How does sodium affect soil structure and how can it be mitigated in irrigated systems?

• A. Sodium improves soil aggregation.
• B. Sodium disperses clays, reduces infiltration and soil structure; mitigated by gypsum application, improving drainage, and using lower-sodium irrigation water.
• C. Sodium increases nutrient availability.
• D. Sodium only affects salinity; there is no mitigation.

Answer: (B)

Sodium disrupts soil structure by dispersing clay particles instead of letting them form stable aggregates, which collapses the soil’s pore network, reduces infiltration, and leads to poor drainage in irrigated systems. In sodic or saline-sodic soils, exchangeable sodium causes clays to repel each other, creating crusts and hard-to-work surfaces that limit water movement and root growth.

Mitigation hinges on replacing sodium with calcium and improving drainage and leaching. Gypsum supplies calcium that swaps onto the soil’s exchange sites in place of sodium, promoting flocculation and better aggregation so the soil can drain and allow water to infiltrate again. Improving drainage and ensuring enough leaching beyond the root zone helps flush accumulated salts, reducing the overall salt and sodium load. Using irrigation water with lower sodium (lower SAR) lessens the sodium input to begin with, helping prevent buildup and sodicity.

Sodium doesn’t inherently increase nutrient availability, and sodicity is not just about salinity—it involves the soil’s structure and exchange processes and does have practical mitigation.