A sodic soil is best described as which of the following?

• A. Soil with high sodium content
• B. Soil with high calcium content
• C. Soil with high potassium content
• D. Soil with high magnesium content

Answer: (A)

Sodic soils are defined by a high amount of exchangeable sodium on soil colloids. When sodium dominates the cation exchange sites, clay particles disperse rather than flocculate, causing poor soil structure, surface crusting, and very slow water infiltration. This issue can occur even if total salt isn’t high; the key factor is the relative proportion of sodium on the exchange complex, often measured as exchangeable sodium percentage or in irrigation water as SAR. The other nutrients listed describe different cation contents, which don’t produce the same dispersion and infiltration problems characteristic of sodicity. Therefore, a soil with high sodium content best captures what sodic means and why it leads to degraded structure and permeability.