AGRIPED

Human activities, notably agriculture, represent a major threat for soils. As a consequence, if we want to be able to protect soils, we have to be able to predict their future evolution under agricultural impact. However, some main soil processes are insufficiently known in terms of quantification and kinetics to be able to model them. It is notably the case of lessivage (vertical translocation of fine particles) that was described in many soils but rarely quantified. In this project, we propose to investigate, the impact of two agricultural practices, no-tillage and the use of organic amendment, on lessivage in soils in order to better characterise, quantify and model this widespread soil process. The proposed methodology combines approaches based on field characterisation, lab-experiments and modelling. The experimental sites (long-term experiment on tillage reduction in Boigneville and at the ORE ACBB of Mons en Chaussée on the use of organic input to soil at the ORE Qualiagro) will allow quantification of the impact of agriculture in general and of the two targeted agricultural practices in particular on lessivage thanks to an original approach: the multi-isotope analysis. We will analyse isotopes that are brought to the soil by its top and that strongly link to the soil phases once in the soil (14C, 137Cs, 210Pb, 206Pb/207Pb, 26Al, atmospheric 10Be). Thus isotope depth profiles are mainly due to vertical movement of matter within the soil profile due to, both, lessivage and bioturbation, redistribution under dissolved forms being supposed of secondary order. Fitting the multi-isotopic data by a diffusion-convection equation will allow quantifying the respective impact of lessivage and bioturbation on the isotope depth-profiles. Comparing the result obtained for the different isotopes will allow the estimation of the transfer in the soil of the different isotopes under soluble form. This approach will also give mean kinetics of the different considered soil processes. Lab-experiments under controlled conditions will allow the quantification of the impact of climatic conditions (rain intensity and initial soil moisture) and of the soil structure on lessivage. The impact of the chemistry of the percolating water on the particle aggregation and stability will also be studied as well as the location of the water transfer in the columns. These experiments will provide a complete dataset for testing and parameterization of a lessivage model that will be adapted from those existing in the literature on colloidal transfer. Once parameterized, the results obtained on the long-term experiment sites will be simulated. At last, in the two types of experiments (field and lab-experiments), the impact of lessivage on soil structure will be quantified by image analysis from Optical microscopy or tomography acquisitions. This project will allow a better understanding and prediction of soil evolution under external drift as human activities or climate change. It will allow for the (i) assessment of the importance of lessivage and other long term vertical redistribution of matter in soils and their role into pedogenesis; (ii) determination of their kinetics (iii) improvement the modelling skills in terms of soil evolution modelling.