Which of the following indicate good irrigation water quality? 1.Low SAR 2.High EC 3.Low sodium % 4.High residual sodium carbonate
- A1 and 3 onlyCorrect
- B2 and 4 only
- C1, 3 and 4 only
- DAll of the above
Solution
Concept
Evaluation of irrigation water quality based on salinity (EC), sodicity (SAR, Sodium percentage), and alkalinity (RSC).
Formula
SAR = Na / √((Ca + Mg)/2)
Step-by-step solution
1. Understand the parameters affecting irrigation water quality: Salinity (measured by Electrical Conductivity - EC), Sodium hazard (measured by Sodium Adsorption Ratio - SAR and Sodium percentage), and Bicarbonate hazard (measured by Residual Sodium Carbonate - RSC). 2. Low EC indicates low total dissolved solids, which is desirable (High EC causes high salinity and osmotic stress). 3. Low SAR and low sodium percentage prevent the replacement of calcium and magnesium in soil by sodium, thus maintaining soil structure and permeability. 4. High RSC leads to the precipitation of calcium and magnesium, increasing relative sodium concentration, which is undesirable. 5. Therefore, statements 1 and 3 indicate good irrigation water quality.
Explanation
Good quality irrigation water should have low Electrical Conductivity (EC) indicating low salinity, low Sodium Adsorption Ratio (SAR) and low sodium percentage to prevent soil sodicity and permeability reduction. High Residual Sodium Carbonate (RSC) and high EC are harmful to crops and soil structure.
Why the other options are wrong
2: High EC means high salinity, which is harmful to crops. 4: High residual sodium carbonate (RSC) causes soil sodicity and is harmful.
Shortcut
Remember: For good irrigation water, 'Low' is good for SAR, Sodium %, EC, and RSC.
Common mistake
Confusing high EC with good water quality; high EC actually means high salinity, which is harmful to plants.
Correct answer: A) 1 and 3 only