THE ASSOCIATION OF IONS IN THE SOIL SOLUTION OF SALINE SOILS

Abstract

The chemical equilibrium in the soil solution determines the dynamics of its material composition, migration and accumulation of salts. In the soil solution are formed electrically neutral ion pairs CaCO₃°; CaSO₄°, MgCO₃°, MgSO₄°, charged ion pairs CaHCO₃⁺, MgHCO₃⁺, NaCO₃^-, NaSO₄^-, CaOH⁺, MgOH⁺. The calculation method proposed for quantitative assessment of real ion forms in the soil solution of solonetz taking into account the ions association. Determination of real condition of the main ions in soil solution is based on ion association and its influence on physical and chemical properties of solution. Were calculated the free and associated ion form concentration according to analytical ion concentration. Were used an iteration to solve the equations of ion material balance, a linear interpolation of equilibrium constants, a Method of Ionic Pairs including a law of initial concentration preservation, a law of the operating masses of equilibrium system, the concentration constants of ion pair dissociation following the law of operating masses. Upon completion of iterative procedure, was determined the quantity of ion free form and a coefficient of ion association γ_e as the ratio of ions free form to its analytical content γ_e = C_ass/C_an. For calculation procedure were used the own software products. The association of ions varies in individual soils and soil layers, Шncreasing the soil solution salinity amplifies the ions association. Depending on concentration and composition of soil solution the ionic pairs are: 15-45% Ca²⁺; 16-49% Mg²⁺; 0,6-8,4% Na⁺; 2,2-17,6% HCO₃^-, 16-51% SO₄^2-, up to 88% CO₃^2-. The proposed thermodynamic calculation method for quantitative assessment of real ion forms in the soil solution helps to explain the evolution of salted soils, maintain the soil, improve plant nutrition and irrigation.