Classification of Irrigation Water
Several different measurements are used to classify the suitability of water for irrigation, including ECiw, the total dissolved solids, and SAR. Some permissible limits for classes of irrigation water are given in Table 4 . In Table 5, the sodium hazard of water is ranked from low to very high based on SAR values.
Table 4. Permissible limits for classes of irrigation water
|
Classes of Water |
Concentrations, Total Dissolved Salts | |
| Electrical conductivity mhos* |
Gravimetric ppm | |
| Class 1. Excellent | 250 | 175 |
| Class 2. Good | 250 - 750 | 175 - 525 |
| Class 3. Permissible1 | 750 - 2,000 | 525 - 1,400 |
| Class 4. Doubtful2 | 2,000 - 3,000 | 1,400 - 2,100 |
| Class 5. Unsuitable2 | 3,000 | 2,100 |
| *Micromhos/cm at 25 degrees C.
1Leaching needed if used. 2Good drainage needed and sensitive plants will have difficulty obtaining stands | ||
Table 5. The sodium hazard of water based on SAR values
| SAR Values | Sodium Hazard of Water | Comments |
| 1 - 10 | Low | Use on sodium sensitive crops such as avocados |
| 10 - 18 | Medium | Amendments (such as Gypsum) and leaching needed |
| 18 - 26 | High | Generally unsuitable for continuous use |
| > 26 | Very High | Generally unsuitable for use |