Table 6.
Guidelines for water quality parameters for irrigation (
modified from FAO, 1985)
| Probable irrigation limitation | Units | Degree of restriction on use | |||||
|---|---|---|---|---|---|---|---|
| None | Slight to moderate | Severe | |||||
| Salinity (mediate water availability) | |||||||
| ECw | dS m−1 | < 0.7 | 0.7–3.0 | > 3.0 | |||
| TDS | mg L−1 | < 450 | 450–2000 | > 2000 | |||
| SAR | = 0–3 | > 0.7 | 0.7 – 0.2 | < 0.2 | |||
| = 3–6 | > 1.2 | 1.2–0.3 | < 0.3 | ||||
| = 6–12 | > 1.9 | 1.9–0.5 | < 0.5 | ||||
| = 12–20 | > 2.9 | 2.9–1.3 | < 1.3 | ||||
| = 20–40 | > 5.0 | 5.0–2.9 | < 2.9 | ||||
| Specific ion toxicity (affects sensitive crops) | |||||||
| Sodium (Na) | |||||||
| Surface irrigation | SAR | < 3 | 3–9 | > 9 | |||
| Sprinkler irrigation | mgL−1 | < 3 | > 3 | ||||
| Chloride (Cl) | |||||||
| Surface irrigation | mgL−1 | < 4 | 4–10 | > 10 | |||
| Sprinkler irrigation | mgL−1 | < 3 | > 3 | ||||
| Boron (B) | mgL−1 | < 0.7 | 0.7–3.0 | > 3.0 | |||
| Miscellaneous effects | |||||||
| Nitrogen (NO3—N) | mgL−1 | < 5 | 5–30 | > 30 | |||
| Bicarbonate (HCO3) | mgL−1 | < 1.5 | 1.5–8.5 | > 8.5 | |||
| pH | Normal range 6.5–8.4 | ||||||