Irrigation water having the concentration of Na++, Ca++ and Mg++ as 20, 3 and 1 Milli equivalent per litre respectively will be classified as

Answer: Option D

Irrigation water is classified based on its sodium concentration relative to the concentrations of calcium and magnesium ions. The classification is determined by the sodium absorption ratio (SAR), which is calculated using the following formula:

SAR = (Na⁺⁺ / √(Ca⁺⁺ + Mg⁺⁺)) * 100

Given the concentrations provided:

Na⁺⁺ = 20 meq/L
Ca⁺⁺ = 3 meq/L
Mg⁺⁺ = 1 meq/L


Plugging these values into the SAR formula:
SAR = (20 / √(3 + 1)) * 100
SAR ≈ (20 / √4) * 100
SAR ≈ (20 / 2) * 100
SAR ≈ 10 * 100
SAR ≈ 1000

According to the classification:

SAR < 10: Low sodium water
10 ≤ SAR < 18: Medium sodium water
18 ≤ SAR < 26: High sodium water
SAR ≥ 26: Very high sodium water

Since the calculated SAR is approximately 100, the irrigation water falls into the category of very high sodium water.