Solute transport and reactions in salt-affected soils

Modeling solute transport and reactions in salt- and sodium-affected soils can be considered as three simultaneous processes: (i) solute transport; (ii) precipitation-dissolution reactions; and (iii) cation exchange. Solute transport is the physical movement of ions by convective transport (water transport) and ion dispersion within the solvent system (due to concentration gradients). Precipitation-dissolution reactions are dominated by carbonate or lime and gypsum reactions. Mineral weathering reactions are important in special cases, but are not considered here. Cation exchange models usually consider only calcium (Ca), magnesium (Mg), and sodium (Na) exchange on the negatively charged soil surfaces. However, in some cases it may be necessary to consider potassium (K) exchange if K constitutes a substantial portion of the solute or exchangeable ions. These three processes will be discussed separately and will be presented as separate subroutines that can be called by water flow and plant growth models similar to that described in Ch. 11