Salinity, sodicity, and when soil analysis is required
Quick answer. Salinity and sodicity are not the same thing. Salinity is the total concentration of soluble salts, measured as ECe, and it damages plants osmotically — making water harder to take up even when the soil is wet. Sodicity is the proportion of sodium on the exchange complex, measured as ESP or SAR, and it damages soil structure. They need different measurements and different remedies, and a crop tolerant of one is not necessarily tolerant of the other.
Why the distinction is not academic
The clearest illustration is in this library's own crop guides. FAO's Table 26 ranks crops by tolerance to exchangeable sodium percentage: beets at 50–60, garlic at 25–30, onion at 20–25, peas at 10–15 — the most sensitive class in the table. Those figures describe sodicity only.
Reading beetroot's high ESP tolerance as permission to irrigate with saline water is a serious error, and an expensive one, because it looks like it is supported by a source. The source says nothing of the kind. If you take one thing from this page: the ESP figure and the ECe figure answer different questions.
What each problem does
Salinity raises the osmotic pressure of the soil solution, so a plant must work harder to extract water. The symptoms — stunting, leaf-margin scorch, poor growth despite adequate irrigation and feeding — resemble drought and resemble deficiency, which is why salinity is so frequently misdiagnosed and then "treated" with more fertiliser, which adds salts and worsens it.
Sodicity is a structural problem. Sodium held on the exchange complex disperses soil aggregates, and a dispersed soil loses its pore structure — it seals, infiltration collapses, and the soil becomes both waterlogged and hard. FAO notes that among cations, sodium is held most loosely on the exchange complex, which is relevant to how it is displaced.
Where the salts come from here
Frequently, the irrigation water. FAO lists occasional excess of soluble salts, adsorbed sodium and boron among the special problems of nutrient management in arid soils. Every irrigation with saline water adds salt, and in a climate where most of the water applied evaporates or transpires rather than draining through, what is left behind accumulates.
This is why containers are especially vulnerable — a closed volume with no through-drainage accumulates continuously — and why leaching, applying enough water that some drains through and carries salts below the root zone, is a routine practice rather than an emergency measure. Leaching requires drainage to work; on a soil with a hardpan or lime crust there is nowhere for the salts to go.
When analysis is required — not optional
This library declines to state fertiliser rates because they cannot be responsibly given without analysis. There are specific situations where testing is not merely advisable:
- Before establishing any permanent planting — a tree or palm will live with the site for decades.
- When symptoms suggest salinity, sodicity, or a micronutrient problem — because deficiency and toxicity produce similar-looking damage and opposite remedies.
- Before applying boron or molybdenum, always. The margin between sufficiency and toxicity in boron is narrower than for any other nutrient covered here, and local irrigation water may already supply more than the crop needs. FAO names boron for the brassica family and requires deficiency to be confirmed first.
- Before applying an amendment such as gypsum, which addresses sodicity and is the wrong response to salinity alone.
- When importing soil or compost for a raised bed or container, since imported material can arrive saline.
- Periodically under irrigation with water of known or unknown salt content, because accumulation is gradual and invisible until it is severe.
What to ask for
At minimum: pH, ECe (salinity), and — where sodicity is suspected or the soil seals and infiltrates poorly — ESP or SAR. An analysis of the irrigation water alongside the soil, since in this region the water is often the source. Boron specifically, before any consideration of applying it.
This is the stopping point for self-diagnosis. Salt injury, drought, wind scorch, potassium shortage and heat damage all produce leaf-margin browning, and they are corrected by five different actions — one of which (adding fertiliser) makes salinity worse. No photograph and no symptom list can distinguish them. A visual symptom alone is not a confirmed diagnosis. Where a salinity or sodicity problem is confirmed, the remedy involves leaching, drainage and possibly amendments, and should be planned with a qualified agronomist rather than attempted from a general guide.
Sources
FAO — Fertilizer and Plant Nutrition Bulletin 16, Table 26 (relative tolerance of crops to exchangeable sodium percentage; Tyagi 2000, Gupta and Abrol 1990), Chapter 4 (cation exchange complex and relative bonding strength; CEC), Chapter 5 (special problems of nutrient management in arid soils; soil amendments including gypsum), Chapters 3 and 7. Accessed 27 August 2026. No threshold, rate, amendment quantity or leaching volume is stated — these require site-specific analysis.
Last reviewed 27 August 2026