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تغطي منظومة البلوط الفليني الأصيلة أزيد من نصف مساحة غابة المعمورة بالشمال الغربي من المغرب. وقد ساهمت لمدة طويلة و ما زالت تساهم في صون التنوع الحيوي البيئي في المنطقة على مستوى الطابقين النباتيين التحت شجيري و العشبي. يسمح البلوط الفليني، بشكل عام، بتزويد التربة بكميات وفيرة من الأنفوضة سريعة التحلل والتي توفر بدورها مادة عضوية مخصبة تشكل مخزونا هاما للكاربون، كما يزود التربة بكمية إضافية من الرطوبة ويوفر بذلك ظروفا مواتية لاستقرار المنظومة البيئية بأكملها. غير أن هذه المنظومة عرفت، محليا، عدة تحولات بعلاقة مع تدخل الإنسان، فإلى جانب المنظومة الأصيلة و التي ماتزال تحافظ على خصائصها البيو جغرافية، نجد منظومات أخرى أقل أصالة كمجالات البلوط المفتوحة أمام نشاط الرعي والتي عرفت تراجعا كبيرا لمميزاتها الأصيلة و المنظومات الدخيلة على غابة المعمورة كالأكاسيا والصنوبر والأوكاليبتوس والتي غيرت جذريا معالم المنظومة الأصيلة. بناء على هذه الملاحظة الأولية، تحاول هذه الدراسة إبراز دور منظومة البلوط الفليني في صون التنوع الحيوي البيئي بغابة المعمورة من خلال المقارنة بين المنظومات الثلاث المتواجدة بالمعمورة, Territoires, Environnement et Développement (TED), Vol. 1, No 1 (2022)

L'agroforesterie, association d'arbres à des cultures ou de l'élevage, se pose désormais en alternative à l'agriculture industrielle. Ses principaux atouts sont la protection du sol, de l'eau et de la biodiversité, tout en maintenant une production agricole, et son rôle pour atténuer le changement climatique ou s'y adapter, sans oublier les multiples productions des arbres (bois, fruits, fourrage, médicaments, etc.). Retours d'expérience et données scientifiques sont maintenant disponibles mais il n'existait pas à ce jour d'ouvrage synthétique en français sur ce sujet. Mettre cette information à la disposition d'un large public afin d'encourager cette pratique innovante et mal connue : tel est le but de ce livre, afin de susciter de nouvelles initiatives et d'aider au changement. D'une lecture facile et incluant beaucoup d'exemples, accompagné d'une riche iconographie, d'un index détaillé et de nombreuses références scientifiques, Le Livre de l'agroforesterie permettra à tous, agriculteurs, techniciens, étudiants, chercheurs ou tout simplement curieux, de découvrir cette pratique et d'approfondir leurs connaissances.

International audience; Background and aims The trend of soil degradation in intensive open coffee systems is well-documented. This study highlights the impact of young shade trees on soil quality only 4 years after their intercropping with coffee. Methods 18 young shade trees belonging to three tree species (Cinnamomum camphora, Bishofia javanica and Jacaranda mimosifolia) were selected in an intensive coffee system in Southern Yunnan. Soil samples (0-20 cm) were tested for chemical composition, soil communities and soil enzyme activities under their canopies and in open areas, both in coffee rows and inter-rows, once during the rainy and once during the dry season. Additionally, root systems were characterized using trenches. Soil water profiles and litterfall were monitored along the production cycle. Coffee yield was recorded for two consecutive years. Results We detected a positive impact of all shade tree species on soil chemical, biological and biochemical components, especially during the dry season. This positive impact included higher soil organic matter (+10%) and more abundant soil microbial communities (+64%) under shaded coffee than under open coffee. Furthermore , shaded coffee trees yielded as much as open coffee trees, except under C. camphora, probably due to high below-ground competition. Conclusions These results demonstrate that carefully selected shade trees can rapidly contribute to preserving and/or restoring soil quality in intensive coffee systems, while maintaining high coffee yield.

Maize monoculture systems often cause environmental impacts such as soil erosion, nitrate leaching and pesticide transfer. Conservation tillage and the use of cover crops appear to hold promise for limiting these impacts, but questions about their performance remain, particularly during the transition period after conventional soil tillage ceases. In this study, effects of no-tillage maize and fallow-period management with different cover crop species, either pure or in mixtures, were studied on the agronomic performance of maize and on soil N and water dynamics. The study combined field experiments over three years (2012–2014) and simulation modelling with the STICS model. The biomass of cover crops produced during the fallow period varied from 0.8 to 10.5 t dry matter ha−1 depending on the cover crop species and date of termination. Differences in soil water content were quantified among the treatments studied, with the lowest water content at the beginning of the maize growing season with late termination of a cover crop composed of pure faba bean or a vetch-oat mixture in 2014 (25–50% of plant-water available capacity). Maize grain yields ranged from 8.5 to 13.6 t dry matter ha−1, with the lowest yields in the bare soil treatment. Simulations with STICS were consistent with the observations and indicated a decrease in drainage of 8–38 mm year−1, depending on the year and cover crop. Introducing cover crops into maize systems is a powerful mechanism for maintaining production while improving environmental performances during the transition phase of soil properties in conservation tillage.

L’érosion des sols est un risque naturel qui est exacerbé par les activités anthropiques en République démocratique du Congo. Cependant, il existe peu d’information sur la spatialisation de ce phénomène à l’échelle territoriale. Cette étude est basée sur l’utilisation du modèle USLE (Universal Soil Loss Equation) et des données en accès libre pour cartographier les zones à risque d’érosion et faire la priorisation des zones pour la conservation des sols dans le territoire d’Uvira. Au regard de résultats, 52,79 % du territoire est caractérisé par un risque d’érosion faible tandis que 47,21 % font face à un risque de perte de sol supérieure à la limite tolérable de 11 t/ha/an dans le contexte des paysages tropicaux et montagneux. Ce risque est accentué par la perte du couvert végétal au profit de l’extension des zones urbaines et agricoles. Le faible niveau de sensibilité à l’érosion se trouve au niveau de la plaine de la Ruzizi tandis que les zones situées dans les plateaux présentent une forte sensibilité en raison de leur relief accidenté et une pluviosité forte. L’analyse statistique des rapports de fréquence des glissements de terrain montre l’existence d’une relation entre leur occurrence et les zones d’intensité d’érosion. La modélisation de la perte de sol en fonction des différentes méthodes de protection de sol montre que l’approche de mise en place des bandes enherbées et l’aménagement des terrasses sont les plus appropriés pour réduire le risque d’érosion dans ce secteur. Ces méthodes peuvent être associées aux efforts d’afforestation pour une protection efficace des sols., Soil erosion is among the natural hazards that are exacerbated by human activities in the Democratic Republic of Congo (DRC). However, there is little information on the spatialization of this phenomenon at the territorial level in the DRC. This study assesses the potential use of Geographic Information System (GIS) techniques and open access data to map areas at risk of erosion and prioritize areas for soil conservation in Uvira’s territory. In terms of results, 52.79% of this territory is characterized by a low risk of erosion with an average soil loss of 6.08 t ha-1 year-1 while 47.21% faces a risk of soil loss which excess the tolerable limit of 11 t ha-1 year-1 for highlands of tropical areas. This risk is accentuated by the loss of vegetation cover in profit of agricultural activities and urbanization. The low level of sensibility to erosion is found in the Ruzizi plain while the areas in the plateaus are highly susceptible due to their rugged terrain and high rainfall intensity. The statistical analysis of the frequency ratios of landslide shows the existence of a relationship between their occurrence and erosion intensity zones defined on the basis of the Universal Soil Loss Equation (USLE model). Soil loss modeling for different soil protection methods shows that the grassland banding and terracing approach are most appropriate to reduce the risk of erosion in this area. These methods can be combined with afforestation efforts for effective soil protection in Uvira.

Tropical island saprophagous invertebrates have received little attention despite their important role in sustaining soil fertility. Soil biodiversity in the agroecosystems of the Lesser Antilles is subject to various anthropic and environmental perturbations; therefore, it is crucial to promote agricultural practices that help preserve it. Here, we investigate the effect of conversion to organic farming in sugarcane production on soil saprophagous invertebrates in a Martinique plantation (Lesser Antilles). The abundance, biomass and diversity of communities were measured in three fields undergoing organic conversion and in two control fields under conventional production. Invertebrates were sampled both by pitfall trapping and Tullgren extraction. The results indicated that abundance was significantly higher in fields undergoing conversion (342 ± 78 ind.m−2) compared to fields under conventional farming (146 ± 34 ind.m−2). The response of the whole community's biomass to organic conversion was not significant, reflecting a contrasting response of each invertebrate taxa: isopod biomass was the most impacted, earthworm biomass was moderately impacted and diplopod biomass was not significantly affected. A total of 25 morphospecies for all taxa were distinguished in this study. However, the diversity did not differ and community composition remained similar under both farming practices. The response of invertebrate abundance and biomass could be either due to the direct toxicity of herbicides intensively used in conventional sugarcane cultivation or to the indirect effects of herbicides modifying micro-habitat parameters (weed biomass, amount of mulch and litter humidity). In conclusion, the study shows that organic farming has a beneficial effect on soil saprophagous invertebrates even after a short period of conversion (between one and two years), which is promising for restoring soil biological processes in the context of agroecological transition.

National audience; La méthanisation est une technologie basée sur la dégradation par des micro-organismes de la matière organique, en conditions contrôlées et en l'absence dioxygène. Cette dégradation aboutit à la production d'un biogaz utilisé comme énergie renouvelable et d'un co-produit riche en matière organique appelé digestat. Ce digestat est au cœur de nombreuses interrogations, concernant les impacts engendrés par son épandage sur les sols. Avec l'essor de la méthanisation, la recherche s'intéresse à ses effets, afin de conserver des sols de qualité.

International audience; pas de résumé

Cet article propose d'exposer d’évaluations initiales sur l’effet des pratiques agricoles pluviales à s'élever l’érosion hydrique dans le bassin moyen de l’Oued Nefifikh (Maroc atlantique). Le premier résultat via le modèle RUSLE et l’observation du terrain, a montré que les versants triasiques sont plus érosifs en comparaison avec les autres pentes géologiques. Cette érodibilité élevéesne dépend pas seulement des caractéristiques des faciès triasique friable et des intensités irrégulières des pluies orageux, mais il est liéaussi à lagrande extension de pratiques agricoles conventionnelles inappropriées. Les résultats sur les parcelles expérimentales (mesure l’infiltration via l’approche MUNZ et de l’état de surface par la méthode points quadras) ont montré que les champs d’olivier, et bien les parcelles d’assolement continu (légumineuse/céréale) avec un apport maximum de résidus en surface, donner un bon équilibre hydrique et structural du sol, par contre les rotations de jachère (jachère-blé) avec le labour conventionnel a révélé le mauvais rythme d’infiltration et la sensibilité élevée à la compaction et à la formation des croûtes de battances sous l'action des pluies agressives. Donc, ce résultat initial a permet d'exposer notre point de vue sur quelques pratiques locales, qu’ils améliorent le sol et maintiennent son stabilité structural et hydrique, et avec lesquellespouvant faire face à l’effet des forces érosives sur les sols agro-pastoraux

International audience; Aims: Understanding how soil aggregate stability (MWD) is influenced by microbial diversity and abundance can be crucial for ecological restoration in severely disturbed areas. We investigated the relationships between plant and soil microbial diversity and MWD of an ultramafic Ferralsol along a vegetational succession gradient in New Caledonia, where wildfires and extensive nickel mining have degraded the landscape. Methods: Five plant communities were studied. For each one, MWD, soil physicochemical parameters (e.g. soil organic carbon (SOC)), plant root traits and fungal abundance were measured. The diversity and structure of plant and microbial communities were respectively assessed via botanical inventories and a metagenomic approach. A generalized linear model (GLM) was used to assess the influence of diversity indexes on MWD. Constrained ordinations (CCA) were performed to assess the influence of communities' structures on MWD. Results GLM highlighted the linkage between SOC and MWD but did not identify any significant influence of diversity indexes on MWD. CCA revealed a significant influence of communities' structures, especially the abundance of saprotrophic fungi, on MWD. Conclusions: We showed that the structure, but not species richness and diversity of plants, soil fungi and bacteria influence aggregate stability on Ferralsols.

On upland soils in tropical Africa, common production constraints of rice and maize on smallholder farms are poor soil fertility—resulting from soil erosion and nutrient depletion—and infestation by witchweeds (Striga spp.). In Madagascar where these crops are often grown in rotation, combining legume cover crops with no-till and crop residue mulching—labelled conservation agriculture (CA)—may address these problems. Previously, it was shown that CA practices contribute to steep reductions in Striga asiatica infection. In the current study, a 4-year field experiment was conducted to test, for the first time, the hypothesis that CA practices also contribute to crop yield and soil improvements under Striga-infested conditions. The conventional mono-crop rice–maize rotation practice, involving seasonal tillage and crop residue removal, was compared to three rice–maize rotation systems following CA practices, each with a different legume cover crop option: (1) two short-cycle annual species, cowpea (Vigna unguiculata) and mucuna (Mucuna pruriens); (2) a long-cycle annual, ricebean (Vigna umbellata); and (3) a perennial, stylosanthes (S. guianensis). Rice yields, as well as yield variability, generally increased by changing from the conventional to a CA practice, and maize yields were variable and low in particular under the CA practices. CA practices significantly reduced soil displacement by rainwater runoff and increased soil nitrogen and pH levels (0–20 cm depth), in particular with stylosanthes as cover crop, but did not result in a significant change in soil organic carbon concentration. Rice yields correlated negatively with Striga asiatica plant numbers in years with moderate infection levels. This is the first study that shows mixed outcomes from CA practices in tropical cereal rotation systems on degraded, Striga-infested soils, and subsequent entry points for system improvements. Suggested improvements include judicious cover crop management, complementary fertilizer applications and selection of competitive, resistant and adapted crop varieties.

International audience; Background and aims: Agroforestry systems combining trees with crops or pastures have been widely used to reduce water, soil, and nutrient losses and associated water pollution from agricultural lands in both temperate and tropical regions. However, reviews on improvement/efficiency and the scope of such reductions by soil, management, climate, and hydrological processes are limited.Methods: This paper synthesized the available evidence on the reduction in surface runoff, soil erosion, nutrient, and pollutant losses (e.g., herbicides, pesticides, and antibiotics) to quantify the effectiveness of agroforestry systems on water quality improvement based on published studies.Results: On average, agroforestry systems reduced surface runoff, soil, organic carbon, and related nutrient losses by 1–100%, 0–97%, –175–92%, and –265–100%, respectively, with average values of 58%, 65%, 9%, and 50%, respectively. They also lowered herbicide, pesticide, and other pollutant losses by –55–100% (49% on average).Conclusions: Reduction efficiency of agroforestry systems is site-dependent and varies widely depending on different biophysical factors. A comprehensive science-based review is needed to generalize agroforestry design and site adaptability for water and soil conservation where climatic, geographical, ecological, and socio-economic conditions are relatively similar in the world.

It has been widely asserted that a high grazing pressure has led to a reduction in vegetation production at decadal time scales, implying land degradation, in African drylands, and in the Sahel in particular. We test this hypothesis by analyzing spatiotemporal patterns of vegetation production in the northwestern Ferlo in Senegal. Normalized difference vegetation index (NDVI) patterns, here used to represent vegetation production, were determined on the basis of Earth observation MODIS and PROBA‐V data. Furthermore, woody cover was assessed by very high spatial resolution (VHR) imagery. Because livestock is concentrated around deep wells in the dry season for watering, while for management they concentrate daily around pastoral family settlements or camps all year round, we studied the dependence of NDVI on distance from deep wells and camps. Locations of wells and camps were determined by visual inspection of VHR images. We found that 'inverse grazing gradients,' defined as decreasing NDVI/production with increasing distance, dominated both around wells and camps. Further, we found neither decrease nor increase in woody cover with distance to wells. Both positive and negative trends in wet season NDVI over the period 2000–2016 were identified within the study area, yet temporal trends were predominantly positive in proximity to deep wells. Around pastoral camps, positive NDVI trends were generally elevated relative to the regional average. The results question the validity of claims that high grazing pressure causes land degradation at the landscape scale, yet they show that grazing does lead to substantial spatial redistribution of vegetation production.

In Montane Southeast Asia, deforestation and unsuitable combinations of crops and agricultural practices degrade soils at an unprecedented rate. Typically, smallholder farmers gain income from "available" land by replacing fallow or secondary forest by perennial crops. We aimed to understand how these practices increase or reduce soil erosion. Ten land uses were monitored in Northern Laos during the 2015 monsoon, using local farmers' fields. Experiments included plots of the conventional system(food crops and fallow), and land uses corresponding to new market opportunities (e.g. commercial tree plantations). Land uses were characterized by measuring plant cover and plant mean height per vegetation layer. Recorded meteorological variables included rainfall intensity, throughfall amount, throughfall kinetic energy (TKE), and raindrop size. Runoff coefficient, soil loss, and the percentage areas of soil surface types (free aggregates and gravel; crusts; macro-faunal, vegetal and pedestal features; plant litter) were derived from observations and measurements in 1-m(2) micro-plots. Relationships between these variables were explored with multiple regression analyses. Our results indicate that TKE induces soil crusting and soil loss. By reducing rainfall infiltration, crusted area enhances runoff, which removes and transports soil particles detached by splash over non-crusted areas. TKE is lower under land uses reducing the velocity of raindrops and/or preventing an increase in their size. Optimal vegetation structures combine minimum height of the lowest layer (to reduce drop velocity at ground level) and maximum coverage (to intercept the largest amount of rainfall), as exemplified by broom grass (Thysanolaena latifolia). In contrast, high canopies with large leaves will increase TKE by enlarging raindrops, as exemplified by teak trees (Tectona grandis), unless a protective understorey exists under the trees. Policies that ban the burning of multi-layered vegetation structure under tree plantations should be enforced. Shade-tolerant shrubs and grasses with potential economic return could be promoted as understorey.

Soil organic carbon (SOC) sequestration was evaluated for several long-term rain-fed cropping systems for conservation agriculture (CA) and conservation tillage (CT) in Cambodia using the Environmental Policy Integrated Climate (EPIC) model. The mean crop yield, biomass and SOC stocks of four treatments and three replication in each primary cropping system (rice, soybean and cassava) were used for calibration and validation during the period 2009–2013. The CT and CA1 treatments were assigned to continuous cropping of primary crops. CA2 and CA3 treatments were assigned to rotated primary crops with maize. In all CA treatments, forage or legume cover crops were prior planted and intercropped with the primary crops to maintain full soil cover. The results show that EPIC successfully simulated crop yields, biomass, and SOC. However, the model tended to underestimate SOC in the CT treatments and overestimate SOC in the CA2 and CA3 treatments. Crop residue was found to highly influence SOC sequestration. Sediment loss in the CT treatments was found to be four times greater than CA treatments due to the CT tillage effects. The 20-year future simulations, using historical weather and automatically generated by EPIC, showed a decrease trend in SOC stocks in all CT treatments and an increase trend in most CA treatments, with the greatest increase for CA2 and CA3 treatments. Thus, the CA treatments in combination with the maize rotation were demonstrated to be more efficient to manage SOC sequestration over CA with one continuous primary crop.

Cocoa is among the most desirable and palatable food in the world. Soil under cacao trees in Papua New Guinea (PNG) is fertile, however, it's been identified that to sustainably reach a production goal of 310,000 t by 2030, PNG needs soil-based recommendations. For this purpose, a cost-effective, rapid and non-invasive soil testing approach using near infrared diffuse reflectance spectroscopy (NIR-DRS), to cater for soil testing needs of numerous small landholdings was assessed. This study investigated whether spectral data collected from smallholder farms across provinces can be used to estimate soil conditions for cacao farming. To assess this, a spectral library was generated by measuring 17 different soil parameters and spectral reflectance data over visible to near-infrared region (350–2500 nm) in 507 soil samples collected from four production systems in Autonomous region of Bougainville (AroB), New Ireland province (NIP), East New Britain province (ENB) and East Sepik province (ESP). Analysis of spectral data showed that the shallow limestone soil of NIP is dominantly montmorillonite mixed with kaolinite clay minerals, while the three other sampling sites are mostly vermiculite with mixed illite type of clay. Among Cubist, partial-least-square regression (PLSR), and support vector regression (SVR) chemometric approaches, Cubist model outperformed both SVR and PLSR. Most soil properties were estimated with high accuracy (concordance coefficient ≥ 0.7) using the Cubist model, except for pH, electrical conductivity (EC), available K and B. The high quality of the prediction models maybe owing to the variability in properties of the four different soils captured through conditioned Latin hypercube sampling. Results from this study also suggest that soil samples collected from multiple depths may be used for predicting both surface (0–30 cm) and sub-surface (30–90 cm) soil properties. Thus, this tool can help reduce the cost of laboratory analysis, even if it requires analysis of samples for calibration for the development of a successful spectral library across provinces.

Dans l’Extrême-Nord-Cameroun, les nombreuses populations des monts Mandara avaient conscience, lors de leur installation, du caractère difficile de leur milieu : difficultés climatiques, édaphiques et topographiques. Ces conditions se détériorent avec les changements climatiques marqués surtout par un assèchement généralisé et la pression croissante de la population sur des ressources très limitées. De plus les stratégies séculaires de survie ont à peine évolué et se limitent à la réalisation de terrasses de pierres sèches et de techniques associées telles que l’alignement simple de pierres, le paillage, l’élevage en case et le fumier, l’agroforesterie sur les pentes les moins fortes et le contrôle du ruissellement par l’association des cultures et, dans une moindre mesure, le labour profond sur les replats et dans les vallées.L’objectif de notre communication est d’établir un inventaire des techniques de gestion des sols et de faire ressortir leur niveau d’efficacité : on a montré que la grande difficulté de ces milieux est avant tout le décalage entre la pression démographique et la ressource. Les résultats de nos travaux sont étayés par des observations et des enquêtes de terrain effectuées sur plus de deux décennies et dans le cadre du programme de recherche AUF P2 – 2092RRR521 du réseau érosion de l’AUF. In the Extreme Northern Cameroon, physical, pedological, hydrological and topographical conditions are difficult but numerous populations found a protection against the Muslims coming from the peulh emirate of SOKOTO (NE of present Nigeria) in 1904. The mountains were covered by lithosols and dry forest before the populations built terraces quite everywhere, associated with agroforestry, stone lines, breeding, manuring, mulching or deep plowing in the flat areas. This paper wants to describe the terracing system, to analyze their efficiency and to show the difficulties to nourish the increasing population in this difficult semi-arid environment.The study is a synthesis of more than 20 years observations & inquiries on the fields.

Le problème de la conservation des sols en Haïti est fondamentalement un problème social et l’une des conséquences de la pauvreté extrême des paysans de morne. La forte densité et le mode d’occupation de la terre constituent des entraves majeures à la conservation des sols et de l’eau. En général les petits cultivateurs haïtiens utilisent des techniques de production originaires de la plaine telles que le brûlis qui crée de l’érosion dans les champs agricoles montagneux. Les paysans haïtiens sont conscients de la dégradation des sols et appliquent certaines pratiques traditionnelles de conservation. Pour arriver à un meilleur résultat de la lutte antiérosive, il est impératif d’adapter l’expertise des techniciens à la réalité quotidienne du paysan.Depuis 1950, toute une série d’approches de la conservation des sols se sont succédées : des approches équipement du territoire, la construction de murs secs par des projets « nourriture pour le travail », des approches au niveau de parcelles éparpillées, des approches collectives au niveau du micro bassin versant, et des approches économiques : la production durable pour des nouveaux marchés et récemment, la protection des bassins versants en amont et en aval.Les leçons qu’on peut tirer d’une lecture des éléments d’histoire. Approche économique : Identifier des cibles d’opportunité économique comme le point de départ à la lutte antiérosive. Adapter l’approche au contexte réel. L’innovation réussie se construit sur des pratiques déjà familières aux paysans et accessibles par application de la main d’œuvre avec très peu de coût monétaire, et surtout avec le résultat tangible d’une augmentation significative des revenus à court et moyen terme. Incitations intrinsèques : Faire la vulgarisation des techniques de conservation à base des incitations intrinsèques, et surtout économiques, tout en évitant la dépendance sur des incitations extrinsèques et artificielles de projet. Zonage hydrographique : Pour maximiser l’impact il faut concentrer les efforts géographiquement, atteignant une masse critique de planteurs d’une zone et ciblant des sites prioritaires d’opportunité économique aussi bien que des sites de risque élevé. Utiliser une approche participative à base de subsidiarité : Pour des actions collectives ou publiques et pour les plans locaux d’aménagement, la responsabilité organisationnelle doit être allouée à la plus petite entité capable de résoudre le problème, par exemple les parties prenantes d’une ravine, un micro bassin versant, un petit périmètre irrigué. From 1950 a lot of SWC strategies have been tested in Haïti. The author tried to extract lessons. Develop strategies adapted to local context, test techniques familiar to farmers, adopt economic intrinsic incitement but avoid dependence of extrinsic incitements. Concentrate the efforts of management on geographical areas like watersheds or gullies or one hydrological unit where people usually are working together : you will get better participation.

Depuis 1985, différents systèmes agroforestiers ont été testés sur l’érosion et l’amélioration de la productivité des sols sur le Plateau Central Rwandais. Les études ont été menées sur un sol ferrallitique fortement dégradé, très acide (pH < 4) et pauvre en éléments nutritifs. Les conditions agro-écologiques peuvent être caractérisées par une altitude de 1.700 m, une précipitation annuelle moyenne de 1.280 mm (régime bimodal) et une température annuelle moyenne de 20°C. Les parcelles ont été cultivées selon les méthodes de l’agriculture écologique agroforestière. Ses éléments principaux sont : l’intégration des arbres et des haies dans les parcelles de cultures, la mise en place de cultures associées, la substitution de la jachère par l’emploi d’engrais verts, l’intégration de l’élevage dans le système de culture, le recyclage de la biomasse dans un cycle presque fermé et l’intégration des mesures pour la conservation des eaux et des sols.Malgré une érosivité des pluies relativement faible (facteur R d’après WISCHMEIER et SMITH autour de 350) on a constaté une érosion énorme sur les parcelles non protégées (468 t/ha/an sur sol nu (avec un ruissellement autour de 15 % des précipitations annuelles) et 245 t/ha/an sous manioc (ruissellement environ 9 %) sur une pente de 28 %. Sous ces conditions, l’intégration des arbres et surtout des haies de Calliandra calothyrsus, plantées en lignes isohypses, permettent une réduction de l’érosion et des pertes en matière organique et en éléments nutritifs, à un niveau « tolérable » (1-3 % des valeurs initiales). Par l’intégration des arbres et des arbustes dans le système de production agricole, l’agroforesterie permet une haute production en biomasse même sur des sites dégradés. Des relevés dendrométriques qui ont été fait pour 32 différentes espèces d’arbres plantées en novembre 1985 montrent que les meilleurs résultats ont été obtenus avec les arbres autochtones Maesopsis eminii et Polyscias fulva. Si les arbres exotiques (p. ex. Grevillea robusta, Cedrela serrata) montrent une bonne croissance initiale, les espèces autochtones sont, à la longue, plus productives et concurrencent moins les cultures vivrières. L’agriculture agroforestière contribue non seulement à la sauvegarde de la fertilité des sols, mais aussi a son approvisionnement en azote et en matière organique. Néanmoins, les méthodes biologiques seules ne sont pas capables d'améliorer la fertilité du sol sur des sites déjà fortement dégradés. Pour rétablir la fertilité de ces sols, un apport supplémentaire en éléments nutritifs qui ont été emportés par l’érosion et par exportation des cultures pendant des décennies est inévitable. L’article présente les effets positifs d’une application des cendres volcaniques et du travertin sur le rendement des cultures vivrières dans des systèmes agroforestiers. In densely populated areas in Rwanda, soil erosion and degradation are severe threats to agriculture. In this situation, agroforestry can help to achieve a sustainable agricultural production (“ecofarming”). Agroforestry systems also play an important role in climate change mitigation by storing important quantities of carbon (10-20 t C/ha, which is equivalent to 35 to 70 t CO2/ha). Based on measurements of runoff and soil losses, of biomass production and nutrient fluxes, the author resumes more than twenty years of research experience from Projet Agricole et Social Interuniversitaire (PASI) at Butare, Rwanda (1700 m a.s.l., mean annual rainfall : 1280 mm, mean temperature : 20° C) on a severely degraded ferralitic soil (pH 4).

Rice production in Southeast Asia is significantly affected by root-parasitic nematodes (RPN). The Green Revolution has encouraged new agricultural practices (e.g. intensive monoculture, high yielding rice variety) to respond to the high rice demand; however, these methods have promoted the spread of these pests. The recent banning of chemical nematicides resulted in a need for alternative sustainable control strategies. In the present study, we assessed the effects of a direct-seeding mulch-based cropping system (DMC) vs conventional plough-based tillages (CT) on soil properties, rice yield and RPN communities during a two-year trial in Cambodia. Our results show that on average the population densities of RPN were significantly higher in DMC than in CT. Molecular identification revealed only two RPN species associated with roots: Meloidogyne graminicola, not previously reported from Cambodia, was predominant and was present throughout the plant’s development, whereas Hirschmanniella mucronata was only found at the tillering and milky stages. We conclude that DMC had a significant positive impact on rice yield, despite higher RPN short-term pressure. In order to increase the efficiency of such cropping systems, further studies and an evaluation of the long-term relationships between DMC, the nature of cover crops used, the soil biota including RPN, and rice yield should be conducted.

La region du Lac Alaotra est un des greniers a riz de Madagascar avec de nombreuses contraintes pedoclimatiques importantes. Dans une perspective de developpement durable, des organismes de recherche ont mis au point des itineraires techniques issus de l'Agriculture de Conservation (AC).La dissemination a ete assuree de 2003 a 2013 par le projet de developpement BV-Lac. Comme definie par la FAO en 2008, l'AC repond a trois principes : i) perturbation minimale du sol, ii) protection du sol par une couverture vegetale, iii) rotation de culture et association de plantes qui impliquent un double changement de paradigme sur les techniques de cultures et les strategies. Une enquete realisee en 2013/2014 montre que depuis le demarrage du projet, les paysans ont su adapter ces techniques a la structure de leur exploitation pour repondre a leurs propres contraintes dans des processus d'appropriation aboutissant un continuum de pratiques entre conventionnel et AC mettant en exergue un long temps d'apprentissage et une recombinaison des savoirs. (Resume d'auteur)