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For almost two decades, the French Institut de Recherche pour le Développement (IRD) has been working in partnership with the Soils and Fertilizer Research Institute (SFRI) to study soil erosion and land use change in the small catchment of Dong Cao, Tien Xuan, North Vietnam. This partnership forms one of the main pillars of the regional Multi - Scale Environmental Changes observatory (MSEC, http://msec.obs - mip.fr/) that was launched in 1998. This network studies three headwater catchments representative of the sloping lands of Southeast Asia (Vietnam, Laos and Thailand) and collects data on weather, land use, agricultural practices, soil, stream discharge, and sediment yields in these catchments. The research conducted within the MSEC framework in Vietnam has demonstrated that the conversion of cassava crops to planted forests and fallows results in reducing erosion. It has also shown the importance of soil biological activity (earthworms - termites) in reducing erosion. Other work has focused on the impacts of erosion on downstream aquatic ecosystems and has shown the importance of studying this often ignored aspect of erosion. All of these results underline the advantages of collaborative research on the long term and further highlight the effectiveness of the long term partnership between SFRI and IRD.

In the field of engineering, knowing the loading applied to a structure makes it possible to solve direct problems whose result is the field of displacement, of deformation in a structure. It is then possible to carry out a dimensioning. However, sometimes this loading must be identified a posteriori. Unfortunately, it is not always possible to measure this load: for example, it is not known a priori where the loading will take place, or it is not possible to place a sensor without damaging it or May require too much space. Indirect measures of displacement, of deformation, of acceleration are then used, and we then have to solve inverse problems, which are generally badly posed. It is then necessary to add additional condition (s) to obtain a unique and stable solution: it is the regularization of the problem. These techniques are well known and their rise is due to the use of the decompositions in singular values of the transfer matrices. However, they require the use of an additional parameter which weights this additional condition: the determination of this parameter is difficult. Few studies have been carried out to intensively test the usual methods of regularization (Tikhonov and truncation of the (G) SVD), in association with the different criteria for determining the regulation parameter and the different possible responses. Work to draw conclusions on the optimal methodology. It has been demonstrated that the measurement of the acceleration associated with a criterion involving the derivatives of the signal to be reconstructed generally gives the best results provided that the GCV criterion is used to determine the regulation parameter. These methods assume that the location of the loading area is known. We have also been interested in deducing this loading area by attempting to reconstruct identically zero loads. This identification was easily carried out provided that there was little force to be identified in relation to the number of available measurements. On the other hand, such identification is difficult when there are no more measures than forces to be identified. Finally, we turned to the loading identification that plasticized the structure studied. It was then attempted to reconstruct the loading assuming that the structure remained linear elastic, whereas it was plasticized: the double loading method was used and simulations were carried out using the Ls-dyna simulation software. The reconstructed force then reveals a static component representing the residual deformation in the structure. In this case, the response to be used to identify the loading is a deformation in a non-plasticized zone.; Dans le domaine de l'ingénierie, connaître le chargement appliqué sur une structure permet de résoudre des problèmes directs dont le résultat est le champ de déplacement, de déformation dans une structure. Il est alors possible d'effectuer un dimensionnement. Cependant, parfois ce chargement doit être identifié a postériori. Malheureusement, il n'est pas toujours possible de mesurer ce chargement : ainsi, par exemple, on ne sait pas a priori où aura lieu le chargement, ou bien il n'est pas possible de placer un capteur sans l'endommager ou encore il peut nécessiter un encombrement trop important. On a alors recours à des mesures indirectes de déplacement, de déformation, d'accélération et on est alors amené à résoudre des problèmes inverses, qui sont en général mal posés. Il est alors nécessaire d'ajouter une (des) conditions supplémentaire(s) pour obtenir une solution unique et stable : c'est la régularisation du problème. Ces techniques sont bien connues et leur essor est dû à l'utilisation des décompositions en valeurs singulières des matrices de transfert. Toutefois, elles nécessitent l'utilisation d'un paramètre additionnel qui pondère cette condition supplémentaire : la détermination de ce paramètre est délicate. Peu de travaux ayant été réalisé pour tester de façon intensive les méthodes usuelles de régularisation (Tikhonov et troncature de la (G)SVD), en association avec les différents critères de détermination du paramètre de régularisation et les différentes réponses possibles, on a effectué un tel travail pour tirer des conclusions sur la méthodologie optimale. On a pu mettre en évidence que la mesure de l'accélération associée à un critère faisant intervenir les dériÎes du signal à reconstruire donne en général les meilleurs résultats sous réserve d'utiliser le critère GCV pour déterminer le paramètre de régularisation. Ces méthodes supposent que la localisation de la zone de chargement est connue. Aussi on s'est intéressée à déduire cette zone de chargement en tentant de reconstruire des chargements identiquement nuls. Cette identification a été effectuée aisément sous réserve qu'on ait peu de forces à identifier par rapport au nombre de mesures disponibles. En revanche une telle identification est délicate lorsqu'on n'a pas plus de mesures que de forces à identifier. Finalement on s'est tourné vers l'identification de chargement ayant plastifié la structure étudiée. On a alors essayé de reconstruire le chargement en supposant que la structure reste linéaire élastique, alors qu'elle a été plastifiée : on a utilisé la méthode du double chargement et effectué des simulations à l'aide du logiciel de simulation Ls-dyna. La force reconstruite fait alors apparaître une composante statique traduisant la déformation résiduelle dans la structure. Dans ce cas, la réponse à utiliser pour identifier le chargement est une déformation dans une zone non plastifiée.

International audience; While considered as sustainable and low-cost agricultural amendments, the impacts of organic fertilizers on downstream aquatic microbial communities remain poorly documented. We investigated the quantity and quality of the dissolved organic matter leaching from agricultural soil amended with compost, vermicompost or biochar and assessed their effects on lake microbial communities, in terms of viral and bacterial abundances, community structure and metabolic potential. The addition of compost and vermicompost significantly increased the amount of dissolved organic carbon in the leachate compared to soil alone. Leachates from these additions, either with or without biochar were highly bioavailable to aquatic microbial communities, though reducing the metabolic potential of the community and harboring more specific communities. Although not affecting bacterial richness or taxonomic distributions, the specific addition of biochar affected the original lake bacterial communities resulting in a strongly different community. This could be partly explained by viral burst and converging bacterial abundances throughout the samples. These results underline the necessity to include off-site impacts of agricultural amendments when considering their cascading effect on downstream aquatic ecosystems. This article is protected by copyright. All rights reserved.

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International audience; This paper discusses the design of an incentive based framework for the promotion and possible upscaling of a biogas-based pilot scheme to manage soil fertility and erosion control on sloping lands, with a focus on policy implications. The study is based on research conducted in 2007 within a small agricultural village of the Hoa Binh Province in Northern Vietnam.

Earthworms are known to significantly influence soil aggregate stability and hence to regulate underlying ecosystem functions such as soil organic matter (SOM) decomposition and soil erosion. However the, available research information on this aspect in the tropics, and especially in Asia, is rather scanty. The aims of this paper are therefore to study the influence of Amynthas khami, an anecic earthworm species, on soil structural properties on one hand, and to determine the factors involved and the consequences for the soil matrix properties on the other hands. Investigations were carried out in different management systems ranging from low to high above-ground casts density. We measured the physical and chemical properties and water behavior (mean weight diameter: MWD, and water drop penetration time: WDPT) of casts and those of the surrounding soil aggregates (control). Pore space was quantified using a morphological approach and 2D image analysis. Soil aggregate stability was primarily specific for each-land use type and afterwards affected by earthworm activity within each ecosystem. Earthworm casts were always more stable than control surrounding soil aggregates. Casts were characterized by higher pH. C, polysaccharides, Ca(2+), Mg(2+) and K(+) contents. Conversely, the particle size fraction and the content of oxides (Al(cbd) and Fe(cbd)) were not significantly affected by earthworm activity. Soil porosity was sharply decreased in casts as compared to the surrounding soil aggregates and casts were characterized by the absence of packing void poroids and large pores > 50,000 mu m(2). Regressions between soil physico-chemical properties and MWD underlined the relationships between SOM (C and polysaccharide content), pH, Ca(2+) content, soil porosity, and the structural stability of cast aggregates. Surprisingly, the abundance of casts on the soil surface was not related to the bulk density of the soil matrix, suggesting that cast aggregates are not integrated into it or that they are integrated with different soil structural characteristics. (c) 2008 Elsevier B.V. All rights reserved.

Rapid changes in upland farming systems in Southeast Asia generated predominantly by increased population pressure and 'market forces' have resulted in widespread land degradation that has been well documented at the plot scale. Yet, the links between agricultural activities in the uplands and downstream off-site effects remain largely unknown because of the difficulties in transferring results from plots to a larger scale. Many authors have thus pointed out the need for long-term catchment studies. The objective of this paper is to summarize the results obtained by the Management of Soil Erosion Consortium (MSEC) over the last 5 years from 27 catchments in five countries (Indonesia, Laos, Philippines, Thailand, and Vietnam). The purpose of the study was to assess the impacts of cultivation practices on annual runoff and erosion rates. Initial surveys in each catchment included topography, soils and land use. Monitoring included climatic, hydrologic and erosion (total sediment yield including bed load and suspended sediment load) data, land use and crop yields, and farmers' income. In addition, new land management options were introduced through consultations with farmers and evaluated in terms of runoff and erosion. These included tree plantations, fruit trees, improved fallow with legumes, maize intercropped with legumes, planted fodder, native grass strips and agro-ecological practices (direct sowing and mulch-based conservation agriculture). Regressions analyses showed that runoff during the rainy season, and normalized runoff flow coefficient based on erosive rainfall during the rainy season (rainfall with intensity exceeding 25 mm h(-1)) increase with the percentage of the catchment covered by maize. Both variables decrease with increasing soil depth, standard deviation of catchment slope (that reflects terrain roughness), and the percentages of the catchment covered by fallow (regular and improved), tree plantations and planted fodder. The best predictors of sediment yield were the surface percentages of maize, Job's tears, cassava and footpaths. The main conclusions generated from this study were: (i) soil erosion is predominantly influenced by land use rather than environmental characteristics not only at the plot scale but also at the catchment scale; (ii) slash-and-burn shifting cultivation with sufficiently long rotations (I year of cultivation, 8 years of fallow) is too often unjustly blamed for degradation; (iii) in its place, continuous cropping of maize and cassava promotes high rates of soil erosion at the catchment scale; (iv) conservation technologies are efficient in reducing runoff and total sediment yield at the catchment scale; (v) the adoption of improved soil management technologies by upland farmers is not a function of the degree of intensification of their farming system and/or of their incomes. The results suggest that if expansion of maize and cassava into already degraded upland systems were to occur due to increased demand for biofuels, there is a risk of higher runoff and sediment generation. A failure to adopt appropriate land use management strategies will result in further rapid resource degradation with negative impacts to downstream communities.

Getting farmers to adopt new technologies to address soil erosion and fertility problems is not easy. In Vietnam, a multidisciplinary research project to improve soil management in traditional mountainous agricultural farming systems managed to attract farmers¿ interest and stop soil erosion. This success stems from encouraging farmers, extensionists and researchers to jointly define and implement the project. Their different aims could be followed simultaneously: scientific results for researchers, better agricultural practice for extension workers, and economic success and free choice for farmers.

Station 1: Soil erosion and land management focused research; International audience; This poster studies the impact of land-use change on soil loss from sloping lands, presenting research on biophysical processes and their environmental and economic consequences. Farming systems are also analysed to infer the driving forces behind farmer strategies and practices. The Vietnam MSEC research program works in a small agricultural experimental watershed of around 50 ha, northeast of Hanoi. The cultivated steep slopes have been equipped to assess water discharge and sediment loads. Soil erosion here has negative impacts on upstream and downstream communi-ties. Increased sediment from these catchments reflects a loss of the fertile topsoil that farmers depend upon. In addition, increased sediment loads in streams and rivers have a negative impact on water quality and the longevity of water storage structures, both of which have significant economic and environmental implications.

In spite of the green revolution of the 1990s, guaranteeing food security remains a challenge in large parts of the mountains of Southeast Asia. It is largely accepted that the most suitable farming systems for the uplands are based either on tree crops or mixed crop-livestock systems, both to manage the soil fertility and to maintain the soil in place. How can this be applied for a sustainable farming system? This project, from the DURAS international program to promote sustainable development in agricultural systems, aims to develop and enhance sustainable agriculture that makes the best use of: 1) the local knowledge and skills of farmers; 2) social capital - people's capacities to work together to solve common management problems; 3) nature's goods and services; and 4) public goods - rural jobs, clean water, flood protection, landscape quality, etc. More specifically, the Vietnamese part of this project works specifically on a better understanding of local-knowledge implications from the disadvantaged communities living in mountainous areas through the spontaneous innovations of farming systems. Local participation has been strengthened along the research and extension processes by a case study: the introduction of fodder crop in the farming system. After completion and evaluation of the first round of fodder tests within experimental plots, on-farm tests have been conducted under farmer management for the most promising species. The farmers selected the fodder species (temperate and/or tropical), the planting place (upland and/or lowland) and the surface on which to cultivate. Interactions with farmers and local extension officers were initiated at the very onset of the project through a former project on watershed management (MSEC program). In addition, experiments and surveys of fodder crops (yield, harvesting and forage management, agricultural calendar etc.) were conducted in close cooperation with farmers in their own fields. Dissemination of the results of these two activities have after one year been greatly facilitated, not only at the village level but also at the commune level. Thus, it seems that methodologies tested and developed by the project will contribute to an improvement of extension approaches for extension workers and local managers as well as to a better linkage between researchers, development agents and farmers. On the other hand, the project is also carrying out experiments on soil and water quality to improve water and soil fertility management at the watershed level, as well as an assessment of the productivity and nutritional value of tested fodder species and their seed production capacity in Southeast Asian mountain conditions. Based on knowledge gained during farmer meetings and experience from the experimental fields, farmers have already defined their strategy. They cultivate only tropical species in the uplands and temperate species in the lowlands, in keeping with scientific knowledge. During the first year, 2006, around 4 ha of forage have been planted; next year more than 20 ha will be planted with fodder. So, by involving village groups as participants, all arguments are mobilized for the successful identification, definition and extension of new agricultural practices for husbandry integration. Furthermore, effective dissemination can be expected in the future.

Through the lens of the Institutional Analysis and Development (IAD) framework, the paper analyses how the combination of reforestation programs and households uplands allocation has significantly altered land management in a commune of Northern Vietnam. Based on a three villages’ case study, we argue that the government policies implemented in the end of the 1990s have not only impacted on individual farmer land-use, but has also induced the collapse of existing informal institutional arrangements governing uplands management. In turn this has had repercussions on farmers’ strategies and households’ resilience. For instance, important changes in land access and land-use rights broke up the subtle collective rules that enabled grazing and cropping systems co-existence. Further to the analysis of policies’ impacts on land use and farmers livelihoods, this study examines how, and under what conditions for a three decade period, farmers have been able to adopt new strategies, new land management systems and new institutional arrangements. Furthermore, we make recommendations for policy-making: on the one hand, directions for new policies development and on the other, advice to champion policies which match impacts to pursued objectives. We adopt a political ecology perspective by focusing on institutions and policies as driving forces for environmental change, and propose a comprehensive approach for analyzing land-use change in mountainous areas. Methodology for data analysis combines the use of the IAD, a rigorous institutional framework that has been widely used in the field of the commons studies, with an historical perspective. The approach integrates environmental, social, and economic factors – from the micro to the macro level – to explain how uniform national policies have lead to different farmers’ strategies and distinct upland management systems.

Through the lens of the Institutional Analysis and Development (IAD) framework, the paper analyses how the combination of reforestation programs and households uplands allocation has significantly altered land management in a commune of Northern Vietnam. Based on a three villages’ case study, we argue that the government policies implemented in the end of the 1990s have not only impacted on individual farmer land-use, but has also induced the collapse of existing informal institutional arrangements governing uplands management. In turn this has had repercussions on farmers’ strategies and households’ resilience. For instance, important changes in land access and land-use rights broke up the subtle collective rules that enabled grazing and cropping systems co-existence. Further to the analysis of policies’ impacts on land use and farmers livelihoods, this study examines how, and under what conditions for a three decade period, farmers have been able to adopt new strategies, new land management systems and new institutional arrangements. Furthermore, we make recommendations for policy-making: on the one hand, directions for new policies development and on the other, advice to champion policies which match impacts to pursued objectives. We adopt a political ecology perspective by focusing on institutions and policies as driving forces for environmental change, and propose a comprehensive approach for analyzing land-use change in mountainous areas. Methodology for data analysis combines the use of the IAD, a rigorous institutional framework that has been widely used in the field of the commons studies, with an historical perspective. The approach integrates environmental, social, and economic factors – from the micro to the macro level – to explain how uniform national policies have lead to different farmers’ strategies and distinct upland management systems.

The agronomical balance in nitrogen at the commune level has been calculated between livestock-produced manure and the total demand in nutrients by crops and fish ponds, in the district of Vu Thu, Thai Binh province (Vietnam). Based on a conceptual Vietnamese-adapted model, calculations have underlined N surpluses in 50% of the studied communes during winter and the importance of waste waters that are expected to be the most important issue for environment regarding the 2010 provincial pig development plans.

This paper describes automated image annotation as an image retrieval problem, in which the distance metric used to express similarity among images is learnt from available distance metrics on several image descriptors (MPEG-7 and SURF). Rather than describing the problem as an optimization problem, we study it as a regression problem. On a dataset of images of buildings taken in the city center of Brussels, we illustrate the superior performance of the combined dis- tance metrics over any of the considered individual distance metrics in automated image annotation.