Irrigation is a slow experiment in evaporation. The water leaves; the salt it carried stays. Repeat for a few decades without drainage and the field crosses a line — a threshold measured in decisiemens per metre — after which the crop simply stops taking up water. In 2024 the FAO finished counting how much land has already crossed it.
1.38 billion
Hectares of salt-affected soil
10.7% of Earth's total land surface is salt-affected — and roughly another billion hectares is at risk. This is the first global assessment of salt-affected soils in 50 years. FAO, Global Status of Salt-Affected Soils, 2024
10%
of the world's irrigated cropland is salt-affected — and 10% of rainfed cropland too FAO 2024
2,000 ha
of irrigated land degraded by salt every day, on average, for over 20 years across 75 countries Qadir et al. 2014
70%
yield loss possible for rice and beans under salinity stress in the worst-affected countries FAO 2024
01 — The measure
Salinity has a number, and crops have a threshold
Soil salinity is measured as the electrical conductivity of a saturated soil paste extract — ECe, in decisiemens per metre. Salt conducts; the meter counts it. Zero to two is ordinary farmland. Past sixteen, almost nothing agricultural survives. Seawater, for scale, sits around 50–60 dS/m — far off the right edge of this strip.
Bean 1.0
Rice 3.0
Wheat 6.0
Barley 8.0
0pure water
2
4
8
16
20 dS/mand beyond
0–2Non‑saline
2–4Very slightly saline
4–8Slightly saline
8–16Moderately saline
16+Strongly saline
Salinity classes: USDA salinity classification (Handbook 60 / Soil Survey lineage). Crop thresholds: Maas & Grattan 1999, reproduced in FAO Irrigation & Drainage Annex 1. Gradient is a visual scale, not a measured colour.
02 — Tolerance
Some crops drink brine. Most cannot.
Each crop has a threshold ECe below which yield is untouched, and above which it falls at a fixed percentage per additional dS/m. Barley shrugs off eight. Beans and strawberries begin losing yield at one — which is to say, at salinity most farmers would never think to test for.
Barley
8.0
Cotton
7.7
Sugar beet
7.0
Sorghum
6.8
Wheat
6.0
Soybean
5.0
Rice (paddy)
3.0
Maize
1.7
Sugarcane
1.7
Onion
1.2
Bean
1.0
Strawberry
1.0
Threshold ECe, dS/m · 09
Above the threshold, loss is steep: rice sheds 12% of yield per extra dS/m, beans 19%, strawberries 33%. Source: Maas & Grattan 1999, FAO crop salt tolerance tables.
03 — Geography
Ten countries hold seven-tenths of it
Salt-affected soil clusters where evaporation outruns rainfall: continental interiors, irrigated deserts, and old inland basins with nowhere for water to drain. Ten countries account for about 70% of the world total.
01United States
02Argentina
03Sudan
04Russian Fed.
05Kazakhstan
06Uzbekistan
07Iran
08Afghanistan
09China
10Australia
Schematic map — country shapes are hand-simplified, not survey-accurate. Highlighting marks presence, not per-country area. Source: FAO, Global Status of Salt-Affected Soils, 2024.
04 — The rate
Two thousand hectares a day
The clearest long-run number comes from irrigated land specifically. In the early 1990s about 45 million hectares of the world's irrigated area was salt-damaged. By 2013 it was roughly 62 million — about a fifth of all irrigated land, an area the size of France, accumulating at an average of 2,000 hectares every single day.
Measured points: Qadir et al., Economics of salt-induced land degradation and restoration, Natural Resources Forum, 2014 (UNU-INWEH). The dashed segment is an illustrative extrapolation of the stated 2,000 ha/day rate — not a published projection.
05 — The bill
What salt costs, in money and in people
Salinity does not destroy land dramatically. It shaves yields, raises treatment costs, corrodes pipes, and pushes people off marginal fields — a slow tax that shows up in national accounts long before it shows up in headlines.
$27.3B
Estimated annual global loss in crop production from salt-induced degradation of irrigated land.
Qadir et al., Natural Resources Forum, 2014
$332M
Quantified damages per year from salinity in Colorado River water in the United States — projected at $631M/yr without the basin's salinity control program.
US Bureau of Reclamation, Feb 2024
~20M
People along coastal Bangladesh exposed to elevated salinity in drinking water drawn from natural sources, as seawater pushes inland.
Khan et al., Environmental Health Perspectives, 2011
$3.0B
Estimated yearly economic loss in India alone from roughly 6.73 million hectares of un-reclaimed salt-affected soil.
ICAR-CSSRI, via peer-reviewed review, 2020
06 — Ahead
The dry places get drier, and saltier
Salinity is a water-balance problem, so warming moves it. Every figure below is modelled, not measured — but they point the same direction, and they point at the drylands.
24–32%
Share of the total global land surface that could become salt-affected under the existing temperature-increase trend, per global aridity modelling — up from 10.7% today.
Modelled · FAO 2024
+24.9%
Projected mean increase in dryland soil ECe in Botswana by 2071–2100 under SSP5-8.5; South Africa +21.4%, Namibia +17.7%, Brazil +16.2%.
Modelled · Hassani et al. 2021
16.2 Mha
India's projected salt-affected area by 2050 — from 6.73 Mha today, via 11 Mha by 2030, if current trends continue.
Projection · ICAR-CSSRI Vision 2050
Note: the FAO 1970s-era global figure of ~932 Mha and today's 1,381 Mha come from different methods and sensing technology; they are not a clean like-for-like time series, which is exactly why the 2024 assessment was needed.
Why it matters
Salt is reversible — drainage is the whole game
Unlike eroded topsoil, salt can be leached back out. What it takes is water you can afford to lose and somewhere for it to go. Nearly every salinized irrigation scheme on Earth was built with the first and without the second.
Measure before you treat
An ECe reading from a saturated paste extract costs almost nothing and tells you which side of a crop's threshold your field is on. Salinity is invisible until yields drop by a third.
Drainage, not just water
Irrigation without a drain concentrates salt in the root zone by design. Subsurface drains, mulching and loose interlayers are the FAO-listed mitigations.
Match the crop to the number
Barley at 8.0 dS/m, cotton at 7.7, sugar beet at 7.0: on land already past 4, switching crop is cheaper than reclaiming soil.
Watch the coast
Sea-level rise puts more than a billion people in coastal zones at risk of salinity intrusion into soil and drinking water by century's end, per the FAO assessment.
Sources & notes
FAO (2024). Global Status of Salt-Affected Soils — 1,381 Mha (10.7% of global land); +1 Bha at risk; 10% of irrigated and 10% of rainfed cropland; up to 70% yield loss in rice/beans; ten countries = ~70% of total; 24–32% of land surface under current warming trend (modelled); >1 billion people in coastal zones at risk.
Qadir, M. et al. (2014). "Economics of salt-induced land degradation and restoration," Natural Resources Forum 38:282–295 (UNU-INWEH) — 2,000 ha/day across 75 countries; 62 Mha of irrigated land salt-affected, up from 45 Mha in the early 1990s; US$27.3 billion/yr in lost crop production.
Maas, E.V. & Grattan, S.R. (1999), updating FAO Irrigation & Drainage Paper 29 — crop salt tolerance thresholds and yield-decline slopes (Annex 1 crop salt tolerance data, FAO).
US Bureau of Reclamation, news release, 12 Feb 2024 — quantified Colorado River salinity damages ≈$332M/yr; ≈$631M/yr without the Colorado River Basin Salinity Control Program.
Khan, A.E. et al. (2011). "Drinking Water Salinity and Maternal Health in Coastal Bangladesh," Environmental Health Perspectives 119(9) — ~20 million people along the coast exposed to varying degrees of drinking-water salinity.
Hassani, A., Azapagic, A. & Shokri, N. (2021). "Global predictions of primary soil salinization under changing climate in the 21st century," Nature Communications 12:6663 — projected ECe increases, 2071–2100 vs baseline, SSP5-8.5 (modelled).
ICAR-CSSRI (Central Soil Salinity Research Institute) Vision 2050 and associated peer-reviewed reviews — India at 6.73 Mha salt-affected; projected 11 Mha by 2030 and 16.2 Mha by 2050; ~US$3.0 billion in annual losses.
Abrol, I.P. et al. (1988), FAO Soils Bulletin 39, compiling Szabolcs (1974) and Massoud (1977) — the ~932 Mha 1970s-era global estimate, shown here only as a methodological contrast.
FLAGGED AS MODELLED OR ILLUSTRATIVE: the 24–32% land-surface figure (aridity modelling); the Hassani et al. ECe percentages (climate-scenario model output); the ICAR-CSSRI 2030/2050 areas (projection); the dashed segment of the trend chart (our own illustrative extrapolation of a published daily rate, not a published forecast). The seawater reference of ~50–60 dS/m is a standard oceanographic conductivity range given for scale only. Uncertainty in cropland shares remains high, as the FAO report itself states.