Influence of Electrolyte Concentration, Sodium Adsorption Ratio, and Mechanical Disturbance on Dispersed Clay Particle Size and Critical Flocculation Concentration in Alfisols

Abstract

Clay dispersion affects both soil productivity and environmental quality through its effect on structure degradation. The effect of solution concentration (C), sodium adsorption ratio (SAR), and mechanical disturbance on clay dispersion, particle size of dispersed clay and critical flocculation concentration (CFC) was investigated in four Greek Alfisols equilibrated with NaCl/CaCl2 solutions of different C (= 5, 10, 50, and 100 mmol/L) and SAR [= 0, 5, 10, 20, and 40 (mmol/L)1/2]. Suspensions of equilibrated soil samples in solutions or in deionized water received a minimum (30 s) or a prolonged (16 h) shaking. After shaking, the dispersed clay fractions <2 and <1 µm were determined by measuring the optical density of the suspensions. It was found that both clay dispersion and CFC were increased with SAR. Relative dispersed clay of any size obtained in deionized water was always higher than in any NaCl/CaCl2 solution. Prolonged shaking resulted in much higher relative dispersed clay of any size, in greater CFC and in lower coarse (1–2 µm) to fine (<1 µm) clay ratio than minimum shaking. Relative dispersed coarse clay was always higher (p < 0.05) than relative dispersed fine clay. The coarse clay fraction displayed higher CFC than the fine clay fraction. The influence of clay content and mineralogy, organic matter, Fe2O3, pH, and mechanical disturbance on the differences in clay dispersion found between the soils used is discussed. In order to avoid clay dispersion in soils containing large-sized clay particles and/or receive intensive mechanical disturbance, it is suggested to keep the soil solution at a higher concentration.