Coupling effects of surface charges, adsorbed counterions and particle‐size distribution on soil water infiltration and transport

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SummarySoil pores are the channels for water transport. The surface charges, the non‐classic polarizabilities and concentrations of the adsorbed counterions in a soil determine soil particle interaction forces that affect soil pore status. Particle‐size distribution is another important factor that affects soil pore status. Therefore, surface charges, adsorbed counterions and particle‐size distribution would probably be coupled in soil water transport. In this study, two soils with different surface charge densities, different adsorbed counterions and different particle‐size distributions were used to study their coupling effects on soil water movement. The results showed that these factors were strongly coupled in soil water movement. When the soil electric field strength was strong (depending on surface charges, adsorbed counterion polarizabilities and concentrations), the net interaction forces of soil particles was repulsive, thus soil aggregates could be broken. The degree of aggregate breakdown coupled with particle‐size distribution determined soil water movement. For this case we found that (i) increasing attractive forces of soil particles could greatly improve soil water movement and (ii) water movement was slow when the soil had large clay or small silt or sand contents. When the soil electric field was weak, the net interaction force of soil particles was attractive, thus aggregates could not be broken. For this case we found that (i) further increasing the attractive forces of soil particles could not improve soil water movement and (ii) water movement was fast when the soil had large clay or small silt or sand contents.Highlights Coupling effects of particle size and particle interactions on soil water movement are not clear. Large clay contents can decrease or increase soil water movement depending on soil particle interaction forces. Fast water movement occurred in soil with strongly polarized cations and large clay content. Particle interaction forces and particle‐size distribution were strongly coupled in soil water movement.