Soil salinity, the concentration of soluble salts in the soil, is a critical factor affecting plant growth and soil health. Measuring salinity is essential for managing agricultural lands, reclaiming saline soils, and monitoring environmental conditions.
Soil salinity levels are typically measured using two primary methods: Electrical Conductivity (EC) or as Total Dissolved Solids (TDS).
Electrical Conductivity (EC)
The most common method for assessing soil salinity is by measuring the Electrical Conductivity (EC) of a soil water extract. This method works because dissolved salts in water carry electrical current. The higher the concentration of salts, the greater the conductivity of the solution.
- How it works: A sample of soil is mixed with distilled water, and the EC of the resulting extract is measured using an EC meter. Different soil-to-water ratios can be used depending on the specific test standard.
- Units: EC is commonly expressed in units such as deciSiemens per meter (dS/m) or millimhos per centimeter (mmhos/cm). It's important to note that 1 dS/m is equal to 1 mmhos/cm. These units quantify the ability of the water sample to conduct electricity, providing a direct indication of salt concentration.
Total Dissolved Solids (TDS)
Another way to measure salinity is by determining the Total Dissolved Solids (TDS) in a soil water extract. This method quantifies the actual weight of dissolved salts in a given volume or weight of water.
- How it works: A known volume of soil water extract is evaporated, and the remaining residue (the dissolved solids) is weighed.
- Units: TDS is often expressed in parts per million (ppm), indicating the number of milligrams of dissolved solids per liter of water (mg/L), which is roughly equivalent to ppm in dilute solutions. While EC is typically the standard for classifying saline soils, TDS is also a valuable metric.
| Measurement Method | What it Measures | Common Units As Noted |
|---|---|---|
| Electrical Conductivity (EC) | Ability of soil water to conduct electricity | dS/m, mmhos/cm |
| Total Dissolved Solids (TDS) | Total weight of dissolved salts | ppm |
As highlighted by research and common practice, soil salinity levels are typically measured by electrical conductivity (EC) or as total dissolved solids, often expressed in millimhos per centimeter (mmhos/cm), parts per million (ppm), or deciSiemens per meter (dS/m). These measurements provide quantifiable data essential for assessing soil health and managing salinity challenges.
