Why is gypsum applied to sodic soils?

• A. To increase soil moisture
• B. To reduce potassium
• C. To raise pH
• D. To replace sodium and improve structure

Answer: (D)

In sodic soils, the problem is the high amount of exchangeable sodium that keeps clay particles dispersed, making the soil hard, crusty, and poorly infiltrative. Gypsum provides soluble calcium that swaps places with the sodium on the soil’s exchange sites. When calcium takes the place of sodium, the clay particles flocculate and the soil structure improves—more stable aggregates, better porosity, and better water movement. The sulfate from gypsum helps keep the displaced sodium in solution so it can be leached away with irrigation or rainfall. This combination directly addresses the main issue of sodic soils: restoring structural stability and drainage. Gypsum isn’t primarily used to raise pH, nor to reduce potassium.