Using a crop model to account for the effects of local factors on the LCA of sugar beet ethanol in Picardy region, France

CT1 ; CT3 ; EnjS1 ; EnjS4 ; Base de données AgroclimInternational audienceThe results of published Life Cycle Assessments (LCAs) of biofuels are characterized by a large variability, arising from the diversity of both biofuel chains and the methodologies used to estimate inventory data. Here, we suggest that the best option to maximize the accuracy of biofuel LCA is to produce local results taking into account the local soil, climatic and agricultural management factors. Methods We focused on a case study involving the production of first-generation ethanol from sugar beet in the Picardy region in Northern France. To account for local factors, we first defined three climatic patterns according to rainfall from a 20-year series of weather data. We subsequently defined two crop rotations with sugar beet as a break crop, corresponding to current practice and an optimized management scenario, respectively. The six combinations of climate types and rotations were run with the process-based model CERES-EGC to estimate crop yields and environmental emissions. We completed the data inventory and compiled the impact assessments using Simapro v.7.1 and Ecoinvent database v2.0. Results Overall, sugar beet ethanol had lower impacts than gasoline for the abiotic depletion, global warming, ozone layer depletion and photochemical oxidation categories. In particular, it emitted between 28 % and 42 % less greenhouse gases than gasoline. Conversely, sugar beet ethanol had higher impacts than gasoline for acidification and eutrophication due to losses of reactive nitrogen in the arable field. Thus, LCA results were highly sensitive to changes in local conditions and management factors. As a result, an average impact figures for a given biofuel chain at regional or national scales may only be indicative within a large uncertainty band. Conclusions Although the crop model made it possible to take local factors into account in the life-cycle inventory, best management practices that achieved high yields while reducing environmental impacts could not be identified. Further modelling developments are necessary to better account for the effects of management practices, in particular regarding the benefits of fertiliser incorporation into the topsoil in terms of nitrogen losses abatement. Supplementary data and modelling developments also are needed to better estimate the emissions of pesticides and heavy metals in the field

Bayesian calibration of the nitrous oxide emission module of an agro-ecosystem model

Nitrous oxide (N2O) is the main biogenic greenhouse gas contributing to the global warming potential (GWP) of agro-ecosystems. Evaluating the impact of agriculture on climate therefore requires a capacity to predict N2O emissions in relation to environmental conditions and crop management. Biophysical models simulating the dynamics of carbon and nitrogen in agro-ecosystems have a unique potential to explore these relationships, but are fraught with high uncertainties in their parameters due to their variations over time and space. Here, we used a Bayesian approach to calibrate the parameters of the N2O submodel of the agro-ecosystem model CERES-EGC. The submodel simulates N2O emissions from the nitrification and denitrification processes, which are modelled as the product of a potential rate with three dimensionless factors related to soil water content, nitrogen content and temperature. These equations involve a total set of 15 parameters, four of which are site-specific and should be measured on site, while the other 11 are considered global, i.e. invariant over time and space. We first gathered prior information on the model parameters based on the literature review, and assigned them uniform probability distributions. A Bayesian method based on the Metropolis–Hastings algorithm was subsequently developed to update the parameter distributions against a database of seven different field-sites in France. Three parallel Markov chains were run to ensure a convergence of the algorithm. This site-specific calibration significantly reduced the spread in parameter distribution, and the uncertainty in the N2O simulations. The model’s root mean square error (RMSE) was also abated by 73% across the field sites compared to the prior parameterization. The Bayesian calibration was subsequently applied simultaneously to all data sets, to obtain better global estimates for the parameters initially deemed universal. This made it possible to reduce the RMSE by 33% on average, compared to the uncalibrated model. These global parameter values may be used to obtain more realistic estimates of N2O emissions from arable soils at regional or continental scales

Modeling of nitric oxide emissions from temperate agricultural ecosystems.

48 p.Arable soils are a significant source of nitric oxide (NO), most of which is derived from nitrogen fertilizers. Precise estimates of NO emissions from these soils are thus essential to devise strategies to mitigate the impact of agriculture on tropospheric ozone regulation. This paper presents the implementation of a soil NO emissions submodel within the environmentally-orientated soil crop model, CERES-EGC. The submodel simulates the NO production via nitrification pathway, as modulated by soil environmental drivers. The resulting model was tested with data from 4 field experiments on wheat- and maize-cropped soils representative of two agricultural regions of France, and for three years encompassing various climatic conditions. Overall, the model gave correct predictions of NO emissions, but shortcomings arose from an inadequate vertical distribution of fertilizer N in the soil surface. Inclusion of a 2-cm thick topsoil layer in an 'micro-layer' version of CERES-EGC gave more realistic simulations of NO emissions and of the under-lying microbiological process. From a statistical point, both versions of the model achieved a similar fit to the experimental data, with respectively a MD and a RMSE ranging from 1.8 to 6.2 g N-NO ha−1 d−1, and from 22.8 to 25.2 g N-NO ha−1 d −1 across the 4 experiments. The cumulative NO losses represented 1 to 2% of NH+4 fertilizer applied for the maize crops, and about 1% for the wheat crops. The 'micro-layer' version may be used for spatialized inventories of biogenic NO emissions to point mitigation strategies and to improve air quality prediction in chemistry transport models

Disk-Graph Probabilistic Roadmap: Biased Distance Sampling for Path Planning in a Partially Unknown Environment

International audienceIn this paper, we propose a new sampling-based path planning approach, focusing on the challenges linked to autonomous exploration. Our method relies on the definition of a disk graph of free-space bubbles, from which we derive a biased sampling function that expands the graph towards known free space for maximal navigability and frontiers discovery. The proposed method demonstrates an exploratory behavior similar to Rapidly-exploring Random Trees, while retaining the connectivity and flexibility of a graph-based planner. We demonstrate the interest of our method by first comparing its path planning capabilities against state-of-theart approaches, before discussing exploration-specific aspects, namely replanning capabilities and incremental construction of the graph. A simple frontiers-driven exploration controller derived from our planning method is also demonstrated using the Pioneer platform

Avaliação e comparação da resistência à compressão e à traçã diametral de cimentos odontológicos

Objetivo: o objetivo deste estudo foi avaliar e comparar a resistência à compressão e à traçãodiametral de oito cimentos utilizados em prótese fixa: fosfato de zinco (Cimento de Zinco – SS White ePoscal – Voco), ionômero de vidro convencional (Meron – Voco e Ketac Cem – ESPE), ionômero de vidromodificado por resina (Meron Plus – Voco) e cimentos resinosos (Rely-X – ESPE, Enforce – Dentsplye Bifix – Voco). Materiais e métodos: para avaliação da resistência à compressão e à tração diametralforam confeccionados dez corpos de prova para cada teste. As amostras foram carregadas com força decompressão com uma velocidade de carregamento de 0,5mm/min em uma máquina de ensaio universal(EMIC DL 2000) para ambos os testes. Os dados foram submetidos aos testes de ANOVA e Tukey (α=0,05).Resultados: avaliando-se a resistência à compressão, os valores mais baixos foram obtidos pelos cimentosPoscal e SS White que foram similares, estatisticamente, aos do Ketac Cem. Referente à tração diametral,os menores valores, estatisticamente similares, foram obtidos pelos SS White, Poscal, Meron e Ketac Cem.Os melhores resultados em relação à resistência à tração diametral e à compressão foram obtidos peloscimentos resisnosos. Conclusão: verificou-se que os cimentos resinosos apresentaram melhor resistênciaà compressão e à tração diamentral com diferença, estatisticamente, significativa dos demais. Além disso,os cimentos de fosfato de zinco e ionômero de vidro convencional apresentaram os menores valores deresistência para ambos os testes

The « magnégné » State : Imaginaries, practices and relations to the government in Mayotte

La thèse étudie le champ politique local dans le département de Mayotte, en considérant ce microcosme insulaire comme un observatoire privilégié de l’État « au concret » aussi bien qu’idéalisé. En questionnant la dialectique centre-périphérie constitutive de la catégorie « outre-mer », que l’on retrouve dans les discours et les pratiques locales, cette thèse montre en effet comment l’État et ses agents se « réinventent » en outre-mer, à travers entre autres ce qui est souvent désigné sur place comme du « bricolage » (magnégné, en shimaoré). Attentive à l’histoire aussi bien qu’à ses usages politiques, la thèse décrit au moyen d’entretiens, d’observations et d’archives les différents rapports à l’État ainsi que les diverses formes de participation au gouvernement du territoire des agents de l’État métropolitain.es (préfecture, rectorat), de ses représentant.es loca.ux/les (élu.es et agents des collectivités territoriales), mais aussi de ses habitant.es (mahorais.es, « expatrié.es »). Elle analyse ainsi les luttes symboliques, sociales et politiques dans lesquelles l’État est pris à Mayotte, et via lesquelles il se déploie, proposant ainsi une redéfinition du gouvernement des marges en contexte post-colonial.This thesis focuses on the local political field in the department of Mayotte, considering this island microcosm as a privileged observatory of the “concrete” as well as idealized government. By questioning the centre-periphery dialectic constitutive of the "overseas" category, which is found in local discourses and practices, this thesis indeed shows how the government and its agents "reinvent" themselves overseas through, among other things, what is often referred to locally as “tinkering” (magnégné, in Shimaoré). Attentive to history as well as to its political uses, this thesis describes through interviews, observations and archives the different relationships to the government as well as the various forms of participation in the territotial government of the agents, of the metropolitan State (prefecture, rectorate), of its local representatives (elected officials and agents of local authorities), but also of its inhabitants (Mahorais “expatriates. "). This thesis thus analyzes the symbolic, social and political struggles in which the state is caught in Mayotte, and through which it unfolds, thus proposing a redefinition of the government of the margins in a post-colonial context