Read EC first for salt: FAO calls below 0.7 dS/m free of restriction and above 3 severe. Read SAR together with EC. RSC above 2.5 me/L marks alkali water under IS 11624. Onion and gram are sensitive, wheat is more tolerant. Leach before sowing, use gypsum only for high RSC.
Updated 2026-11-09
See also: Soil health and the Immunity range.
FAO says dS/m and mmho/cm are the same thing. If your report shows µS/cm, divide by 1,000 to get dS/m. RSC in me/L is the same as meq/L.
| Test | Safe or good | Caution | High risk | Source |
|---|---|---|---|---|
| EC (dS/m) | Below 0.7 | 0.7 to 3.0 | Above 3.0 | FAO Paper 29 Rev. 1, Table 1 |
| EC (dS/m) | Below 0.7, good | 0.7 to 3.0, marginally saline | Above 3, saline | IS 11624:2019, Table 1 |
| SAR | Below 10 | No middle class given | Above 10 is a high-SAR class | IS 11624:2019, Table 1 |
| RSC (me/L) | Below 2.5 | 2.5 to 4.0, marginally alkali | Above 4.0, alkali | IS 11624:2019, Table 1 |
| pH | 6.5 to 8.4 is normal | Outside this, look closer | No class given | FAO Paper 29 Rev. 1, Table 1 |
The sources are FAO Irrigation and Drainage Paper 29 Rev. 1 by Ayers and Westcot, and the Bureau of Indian Standards guideline IS 11624:2019, hosted by ICAR-CSSRI Karnal. Limits also differ by region. A CSSRI book on poor quality water records Punjab waters with EC above 4 and RSC above 5 as unsuitable.
FAO says a restriction does not mean the water is unsuitable. It means you must manage more carefully. FAO also assumes good drainage, no water table within 2 metres, and sandy-loam to clay-loam soil. Its limits are too strict for drip.
At the same SAR, saltier water enters soil more easily. FAO gives these limits for water entry into soil.
| SAR | No problem if EC is above | Severe problem if EC is below |
|---|---|---|
| 0 to 3 | 0.7 | 0.2 |
| 3 to 6 | 1.2 | 0.3 |
| 6 to 12 | 1.9 | 0.5 |
| 12 to 20 | 2.9 | 1.3 |
| 20 to 40 | 5.0 | 2.9 |
So water with SAR 8 and EC 0.4 is in the severe class. The same SAR with EC 2.0 has no restriction on water entry, but that EC still counts as a salt caution.
IS 11624 sets upper EC limits by soil and rainfall. These apply only when RSC is below 2.5 and SAR is below 10. The figures below are for 350 to 550 mm of yearly rain. The limits are lower in drier areas and higher in wetter ones.
| Soil (clay percent) | Sensitive crops | Semi-tolerant | Tolerant |
|---|---|---|---|
| Fine (above 30) | 1.0 | 2.0 | 3.0 |
| Moderately fine (20 to 30) | 2.0 | 3.0 | 6.0 |
| Moderately coarse (10 to 20) | 2.5 | 6.0 | 8.0 |
| Coarse (below 10) | 3.0 | 7.5 | 10.0 |
Use the next lower figure if the water table comes within 1.5 metres in kharif, or if the soil has a hard layer.
| Crop | Water EC for full yield (FAO) | Water EC for 90% yield (FAO) | Salt group in IS 11624 |
|---|---|---|---|
| Wheat | 4.0 | 4.9 | Medium tolerant |
| Potato | 1.1 | 1.7 | Not listed |
| Onion | 0.8 | 1.2 | Highly sensitive |
| Gram (chickpea) | Not given | Not given | Highly sensitive |
| Cumin | Not listed | Not listed | Not listed |
The EC figures come from FAO Table 4 and assume 15 to 20 percent of the water drains below the roots. They are a guide, not a promise of yield. FAO rates chickpea and potato moderately sensitive. FAO also warns that wheat is less tolerant at germination, and upper soil ECe should stay below 4 to 5 dS/m then.
For sodium, wheat is far more tolerant than gram or onion. IS 11624 Table 8 puts wheat at ESP 30 to 50, chickpea at 16 to 20 and onion at 20 to 25. ESP means exchangeable sodium percentage, a soil test.
Evidence on cumin is thin. In a pot study at CAZRI, Jodhpur, water of EC 10 cut seed yield in all five genotypes, by about 24% in the best and over 50% in the worst. In a study in Iran, the authors called EC 5 the upper limit for an economic crop. Varieties differ, so ask your KVK or state agricultural university.
In Gujarat, the main problem may be salt, not RSC. A Junagadh Agricultural University survey of 180 wells in Gir Somnath found EC from 1.15 to 12.39 dS/m, yet 92.2% of samples were safe for RSC. That is one district, so your well may differ.
Gypsum is for high RSC and sodium. It does not take salt out of water. FAO says it is especially effective when water EC is below 0.5 and much less effective in very salty water.
FAO's figure is that 1 me/L of calcium needs 86 kg of pure gypsum per 1,000 cubic metres of water. That is 10 cm of water on one hectare. As an example, to bring RSC 6 down to 2.5, the sum is 3.5 x 86, or about 301 kg of pure gypsum. At 70% purity it is about 430 kg. Ask your lab or KVK to confirm your target.
Gypsum can go in a bed, or as clods in the water channel. A model chamber design on TNAU Agritech uses 25 to 50 mm lumps and is refilled after 40 to 50 hours of running. One review says wheat after rice usually responds when RSC is above 5, but on light soils with fallow kharif it may not respond below 10. Do not add sulphur to irrigation water: FAO calls it not satisfactory for water application. Gypsum supply and subsidy differ by state and change over time, so check with your state agriculture department.
A guide on Punjab's agriculture website says to run the tube well for half an hour, and TNAU's KVK advice says 10 to 15 minutes for bore wells. Rinse a clean bottle with the same water, fill it, and write your name, village, well depth, crop and soil type. See also our soil health page.
We have worked with farmers since 2006 and make biostimulants at our own plant at GIDC Shihor, Bhavnagar. No biostimulant, ours included, takes salt out of water. Fix the water plan first.
Send us a photo of your water report with your soil type, crop and any second water source. We will help you read it. Our number is +91 99787 91167 (call or WhatsApp).
By Gafar Laiya, founder of Gujarat Bio Organics, working with farmers since 2006. Results differ from farm to farm with soil, weather, crop and management. Farmer experiences on this site are their own reports, not a promise of results.
Yes. The water report shows what you are adding to the field. A soil test shows what has already built up. FAO estimates root zone salt from water salt only by assuming 15 to 20 percent of the water drains below the roots, and many fields do not match that.
FAO pairs TDS with EC in the same table. Below 450 mg/L matches the no-restriction class, 450 to 2,000 mg/L the slight to moderate class, and above 2,000 mg/L the severe class.
Yes. FAO says water with EC below 0.2 dS/m almost always causes water entry problems, because it washes calcium and salts from the surface soil. The soil then disperses and seals.
IS 11624 says water of EC 4 dS/m or more should be kept for winter-season crops. In an emergency it allows no more than one or two protective irrigations to kharif crops.
IS 11624 rates boron below 1.0 mg/L as low, and above 4.0 mg/L as very high. Its crop table lists wheat and potato as semi-tolerant (1.0 to 2.0 mg/L) and onion as tolerant (2.0 to 4.0 mg/L).
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