Soil salinity is measured by testing the electrical conductivity (EC) of a soil-water mixture. The more dissolved salts in the solution, the more easily it conducts electricity, giving you a direct reading of salt concentration. Results are reported in deciSiemens per meter (dS/m), and you can convert that to parts per million by multiplying by 640. The method you choose depends on whether you need a quick field estimate or a lab-grade number.
The Saturated Paste Extract: The Reference Standard
The saturated paste extract is the benchmark method used by soil labs worldwide. All crop salt tolerance data published by the FAO and USDA are referenced to this method, so if you want results you can compare directly to published thresholds, this is the one to use.
To prepare the paste, add distilled water to about 250 grams of soil while stirring with a spatula. Tap the container on your workbench periodically to consolidate the mixture. You’ve hit saturation when the paste glistens under light, flows slightly when you tilt the container, and slides cleanly off the spatula. Let it sit for at least an hour, then recheck. If the surface has lost its shine or the paste has stiffened, add more water and remix. If free water pools on top, you’ve gone too far and need to mix in dry soil.
Once the paste is ready, transfer it onto a filter funnel lined with filter paper and apply vacuum suction. Collect the liquid that passes through. If the first bit of filtrate looks cloudy, discard it or run it through again. Stop the vacuum when air starts passing through the filter. You then measure the electrical conductivity of this extracted liquid with an EC meter. For a basic salinity assessment, you can extract within minutes of making the paste. If you also need a full chemical analysis of the dissolved salts, let the paste sit 4 to 16 hours before extracting.
Dilution Methods for Quicker Results
When you don’t need the precision of a saturated paste, soil-to-water dilution ratios offer a faster alternative. The most common ratios are 1:1, 1:2, and 1:5 (soil to water by weight or volume). You mix the soil and distilled water at the chosen ratio, stir, let it settle, and measure the EC of the liquid.
A 1:1 ratio (equal parts soil and water) is popular for field work because it’s simple and repeatable. A 1:5 ratio uses more water relative to soil, which dilutes the salts further and produces a lower EC reading. This is important to understand: a 1:5 extract will always read lower than a saturated paste extract from the same soil. You can’t directly compare numbers across different methods without applying a conversion factor, and those factors vary by soil texture. If you’re using published crop tolerance thresholds, make sure you know which extraction method those thresholds were based on.
Using a Handheld EC Meter
Regardless of which extraction method you use, the actual measurement happens with an electrical conductivity meter. Handheld models range from simple pen-style devices to more advanced units, but the calibration process is similar across all of them.
Before measuring, calibrate the meter with a standard solution of known EC value. Rinse the probe with distilled water first, then dip it into the calibration solution. Never dip the probe directly into the stock bottle of calibration solution, as repeated dipping will contaminate it over time. Pour a small amount into a clean, dry cup instead, or use a single-use calibration sachet. Check that your calibration solutions haven’t expired. If the meter has been sitting unused for a long time, soak the probe in storage solution for at least an hour before calibrating, since the electrode dries out and needs rehydration to read accurately.
Rinse the probe with distilled water between the calibration step and your soil extract measurement. Then place the probe in your extract, wait for a stable reading, and record the value.
Why Temperature Matters
Electrical conductivity changes with temperature. Warmer solutions conduct electricity more readily, so the same soil extract will give a higher reading on a hot day than a cool one. The standard reference temperature for EC measurements is 25°C (77°F). Most modern meters have built-in temperature compensation that automatically adjusts the reading to what it would be at 25°C. If yours doesn’t, note the temperature of your solution alongside the EC value so you can correct it later.
Temperature also affects field sensors left in the ground for continuous monitoring. Research on soil capacitance sensors has shown that a 10°C swing in soil temperature can shift readings enough to mimic a meaningful change in soil moisture or salt content. If you’re tracking salinity over time with buried sensors, temperature correction is essential to avoid misinterpreting seasonal swings as actual changes in salt levels.
Mapping Salinity Across a Field
Taking individual soil samples works for a garden or a small plot, but it’s impractical for mapping salinity patterns across a large farm. Electromagnetic induction (EMI) sensors solve this problem. These handheld or vehicle-mounted instruments measure the apparent electrical conductivity of the soil below without making direct contact. You walk or drive across the field, and the sensor collects georeferenced data points continuously.
EMI was first used in agriculture specifically for salinity assessment in the late 1970s and early 1980s. It has since expanded to map soil texture, water content, compaction, and organic matter. The strength of EMI is the sheer volume of data it produces. Rather than interpolating between a handful of sample points, you get a dense, spatially detailed map that reveals salt accumulation patterns, diffuse boundaries between soil types, and problem areas you might otherwise miss. One limitation: apparent conductivity responds to clay content and moisture as well as salt, so EMI readings need to be ground-truthed with a few lab-analyzed samples to confirm that the signal you’re seeing is actually salinity.
Interpreting Your Results
Once you have an EC value from a saturated paste extract, you can compare it against published crop tolerance data. The FAO classifies crops into four salt tolerance categories, each with a threshold EC (in dS/m) below which no yield loss occurs.
- Sensitive crops start losing yield at low EC levels. Common beans and strawberries have thresholds around 1.0 dS/m; rice tolerates up to about 3.0 dS/m.
- Moderately sensitive crops like peanuts can handle roughly 3.2 dS/m before yields decline.
- Moderately tolerant crops such as sorghum hold up to about 6.8 dS/m, and sugar beet can reach 7.0 dS/m.
- Tolerant crops like barley (8.0 dS/m) and rye (up to 11.4 dS/m) can produce in soils that would devastate most other plants.
These thresholds represent the point where yield begins to drop. Above the threshold, yield declines roughly in proportion to the increase in salinity. So a reading of 4 dS/m might be perfectly fine for barley but could already be cutting into your bean harvest significantly.
Spotting Salinity Without a Meter
You can sometimes identify a salinity problem before you test. White crystalline crusts on the soil surface after it dries are a classic sign of salt accumulation. In plants, high salinity causes leaf margin burn (the edges of leaves turn brown and crispy), stunted growth, and wilting that looks like drought stress even when the soil is moist. In severe cases, plants die outright. These visual clues tell you where to focus your sampling, but they can’t tell you how salty the soil actually is or whether a particular crop can still succeed there. For that, you need a number.