sodicitet

Sodicitet is the soil condition in which a substantial portion of the soil’s exchangeable cations are sodium ions (Na+). It is typically expressed in terms of an Exchangeable Sodium Percentage (ESP), which is the share of the soil’s cation exchange capacity occupied by sodium, or by related indicators such as the Sodium Adsorption Ratio (SAR) of soil water. Soils with high ESP are considered sodic, while low ESP indicates non-sodic conditions. Sodicity can occur with or without high soluble salts; saline-sodic soils have both high ESP and high soluble salt content.

ESP is calculated as the percentage of CEC occupied by Na+. An ESP above about 15% is commonly used as a threshold for sodicity in many soils, with higher values indicating greater severity. SAR, derived from a soil solution, helps assess the tendency of a soil to release or exchange sodium. The combination of ESP and SAR, along with drainage and texture, influences the overall behavior of the soil.

Sodicity develops when soils accumulate sodium relative to calcium and magnesium, often in regions with low rainfall, poor drainage, or irrigation practices that limit leaching. In arid and semi-arid zones, irrigation water may contribute soluble sodium, and insufficient leaching allows sodium to accumulate on exchange sites.

The main impacts of sodicity are physical and chemical. Physically, high exchangeable sodium causes dispersion of clay particles, reduces aggregate stability, and leads to crusting, poor structure, and very low permeability. Chemically, sodium can limit nutrient exchange and availability, potentially causing plant toxicity or deficiencies.

Management focuses on leaching and replacing exchangeable sodium with calcium. Practices include improving drainage, applying gypsum or other calcium-bearing amendments, managing irrigation to ensure adequate leaching, and incorporating organic matter to improve soil structure.