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Apports de la modélisation structure-fonction des transferts d'azote à différentes échelles pour raisonner la gestion de l'azote et de l'espace dans les agro-écosystèmes.

Abstract : Facing the food needs of a growing population, global agriculture faces multiple challenges (economic, agro-ecological, environmental, social and societal). According to estimates, it would be necessary for meeting these needs that global agriculture increases its production by 70% by 2050, while continuing to provide essential services such as the preservation of air, soil and water quality, landscape maintenance or life quality in rural areas. Agriculture contributes to 10% of the greenhouse gas emissions from human activities and represents the main source of emissions into the environment from agricultural inputs. Better management of resources, inputs and territories, including landscapes, requires a better understanding and assessment of flows especially nitrogen in territories. The general hypothesis underlying the work presented in this report is that mitigation of environmental losses and sustainability of agriculture and agro-ecosystems (economic, agroecological, environmental, social, societal) requires rethinking their structure and thus their functionalities in the context of global change. This general hypothesis was tested in several cases corresponding to different geographical (thus political and socio-economic), scientific and thematic (thus disciplines and teams) contexts and to multiple spatial and temporal scales (from the organ or soil aggregate up to the region through the plant, the stand or the plot, the farm and the landscape scales). My researches therefore focused on complex systems for which modelling is an essential tool in addition to data collected from field experiments or under controlled conditions, farm surveys or landscape inventories. My first experiences in Aquitaine and in Sahelian Africa helped me discover how research can contribute to better management of resources (forestry, agriculture, agro-pastoralism...) at regional scales, using various methods of representation of the structures (remote sensing and satellite data, geographic information systems) and analysis (modelling, statistical analysis of data) of the production functions within territories. The results obtained in my subsequent researches in several INRA teams and in interdisciplinary collaboration showed, using models and scenarios at different scales, the role of spatial interactions between the structures of the studied systems (plants and stands explicitly described in 3D in a first phase, landscapes spatially described in a second phase) and their functions (acquisition and distribution of nitrogen and carbon assimilates in the first phase, biomass production, environmental losses and indirect emissions of nitrogen in the second phase). These studies showed the importance of taking account such interactions to improve the plant and stand management on one hand and the landscape and territoriy management on the other hand, in relation to the management of agriculural inputs and soil and climate forcings. My perspectives are to continue to contribute to researches aiming at better assessing the environmental impacts of agricultural activities, including the understanding and quantification of nitrogen flows and balances and structure-function relationships in agro-ecosystems at different scales. This work will be carried out at least initially on nitrogen flows in relation to carbon and water flows. They may be extended to other inputs (eg pesticides, organic waste products) or other major elements (eg phosphorus). My researches should lead to the production of tools and references (models, databases, agro-environmental scenarios) to test quantitatively (ie from mechanistic, process-based and integrated approaches), various changes in agro-ecosystems. The produced models will be tools to contribute towards proposing insights and recommendations to mitigate environmental losses of nitrogen and/or adapt production systems and territories to global change. My researches have also an applied objective, in the sense that the tools developed may become operational tools for managing nitrogen and space in agro-ecosystems.
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Jean-Louis Drouet. Apports de la modélisation structure-fonction des transferts d'azote à différentes échelles pour raisonner la gestion de l'azote et de l'espace dans les agro-écosystèmes.. Sciences du Vivant [q-bio]. Université Pierre et Marie Curie - Paris 6, 2015. ⟨tel-02800774⟩

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