Compromis entre productivité et biodiversité sur un gradient d'intensité de gestion de systèmes agroforestiers à base de cacaoyers de Talamanca, Costa Rica

Le cacaoyer (Theobroma cacao, L.) est cultivé dans les tropiques humides d'Amérique latine, d'Afrique et d'Asie. Principale source de revenus d'une agriculture essentiellement familiale, les systèmes agroforestiers à base de cacaoyers fournissent de nombreux services écologiques et contribuent à la conservation de la biodiversité. Ces systèmes associent plantes ligneuses et cultures de manière simultanée, dans une gamme importante et peu décrite de richesses et de structures botaniques. Les connaissances actuelles sur leur productivité se limitent à des essais en milieu contrôlé associant un petit nombre d'espèces. Nos travaux testent l'hypothèse d'une relation de compromis entre le niveau de productivité des cacaoyers et le niveau de biodiversité hébergée par les agroforêts à base de cacaoyers. Nous caractérisons ces compromis sur un gradient de situations de production paysannes, reposant sur la structure verticale, l'intensité de gestion de la composante végétale et le contexte bio-physique des agro-systèmes étudiés. Sur un dispositif de 36 cacaoyères paysannes situées dans la région de Talamanca, Costa Rica, nous montrons que des variations significatives de la structure végétale reflètent les modes de gestion de la parcelle et affectent le rendement par cacaoyer (295 à 667g/arbre/an) mais pas le rendement en cacao (136 kg/ha/an), ni le volume végétal global (400 m3/ha). Ces variations de la structure végétale affectent peu la diversité a des peuplements de plantes associées, d'épiphytes, d'amphibiens, de reptiles, de mamifères, d'invertébrés du sol et de la litière, mais leur diversité b répond de manière contrastée à ces variations d'habitat. Les relations de compromis que nous mettons finalement en évidence entre la productivité en cacao marchand à l'hectare ou à l'arbre et les niveaux de biodiversité atteints sont de nature (linéaire, cubique, quadratique) et de tendances (négative, postive) contrastées selon le taxon considéré et remettent en cause les résultats de certains travaux récents. Nos travaux dévoilent également des situations de compromis optimales, offrant des perspectives positives pour l'intensification écologique des systèmes agroforestiers tropicaux.Cacao (Theobroma cacao, L.) is cultivated in the humid tropics of Latin America, Africa and Asia. Cocoa-based agroforestry systems are the main source of income for smallholders' families and provide numerous ecological services and contribute to biodiversity conservation. These systems associate trees with crops simultaneously, in a wide and poorly described range of botanical and structural plant diversity. The current knowledge about their productivity is restricted to controlled trials with a low numer of associated plant species. Our work tests the hypothesis of a trade-off relationship between the level of cocoa productivity and the level of biodiversity hosted in cocoa-based agroforests. We characterize these trade-offs on a gradient of production situations, based on the vertical structure, the management intensity of the vegetal component and the bio-physical context of cocoa-based agroforests. On the base of a 36 on farm cocoa plots network located in Talamanca, Costa Rica, we show that significant variations in the vegetation vertical structure reflect farmer's management strategies and affect the cocoa yield per tree (295 to 667g/tree/year) but neither the cocoa yield per plot (136 kg/ha/year), nor the global plant volume (400 m3/ha). The variations in vegetation structure poorly affected the a-diversity of 7 plant and animal taxa, but their b-diversity gave contrasted and significant responses to habitat variations. Finally, the trade-offs relationships we display between dry cocoa productivity per hectare or per tree and the observed biodiversity levels showed contrasted forms (cubic, quadratic, linear) and tendances (positive, negative) according to the taxa considered and question results from recent publications. Our work also revealed optimal trade-off situations which offer positive prospects for the ecological intensification of tropical agroforestry systems.MONTPELLIER-SupAgro La Gaillarde (341722306) / SudocSudocFranceF

Dry Matter Production, Nutrient Cycled and Removed, and Soil Fertility Changes in Yam-Based Cropping Systems with Herbaceous Legumes in the Guinea-Sudan Zone of Benin

Traditional yam-based cropping systems (shifting cultivation, slash-and-burn, and short fallow) often result in deforestation and soil nutrient depletion. The objective of this study was to determine the impact of yam-based systems with herbaceous legumes on dry matter (DM) production (tubers, shoots), nutrients removed and recycled, and the soil fertility changes. We compared smallholders' traditional systems (1-year fallow of Andropogon gayanus-yam rotation, maize-yam rotation) with yam-based systems integrated herbaceous legumes (Aeschynomene histrix/maize intercropping-yam rotation, Mucuna pruriens/maize intercroppingyam rotation). The experiment was conducted during the 2002 and 2004 cropping seasons with 32 farmers, eight in each site. For each of them, a randomized complete block design with four treatments and four replicates was carried out using a partial nested model with five factors: Year, Replicate, Farmer, Site, and Treatment. Analysis of variance (ANOVA) using the general linear model (GLM) procedure was applied to the dry matter (DM) production (tubers, shoots), nutrient contribution to the systems, and soil properties at depths 0-10 and 10-20 cm. DM removed and recycled, total N, P, and K recycled or removed, and soil chemical properties (SOM, N, P, K, and pH water) were significantly improved on yam-based systems with legumes in comparison with traditional systems

Analyse et évaluation de systèmes agroforestiers complexes sur le long terme (application aux systèmes de culture à base de cacaoyer au Centre Cameroun)

La cacaoculture est aujourd'hui considérée comme un des principaux facteurs de déforestation en milieu tropical. Dans de nombreux pays, elle repose en effet sur un modèle technique peu durable de monoculture intensive impliquant le déplacement des zones de production. Souvent délaissés par la recherche en raison de leurs faibles rendements en cacao marchand, les systèmes agroforestiers à base de cacaoyer apparaissent aujourd'hui comme une alternative crédible pour faire face aux nouveaux enjeux de la cacaoculture mondiale. Au Centre-Sud du Cameroun, la cacaoculture repose en grande partie sur des cacaoyères agroforestières anciennes, ce qui pose l'hypothèse qu'un modèle de cacaoculture durable basé sur des systèmes de culture agroforestiers est possible. Notre objectif est de mieux comprendre le fonctionnement de ces systèmes agroforestiers à base de cacaoyer, à travers leurs caractéristiques, leurs évolutions et leurs déterminants, ainsi que les conditions de leur production en cacao marchand sur le long terme. Notre démarche articule à la fois une évaluation des systèmes agroforestiers complexes à l'échelle de la parcelle et une analyse compréhensive des pratiques techniques sur le temps long. La thèse repose sur un dispositif de recherche mis en place dans la région du Centre, dans trois zones de culture différenciables par leurs conditions pédo-climatiques (Bokito, Zima et Ngomedzap). Une enquête d'agriculteurs a été réalisée à grande échelle (1 171 exploitations regroupant 1 638 cacaoyères), complétée par des observations spécifiques réalisées dans un réseau de 61 cacaoyères exploitées par 40 agriculteurs. Résultats. (1) Nos résultats d'enquête, complétés par des observations spécifiques, ont confirmé la durabilité des systèmes agroforestiers à base de cacaoyer aux plans agro-écologique et socio-économique. (2) Dans la zone de transition forêt-savane, considérée comme sub-optimale pour la cacaoculture, nous avons montré que le modèle technique adopté par les agriculteurs leur permet d'installer sur savane des cacaoyères viables sur le long terme. (3) Une méthode participative de quantification de la valeur d'usage des espèces par les agriculteurs, appliquée sur le réseau d'observation, a confirmé la multifonctionnalité des systèmes agroforestiers et mesuré la place qu'y occupe la composante cacaoyère. (4) L'évaluation des peuplements cacaoyers, réalisée en adaptant la méthode de diagnostic agronomique régional aux systèmes complexes, a permis d'identifier les facteurs limitant le rendement en cacao marchand. Celui-ci s'avère étroitement lié à la structure des peuplements cacaoyers et à celle des peuplements associés. (5) Enfin, l'analyse compréhensive des pratiques des agriculteurs sur le long terme, en lien avec l'évolution technique des peuplements cacaoyers a confirmé la flexibilité des systèmes agroforestiers à base de cacaoyer. Cette flexibilité peut être traduite par des trajectoires d'évolution des pratiques et des trajectoires de structures spécifiques. Ce travail fournit une nouvelle base méthodologique pour l'analyse et l'évaluation des systèmes agroforestiers complexes. L'ensemble des résultats et des connaissances produites dans ce travail permet de formuler des propositions pour la mise au point d'un nouveau modèle technique en cacaoculture.Cocoa cultivation is generally considered as one of the main deforestation factors in the Tropics. Indeed, in many countries it is based on a low-sustainability technical model of intensive monocrops with shifting production zones. Cocoa agroforests, which are often neglected by research due to their low fermented dried cocoa yields, now appear to be a credible alternative for taking up the new challenges facing world cocoa production. In Centre-South Cameroon, cocoa cultivation is largely based on old cocoa agroforests, which suggests that a sustainable cocoa growing model based on agroforestry systems is possible. Our aim was to more effectively understand how these cocoa agroforests function, through their characteristics, their evolution and their determinants, along with the conditions for their long-term fermented dried cocoa production. Our approach consisted of an evaluation of cocoa agroforests on a plot scale and a comprehensive analysis of technical practices over the long term. The thesis is based on an experimental design set up in the Centre region, in three growing zones that could be differentiated through their pedo climatic conditions (Bokito, Zima and Ngomedzap). A large-scale survey was undertaken (1,171 farms grouping 1,638 cocoa plantations) completed by specific observations collected in a network of 61 cocoa agroforests managed by 40 farmers. Results. (1) Our survey results, completed by specific observations, confirmed the sustainability of the cocoa agroforestry systems from an agro ecological and socio-economic viewpoint. (2) In the forest-savannah transition zone, which is considered sub-optimum for cocoa cultivation, we confirmed that the technical model adopted by the farmers enabled them to set up cocoa agroforests on savannah that were viable over the long term. (3) In the network, a participatory method applied to quantify the use value given to the species by the farmers confirmed the multi-functionality of cocoa agroforests and measured the place occupied in it by cocoa. (4) The evaluation of the cocoa tree stands, achieved by adapting the regional agronomic diagnosis method to complex systems, revealed the factors limiting cocoa yield. It was proved that cocoa yield is closely linked to the structure of the cocoa tree stand and that of the intercropped stands. (5) Lastly, a comprehensive analysis of farmer practices over the long term, in association with the evolution of the technical management of the cocoa tree stands, confirmed the flexibility of cocoa agroforestry systems. This flexibility was reflected in the evolution pathways for specific practices and structures. This work provides a new methodological basis to assess the performance of complex agroforestry systems. All the results and knowledge produced by this work make it possible to draw up proposals for developing a new technical model for cocoa growing.MONTPELLIER-SupAgro La Gaillarde (341722306) / SudocSudocFranceF

Vers une agroécologie biodiverse : enjeux et principaux concepts mobilisés

SPEPôle ECOLDURThis text relates to the introduction of the workshop “Using biodiversity” given on October, 18th at the 2013 symposium on Agroecology. It is inspired by the discussions of the working group "Agroecology and soil" of the alliance between institutes on environmental research AllEnvi. Some major issues are exposed and the principles on how the use of biodiversity could improve agroecosystem management are presented.Ce texte constitue l’introduction à l’atelier « utiliser la Biodiversité » du colloque agroécologie du 17 Octobre 2013. Il est inspiré des échanges qui ont eu lieu au sein du groupe thématique ‘Agro-écologie et sol’ d’AllEnvi. Il énonce les enjeux et pose les bases conceptuelles relatives à l’utilisation de la biodiversité pour la gestion des agroécosystèmes

Structure and dynamics of coconut-based agroforesty systems in Melanesia : a case study from the Vauatu archipelago

Coconut (Cocos nucifera)-based agroforestry systems hold promise as a sustainableland use activity in the Melanesian islands, where food dependency on foreign sources andland shortages are increasing drarnatically. This chapter describes the dynamics of thesesmallholder production systems in the Malo Island of northern Vanuatu (Melanesia), where adual economy operates in which resources are dedicated to both subsistence and commercialproduction. The floristic elements found in the coconut plantations were typical of thosedescribed in the hurnid tropical homegardens elsewhere, with an average of 12 tree speciesper plot. Mean Shannon Weaver index was 1.57 with the vertical profile of vegetation havingone-to-five strata. Although the coconut palrns dorninate these production systems, in certaincases other trees may dominate it. Situations in coconut plots evolve throughout thedevelopment phase of the palms. Based on that, five types of smallholder coconut-basedagroforestry systems were recognized, which falls into two main evolutionary patterns: (1) aperennial occupation of the cultivated land by coconut trees, because of coconut replanting,and (2) a gradua1 return to tree fallow in which the coconut palms gradually disappearbecause of changes in the complex multistrata vegetation

Organisation spatiale et dynamiques des systèmes de culture à base de cocotier (Cocos nucifera L.) dans une île mélanésienne: le cas de Malo (Vanuatu).

Copra production has represented a major income source for Vanuatu’s rural population since at least the mid-nineteenth century. European plantations and then smallholder coconut plantations made a significant and rapidly increasing contribution to Vanuatucopra production, particularly in the Northern islands of the Archipelago. The extension of the plantation system substantially modified the traditional smallholder farming and cropping systems. Since the late 1990s, world copra prices and farmer’s net incomes have declined significantly. Consequently, farmers and agricultural extension services are investigating new cropping systems in which ecological sustainability and economical profitability can both be realized. After forest or bush fallow clearing, food gardens and coconut trees are frequently associated in a complex annual-perennial system involving intercropping and other agricultural enterprises, such as livestock production. In such cases, established coconut stands are associated with various crops and enterprises, e.g., fruit trees, cocoa, pineapples, vanilla, cattle pasture and sometimes new coconut plantings. Our objective was to evaluate the performance, evolution and sustainability of this type of mixed cropping system, and the capacity to integrate food gardens in these systems. Due to the difficulty in analysing the long term effects on long duration perennial crops, we chose to study a variety of cultural situations at a given time (plots with coconut trees of various ages and in different types of association) in order to understand the temporal dynamics of the mixed cropping systems. The main steps of this approach are presented in this paper. The study was undertaken on Malo island, Vanuatu. Firstly, a historical analysis of the coconut population of the island was carried out using “zonal mapping through key human resource” methodology. The results have been analysed and used to identify and locate representative target areas for field work. Next, we then characterised coconut plantations in the target locations in order to represent the greatest diversification of cultural situations possible. The two main cropping systems were then identified enabling us to understand their temporal dynamics. Two main systems were identified: (i) agropastoral systems, and (ii) agroforestry systems. These two systems differ from each other when coconut trees begin to produce. The transitional cultural situations between the two systems have been identified, showing their flexibility. The importance of the two main cropping systems varies according to locality. The most dominant system is the agropastoral, which appears more frequently in coastal areas. The agroforestry system appears more frequently on the plateau, where the foreign origin of the farmers may explain their wish to achieve the optimal use and enhanced value of their limited available land resources. The multiple generations system is observed only on the West Coast where the plantations are comparatively older and where the area for cultivation has become limited. The agroforestry coconut-based system may appear as the most profitable in a context of current poor copra profitability. The agronomical and economic evaluation of these systems will permit us to test the validity of this hypothesis. The results show that the association between food gardens and coconut plantations has to be in moderation, at least under the conditions of our study. Both systems appear to be evolving in close association. The integration of food gardens with coconut plantations might be possible both at the beginning of the coconut cycle and also on senile coconut-tree plantations where there is increased light filtering through the canopy. The characterisation of the different cropping systems has been the first step before their evaluation. On a pilot plot scale, the temporal evolution of soil fertility, light availability under the coconut canopy and root colonisation, which are key factors in mixed systems, will be explored. On a regional scale, the spatial location of different cropping systems will be studied using remote sensing data.Dans les îles du nord du Vanuatu, le coprah constitue la première source de revenu. L’extension des cocoteraies, initiée au début du siècle, a profondément modifié les systèmes de culture mélanésiens. Le déclin actuel de la rentabilité du coprah et l’augmentation de la pression démographique motivent maintenant la recherche de nouveaux équilibres agricoles. Les plantations de cocotiers constituent en réalité des systèmes de culture complexes, objet de multiples associations végétales et/ou animales. Les cocotiers en phase juvénile sont fréquemment associés à des jardins vivriers, puis en phase productive à des pâturages pour bovins ainsi qu’à diverses cultures (fruitiers ligneux, cacao, tubercules, etc.). L’évaluation des performances productives et environnementales de ces systèmes nécessite la compréhension de leurs dynamiques temporelles, et notamment du positionnement spatial et temporel des différentes associations (jardins, pâtures, fruitiers) au sein de ces cocoteraies. Une démarche spécifique, utilisant la diversité des situations culturales (en termes de stade de développement des cocotiers et de type d’association) existant sur la zone d’étude, a été mise au point et appliquée sur l’île de Malo (Vanuatu : 15°40’S ;167°10’E). Deux systèmes de culture principaux, l’un de type agropastoral et l’autre de type agroforestier ont ainsi pu être identifiés. Leur localisation géographique est discutée

Décliner les principes de l’agroécologie à la protection des cultures: les contours de l’agroécologie

Décliner les principes de l’agroécologie à la protection des cultures: les contours de l’agroécologi

Multi-criteria evaluation of organic agriculture in sub-Saharan Africa using probabilistic elicitation of expert knowledge

Many African agricultural systems can potentially be described as "organic". However, the capacity of organic agriculture to address food security issues in Africa is poorly known, as only few experimental studies are available in this region. Probabilistic elicitation is used here to represent knowledge of experts on one or more quantities of interest in a quantitative manner, and to describe the associated levels of uncertainty. The objective of this study is to explore how probabilistic elicitation of expert knowledge could be used to overcome the lack of quantitative experimental data on the performance of organic agriculture in Africa. This approach was applied in Senegal, Burkina Faso and Cameroon where 17 experts were interviewed on the relative performance of organic and conventional agriculture on different aspects of the local food security in sub-Saharan Africa. Our results show that the yields of organic systems are about 41% lower than the yields of conventional systems, while the prices of organic products are 34% higher than prices of products from conventional agriculture. According to the experts, the cost of labor, measured in man-days per unit of cultivated land area, is higher in organic systems. This study is the first to demonstrate the interest of the probabilistic elicitation of expert knowledge to evaluate cropping systems in situations where the experimental data are scarce or unreliable

Evidence for farmers' active involvement in co-designing citrus cropping systems using an improved participatory method

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699International audienceAgricultural policymakers are addressing the sustainable development issue by designing new agricultural systems. Farmers are ultimately asked to make deep changes at field scale. Designing cropping systems has previously been done using prototyping methodologies. Prototyping methodologies use a five-step designing process at field scale and request multicriteria analysis of the resulting prototypes. However, sustainable dynamics implies considering changes at larger scales, farm and region, as well as creating feedback and facilitating participation of all the stakeholders involved in the process. Here we studied citrus production in Guadeloupe, French West Indies, where farmers must reduce pesticide loads despite unresolved weed control issues. We designed the DISCS method, which stands for "participatory redesign and assess innovative cropping systems", to improve classical prototyping methods by implementing a multi-scale, multi-stakeholder, participatory approach. Compared to classical prototyping methods, the DISCS method differs by implementing three progress loops, at experimental field, farm, and regional scales. Three categories of professional stakeholders are involved: farmers, researchers, and agricultural advisers, who are collectively in charge of designing and testing cropping system prototypes. In addition, local public stakeholders including representatives of state institutions are consulted. Progress is assessed using scale-specific sets of indicators. The DISCS method was applied to develop low-pesticide citrus cropping systems. Five weed control prototypes were jointly designed by citrus farmers and researchers, and two multicriteria assessment tools were built for use at the experimental station and on the farms. Results show that involved farmers transferred the new techniques to their own farms on their own initiative, thus spontaneously becoming pilot farmers. The DISCS method is therefore the result of a co-design process between farmers and researchers. The DISCS method creates an ongoing dynamic relationship between agricultural and public stakeholders to build a solution that can continuously be adjusted to stakeholders' expectations