Effect of soil particle interaction forces in a clay‐rich soil on aggregate breakdown and particle aggregation

Summary Particle aggregation and aggregate breakdown are important processes that frequently occur in soil under natural conditions. However, how these two opposing processes are affected by the forces that govern soil particle interaction remains unclear. Thus, in this research, we aimed to: (i) investigate the relation between particle aggregation and aggregate breakdown and (ii) probe the mechanism underlying particle aggregation and aggregate breakdown under the influences of soil particle interaction forces. Specifically, we investigated particle aggregation and aggregate breakdown in a permanently charged clay‐rich soil in solutions with different electrolyte (NaNO 3 and Mg(NO 3 ) 2 ) concentrations. We used the fast wetting method in aggregate breakdown experiments and the dynamic light‐scattering method in aggregation experiments. For soils in either NaNO 3 or Mg(NO 3 ) 2 solution, the critical coagulation concentration obtained through particle aggregation experiments was equal to the critical breakdown concentration from aggregate breakdown experiments. This result indicated that the net force, which is defined as the sum of the van der Waals, electrostatic and surface hydration forces, is attractive for aggregation but is repulsive for aggregate breakdown. Although several interaction forces were involved in soil particle interactions, we found that the repulsive electrostatic force solely determines whether the net force is attractive or repulsive and thus determines whether aggregation or breakdown would occur. For a given soil, non‐classical cationic polarization in cation–surface interactions strongly influenced the repulsive electrostatic potential energy of soil particles, thus influencing the occurrence of aggregation or breakdown. Our results suggested that adjusting soil internal forces is a feasible approach to regulate particle aggregation and promote aggregate stability. Highlights The process of soil aggregate breakdown and particle aggregation were evaluated quantitatively. There was equality in the opposing forces for particle aggregation and aggregate breakdown. Electrostatic repulsive force between soil particles controlled processes of aggregation and aggregate breakdown Cationic non‐classic polarization in cation–surface interactions has an important effect on aggregation and aggregate breakdown.