Coordination et qualité dans les filières agricoles du Sud

The objective of the project is to assess the strengths and weaknesses of different forms of coordination in the development of quality chains in developing countries. Such forms of coordination include: signs of quality (labels, brands, geographical references); horizontal coordination (producers' or traders' associations); vertical coordination (personalized relationships, contracts, integration). Our project is attempting to: (i) characterize problems with quality; (ii) characterize the diversity of forms of coordination to deal with quality problems; (iii) assess the effectiveness of forms of coordination and the potential role of government to strengthen it. The project is based on four case studies of specific quality commodity chains ("safe" vegetables in Vietnam, grain in Mali, special coffees in the Dominican Republic, palm oil in Côte d'Ivoire and Cameroon), as well as workshops that bring together researchers from CIRAD,INRA, universities and countries of the South. Setting up a framework to analyze the relationship between coordination and quality problems is one of the pillars of the project. Problems with quality have been characterized in the four case studies, highlighting the increasing costs and measurement errors between physical quality problems (found in all commodity chains), flavor (palm oil and coffee), safety (vegetables in Vietnam) and ethics (coffee). Despite the incentive for integration predicted by institutional theories dealing with quality problems, personalized relationships predominate in the four commodity chains. Such personalized relationships are very resilient but they are not an effective tool to promote the development of quality beyond a minimal level and only partially eliminate opportunism. The integration between production and marketing is observed to take place successfully in a number of vegetable cooperatives in Vietnam. Furthermore, the conditions for successful collective action have been developed more particularly in the case study involving Mali, revealing the effectiveness of coupling government (at the local level) and private sanctions in case of non-compliance with commitments on the requirements for membership in stakeholders' associations. The project has enabled fruitful exchanges between INRA and CIRAD researchers regarding the layout of analytical frameworks as well as on the research outputs. These exchanges led to the production of several papers, a supported thesis and two master science dissertations. In each case study, one type of coordination method was reviewed using an analysis approach (vertical integration in the case of Vietnam, collective action in the case of Mali, signs for palm oil, while the coffee study has not yet been completed). It would be advisable to continue analytical work on all methods of coordination for the four case studies. Cooperation arrangements could be maintained in the framework of the Moisa UMR (Joint Research Unit). ...French Abstract : L'objectif du projet est d'évaluer les forces et faiblesses de différents modes de coordination dans le développement de démarches qualité dans les pays du sud. Les modes de coordination recouvrent : les signes de qualité (labels, marques, référents géographiques) ; la coordination horizontale (associations de producteurs ou de commerçants) ; la coordination verticale (relations personnalisées, contrats, intégration). Notre projet cherche à : (i) caractériser les problèmes de qualité ; (ii) caractériser la diversité des modes de coordination répondant aux problèmes de qualité; (iii) évaluer l'efficacité des modes de coordination et le rôle potentiel de l'Etat pour la renforcer. Le projet s'appuie sur quatre études de cas de filières de qualité spécifique (légumes sains au Vietnam, céréales au Mali, cafés Spéciaux en République dominicaine, huile de palme en Côte d'Ivoire et au Cameroun), ainsi que sur des ateliers de mise en commun associant des chercheurs du CIRAD, de l'INRA, de l'université et des pays du Sud. La mise en forme d'un cadre d'analyse de la relation entre la coordination et les problèmes de qualité est un des acquis du projet. Les problèmes de qualité ont été caractérisés dans les quatre études de cas en mettant l'accent sur les coûts et erreurs de mesure qui vont croissant entre les problèmes de qualité physique (présents sur toutes les filières), gustative (huile de palme et café), sanitaire (légumes au Vietnam) et éthique (café). Malgré l'incitation à l'intégration prédite par la théorie en situation de problèmes de qualité, ce sont les relations personnalisées qui dominent dans les quatre filières. Ces relations personnalisées ont une grande résilience mais permettent difficilement le développement de la qualité au-delà d'un niveau minimal et n'éliminent que partiellement l'opportunisme. L'intégration entre production et commercialisation est observée avec succès dans le cas de quelques coopératives de légumes au Vietnam. Par ailleurs, les conditions de succès de l'action collective ont été particulièrement approfondies pour l'étude de cas du Mali, révélant l'efficacité du couplage des sanctions publiques (à l'échelle locale) et privées en cas de non-respect d'engagements sur la qualité des membres des associations de commerçants. Le projet a permis de fructueux échanges entre chercheurs INRA et CIRAD sur le plan des cadres d'analyse, ainsi que des résultats de recherche. Ces échanges se sont traduits par la rédaction de plusieurs articles, une thèse soutenue et deux mémoires de stage. Dans chaque étude de cas, un type de mode de coordination a fait plus particulièrement l'objet d'analyses (l'intégration verticale dans le cas du Vietnam, l'action collective dans le cas du Mali, les signaux pour l'huile de palme, tandis que l'étude sur le café est encore incomplète). Il serait intéressant de poursuivre le travail d'analyse de l'ensemble des modes de coordination pour les quatre études de cas. Les collaborations engagées pourront être maintenues dans le cadre de l'UMR MOISA.QUALITY; COORDINATION; INSTITUTIONAL ECONOMICS; COMMODITY CHAIN; FARMERS' ORGANISATIONS; DEVELOPING COUNTRIES

The Addition and Cessation of Inorganic Fertiliser Amendments in Long-Term Managed Grasslands: Impacts on Above and Below-Ground Communities

In recent times, land use in the United Kingdom has undergone considerable changes because of social and economic pressures, leading to a fine balance between the demands of highly productive intensive systems and practices which are perceived to be more environmentally acceptable. Plant productivity is governed by the supply of nutrients from the soil, which in turn is dependent on the dynamics of organic matter decomposition driven by soil micro-, meso- and macro fauna. Considerable information is available concerning the impact of inorganic fertiliser additions on communities of macro-fauna and flora, but the effects on specific microbial communities in soils are less clear. The effects of withholding inorganic nitrogen (N) are much less studied. The present study investigated the impact on plant and soil communities of either adding or withholding N from long-term managed plots

Dynamics of a spherical capsule in a planar hyperbolic flow: influence of bending resistance

International audienceWe consider an initially spherical capsule freely suspended in a planar hyperbolic flow and study the influence of the wall bending resistance on the capsule dynamics. The capsule wall is assumed to be made of a three-dimensional homogeneous elastic material. The fluid-structure interaction between the capsule and the external flow is modeled numerically by coupling a boundary integral method with a shell finite element method. It is found that, for given three-dimensional wall mechanical properties, the capsule deformability is drastically reduced as the bending resistance is increased. But, if one expresses the same results as a function of the two-dimensional mechanical properties of the mid-surface, which is how the capsule wall is modeled in the thin-shell model, the capsule deformed shape is identical to the one predicted for a capsule devoid of bending resistance. The bending rigidity is found to have a negligible influence on the shape and deformation: the capsule main deformation mode is thus solely a function of the elastic stretching of the mid-surface. The wall bending resistance still plays a role locally in the regions where buckling occurs. Its influence is studied in the low flow strength regime, for which wrinkling of the wall is observed to persist at steady state. We show that the wrinkle wavelength only depends on the bending number, which compares the relative importance of bending and shearing phenomena, and provide the correlation law. This result is interesting as it allows bending resistance to be estimated from experiments on capsules in a planar hyperbolic flow at low flow strength

Evaluation of a simple approach for crop evapotranspiration partitioning and analysis of the water budget distribution for several crop species

International audienceClimate variability and climate change induce important intra- and inter-annual variability of precipitation that significantly alters the hydrologic cycle. The surface water budgets and the plant or ecosystem water use efficiency (WUE) are in turn modified. Obtaining greater insight into how climatic variability and agricultural practices affect water budgets and regarding their components in croplands is, thus, important for adapting crop management and limiting water losses. Therefore, the principal objectives of this study are: (1) to assess the contribution of different components to the agro-ecosystem water budget and (2) to evaluate how agricultural practices and climate modify the components of the surface water budget. To achieve these goals, we tested a new method for partitioning evapotranspiration (ETR), measured by means of an eddy-covariance method, into soil evaporation (E) and plant transpiration (TR) based on marginal distribution sampling (MDS). The partitioning method proposed requires continuous flux recording and measurements of soil temperature and humidity close to the surface, global radiation above the canopy and assessment of leaf area index dynamics. This method is well suited for crops because it requires a dataset including long bare-soil periods alternating with vegetated periods for accurate partitioning estimation. We compared these estimations with calibrated simulations of the ICARE-SVAT double source mechanistic model. The results showed good agreement between the two partitioning methods, demonstrating that MDS is a convenient, simple and robust tool for estimating E with reasonable associated uncertainties. During the growing season, the proportion of E in ETR was approximately one-third and varied mainly with crop leaf area. When calculated on an annual time scale, the proportion of E in ETR reached more than 50%, depending on the crop leaf area and on the duration and distribution of bare soil within the year

Sharp interface limits of phase-field models

The use of continuum phase-field models to describe the motion of well-defined interfaces is discussed for a class of phenomena, that includes order/disorder transitions, spinodal decomposition and Ostwald ripening, dendritic growth, and the solidification of eutectic alloys. The projection operator method is used to extract the ``sharp interface limit'' from phase field models which have interfaces that are diffuse on a length scale $\xi$. In particular,phase-field equations are mapped onto sharp interface equations in the limits $\xi \kappa \ll 1$ and $\xi v/D \ll 1$, where $\kappa$ and $v$ are respectively the interface curvature and velocity and $D$ is the diffusion constant in the bulk. The calculations provide one general set of sharp interface equations that incorporate the Gibbs-Thomson condition, the Allen-Cahn equation and the Kardar-Parisi-Zhang equation.Comment: 17 pages, 9 figure

The Moment Guided Monte Carlo method for the Boltzmann equation

In this work we propose a generalization of the Moment Guided Monte Carlo method developed in [11]. This approach permits to reduce the variance of the particle methods through a matching with a set of suitable macroscopic moment equations. In order to guarantee that the moment equations provide the correct solutions, they are coupled to the kinetic equation through a non equilibrium term. Here, at the contrary to the previous work in which we considered the simplified BGK operator, we deal with the full Boltzmann operator. Moreover, we introduce an hybrid setting which permits to entirely remove the resolution of the kinetic equation in the limit of infinite number of collisions and to consider only the solution of the compressible Euler equation. This modification additionally reduce the statistical error with respect to our previous work and permits to perform simulations of non equilibrium gases using only a few number of particles. We show at the end of the paper several numerical tests which prove the efficiency and the low level of numerical noise of the method.Comment: arXiv admin note: text overlap with arXiv:0908.026

A partitioned model order reduction approach to rationalise computational expenses in multiscale fracture mechanics

We propose in this paper an adaptive reduced order modelling technique based on domain partitioning for parametric problems of fracture. We show that coupling domain decomposition and projection-based model order reduction permits to focus the numerical effort where it is most needed: around the zones where damage propagates. No \textit{a priori} knowledge of the damage pattern is required, the extraction of the corresponding spatial regions being based solely on algebra. The efficiency of the proposed approach is demonstrated numerically with an example relevant to engineering fracture.Comment: Submitted for publication in CMAM