Influence of aggregate diameter, surface area and antecedent water content on the dispersibility of clay

Abstract

The percentages of spontaneously dispersed clay, Ms, and mechanically dispersed clay, Mm, in a suspension of a given ionic strength were evaluated using different sized aggregates collected from wheat-fallow and continuous pasture rotations established in 1925 on a red-brown earth in southern Australia. Ms increased, as hypothesized, with increasing surface area of aggregates, but the value per unit surface area of aggregates increased with increasing size of aggregates and increasing antecedent soil water content. The effect of water content was greatest in the larger aggregates of the less stable wheat-fallow soil. Mm was approximately 12 times larger than Ms and increased with increasing initial aggregate size and increasing antecedent water content. The sensitivity of Mm to water content was greatest on the least stable soil. Calculations showed that the higher values of Mm on unstable spoils were due to both larger exposed aggregate surface areas and higher dispersibility of the clay on these surfaces. -from Authors