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International audience; Background: While research has shown that vegetarian diets have a low environmental impact, few studies have examined the environmental impacts and nutritional adequacy of these diets together, although vegetarian diets can lead to nutritional issues.Objectives: Our objective is to optimize and compare six types of diets with varying degrees of plant foods (lacto-, ovolacto- and pescovegetarian and diets with low-, medium- and high meat content) under nutritional constraints.Methods: Consumption data in 30,000 participants are derived from the French NutriNet-Santé cohort using a food-frequency questionnaire. Diets are optimized by a non-linear algorithm minimizing the diet deviation while meeting multiple constraints at both the individual and population levels: non-increase of the cost and environmental impacts (as pReCipe accounting for greenhouse gas emissions, cumulative energy demand and land occupation, distinguishing production methods: organic and conventional), under epidemiological, nutritional (based on nutrient reference values), and acceptability (according to the diet type) constraints.Results: Optimized diets were successfully identified for each diet type, except that it was impossible to meet the EPA + DHA requirements in lacto- and ovolactovegetarians. In all cases, meat consumption was redistributed or reduced and the consumption of legumes (including soy-based products), wholegrains, and vegetables were increased, while some food groups, such as potatoes, fruit juices and alcoholic beverages, were entirely removed from the diets. The lower environmental impacts (as well as individual indicators) observed for vegetarians can be attained even when nutritional references were reached except for long-chain omega 3 fatty acids.Conclusions: A low-meat diet could be considered as a target for the general population in the context of sustainable transitions, although all diets tested can be overall nutritionally adequate, except for 3-n fatty acids, when planned appropriately.NutriNet-Santé cohort is registered at: https://clinicaltrials.gov/ct2/show/NCT03335644.

International audience

L’éco-conception du matériel d’épandage passe par l’utilisation d’outils de simulation intégrateurs. Le modèle OSEEP (Outil de Simulation de l’Effet des Épandeurs de lisiers sur les Pertes azotées) a ainsi été construit pour contribuer à l’amélioration des techniques d’épandage du lisier : il restitue les effets sur les émissions d’ammoniac (NH3) et de protoxyde d’azote (N2O) (i) de l’enfouissement du lisier dans le sol, (ii) de la répartition spatiale du lisier sur la parcelle et (iii) du tassement du sol par les engins agricoles. Pour tester le modèle, ces effets ont été simulés sur 5 sites français durant 7 années climatiques, et comparés à des résultats expérimentaux publiés à l’international. L’utilisation du modèle a permis de hiérarchiser la performance des techniques d’épandage sur le critère des émissions gazeuses dans une gamme de situations contrastées. Elle a montré l’intérêt de prendre en compte l’effet du tassement du sol par les machines pour atteindre le meilleur compromis entre la réduction des émissions de NH3 et celle des émissions de N2O.

The general objective of the thesis is to develop and validate an assessment framework of the environmental efficiency of slurry application techniques based on Life Cycle Assessment (LCA). A first LCA showed that the impact of the manufacturing and the use of slurry spreaders were negligible compared to those induced by the nitrogenous emissions (NH3, N2O & NO3-) from the fertilized soil. These emissions depend on soil, climate and agricultural practices and are thus eminently site-specific. This is challenging for LCA, which is a method based on the absence of spatial differentiation. To account for the variability of nitrogenous emissions at field level in the LCA of the slurry application function, two approaches were followed: (A) by using experimental data from the literature which allowed to order four application techniques in a robust way, to quantify the variability of emissions and to discuss the uncertainty induced on LCA final results. (B) by using simulated data with models from soil physics, agro-climatology, and agronomy models. A coherent simulation tool was developed including the effects on nitrogenous emissions from i) the incorporation of slurry into the soil, ii) the soil compaction by the spreaders, iii) the spatial distribution of the slurry over the field. These effects were simulated in 5 sites in France over 7 years. The range of emissions for each technique estimated with both approaches was comparable. The use of models allowed to assess the contribution of each elementary effect on nitrogenous emissions and to order the applications techniques in a range of contrasted situations. Finally, a general methodology for the inclusion of variability in the environmental inventory for agricultural products is proposed., L'objectif général de la thèse est de développer et valider un référentiel d'évaluation de la performance environnementale des techniques d'épandage basé sur l'Analyse de Cycle de Vie (ACV). Une première ACV a montré que la fabrication et le fonctionnement des machines avaient une contribution négligeable par rapport aux impacts générés par les substances azotées (NH3, N2O et NO3-) émises par le sol fertilisé. Ces émissions sont conditionnées par le sol, le climat et les pratiques culturales et ont un caractère éminemment local. Cela pose un défi à l'ACV, méthode globale basée sur une absence de différentiation spatiale des systèmes étudiés. Pour prendre en compte la variabilité des émissions azotées à la parcelle dans l'ACV de la fonction d'épandage, deux approches ont été suivies: (A) l'utilisation de données expérimentales issues de la bibliographie qui a permis de hiérarchiser de manière robuste quatre techniques d'épandage, de quantifier la variabilité des émissions et de discuter l'incertitude induite sur les résultats de l'évaluation. (B) l'utilisation de données simulées avec des modèles de physique des sols, d'agro-climatologie et d'agronomie. Un outil de simulation intégrateur a été construit pour modéliser les effets sur les émissions azotées de i) l'enfouissement de l'effluent dans le sol, ii) du tassement du sol par les engins agricoles, et iii) la répartition spatiale de l'effluent sur la parcelle. Ces effets ont été simulés sur 5 sites en France pendant 7 années. La variabilité des émissions estimées par les deux approches est comparable. L'utilisation de modèles a permis d'évaluer la contribution des effets élémentaires des épandeurs sur les émissions azotées et de hiérarchiser la performance des techniques d'épandage dans une gamme de situations contrastées. Finalement, une méthodologie permettant la prise en compte de la variabilité dans l'inventaire environnemental des produits agricoles est proposée.

Direct seeding mulch-based cropping systems have first been adopted to fight soil degradation caused by wind or water. Different systems have then been developed to face the range of constraints from humid tropical to semi-arid areas, in small farming environment as well as in high-mechanized agriculture. The best direct seeding on plant cover systems (DMC: direct seeding mulch-based systems, conservation tillage) can rapidly restore soil fertility, maximise the use of the available water and control weeds at a lower cost. It gives responses to farmers who aim at a higher profitability, an easier and simplified labour, and perspectives to the global need for a sustainable development and the preservation of natural resources. A generic approach can be defined to build new systems in different ecological and socioeconomic contexts: various hypothesis drawn from a multidisciplinary diagnosis are tested in matrices, i.e. system trials in which several key factors are combined. The Matrices are sites of research, innovation, and training. The involvement of farmers in the elaboration of those systems contributes greatly to their extension: the continuous assessment along with them help establish and further develop the systems to meet their specific needs.