Research paperThe coupling effects of soil organic matter and particle interaction forces on soil aggregate stability

- Particle interaction forces have great influences on soil aggregate stability.
- Organo-mineral interactions can largely change soil particle surface properties.
- Changes of surface properties induce great changes of particle interaction forces.
- Mineral-associated SOM has a profound influence on soil aggregate stability.

Soil organic matter (SOM) and particle interaction forces (electrostatic repulsive force (ERF), van der Waals (vdW) attractive force and surface hydration repulsive force) profoundly influence the stability of soil aggregates. However, few studies have investigated the coupling effects of SOM and particle interaction forces on soil aggregate stability. Therefore, the objectives of this study were to: (1) quantitatively determine the particle surface properties before (control) and after SOM removal and after straw incubation for 240 days, and then calculate the particle interaction forces based on the measured data; and (2) quantitatively evaluate the coupling effects of SOM and particle interaction forces on the stability of soil aggregates by measuring the quantities of released small particles after aggregate breakdown. Compared to the control treatment, SOM removal decreased the surface charge number, specific surface area and the effective Hamaker constant and increased the surface charge density, which, in turn, decreased the vdW attractive force and increased the ERF, DLVO repulsive force (ERF + vdW attractive force) and the net repulsive force between two adjacent soil particles, while straw incubation had opposite effects. Compared to the control treatment, SOM removal increased the mass percentage of released small particles (<10, <5, and <2 μm) w (< d)%, while straw incubation decreased the w (< d)%. Hence, we concluded that aggregate stability is influenced by particle interaction forces, while organo-mineral interactions can increase the vdW attractive force between two adjacent particles within soil aggregates and decrease the ERF, DLVO repulsive force, and net repulsive force, resulting in increased stability of soil aggregates.