Why do sodic soils often experience increased runoff and erosion?

• A. Sodium disperses clay particles and reduces infiltration
• B. High calcium blocks infiltration
• C. Organic matter crust forms
• D. Fine texture prevents infiltration

Answer: (A)

Sodic soils experience increased runoff and erosion because the high amount of exchangeable sodium causes clay particles to disperse rather than stick together. When clays disperse, the soil structure breaks down, pore spaces become poorly connected, and surface conditions seal or crust. This greatly reduces water infiltration, so rainfall or irrigation water flows over the surface instead of soaking in. The resulting surface runoff carries loosened soil more easily and can drive rapid erosion. In contrast, calcium helps clays flocculate and maintain stable aggregates with larger pore networks, which promotes infiltration and lowers runoff. Other factors like a crust from organic matter or simply fine texture can influence infiltration, but they don’t capture the specific dispersion and pore-structure disruption caused by sodium that leads to the runoff and erosion characteristic of sodic soils.