Differential Regulatory Roles of Organic Matter Components in Soil Colloid Cohesion and Aggregate Stability

The soil organic matter (SOM) significantly influences the aggregation and stability of soil colloids. Investigating the stability of black soil colloids and aggregates during SOM removal holds theoretical and practical importance for elucidating the interaction mechanisms among soil colloids, ions, and SOM, as well as for regulating soil structure and fertility. This study focuses on the typical constant charge soil colloid in Northeast China—black soil colloids and explores the coagulation and sedimentation processes of soil colloidal particles both pre- and post- SOM removal, along with the breakdown process of micro-aggregates. The following conclusions are drawn: (1) Divalent ions are more effective in promoting the coagulation and sedimentation of colloidal particles than monovalent ions, thereby reducing the intensity of soil aggregate disintegration upon contact with water; (2) In terms of site and mechanism of action, hydroxyl and carboxyl groups are the primary sites for K⁺ ion substitution reactions, whereas bridge bonds and intermolecular hydrogen bonds are the main mechanisms of interaction between colloidal particles and Ca²⁺; (3) The removal of SOM significantly reduces the stability of black soil colloids while enhancing the stability of soil aggregates and increases the Hamaker constant and weakening the steric hindrance effect of black soil colloids, thereby increasing the van der Waals attractive pressure between particles. This is the main reason for the decrease in colloidal particle stability and increase in aggregate stability.