Soil salinity (EC): measurement, interpretation and leaching requirement

Full article available in Uzbek and Russian.

Soil salinity (EC): the short version

A field EC meter and a lab result are not the same measurement. Field probes (capacitance/FDR sensors, 1:5 soil-water extracts) read bulk or diluted EC, which depends on moisture and soil texture. The agronomic reference standard is ECe — EC of a saturated paste extract — and it's what crop tolerance tables are built on. A rough conversion is ECe ≈ EC(1:5) × 5–8, depending on soil texture.

Salinity classes (ECe, dS/m): non-saline < 2, slightly saline 2–4, moderately saline 4–8, strongly saline 8–16, very strongly saline > 16.

Crop thresholds (approximate ECe where yield starts dropping): beans/onion ~1.0–1.2, maize ~1.7, alfalfa ~2.0, tomato ~2.5, wheat ~6.0, sugar beet ~7.0, cotton ~7.7 (relatively tolerant), barley ~8.0 (most tolerant cereal). Beyond threshold, yield typically falls 5–15% per additional dS/m.

Leaching requirement (LR) — the extra irrigation water needed to push salts below the root zone:

LR = ECw / (5 × ECe − ECw)
Total irrigation = ETc / (1 − LR)

Example: irrigation water ECw = 2.0 dS/m, wheat threshold ECe = 6.0 → LR ≈ 7.1%. For ETc = 600 mm, total water ≈ 646 mm.

In Uzbekistan, leaching is standard practice in autumn-winter (after harvest, before spring planting), when evaporation is low. It only works if drainage is functioning — otherwise leached salts rise back with the water table.

Approximate figures based on general agrochemical literature (FAO, USDA); verify against your local soil lab and irrigation authority.