Sodische

Sodische, or sodic soils, are soils in which exchangeable sodium dominates the soil’s cation exchange capacity (CEC) relative to calcium, magnesium, and potassium. A common indicator is the exchangeable sodium percentage (ESP), with values above about 15% classifying a soil as sodic. The sodium adsorption ratio (SAR) of soil water extract can also be elevated, signaling a high tendency for sodium to occupy exchange sites. Sodic soils are often alkaline, with pH commonly above 8.5, and they frequently occur in association with poor drainage or long-term use of saline or sodic irrigation water.

Formation of sodicity is typically linked to management and water quality. Insufficient leaching of sodium from the root zone, prolonged use of saline or sodic irrigation water, and the loss of calcium and magnesium from soils can lead to sodium dominating the exchange complex. Over time, this disrupts soil structure and function.

Effects on soil and crops include dispersion of clay particles, loss of soil structure, reduced aggregation, lower porosity and infiltration, surface crusting, poor seedling emergence, and increased erosion. These physical changes, together with nutrient imbalances (notably Ca and Mg), often result in lower crop yields and limited root growth.

Management and reclamation focus on replacing exchangeable sodium with calcium, typically through gypsum (calcium sulfate) applications and subsequent leaching with adequate-quality irrigation water. Additional measures include improving drainage, maintaining soil organic matter, selecting tolerant crops, and regular soil and water testing to monitor ESP and SAR. Preventive practices emphasize proper irrigation management and avoiding long-term accumulation of sodium in the root zone.