Lessivage as a major process of soil formation: A revisitation of existing data

Lessivage consists of a substantial vertical transfer of fine particles from an eluvial E-horizon to an illuvial B-11horizon. It has been described as a major or secondary pedogenetic process for many soil types. However, lessivage fluxes have never been measured because of obvious technical difficulties; thus, lessivage has been poorly quantified, if at all, and has rarely been modelled. For those reasons, the existence of lessivage is somewhat controversial. In this paper, we synthesised existing knowledge about lessivage and particle transfer from the literature and reanalysed data from the literature on particle transfer in soils using laboratory experiments and data from the French soil database. This analysis was performed to estimate (i) the occurrence of lessivage as a major soil forming process; (ii) the quantity of particles that migrate through soils; and (iii) the duration of lessivage in soil, which must be consistent with the mass of particles accumulated in the illuvial B-horizon. We showed that lessivage is responsible for the formation of Luvisols and Albeluvisols in only 1% to 12% of cases. In half of the cases, the current pH of the soil profiles is no longer favourable to lessivage due to agricultural liming practices. We also calculated that lessivage may have occurred over a minimum of 710 to 9100 years in soils developed on loess, a time period long enough to account for the observed accumulations of particles in the B-horizons in 64% of the cases, judging by the quantities of particles that migrate in soils.