Dynamics of Sodium in Saline and Sodic Soils

Soil salinization and sodication affect large areas of agricultural land in the world. Amelioration of these soils to make them suitable for agricultural production depends on understanding sodium dynamics and chemical interactions governing nutrient availability. Three locations in eastern Croatia were characterized to the 5-m depth. The two solonetz-solonchak soils were alkaline, whereas the solonetz soil had near-neutral A/E horizon and alkaline deeper horizons. Electrical conductivity of the saturated extract (ECe) was greater than 4 dS m(-1) in the top horizons in the solonetz-solonchak soils. The solonetz soil had 2.8-4.7 dS m(-1) in shallow A/E, CG, and G horizons and up to 6.3 dS m(-1) below 1.5 m. Highly alkalinized sodic horizons (exchangeable sodium percentage, ESP > 20) had 24-47% Ca2+ and 27-33% Mg2+ on the cation exchange complex. Sodium adsorption ratio (SAR) was high (18-26) in the P horizon and even more so in Bt,na horizon (35-36) of solonetz-solonchak soils. A strong negative exponential relationship existed between soluble Ca2+ and SAR (SAR increased greatly when Ca2+ dropped to around 3 mg dm(-3)). An increase in pH to greater than 8.4 resulted in an exponential increase in SAR. Leaching of Na+ with successive volumes of water was similarly effective for the P and Bt,na horizons in the solonetz-solonchak soils, but SAR remained greater than 15 even after six successive cycles of leaching. In conclusion, extensive amelioration of tested soils with gypsum and leaching will be required to overcome poor physical and chemical characteristics caused by various degrees of alkalization and sodication to bring these soils into production.