Water dispersible colloids and factors influencing their dispersibility from soil aggregates

Abstract

Since water dispersible colloids (WDC) influence many aspects of soil processes, development of a better understanding and characterization of this soil fraction is necessary. This study involved the fractionation of WDC from 6 soil samples with diverse physicochemical and mineralogical composition and the evaluation of soil and colloidal properties affecting colloid dispersibility from soil aggregates. The percentage of the WDC fraction recovered from the samples ranged from 1.0 to 29.9%, depending on the soil properties and the mineralogical composition of the soil clay (< 2 μm) and WDC fractions. The kaolinite content in the soil clay or colloidal fraction, and the Fe, and Al content in the soil accounted for most of the variability in soil dispersibility. Total clay, cation exchange capacity (CEC), organic carbon (OC), exchangeable sodium percentage (ESP), sodium adsorption ratio (SAR), and ionic strength (1) in the ranges of thesoils studied, and mica, quartz and surface area (SA) of the clay or WDC fractions were not significant contributors. The most significant single-variable linear regression relationship ( P≤ 0.01) was between log Al and WDC ( R 2 = 0.85). The highest correlation coefficient ( r = − 0.87) through an exponential function was obtained between colloid kaolinite and WDC. The coefficient of determination ( R 2) was improved only slightly by combining the effects of kaolinite, Fe and Al in the multiple regression, apparently due to synergistic effects. Potentiometric titration data suggested that the dispersibility of colloids is controlled by their mineralogical composition and the magnitude of charges on particle surfaces. soils dominated by kaolinitic minerals due to low charge were less dispersed than those dominated by more reactive minerals.