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Identification des processus dominants de transfert des produits phytosanitaires dans le sol et évaluation de modèles numériques pour des contextes agro-pédo-climatiques variés

Abstract : (trad auto)Phytosanitary products are widely used in so-called intensive agriculture, particularly in the context of large-scale cereal crops. In order to combine productivity and environmental risk management, it is necessary to understand the transfer processes involved. One of the two main objectives of this thesis is to provide elements of understanding of the major processes controlling exports of plant protection products at the plot level and in various agro-pedo-climatic contexts. However, the mere use of observational data often suffers from the limited number of cases encountered, limiting the interpretation of transfers of plant protection products. It also faces the transition from understanding the system to predictability (or prediction) and the recommendation of actions. \In this respect, the numerical models called mechanistic models appearing as interesting tools. However, this approach requires ensuring the validity and replicability of the modelling results. The second objective of the thesis is thus to assess the ability of numerical models to represent the behaviour of plant protection products on different sites, with an operational aim. This thesis work was based on extensive data from three Arvalis-Institut-du Végétal sites. The first, that of the Jaillière, represents the typical case of clayey-silt soils drained in the northwest of France. The second, that of Magneraud, also subject to an oceanic climate, has clayey soils, rich in organic matter, thin and based on a succession of marl and limestone banks. The third and last site -Saint Exupery- is located in eastern Lyon, on the glaciofluvial deposits of the Rhône and is characterised by a high coarse element load and a low clay content at depth. Simulations of water and plant protection product flows were carried out on three models, selected on the basis of the literature review: MACRO, root zone water quality model (RZWQM) and HYDRUS-2D. The substances most at risk differ according to the context, in particular soil and geological. Thus, the molecules at risk at the La Jaillière site are mainly those applied in autumn-winter before the start of the drainage season, regardless of their physico-chemical properties. On the contrary, on the Magneraud site, despite a close climate, it is the molecules applied in spring that are most exported, through shrinkage slits not present in winter. Finally, no molecule has so far appeared to be at risk at the Saint Exupery site, although the high glyphosate exports, more than two years after its last application, raise doubts about the potential delayed effect of contamination at this site. The results of the data analysis and simulations confirm the importance of taking into account the preferential transfer to represent losses in plant protection products. Thus, the representation of this process is necessary to correctly estimate the high losses in drainage at the La Jaillière site. On the contrary, modelling with MACRO and HYDRUS-2D confirmed that the low quantifications at the Saint Exupery site were due to a predominantly matrix water flow, possibly accentuated by the presence of coarse elements, then playing the role of... Finally, simulations at the Magneraud site highlighted the temporal variability of flows and transfers - and ultimately of the results - as well as the sensitivity of the parameters to the description of the limestone substrate. Simulations at all study sites also showed the need for a sensitivity and calibration analysis step, as the initial parameter sets do not allow accurate reproduction of flow chronicles, let alone solutes. The results of the overall sensitivity analysis indicate that the greater the preferential transfer, the more influential the hydrodynamic parameters are. On the contrary, when the preferential flows are less important, it is the physico-chemical characteristics that become so. Sensitivity analysis and validation tests have highlighted the need to integrate a kinetic adsorption or bound residue module for persistent molecules. From an operational point of view, the three models used appeared to be complementary in their use. Thus, MACRO is interesting for estimating the average transfer potential, provided that the soil and macroporal system are well described, while RZWQM appears as a complete agronomic management model. Finally, HYDRUS-2D is relevant for the study of dominant transfer processes as shown by the analysis of fine time step data at the La Jaillière and Saint Exupery sites.
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Submitted on : Saturday, May 16, 2020 - 7:37:23 AM
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  • HAL Id : tel-02602274, version 1
  • IRSTEA : PUB00046144



Romain Dairon. Identification des processus dominants de transfert des produits phytosanitaires dans le sol et évaluation de modèles numériques pour des contextes agro-pédo-climatiques variés. Sciences de l'environnement. Doctorat, Université de Lyon I, 2015. Français. ⟨tel-02602274⟩



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