Salt Tolerance & Plant What Survives the Salinity

It is a two-segment (piecewise-linear) curve. A crop holds 100% of its yield until soil salinity reaches its threshold ECe; above that, relative yield falls by a fixed slope percentage for every extra 1 dS/m. So relative yield = 100 − slope × (ECe − threshold), clamped at zero. Cotton, for example, has a 7.7 dS/m threshold and a 5.2% per dS/m slope, while beans drop 19% per dS/m above just 1.0 dS/m.

At ECe 4 dS/m the tolerant and moderately tolerant crops are safe: barley, cotton, sugar beet, bermuda grass and wheat all retain close to full yield. Moderately sensitive crops like maize, tomato and alfalfa lose roughly 25–40%, and sensitive crops such as beans, carrots, strawberries and most fruit trees lose more than half. The ranking rail sorts every crop by the exact yield it retains at your ECe.

ECe is the electrical conductivity of the saturated-paste extract of the soil — the salinity the roots actually feel — measured in deciSiemens per metre (dS/m). ECw is the conductivity of the irrigation water. As a rule of thumb at a 15–20% leaching fraction, root-zone ECe is about 1.5 × ECw, so 2 dS/m water gives roughly 3 dS/m soil. The calculator converts ECw to ECe for you.

Only if you match the crop to the salinity. A salt-sensitive crop on ECe 6 dS/m soil may retain barely 40% of its potential, so a 4 t/acre target collapses to under 2 t. Pick a tolerant crop — barley keeps full yield to 8 dS/m — or leach the salts down before sowing. The tool shows the exact retained-yield percent so you can set a realistic target.

It is the maximum soil salinity a crop tolerates with no measurable yield loss. Below it the Maas–Hoffman curve is flat at 100%. Tolerant crops have high thresholds (barley 8.0, cotton 7.7, sugar beet 7.0 dS/m); sensitive crops have low ones (beans and carrots 1.0, strawberry 1.0 dS/m). Keeping root-zone ECe under the threshold is the cheapest way to protect yield.

For most agricultural waters and soils, 1 dS/m is approximately 640 ppm (mg/L) of total dissolved salts. So 1,280 ppm ≈ 2 dS/m. The conversion drifts a little with salt composition, but 640 is the standard factor used in FAO guidelines, so enter your reading in dS/m after dividing ppm by 640.

Among the field crops, barley is the benchmark (threshold 8.0 dS/m, slope 5%), followed by cotton, sugar beet, triticale and guar. Tall wheatgrass and bermuda grass top the forages, and the date palm is the standout fruit. These crops are the right choice when leaching is impractical and the soil is already saline.

The slope is how fast yield falls once salinity passes the threshold. A 5% slope means each extra dS/m costs 5 percentage points of yield; a 19% slope (beans) means the same 1 dS/m costs nearly four times as much. So two crops with the same threshold can behave very differently — always read the threshold and the slope together, which the tool charts for you.

Yes — applying water beyond the crop's need (a leaching fraction) flushes salts below the root zone, lowering ECe. Improving drainage, adding gypsum on sodic soils, and avoiding salty irrigation water all help. The calculator's threshold tells you the ECe target to leach down to; if leaching is impractical, switch to a more tolerant crop from the ranking.

Yield hits zero when ECe = threshold + 100 ÷ slope. For beans that is 1.0 + 100÷19 ≈ 6.3 dS/m; for barley it is 8.0 + 100÷5 = 28 dS/m. The 50%-yield point (threshold + 50÷slope) is the more useful planning figure, and the tool reports it for the focused crop.

Rarely. Salts concentrate in low spots, near the soil surface as water evaporates, and at the far end of furrows. A single ECe number is an average, so sample several spots and use the highest reading for sensitive crops. The model assumes a steady root-zone ECe, which is the standard FAO basis for these threshold and slope values.

From Maas & Hoffman's 1977 review of field salt-tolerance trials, as tabulated in FAO Irrigation & Drainage Paper 29 Revision 1 (Ayers & Westcot, 1985) Table 4 and Paper 61. They are field means for ECe (saturated-paste extract). Variety, climate, growth stage and salt composition shift the real numbers, so treat the output as a well-grounded planning estimate, not a guarantee.