14. Transport of Solutes in Soils

Soil water is in fact a solution; but in the majority of cases, the concentrations of soil solutes are small, and therefore soil-water physical characteristics are treated as the characteristics of pure water. Pollution transport, transport of dissolved fertilizers in infiltration water or transport of solutes in salt-affected soils should be treated as transport of solutions. Concentration of a solute is defined, and transport mechanisms of dissolved compounds in soil are described qualitatively and quantitatively in this chapter. Diffusion, convection and hydrodynamic dispersion are involved together with the continuity equation to derive the convective–diffusion transport equation. The Péclet number is used to evaluate the transport mechanisms of dissolved compounds. Outflow and breakthrough curves are defined, described and explained to identify the character and significance of the solute transport.