangeable Sodium Percentage)

• A. \(\text{EC} 15, \text{pH} = 10.0\)
• B. \(\text{EC} < 4, \text{ESP} < 15, \text{pH} = 8.0\)
• C. \(\text{EC} > 4, \text{ESP} < 15, \text{pH} = 8.0\)
• D. \(\text{EC} > 4, \text{ESP} > 15, \text{pH} = 10.0\)

Hint:

USSL Criteria:
Saline: $\text{EC} > 4$, $\text{ESP} < 15$, $\text{pH} < 8.5$
Sodic: $\text{EC} < 4$, $\text{ESP} > 15$, $\text{pH} > 8.5$
Saline-Sodic: $\text{EC} > 4$, $\text{ESP} > 15$, $\text{pH} \le 8.5$.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The US Salinity Laboratory (USSL, Richards 1954) classifies salt-affected soils into Saline, Sodic (Alkali), and Saline-Sodic categories based on Electrical Conductivity (EC), Exchangeable Sodium Percentage (ESP), and pH.
Key Formula or Approach:
\[ \text{Saline Soil: } \text{EC} > 4\text{ dS/m (at } 25^\circ\text{C)}, \quad \text{ESP} < 15\%, \quad \text{pH} < 8.5 \]

Step 2: Detailed Explanation:
According to the standard USSL diagnostic criteria:
1. Saline Soil (White Alkali): High soluble salts (\(\text{EC} > 4\text{ dS/m}\)), low exchangeable sodium (\(\text{ESP} < 15\%\)), and neutral to slightly alkaline reaction (\(\text{pH} < 8.5\), typically around 7.5 to 8.0).
2. Sodic Alkali Soil (Black Alkali): \(\text{EC} < 4\text{ dS/m}\), \(\text{ESP} > 15\%\), \(\text{pH} > 8.5\) (often up to 10.0).
3. Saline-Sodic Soil: \(\text{EC} > 4\text{ dS/m}\), \(\text{ESP} > 15\%\), \(\text{pH} \approx 8.5\).
4. Normal Soil: \(\text{EC} < 4\text{ dS/m}\), \(\text{ESP} < 15\%\), \(\text{pH} \approx 6.5\text{--}7.5\).
Therefore, the condition defining saline soil is \(\text{EC} > 4\), \(\text{ESP} < 15\), \(\text{pH} = 8.0\).

Step 3: Final Answer:
Hence, the conditions defining saline soil are \(\text{EC} > 4, \text{ESP} < 15, \text{pH} = 8.0\), corresponding to option (C).