Question

In the irrigation water quality classification, high salinity class represents EC (dS/m) in the range of-

• A. 0--0.25
• B. 0.25--0.75
• C. 0.50--0.75
• D. 0.75--2.25

Hint:

Salinity Scale for Irrigation:
C1: $< 0.25$
C2: $0.25 - 0.75$
C3: $0.75 - 2.25$ (The "Danger Zone")
C4: $> 2.25$

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks for the range of Electrical Conductivity (EC) that defines "High Salinity" water according to the standard US Salinity Laboratory (USSL) classification for irrigation.
Detailed Explanation:

• USSL Classification System:
Irrigation water is classified into four groups based on its salinity hazard (EC) and sodium hazard (SAR). Salinity is designated by the letter 'C'.

• Specific EC Ranges:
C1 (Low Salinity): EC $< 0.25$ dS/m ($250$ $\mu$mhos/cm). Safe for most crops on most soils.
C2 (Medium Salinity): EC $0.25$ to $0.75$ dS/m ($250$--$750$ $\mu$mhos/cm). Can be used if a moderate amount of leaching occurs.
C3 (High Salinity): EC 0.75 to 2.25 dS/m ($750$--$2250$ $\mu$mhos/cm). Cannot be used on soils with restricted drainage. Even with adequate drainage, special management for salinity control may be required.
C4 (Very High Salinity): EC $> 2.25$ dS/m ($>2250$ $\mu$mhos/cm). Generally not suitable for irrigation.

• Agronomic Impact:
Using C3 water regularly increases the salt concentration in the root zone, making it harder for plants to absorb water due to osmotic stress. Only salt-tolerant crops should be grown with such water.

• Unit Conversion:
Note that $1$ dS/m is equal to $1000$ $\mu$mhos/cm. The options are provided in dS/m.

Step 2: Final Answer: The "High Salinity" (C3) class encompasses the range of $0.75$ to $2.25$ dS/m.