Le lessivage, compris comme la translocation de particules fines dans les sols à partir d’un horizon dit éluvié vers un horizon d’accumulation dit illuvié, est considéré comme un processus pedogénétique majeur. Il a été décrit dans de nombreux sols mais reste assez peu connu, mal caractérisé et son existence même est encore sujette à débat dans la communauté scientifique. Pour améliorer nos connaissances, ce projet a eu pour objectif de mettre en place des expérimentations au laboratoire pour permettre une quantification et une approche cinétique du lessivage. Nous avons ainsi construit trois dispositifs expérimentaux, deux étant dédiés à l’étude de l’éluviation sur sols remaniés et non perturbés, et le troisième dédié à l’étude de l’illuviation. Ces expériences associées à une approche de bilan de masse sur les bases de données pédologiques existantes nous ont permis de : (i) déterminer la nature des particules migrantes, (ii) quantifier les particules mobilisées et identifier certains processus responsables de cette mobilisation, (iii) quantifier les quantités de particules fixées au sein des horizons d’accumulation et identifier quelques processus responsables de cette fixation, (iv) déterminer l’impact de la structure du sol et des événements climatiques extrêmes sur le lessivage, (v) extrapoler ces résultats expérimentaux sur les durées de la pédogenèse et les confronter aux profils de sols décrits dans la littérature. Nos résultats montrent que : (1) les particules qui migrent ont la signature de la fraction 0-2 μm, légèrement enrichie en smectites lors des premières pluies ; (2) le transfert des particules dépend du mode de fonctionnement hydrodynamique, matriciel ou préférentiel ; (3) seule une fraction des particules mises en suspension dans l’horizon d’éluviation est fixée dans l’horizon d’illuviation ; (4) le lessivage est le processus majeur responsable de la formation de profils à texture contrastée dans 1 à 12% des cas. / Lessivage - understood as a substantial vertical transfer of fine particles from an eluvial horizon to an illuvial horizon - is one of the major pedogenetic processes. It has been described in many soil types but remains poorly known and characterized. Its existence is still subject to debate in the scientific community. To improve our knowledge, this project aimed at conducting laboratory experiments allowing both a quantification and a kinetic approach of lessivage. We thus designed three experiments, two to study eluviation on disturbed and undisturbed soils, and the third one to study illuviation. Theses experiments associated to a mass balance approach performed on existing pedological data allowed: (i) determing the nature of migrant particles, (ii) quantifying the mobilized particles and identifying some of the processes responsible for their mobilization, (iii) quantifying the quantities of particles retained in the illuvial horizon and identifying some of the processes responsible for this fixation, (iv) determining the impact of soil structure and extreme climatic events on lessivage. At last, we extrapolated these experimental results on the pedogenese duration and confronted them to soils profiles described in the literature. Our results show that: (1) the migrating particles have the signature of the 0-2 μm fraction, slightly enriched in smectites for the first rain events, (2) the particle transfer depends of the hydrodynamic functioning, either matricial or preferential, (3) only a fraction of particles mobilised in the eluvial horizon is fixed in the illuvial horizon, (4) the lessivage is the process mainly responsible for the formation of textural contrast in 1 to 12 % of the studied profiles.

Technosols combine soils subjected to strong human influence and whose pedogenesis is dominated by its technical origin. They contain a significant amount of materials made, modified or directly transported by human activity, defined as artefacts. Soils formed from technogenic parent materials are spreading and their pedogenesis is still little understood. Given that the sustainable use of the soil resources demands wide knowledge about its genesis, it is necessary to bring further information about Technosols, especially in the tropical environment, where they have been poorly explored. Thus, in this study we characterized three Technosols constructed from dolomitic limestone mine spoils, cultivated with sugar cane (for 2 and 6 years) and pasture (for 20 years). The Technosols experienced a rapid morphological evolution expressed by color development and aggregation. Pedoplasmation, melanization and redoximorphic were the mainly processes occurring in these constructed soils. The combination of grasses over Ca-rich mine spoils triggered organic carbon accumulation and originated a well-developed surface horizon with strong crumb structure and dark color. The rhizosphere played a pivotal role in mineral weathering of the Technosols. Exudation and microbial activity were about two times higher in the rhizosphere than in the bulk soil leading to an enhanced mineral dissolution. Overall, the primary minerals in the rhizosphere presented a medium to high degree of weathering while those from bulk soil were little weathered. Our data indicates that the rhizosphere may provide a favorable biogeochemical environment to the formation of secondary clay minerals. This study evidences that constructed tropical soils may evolve in an accelerated rate of pedogenesis and, thus, are a real alternative for the reclamation of degraded areas, potentially restoring original soil ecosystem services. / Tecnossolos são uma classe de solos cuja pedogênese é dominada por sua origem antrópica. Esses solos contêm uma quantidade significativa de materiais feitos, modificados ou transportados diretamente pela atividade humana, definidos como artefatos. Solos formados a partir de materiais de origem antrópicos são muito comuns, entretanto sua pedogênese ainda é pouco compreendida. O uso sustentável do recurso solo exige um amplo conhecimento sobre sua gênese, sendo assim, entender a formação de Tecnossolos, especialmente no ambiente tropicalé crucial para seu uso e manejo visando sua incorporação na produçao de alimento, fibras e energia. Neste estudo foram estudados três Tecnossolos construídos a partir de rejeitos de mineração de calcário dolomítico, cultivados por dois e seis anos com cana-de-acúcar e por 20 anos sob pastagem. Os Tecnossolos apresentaram uma rápida evolução morfológica expressa principalmente pelo desenvolvimento de cor e agregação. Dentre os processos identificados, os mais importantes foram pedoplasmação, melanização e os redoximórficos. Devido à combinação de gramíneas e rejeitos ricos em cálcio desenvolveu-se um horizonte de superfície com estrutura grumosa forte e cor escura, com altos teores de carbono orgânico. A rizosfera desempenhou um papel fundamental no intemperismo mineral dos Tecnossolos. A exsudação e a atividade microbiana foram cerca de duas vezes maiores na rizosfera do que no solo não rizosférico, levando a uma dissolução mineral mais proeminente na rizosfera. No geral, os minerais primários da rizosfera apresentaram um grau médio/alto de intemperismo, enquanto aqueles do solo não rizosférico foram pouco intemperizados. As condições biogeoquímicas da rizosfera apontam para um ambiente favorável à formação de minerais de argila na rizosfera. O estudo demonstra que a pedogênese de Tecnossolos emambiente tropical parece avançar rapidamente; o que pode garantir não só o sucesso da reabilitação das áreas, mas ainda a retomada de serviços ecossistêmicos prestados pelos solos.