What are salinity and sodicity, how are they measured, and how do they affect plant growth and soil physical properties?

• A. Salinity is measured by EC of soil extract; sodicity is measured by ESP or SAR; high levels reduce infiltration, cause dispersion of clays, and decrease plant growth.
• B. Salinity and sodicity are the same thing and measured by pH.
• C. Salinity is measured by pH; sodicity by EC.
• D. They do not affect plant growth.

Answer: (A)

Salinity and sodicity describe two different soil water problems and have distinct ways to measure them. Salinity refers to the total salt content in soil water and is measured by the electrical conductivity of a soil extract (often the saturated paste extract, giving ECe, or an equivalent soil-to-water extract). Sodicity, on the other hand, concerns the proportion of sodium on the soil’s exchange sites and is expressed as exchangeable sodium percentage (ESP) or estimated from the sodium adsorption ratio (SAR) in the soil solution.

High salinity creates osmotic stress for plants, meaning the soil solution has a high solute concentration that makes it harder for roots to draw water, reducing growth. It can also bring potentially toxic ions depending on the salt composition. High sodicity causes clay particles to disperse rather than flocculate, breaking soil structure. This leads to reduced porosity and permeability, infiltration problems (water moves more slowly into the soil), crusting at the surface, poorer aeration, and ultimately poorer plant growth.

This option correctly identifies salinity as measured by electrical conductivity of soil extract and sodicity by ESP or SAR, and it notes the key physical and plant-growth impacts—reduced infiltration, clay dispersion, and decreased plant growth—so it best matches what these properties do and how they’re evaluated.