Abstract

Volcanic ash-derived soils (VADS, variable-charge soils) are predominant in some regions of the world, being of great importance in the agricultural economy of several emerging countries. Their amphoteric surface charge characteristics confer physical/chemical properties different to constant surface charge-soils, showing a particular behaviour in relation to the herbicide adsorption kinetics. Volcanic soils represent an environmental substrate that may become polluted over time due to intensive agronomic uses. Solute transport models have contributed to a better understanding of herbicide behaviour on variable- and constant-charge soils, being also necessary to evaluate the fate of herbicides and to prevent potential contamination of water resources. The following chapter is divided into four sections: physical/chemical properties of variable and constant-charge soils, kinetic adsorption models frequently used to obtain kinetic parameters of herbicides on soils, solute transport models to describe herbicide adsorption on VADS, and impact of experimental conditions of kinetic batch studies on solute transport mechanisms.