Assessing the stability of size-dependent aggregates: The critical role of electrostatic repulsion in interparticle force distribution

Abstract

Soil aggregate stability is critical for maintaining soil fertility and mitigating environmental issues like erosion, yet the mechanisms by which interparticle interactions (van der Waals attraction, and electrostatic and hydration repulsion) govern stability across aggregate sizes remain unclear. This study investigated the distribution characteristics, influencing factors, and mechanisms of interparticle forces affecting aggregate structure stability for different-sized aggregates (2–5, 1–2, 0.25–1, 0.053–0.25 mm) using the pipette method and soil electrochemical theory. Results revealed that aggregate stability decreases significantly as electrolyte concentration decreases, with larger aggregates exhibiting stronger stability due to net attractive forces dominating interparticle interactions. In contrast, smaller aggregates experienced repulsion-dominated forces, reducing stability. The differential distribution of clay particles within aggregates of varied sizes altered surface charge density, surface potential, and electric field strength. Specifically, the high clay content in larger aggregates increased specific surface area, reducing surface charge density and weakening electrostatic repulsion, thereby enhancing stability. Electrochemical trends aligned with stability patterns, providing a robust explanation for size-dependent behavior. These findings clarify how clay distribution and interparticle forces govern aggregate stability, advancing mechanistic insights into soil structure dynamics. By quantifying the role of internal forces at the mesoscale, this study offers a foundation for targeted management practices to enhance soil resilience against environmental stressors like erosion and nonpoint source pollution.