Experimental approach of lessivage: Quantification and mechanisms

Abstract Lessivage, also called argilluviation, consists of a substantial vertical transfer of particles less than 2 μm from a superficial departure horizon to a deeper horizon. This process is common in many soil types and responsible for the development of a textural differentiation in soil profiles in the subsurface. However, the mechanisms of lessivage are still poorly understood, and to our knowledge, lessivage has rarely been quantified. We propose here two original experiments of in vitro pedogenesis on soil columns to analyse the mechanisms acting in eluviation and illuviation, the two phases of lessivage, and to quantify these two phases in terms of particle export and fixation. We paid special attention to the experimental conditions, so that the conditions were favourable for lessivage and as close as possible to field conditions. The eluviation experiment showed that the release of particles was not the determining process for lessivage. We also showed that the smectite selectivity of eluviation was not continuous over time. Both physical and chemical processes were identified as acting on both eluviation and illuviation. Concerning illuviation, experiments showed that from 25 to 90% of the eluviated particles were retained in the deeper horizon. Although large, to our knowledge this range represents the first quantification of illuviation.