Nitrate Sorption in a Mexican Allophanic Andisol using Intact and Packed Columns

Abstract

Contamination of groundwater by nitrate is a worldwide environmental issue. A better knowledge of nitrate sorption characteristics by soils contributes to efficient fertilizer use and prevents aquifer contamination. In volcanic soils, nitrate sorption is induced by variable charges due to the presence of amorphous materials and aluminum (Al) and iron (Fe) oxides. Anion transport in packed and intact columns was investigated in a Mexican Allophanic Andisol, under different permanent flow regimes in unsaturated conditions and several NO₃ ⁻‐N and Br⁻ input concentrations. In the packed columns, the NO₃ ⁻‐N adsorption in the soil was nonlinear. In the intact columns, the retardation coefficient variation was directly correlated to the increase of amorphous material with depth. The presence of preferential flow in the intact columns significantly increased the mobility and velocity of nitrate moving through the columns, whereas in the packed columns, NO₃ ⁻‐N fate was only affected by soil chemical composition and mineralogy.

Keywords:

• Allophane
• physical nonequilibrium
• retardation
• volcanic soil

Acknowledgments

Blanca Prado is indebted to Consejo Nacional de Ciencia y Tecnologia (Mexico) and Société Française d′Exportation des Resources Educatives (France) for her PhD grant. The authors thank the ‘Laboratorio de Fertilidad de Suelo’ of ‘Colegio de Postgraduados, Montecillo’ for the soil analyses. The research was funded by the ‘Institut de Rercherche pour le Développement’ (IRD), France.