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Summary Cassava flour is the main source of carbohydrates for family farmers in the Amazon region of Brazil. Cassava is mainly grown under shifting cultivation, in recurrent cultivation periods initiated through slash-and-burn. Its sustainability is, however, questioned due to the associated deforestation and often rapidly decreasing crop productivity. There is an urgent need to make these cassava systems more sustainable and more profitable, but we currently lack a deep understanding of the key factors governing their productivity. We conducted an on-farm study on 37 cassava fields of smallholder farmers at three locations that spanned a range of crop-fallow frequencies, some of which were initiated through slash-and-burn while others through fire-free land clearance. First, we analysed how cassava plant density at harvest was related with pedoclimatic and management factors in slash-and-burn systems. Second, we assessed the relationship between plant density and cassava root yield at harvest and conducted a yield gap analysis to better understand which factors govern cassava productivity beyond plant density in slash-and-burn systems. Finally, we compared cassava productivity between slash-and-burn and the fire-free land clearing techniques that some farmers started to adopt in the study region. Cassava yields averaged 7.2 ± 5.4 Mg ha–1 (50% of the average yield of 14.2 Mg ha–1 in the Pará State), and ranged from 0 (in case of root rot diseases) to 24 Mg ha–1. Cassava yield was associated with plant density at harvest (ranging from 0 to 10 000 plants ha–1), suggesting that managing plant density is a key determinant of the attainable yield levels. In addition, differences in cassava root yields could be largely explained by differences in labour inputs for weeding and fallow clearing, the effect of the latter depending on soil texture. Therefore, our results suggest that labour is a key production factor for cassava in the shifting cultivation systems of the Eastern Amazon in which the use of external inputs, such as chemical fertilizers and herbicides, is limited. Further, root yields were influenced by the method of field preparation, whereby yields were about 50% lower (and more variable) when fields were prepared by slash-and-burn than by mechanical ploughing or herbicide application. Despite the significantly higher yields, these alternatives to burning the vegetation are, however, still hardly adopted in Paragominas. Hence, there is a need for supporting more sustainable production systems through local and national public policies. These new systems should not only focus on soil fertility management but also on weed control and, more generally, on labour productivity.

Poor soil fertility and erratic rainfall constrain crop production in rain-fed smallholder farming systems in sub-Saharan Africa. Integration of drought tolerant and N2-fixing crops into maize-based cropping systems is a risk-averse strategy that also improves nitrogen cycling. A field experiment was carried out during the 2017/18 and 2018/19 cropping seasons in Goromonzi district in Zimbabwe. The trials were established on 14 farms, and on two field types (homefields and outfields), with eight treatments from a combination of cropping systems (maize and cowpea monocrops or maize/cowpea intercrops) and with or without nitrogen fertilizer (+N; -N). The trials were implemented on the same field plots for the two consecutive seasons. An improved cowpea variety and a landrace were used. The objectives were to determine 1) the productivity of the different cropping systems under variable soil fertility conditions, 2) N2-fixation of the two cowpea types when planted as monocrops or intercrops, and 3) mineral composition of maize and cowpea grains from intercrops and sole crops. Contrary to expected results, soil properties were not significantly different (P > 0.05) between field types. The land equivalent ratios (LER) were >1 for both seasons, implying improved land productivity under intercropping. Intercropping significantly reduced cowpea nodulation and active nodules, but not the total nodule weight, resulting in similar proportion of nitrogen derived from the atmosphere (%Ndfa) for cowpea grown as monocrop or in intercropping with maize. However, the total amount of fixed nitrogen was reduced in intercropping systems due to the smaller cowpea biomass compared to monocropping. Maize and cowpea grain mineral contents (Fe, Zn, Mn, Cu, Ca, Mg, P, K) were significantly affected by the cropping season only. We showed that intercropping maize with cowpea generally increases system productivity, in addition to substantial amounts of nitrogen being added to the system through N2-fixation. However, intercropping was not an agronomic biofortification option in these nutrient-depleted soils. Finally, annual variation in grain mineral quality can be larger than the annual variation in grain yield, potentially posing serious challenges to human nutrition.

International audience; Agricultural research has to tackle complex questions such as the design of sustainable cropping systems. System experiments are innovative approaches to address this challenge and a framework to iteratively design annual cropping systems has been proposed by Debaeke et al. (2009). However, specificities of some other cropping systems are not considered. Orchards are complex perennial agroecosystems formed of grass and tree layers aiming at the production of fresh fruit that require specific design and management over space and time. To identify orchard specificities and adapt the design framework to such perennial systems, we used two case studies of orchards aiming at decreasing pesticide use in temperate (apple, system experiment) and tropical (citrus, on-farm network) fruit productions. Specificities to take into account in the design framework are: (1) the spatial heterogeneity of the orchard with grass and tree layers, and tree rows and alleys; (2) the succession and interrelations among a young unproductive and then a productive stage; (3) the permanency of the fruit-tree crop constraining the management of soil fertility, (4) ground cover and (5) pest control, especially for pests that complete their lifecycle in the orchard and can build up important populations or inoculum across years. This is especially true in tropical areas where there is no dormant season. (6) Conversely, the permanency of the orchard habitats facilitates the sowing, planting or conservation of plant assemblages (e.g., ground covers, lining hedgerows) to enhance conservation biocontrol and/or compete weeds, provided non-disruptive practices are applied. Because of their longevity, orchards contribute to foster both plant-mediated (e.g., bottom-up) and natural enemy-mediated (e.g., top-down) processes in the foodweb to avoid direct measures against pests. Interactions among the orchard life stages, spatial and functional dimensions and practices need to be explicitly considered to optimize the efficiency of the system as a whole. Using the generic framework proposed by Debaeke et al. (2009) to design annual cropping systems, our framework includes adaptations to account for orchard specificities: (i) Agronomic objectives have to be fixed for each orchard stage; (ii) The cultivar choice and the composition and spatial arrangement of plants within the orchard are key elements to provide the expected services in the long term. This entails to include an additional step of perennial spatial design; (iii) Within-time and −space interactions have to be considered in the decisional system; (iv) Evaluation has to consider all the orchard stages in the global impact or performance, to account for carry-over effects and possible ‘paybacks’ of a given stage or period to the orchard whole lifetime. Last, to handle such complex interactions, design needs knowledge from many stakeholders in the food system (growers, advisors, scientists etc.) and requires more and renewed interactions among those stakeholders in a co-design process.

International audience; Soil organic carbon (SOC) balance is an important component of the terrestrial carbon (C) budget. However, effect of cropland management changes on SOC dynamics has not been recently assessed in the tropics. Studies were compiled in the tropics where SOC stocks were measured in the topsoil (0–20 or 0–30 cm depth) after the adoption of management practices that are expected to enhance SOC stocks, including tillage reduction, crop rotation, exogenous organic amendments, restitution of crop residues, mineral amendments, and combinations of these practices. Random forest regression was used to identify the determinants of SOC accumulation rates (ΔSOC) depending on the climate, soil characteristics and changes in management practices. 214 cases were identified in 48 studies in 13 different countries. The average ΔSOC was 0.41 ± 0.03 Mg C ha−1 yr−1 (significantly greater than zero), for an average experiment duration of 13.6 ± 0.6 years. Although a large part of the variability remained unexplained due to methodological bias in the studies or a lack of relevant predictors. The strongest predictors of ΔSOC were C inputs, duration of the experiments, and the management practices, whereas neither soil characteristics (soil type, clay content, and initial SOC stock) nor climate variables (mean annual temperature and rainfall, aridity index) affected ΔSOC. The SOC accumulation rates increased linearly with C inputs, and the conversion rate of C inputs to SOC was 8.2 ± 0.8%. Given the competing uses of organic matter on many tropical farms, the benefits of using changes in management practices for climate change mitigation might be overrated. As ΔSOC decreased with the duration of the experiments, ΔSOC would probably be smaller if a period of 20 years were considered, as recommended by the IPCC guidelines. The management practice with the greatest ΔSOC was diversified crop rotation. Cropping systems where diverse practices were combined resulted in higher ΔSOC than individual practices such as reduced tillage and mineral fertilization on their own. The adoption of improved management practices that increase C inputs is still relevant for meeting the challenges of food security and adaptation to climate change.

Global demand for renewable energy from plant biomass is growing steadily as a result of policy choices, demographics, and rising per capita energy needs. This energy requirement is turning out to be a major obstacle to economic development on tropical islands and remote landlocked areas. Thus, sugarcane is no longer cultivated exclusively for sugar but also for its biomass which, when burnt, helps produce electricity. In Guadeloupe, there are plans to generate electricity from almost total sugarcane combustion. It has also become possible to produce second-generation ethanol from aboveground plant parts. To this end, CIRAD selected sugarcane and sorghum as model plants to conduct several projects in partnership that helped identify suitable planting material and agricultural practices producing 67–85 T/ha/year of sugarcane dry matter (DM) and 30–50 T/ha/year of sorghum DM. Various cultivation models were calibrated to extend the scope of the results to other areas or climatic conditions. In projects on sugarcane, biomass is used to generate electricity through combustion, while the Sweetfuel project uses sorghum biomass to produce bioethanol. The diversification of products in sugarcane and sorghum chains can offer producers and industrial actors new outlets in an environmental context that is not only increasingly constrained (pesticide reduction, climate change) but is also becoming increasingly competitive due to the liberalization of the sugar market.

La couverture végétale du sol constitue un moyen efficace de réduire le ruissellement et l'érosion en Afrique soudano-sahélienne. Elle contribue aussi à enrichir le sol superficiel en matière organique et en nutriments. Cette pratique constitue un élément central du système de culture sous couvert végétal (SCV) qui a été vulgarisé au nord du Cameroun. Mais il existe de fortes concurrences entre les usages des biomasses mobilisables pour cette couverture, en premier lieu l'alimentation du bétail qui reste en saison sèche une préoccupation majeure des producteurs de cette région. L'introduction du Brachiaria ruziziensis en culture pure ou associée aux céréales donne de nouvelles perspectives pour accroître l'offre en biomasse pour le bétail, mais aussi pour la couverture du sol. L'usage des émondes des arbres ou des haies vives et des légumineuses herbacées comme paillis existe, mais plus rarement. Il apparaît comme une voie d'amélioration possible de l'offre en biomasse fourragère et de couverture. Par ailleurs, il convient d'associer aux innovations techniques des innovations organisationnelles indispensables pour modifier les modes de gestion des ressources naturelles et des espaces et assurer un partage équitable de la biomasse disponible entre les différents usages (paillage, fourrage-vaine pâture, feux).

National audience

International audience; Due to the role of soils in the global carbon cycle, there is increasing demand for data on soil organic carbon (SOC) stock, but the conventional determination of SOC stock (SSOC) is tedious and hardly allows meeting this demand. Visible and near infrared diffuse reflectance spectroscopy (VNIRS) is a time- and cost-effective approach that has been successfully used for characterizing SOC concentration, even in the field. The present study aimed at testing the potential of VNIRS for characterizing SSOC in the field, from spectra acquired on partially disturbed cores collected using a manual auger (thus not using cylinder sampling except for calibration), at 0–10, 10–20 and 20–30 cm depth in two agroforestry fields in France. Both fields were on silty Luvisols under temperate climate and included tree rows with grass cover, plowed interrows with cereals, and a conventional agricultural plot without trees. Conventional determination of SSOC involved bulk density measurement (cylinder method) and SOC concentration analysis (dry combustion) on the same samples, and was calculated as their product. VNIR spectra were acquired using an ASD LabSpec 2500 spectrophotometer, on the outer side of cores collected using a manual auger, at three points around the place where SSOC was determined. In total, 288 samples were studied (144 per field). Calibration with partial least squares regression was carried out on the 200 most spectrally representative samples, and validation was performed on the remaining samples. Considering the determination coefficient for validation (R2val), standard error of prediction corrected for bias (SEPc) and ratio of standard deviation of the validation subset to SEPc (denoted RPDval), the VNIRS prediction of SOC concentration was accurate (R2val = 0.75; SEPc = 1.6 gC kg− 1 soil < 2 mm, i.e. 13% of the mean; RPDval = 2.0). The prediction of SSOC was acceptable (R2val = 0.70; SEPc = 2.0 gC dm− 3, representing 13% of the mean; RPDval = 1.8). Part of the VNIRS prediction error could be attributed to the fact that conventional and spectral measurements were not made on the same samples. Scanning the cylinder cores would probably result in better VNIRS predictions but is not consistent with the objective of determining SSOC without tedious cylinder sampling (except for calibration). However, conventional determination of SOC concentration on auger cores (rather than on cylinder cores) could be a valuable solution for improving calibration, with the perspective to develop a rapid procedure for accurate VNIRS prediction of SOC stock in the field.

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 ofAndropogon gayanus-yam rotation, maize-yam rotation) with yam-based systems integrated herbaceous legumes (Aeschynomene histrix/maize intercropping-yam rotation,Mucuna pruriens/maize intercropping-yam 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.

Le recyclage des produits résiduaires organiques participe au développement durable des territoires. Il contribue à l'amélioration de la fertilité des sols, notamment via les apports en matière organique, et à une économie circulaire des nutriments (azote, phosphore et potassium principalement) à des échelles très variées. Il faut cependant veiller à la maîtrise des impacts environnementaux, notamment en raison de la difficulté à ajuster les pratiques de fertilisation et de la présence éventuelle de contaminants. L'impact du recyclage est global ; il peut se traduire par une substitution des engrais, préservant ainsi des ressources minières ou les sources d'énergie fossile. Comprendre les processus biogéochimiques impliqués dans le recyclage des produits résiduaires organiques, préciser les usages et proposer des solutions adaptées à différents contextes au Nord comme au Sud ont été les objectifs du travail pluridisciplinaire présenté dans cet ouvrage. Il s'appuie sur les résultats du projet "Intensification des systèmes de production agricole par le recyclage des déchets" (Isard), conduit de 2009 à 2013 avec le soutien financier de l'Agence nationale de la recherche française. Ainsi, de la plaine de Versailles à l'île de la Réunion, en France, et de la péninsule dakaroise, au Sénégal, à la zone périurbaine de Mahajunga, à Madagascar, anthropologues, sociologues, biogéochimistes, modélisateurs, technologues et agronomes se sont associés pour caractériser les déchets organiques et leurs usages, documenter l'intérêt de leur recyclage, mais aussi les risques inhérents à leur emploi. Cet ouvrage est destiné aux professionnels soucieux de pratiques agro-écologiques au Nord comme au Sud. De plus, les études de cas très approfondies intéresseront les scientifiques de diverses disciplines.

International audience; In French West Indies, the high dependency of the electricity mix on imported fossil fuels has led local authorities to propose the conversion of some land to the production of energy cane. This conversion mainly concerns land polluted by the pesticide chlordecone, where most crops for human consumption have been banned. This molecule has a strong affinity for soil organic matter (SOM). The aims of this study were to assess the impact of crop residue management and compost application on the stocks of SOM and chlordecone in soils cultivated with energy cane and to determine the minimum SOM input required to maintain SOM stocks. A field experiment was conducted to determine the yield and biomass partitioning of energy cane, and laboratory incubations were performed to estimate humification from crop residues. Changes in SOM and chlordecone stocks over a 30-year period were investigated using models already calibrated for the land under study. Non-harvestable biomass left on the field (tops, litterfall and roots) covered >60 % of SOM mineralization. A full offset of mineralization required the return of 10 % of harvestable biomass or the application of compost at a rate of 40 Mg ha−1 every 5 years. With the total removal of harvestable biomass and without compost applications, SOM and chlordecone losses increased by 23 and 13 %, respectively, which was associated with high SOM mineralization and chlordecone leaching under tropical climate. The estimated break-even price for cane biomass indicated that compost application would be more profitable for farmers than the return of a part of the harvestable biomass.

Ce livre présente une série d'études effectuées entre 2007 et 2013 sur diverses régions de Madagascar pour en appréhender la très grande diversité de situations de l'agriculture familiale (Lac Alaotra, hautes terres autour d'Antsirabé et Moyen Ouest/Mandoto de la région du Vakinankaratra, côte est dans les zones de Manakara et Sainte Marie). Madagascar est un des pays les plus pauvres du monde, avec une très forte incertitude politique et économique aboutissant à des situations sociales extrêmement difficiles. La relative stabilité des campagnes où vit plus de 80 % de la population vient de la très grande résilience des systèmes de production locaux et d'une grande capacité des producteurs locaux à s'adapter et à innover, malgré ces conditions extrêmement difficiles. Ce livre tente de montrer les différentes formes de cette résilience de l'agriculture familiale malgache en présentant des exemples variés de l'agriculture de conservation, de l'agroforesterie, la diversification des productions, l'adaptation des systèmes rizicoles aux contraintes multiples sur la côte est, la sécurisation foncière, l'intégration agriculture-élevage, la pluriactivité.

Stable soil aggregates and high microbial diversity are essential for efficient nutrient recycling in soil. This study evaluated effects of different arable land-use systems on soil aggregation and associated composition and total diversity of bacteria and fungi. For this purpose, 5- and 3-year-old field trials were selected, two in sub-humid (orthic Acrisols and oxidic Ferralsols) and one in semi-arid (chromic Cambisol) region in Kenya. The treatments included combinations of tillage (conventional tillage [CT] and reduced tillage [RT]), crop residue management (0 and 2 t ha?1 maize stover) and cropping systems (continuous maize, maize-soybean intercropping and rotation) in the sub-humid sites, and of different tillage (CT, no-till and tied-ridging) and organic fertilization management (manure and crop residue) in semi-arid Kenya. The innovativeness of this study is the research in tropical soils where the concept of aggregate hierarchy is not generally accepted yet. The results showed that aggregate mean weight diameter (MWD) at 0-15 cm depths had increased from 19 to 34% under RT relative to CT management (P < 0.05). Crop residue additions also significantly increased MWD by 22% at the top 5 cm (P < 0.01) compared to treatments without residue in oxidic Ferralsols. At all the three sites, tillage resulted in greatest shifts of bacterial and fungal community composition, while cropping system had largest positive effect on the total microbial diversity indices. Total microbial diversity indices as well as MWD were higher in soybean-maize intercropping systems than under rotation or continuous maize cropping. Changes in total bacterial diversity related inversely to changes in the amount of free silt + clay, while fungal diversity related inversely to the contents of soil macro-aggregates >2 mm (P < 0.05). We conclude that RT plus supply of organic resources and intercropping are best strategies to increase total diversity of soil bacteria and fungi and improve soil structure in these tropical soils.

Technological interventions to address the problem of poor productivity of smallholder agricultural systems must be designed to target socially diverse and spatially heterogeneous farms and farming systems. This paper proposes a categorisation of household diversity based on a functional typology of livelihood strategies, and analyses the influence of such diversity on current soil fertility status and spatial variability on a sample of 250 randomly selected farms from six districts of Kenya and Uganda. In spite of the agro-ecological and socio-economic diversity observed across the region (e.g. 4 months year_1 of food self-sufficiency in Vihiga, Kenya vs. 10 in Tororo, Uganda) consistent patterns of variability were also observed. For example, all the households with less than 3 months year_1 of food self-sufficiency had a land:labour ratio (LLR) < 1, and all those with LLR > 1 produced enough food to cover their diet for at least 5 months. Households with LLR < 1 were also those who generated more than 50% of their total income outside the farm. Dependence on off/non-farm income was one of the main factors associated with household diversity. Based on indicators of resource endowment and income strategies and using principal component analysis, farmers' rankings and cluster analysis the 250 households surveyed were grouped into five farm types: (1) Farms that rely mainly on permanent off-farm employment (from 10 to 28% of the farmers interviewed, according to site); (2) larger, wealthier farms growing cash crops (8-20%); (3) medium resource endowment, food self-sufficient farms (20-38%); (4) medium to low resource endowment relying partly on non-farm activities (18-30%); and (5) poor households with family members employed locally as agricultural labourers by wealthier farmers (13-25%). Due to differential soil management over long periods of time, and to ample diversity in resource endowments (land, livestock, labour) and access to cash, the five farm types exhibited different soil carbon and nutrient stocks (e.g. Type 2 farms had average C, N, P and K stocks that were 2-3 times larger than for Types 4 or 5). In general, soil spatial variability was larger in farms (and sites) with poorer soils and smaller in farms owning livestock. The five farm types identified may be seen as domains to target technological innovations and/or development efforts.

En culture cotonnière biologique, la fertilité des sols et la maitrise des bioagresseurs sont les deux contraintes agronomiques majeures. Au Paraguay, la filière cotonnière biologique se développe depuis 2003. Le présent article fait suite à une étude exploratoire qui a été réalisée en 2008 dans le but d'appréhender la construction de la filière et d'identifier des contraintes économiques et organisationnelles. Ce deuxième article rapporte une analyse de la production et des contraintes agronomiques. L'étude a été effectuée en période de récolte du coton sous la forme d'entretiens avec les acteurs institutionnels et les producteurs. Avec plus de 200 tonnes de coton-graine produites dès 2006-2007, le Paraguay est devenu le deuxième producteur de coton biologique sud-américain derrière le Pérou. En 2007-2008, le rendement moyen enregistré de 492 kg.ha-1 de coton-graine a été sous-estimé en raison d'importantes fuites de production vers la filière conventionnelle. Les pratiques de gestion de la fertilité des sols, de fertilisation de la culture et de lutte contre les ravageurs, notamment contre le charançon des capsules Anthonomus grandis, s'inscrivent dans un système de culture avec rotation sans brûlis, avec fumier de ferme, cultures d'engrais verts et des intrants fermiers, diversement préparés et appliqués. Leur efficacité, jugée bonne par les prescripteurs et les utilisateurs, n'a pas été formellement étudiée. Dans tous les cas, des recherches sont nécessaires pour identifier les processus biologiques mis en oeuvre lorsqu'ils sont peu ou pas connus, pour appréhender qualitativement et quantitativement la variabilité des pratiques paysannes et enfin pour intégrer leurs effets à différentes échelles d'espace et de temps.

In Southeast Asia (SEA), the joint process of deforestation, agricultural land expansion, and intensification has led to vast soil erosion and a general decrease in soil and water quality. In addition, current agricultural practices such as deep plowing of soil or burning of forest and crop residues favor CO2 emissions and contribute to global warming. The deforestation rate in SEA is important (0.91 % per year of the forest area) and soil degradation is important either by erosion or acidity (63 % of the total land area). Conservation agriculture (CA) is an alternative land-use system reconciling economic viability, social balance, soil fertility restoration, and environmental conservation as well as climate change adaptation, which are crucial elements for the long-term improvement of smallholders’ living conditions and poverty alleviation. A basket of CA technologies, including zero or reduced tillage, direct seeding, crop rotations, soil cover, and residue management has been developed in different countries. Adoption of CA technologies has regenerated fertility of degraded soils, provided livestock with high-quality forage, and increased soil carbon sequestration. New innovative farming systems need to be developed to successfully integrate crops and livestock by offering numerous advantages such as diversification of income through animal products such as milk, meat, fiber and manure, weed control, soil erosion control, increased yield of main crops, and income during the “start-up” period for tree crops. The development of farming systems, which are more intensive and respectful of natural resources and the environment, requires acquisition of new stakeholder knowledge and skills. This is a priority since these stakeholders will initiate the required changes. The Conservation Agriculture Network for Southeast Asia (CANSEA) was created in 2009 to optimize similarities and complementarities among countries and institutions in SEA to improve the efficiency of research carried out by the various programs, and to optimize resources and means.

La fertilité des sols, notion centrale pour accroître la production des écosystèmes cultivés, est une réalité complexe : elle résulte de l'expression des composantes biologiques, physiques et chimiques des sols et de leurs interactions. Comprendre les mécanismes impliqués permet d'envisager les effets de modifications de pratiques ou de système de culture sur la fertilité. La fertilité est ici décrite comme la capacité des sols à fournir les éléments nutritifs nécessaires à l'alimentation des plantes. Le cycle de l'azote et ses relations avec la dynamique des matières organiques y joue un rôle central ; il est couplé au cycle du carbone par l'activité microbienne hétérotrophe qui minéralise (parfois très rapidement) les résidus de récolte. Les interactions entre processus chimiques, physiques et biologiques du sol sont décrites. Il est ainsi possible d'analyser l'influence de pratiques culturales comme la simplification ou la suppression du labour, l'insertion ou la destruction de prairies temporaires dans les rotations et d'envisager une agriculture reposant davantage sur le recyclage des matières organiques et le fonctionnement biologique du sol., In this study, soil fertility is defined as the ability of soils to furnish necessary nutrients to plants. It is a consequence of the biological, chemical, and physical properties of soils and their interactions. The nitrogen cycle and its relationship with soil organic matter dynamics play a key role; the nitrogen cycle is linked to the carbon cycle by the activity of soil bacteria. Here, we describe the interactions between various biological, chemical, and physical processes that take place in the soil. It is thus possible to examine the effects of cultivation practices, such as limiting or eliminating ploughing, including temporary pastures in rotations, and destroying temporary pastures as part of the rotation cycle. One can also envision an agricultural approach that promotes the recycling of organic matter and the soil's biological functions.

Intervention présentée aux Journées de l'AFPF, "La fertilité des sols dans les systèmes fourragers", les 8 et 9 avril 2015; Les atouts des légumineuses (fixation symbiotique, diversité fonctionnelle...) leur permettent de contribuer à la fertilité des sols, à l'amélioration de la durabilité de l'agriculture et de l'autonomie protéique des systèmes alimentaires. Il convient donc de mieux connaître leurs rôles, directs et indirects, dans les flux d'azote des rotations.Les légumineuses fourragères (en culture pure ou dans des couverts multispécifiques) représentent une grande part des apports azotés symbiotiques. Il existe une grande diversité d'implication des légumineuses dans les rotations. Des bilans d'azote du sol sont présentés pour plusieurs espèces de légumineuses ; ils varient selon de nombreux facteurs (type de couvert, autres sources d'azote...). Lorsque la fixation est active, elle peut représenter un apport d'une centaine d'unités d'azote. On connaît mieux maintenant les rôles, direct et indirect, des légumineuses dans les flux d'azote sous cultures et prairies (fixation, arrière-effets...) mais il faut poursuivre les recherches pour intégrer ces effets à l'échelle de l'exploitation (ou du territoire) et des rotations afin de développer des pratiques et systèmes de production productifs et durables.

Foram estudados os efeitos do uso do solo sobre a fertilidade, em Gleissolo sob três diferentes sistemas de manejo. As coletas foram feitas antes do período chuvoso nos seguintes sistemas de manejo: área cultivada com arroz (Oriza sativa L.) há aproximadamente 40 anos, com algumas interrupções ao longo deste período, com o cultivo algumas vezes mecanizado e uso de aração e gradagem; área sob pastagem de canarana erecta lisa (Echinochloa pyramidalis Hitch.), formada há cerca de 20 anos sem uso de adubações ou calagens; e área sob vegetação natural de floresta típica das áreas de várzea alta. As amostras de solo foram coletadas em dez pontos a partir de um transecto nas áreas, em quatro profundidades 0-10, 10-20, 20-30 e 30-40 cm. Os resultados demonstraram que o solo em condições naturais, de modo geral, apresentou atributos químicos que variaram de bons a muito bons, o que demonstra um grande potencial para o uso agrícola. O cultivo agrícola dos solos das várzeas do rio Guamá provocou uma redução da concentração de P e de K. O sistema de uso com pastagem apresentou maior sustentabilidade da fertilidade do que o sistema sob cultivo com arroz, visto que, além da melhoria das características químicas, a matéria orgânica elevou-se, também, em relação ao sistema natural. The effect of the use of the soil on the fertility has been studied, in Gleyssoil under three different management systems. Collections had been made before the rainy period in the following handling systems: rice (Oriza sativa L.) plantation area, cultivated for approximately 40 years, with some interruptions in during this period. Some times the culture was mechanized, with use of plowshare and harrow; pasture area with plantation of canarana (Echinochloa pyramidalis Hitch.), cultivated for 20 years, without the use of fertilizers; and lowland area with natural vegetation. The samples of soil were collected in ten points, set by using the transect methodology, to four depths 0-10, 10-20, 20-30 and 30-40 cm in each point. The results demonstrate that the soil under natural conditions, presented chemical characteristics which insure to the soil a high potential for the agricultural use. The agricultural culture of the lowland soil in the Guamá River provoked a reduction in the concentration of P and K. The soil usage system with pasture presented better sustainability on it fertility than the system with rice cultivation, beyond the improvement of the chemical characteristics and raise in the organic matter concentration, when related to the natural vegetation system.

L'intensification écologique de la production en Afrique amène la recherche agronomique à observer autrement les systèmes agricoles. Dans le cadre d'une approche intégrée associant les approches disciplinaires de l'écologie du paysage, de l'agronomie et des sciences de l'action, la thèse questionne les logiques d'action à l'oeuvre dans les pratiques agricoles au niveau d'un territoire agricole et en propose une typologie. Sur le territoire de Kajulu (Ouest Kenya), caractérisé par une densité de population supérieure à 1100 hab km², les Luos perpétuent des règles coutumières quant à l'organisation de l'espace agricole et l'attribution des terres en fonction de l'âge et du sexe des individus au sein de l'exploitation. Dans ce contexte particulier, nous émettons l'hypothèse que l'accès à la terre et la structure spatiale des espaces cultivés sont des facteurs déterminant des logiques des logiques d'action à l'oeuvre au sein du territoire. Les logiques d'action qui nous intéressent sont celles de l'individu, sur les espaces agricoles dont il est gestionnaire, selon (i) les liens qu'il entretient avec les institutions de recherche, les marchés et les réseaux locaux d'échange de matières et de connaissances, et (ii) le contexte local de l'action auquel nous accédons par l'analyse du paysage et les savoirs qu'ont les agriculteurs de leurs parcelles et de leur environnement et qu'ils mettent en oeuvre dans leurs pratiques agricoles. L'analyse les données recueillies nous permet de discuter de la diversité des techniques culturales appliquées dans un espace hétérogène et densément peuplé, et notamment de la propension des agriculteurs à l'innovation.

Conservation agriculture (CA) constitutes a potential set of management practices to restore soil total N (STN), soil organic C (SOC) and its labile fractions (i.e., particulate organic C-POC, hotwater extractable organic C-HWEOC, permanganate oxidizable C-POXC), to increase soil enzyme activities and to enhance soil aggregation. After five years, CA averagely increased SOC stocks over CT at 0-5 cm by 10%, 20% and 18%, STN stock by 8%, 25% and 16% , POC stocks by 22%, 20% and 78%, HWEOC stocks by 61%, 55% and 53%, and POXC stocks by 23%, 21% and 32% for rice-, soybean- and cassava-based cropping systems (RcCS, SbCS and CsCS, respectively). In general, no noticeable changes in the subsoil layers were observed. When monitoring after three years, stocks of SOC fractions (i.e., mineral-associated organic C-MAOC, pyrophosphate extractable organic C-PEOC, chemically stabilized organic C-CSOC) were almost constant in each depth among land uses, except MAOC in SbCS and PEOC in CsCS at 0- 5 cm where CA showed significant effects. In contrast, ?-glucosidase activity was 18%, 28% and 49% greater in CA than in CT soils at 0-5 cm under RcCS, SbCS, CsCS, respectively, whereas arylsulfatase activity under CA was greater than CT by 36% in SbCS and 39% in CsCS. The proportions of large macroaggregates (8-19 mm) at 0-5 cm under CA averagely increased 23%, 39% and 53% in RcCS, SbCS and CsCS, respectively, and consequently increased soil aggregation indices (i.e., mean weight diameter-MWD, mean geometric diameter-MGD and aggregate stability index-ASI) compared with those under CT. On average, and across all aggregate size classes, CA accumulated SOC concentrations over CT by 11%, 7% and 6%, total N concentrations by 3%, 11% and 15% and POXC concentrations by 18%, 20% and 15% for RcCS, SbCS and CsCS, respectively, at 0-5 cm. These increases led to positive correlations between large macroaggregate-associated SOC and soil aggregation indices in 0-5 cm depth in the three cropping systems. The results of CP-MAS 13C NRM measurement showed that humic acid from soils under CT tended to have higher proportions of aliphatic C than under CT while in reverse for aromatic C. This supports the promotion of CMI under CA indicating greater lability of SOC. In conclusion, short-term CA practices in the three cropping systems increased the storage of STN, SOC and labile SOC pool and enhanced soil enzyme activities in the surface soils with potential effects in the subsoil layers through increased proportion of large macroaggregates and soil aggregation indices resulting from high and diversified biomass-C inputs and the absence of physical soil disruption.

Afin d'étudier l'influence de la jachère sur les nématodes phytoparasites et la fertilité du sol, la croissance du mil en serre a été comparée dans des sols stérilisés et naturellement infestés de la région de Thyssé-Kaymor au Sénégal. Ces sols sont ferrugineux et ont été collectés dans des parcelles voisines, l'une en jachère depuis 17 ans et l'autre cultivée depuis plusieurs années. Le peuplement de nématodes du sol cultivé est constitué principalement de deux espèces : un ectoparasite, #Tylenchorhynchus gladiolatus$ et un endoparasite, #Scutellonema cavenessi$. Le sol de la jachère est infesté par de nombreuses espèces, mais sous l'influence de la culture du mil, il évolue vers la situation simplifiée observée dans les sols cultivés, exception faite que dans nos conditions expérimentales, en pots, #Pratylenchus pseudopratensis$ remplace #S.cavenessi$. Que le sol soit ou non infesté de nématodes, la jachère précédente a un effet positif sur le développement du mil à chaque cycle. L'appauvrissement du sol, comme l'impact des nématodes, réduisent la croissance du mil. Les deux facteurs évoluent dans le même sens, c'est-à-dire une diminution du développment du mil au fur et à mesure que le nombre de cycles culturaux augmentent. Les symptômes d'épuisement du sol peuvent être rectifiés, soit en supprimant les nématodes, soit en pratiquant la jachère. (Résumé d'auteur)

Key words: crop production, intensification, extensification, farming systems, tradeoff analysis, maize, legume, manure, fertiliser, southern Africa Soil fertility decline and erratic rainfall are major constraints to crop productivity on smallholder farms in southern Africa. Crop production intensification along with efficient use of chemical fertiliser is required to produce more food per unit area of land, while rebuilding soil fertility. The objective of this thesis was to identify appropriate crop production intensification options that are suitable to the socio-economic and biophysical conditions of selected smallholder maize-based farming systems in southern Africa. Three sites that formed a gradient of intensity of crop and livestock production were selected for the study. Murehwa in Zimbabwe is characterised by the largest intensity followed by Ruaca and lastly Vunduzi both in central Mozambique. In all three sites, maize is a key staple and cash crop.A literature review, field methods based on participatory research, and modelling tools were combined in analysing potential crop production options across an agricultural intensification gradient. A meta-analysis on maize grain yieldunder rain-fed conditions revealed thatconservation agriculture required legume rotations and high nitrogen input use especially in the early years.Reduced tillage without mulch cover leads to lower yields than with conventional agriculture in low rainfall environments. Mulch cover in high rainfall areas leads to smaller yields than conventional tillage due to waterlogging, and improved yields under CA are likely on well drained soils. Crop productivity underconservation agriculture depends on the ability of farmers to achieve correct fertiliser application, timely weeding, and the availability of crop residues for mulching and systematic crop rotations which are currently lacking in southern Africa. Anadditive design of within-row intercropping was compared to a substitutive design with distinct alternating rows of maize and legume (local practice) under no-tillin the Ruaca and Vunduzi communities of central Mozambique. Intercropping increased productivity compared to the corresponding sole crops with land equivalent ratios (LER) of between 1.0 and 2.4. Maize yield loss was only 6-8% in within-row intercropping but 25-50% in the distinct-row option. Relay planting of maize and cowpea intercropping ensured cowpea yield when maize failed thus reduced the negative effects of dry spells. The residual benefits of maize-pigeonpea intercropping were large (5.6 t ha-1) whereas continuous maize (0.7 t ha-1) was severely infested by striga(Striga asiatica). The accumulation of biomass which provided mulch combined with no tillageincreased rainfall infiltration. Intensification through legume intercropping is a feasible option to increase crop productivity and farm income while reducing the risk of crop failureespecially where land limitation. Cattle manure in combination with chemical fertiliser that included N, P, Ca, Zn, Mn were evaluated for their potential to recover degraded soils and to support sustainable high crop productivity in Murehwa, Zimbabwe over nine years. The experiment was established on sandy and clay soils in two field types. Homefields were close to the homestead and relatively more fertile than the outfields due to previous preferential allocation of nutrients. Maize grain yields in sandy soils did not respond to the sole application of fertiliser N (remained less than 1 t ha-1); manure application had immediate and incremental benefits on crop yields in the sandy soils. A combination of 25 t ha-1 manure and 100 kg N gave the largest treatment yield of 9.3 t ha-1 on the homefield clay soils, 6.1 t ha-1 on clay outfield, 7.6 t ha-1 on sandy homefield and 3.4 t ha-1 in the eighth season. Despite the large manure applications of up to 25 t ha-1, crop productivity and soil organic carbon build-up in the outfield sandy soils was small highlighting the difficulty to recover the fertility of degraded soils. Manure can be used more efficiently if targeted to fields closest to homesteads but this exacerbates land degradation in the outfields and increases soil fertility gradients. The NUANCES-FARMSIM model for simulating crop and animal productivity in mixed crop-livestock farming systems was used to perform trade-off analysis with respect to crop residue management, animal and crop productivity in Murehwa, Zimbabwe. Retaining all maize residues in the field led to severe losses in animal productivity but significant gains in crop productivity in the long-term. Yield increased 4 to 5.6 t farm-1 for RG1, and from 2.8 to 3.5 t farm-1 for RG2. Body weight loss was on average 67 kg per animal per year for RG1 and 93 kg per animal per year for RG2. Retention of all crop residues reduced farm income by US37 and US38 per year for RG1 and RG2 respectively.Farmers who own cattle have no scope of retaining crop residues in the field as it results in significant loss of animal productivity. Non-livestock farmers (60% of the farmers) do not face trade-offs in crop residue allocation but have poor productivity compared to livestock owners and have a greater scope of retaining their crop residues if they invest in more labour to keep their residues during the dry season. This study has revealed that crop production intensification options developed without considering the biophysical conditions as well as socio-economic circumstances of farmers are nuisances. External ideas should be used to stimulate local innovations to push the envelope of crop production without creating new constraints on resource use.

Living organisms and their enzymes are responsible of most of the soil biotic interactions in agro-ecosystems. This study was to evaluate the impact of land use (cropping systems and farming practices) on the physical, chemical and biological properties of soil in Western Cameroon. We sampled soil (0-20 cm) in four different land use systems (extensive, intermediate, intensive and an undisturbed natural habitat). We also measured soil health indicators in each land use type. We observed that the total organic carbon (Corg) and P availability was significantly higher in agro-ecosystems as compared to undisturbed natural habitat. Similar trends were recorded for pH, electrical conductivity, and ?-glucosidase, dehydrogenases and acid phosphatase activities. We also recorded a significant variation in microbial biomass C (Cmic: 312.0 to 544.5 mg kg-1 dry soil) and microbial biomass N (Nmic: 5.40 to 25.31 mg kg-1 dry soil) with land use intensity. The Cmic/Corg ratios of soils were two-fold lower in agricultural lands with vegetables than the undisturbed control plot indicating a decrease in soil microorganisms. Regression analysis revealed a negative correlation (r = - 0.806, P < 0.01) between soil clay content and microbial biomass C, and a high Corg/N ratio suggesting a heterogeneous distribution of the population of microorganisms between soils and the immobilization of P, respectively. Our results suggest that the selected soil health indicators were sensitive to farming practices and cropping systems.

Many studies have shown the relationship between fire clearing and mercury contamination of aquatic ecosystems in the Brazilian Amazon. This study aimed at quantifying mercury content in long-time cultivated soils and at assessing the potential of a fire-free alternative clearing technique on mercury retention for long-time cultivated soils compared to traditional slash-and-burn. This case study included five land uses: one crop plot and one pasture plot cleared using slash-and-burn, one crop plot and one pasture plot cleared using chop-and-mulch, and one 40-year-old forest as a control. Low mercury concentrations were recorded in the surface horizon (24.83 to 49.48 ng g−1, 0–5 cm depth). The long-time cultivation (repeated burnings) of these soils triggered large mercury losses in the surface horizon, highlighted by high enrichment factors from surface to deeper horizons. The predominant effect of repeated burnings before the experimental implementation did not let us to distinguish a positive effect of the chop-and-mulch clearing method on soil mercury retention for crops and pastures. Moreover, some processes related to the presence of the mulch may favor mercury retention (Hg volatilization decrease, cationic sites increase), while others may contribute to mercury losses (cationic competition and dislocation, mobilization by the dissolved organic matter).

La connaissance des différentes unités agronomiques au niveau d'un terroir et leur utilisation par les agriculteurs est indispensable si l'on veut adapter les propositions de systèmes SCV aux contraintes du milieu. Ces unités agronomiques sont définies de manière à constituer des ensembles homogènes, pour lesquels les systèmes de cultures que l'ont peut proposer sont identiques. Ainsi, l'origine d'un sol n'est pas vraiment discriminante (il ne s'agit pas d'unités pédologiques), mais on s'attache avant tout à prendre en compte les caractères discriminant les possibilités de culture. Dans la zone agro-écologique de moyenne altitude, avec longue saison sèche, la différenciation agronomique des sols se fait sur la base de leur niveau de fertilité, de leur compaction, et de leur régime hydrique (en saison et en contre-saison). Ainsi, les pratiques agronomiques peuvent faire évoluer une parcelle d'une unité à une autre. Par exemple, un sol compacté sur lequel on installe des plantes de couvertures au système racinaire très puissant, peut ainsi évoluer en quelques années vers un sol non compacté. De même, la fertilité du sol peut évoluer, dans un sens ou dans un autre. En pratique, on peut distinguer ces unités en se basant sur la couleur du sol, la flore en place et les performances des cultures conduites par les paysans.

L'intensification écologique (IE) constitue une voie intéressante pour accroitre durablement la production agricole en substituant à des facteurs de productions industriels, des processus biologiques. La littérature nous enseigne que les légumineuses jouent un rôle important dans l'amélioration des systèmes de culture. Toutefois, leur intégration semble insuffisamment assurée dans les systèmes de culture à base de coton et céréales, à l'Ouest du Burkina Faso. La présente étude vise à comparer les performances agronomiques et économiques des systèmes intégrant des légumineuses annuelles en culture pure et en culture associée, dans le cadre d'une démarche d'expérimentation chez et par les paysans (ECPP). Au cours d'une campagne agricole (2011), nous avons utilisé les indicateurs économiques (temps de travaux, productivité de la terre et du travail) et agronomiques (rendement, valorisation fourragère, valorisation de l'espace) pour établir cette comparaison. Les résultats obtenus indiquent que les agriculteurs préfèrent le système de culture à base de niébé (24 paysans) par rapport à celui à base de mucuna (13 paysans). Les résultats montrent que la teneur en azote de la biomasse de mucuna en culture pure est la plus élevée. Cette légumineuse est suivie par l'association maïs-légumineuse, qui n'a pas occasionné de travail supplémentaire, par contre l'association a permis d'économiser près de 30 % de l'espace, et de diversifier les produits agricoles. L'étude a permis en outre de conclure que les cultures associées présentent un réel intérêt pour les agriculteurs engagés dans l'intensification agricole. Elles offrent l'opportunité de produire plus de biomasse par unité de surface, avec une qualité meilleure qu'en système de culture conventionnel.Mots clés: Intensification écologique, système à base de coton et céréales, indicateurs économiques, économie d'espace, Burkina FasoThe ecological intensification (EI) represents an interesting way to increase durably the agricultural production by replacing the industrial factors of production by biological processes. Literature teaches us that the legumes play a significant role in the improvement of cropping systems. However, their insertion is inadequate in cropping systems based on cotton and cereals in Western Burkina Faso. This study aims to compare the agronomic and economic performances of cropping systems integrating annual legumes in pure culture or mixed cropping in a process of experimentation to the and by farmers (ETBF). During a crop year (2011), we used economic indicators (work time, productivity of land and labor) and agronomic data (yield, forage enhancement, development of space) for this comparison. The results indicate that farmers preferred the cropping system based on cowpea (24 farmers) compared to that based on mucuna (13 farmers). Observations show that content of biomass in nitrogen of mucuna in pure culture is highest. Mucuna is followed by corn/legumes associations which do not cause additional work but can save nearly 30 % of the space, and diversify agricultural products. This study makes it possible to conclude that the associated cultures have a real interest for the farmers engaged in the intensification of their exploitation. They offer the opportunity to produce more biomass per unit of area, with a better quality than in conventional cropping system.

En Algérie du Nord, le développement agricole pose le problème de la conservation de l'eau et de la fertilité des sols. Après quatorze années de gestion conservatoire de l’eau, de la biomasse et de la fertilité des sols (GCES), les auteurs analysent les effets de la GCES sur le ruissellement, l'érosion, l'amélioration des systèmes de cultures, la productivité des terres et du travail dans des situations agro-écologiques diverses.Dans quatorze sites expérimentaux de l’INRF (88 à 222 m2), situées en moyenne montagne méditerranéenne (10 à 45 % pentes entre 400 à 900 m d'altitude et recevant 300 à 650 mm de pluie), les améliorations apportées aux témoins régionaux de 1986 à 1995 (labours dressés grossiers, emploi de pesticides, graines sélectionnées, fertilisation équilibrée, jachère fourragère de légumineuses, cultures associées en rotation sous verger), ont réduit les risques d’érosion et de ruissellement au champ. Mais ce qui est encore plus important, c'est l'amélioration très significative des rendements des cultures et des revenus des agriculteurs. Les rendements augmentent en moyenne de six à dix fois. De plus, la paille, les feuilles des légumineuses et autres résidus de culture ont aussi augmenté significativement de telle sorte que la production animale et la disponibilité en fumier ou en résidus organiques peuvent, à terme, améliorer la fertilité du sol et sa résistance à l'érosion. Le revenu net à l ‘ hectare est multiplié par trois à vingt selon le système de production choisi.Sur les hauteurs de l’oued Chélif en zone semi aride steppique (pentes 10 à 20 %, altitude 900 m), à 150 km au sud d’Alger, sur les champs des paysans (1 hectare) en combinant les haies vives d’Atriplex aux cordons empierrés, le fumier et diverses matières organiques indispensables à la croissance des cultures dans les rotations biennales blé-fèves, les essais entrepris entre 2000-2004 ont confirmé que ces changements sont rentables pour le paysan. Ces résultats démontrent qu'il est possible à la fois d'intensifier l'agriculture de montagne et de réduire les risques de dégradation de l'environnement rural. Dans ces conditions, il est possible d'intéresser les paysans à modifier leur système de culture et à améliorer leurs méthodes culturales pour mieux conserver l'eau et la fertilité des sols. In northern Algeria, agricultural development poses the problem of water conservation and soil fertility. After fourteen years of sustainable management of water, biomass and soil fertility (GCES in french), the authors analyze the effects of GCES on runoff, erosion, improvement of crop systems, productivity land and labor in various agro-ecological situations.In fourteen of the experimental plots (88 to 222 m2), located in mountainous Mediterranean regions (10 to 45 % slopes between 400-900 m of altitude and receiving 300 to 650 mm of rainfalls), various improvements (coarse tillage, fertilization, high quality seeds, pesticides, forage legumes fallow, cereals/legumes rotation, associated cultures with orchard) have been made to regional control from 1986 to 1995. They reduced the risk of erosion and runoff in the field. But what is even more important is the very significant improvement in crop systems and incomes of farmers. The yields increased on average from six to ten times. Moreover, the straw, leaves of leguminous and other crop residues also increase significantly so that the animal production and the available manure or organic residues can, in the future, to improve soil fertility and resistance to erosion. The net income per ha is increased by three to twenty according to the selected production system.On the high valleys of Chelif river in semi-arid area (slopes of 10 to 20 %, altitude of 900 m), 150 km to Algiers, from 2000-2004, tests combining hedge Atriplex on stone lines, manure and organic matter in wheat/broad beans rotation, have confirmed that these changes are profitable for the farmer. These results show that it is possible both to increase mountain farming intensity and reduce the risk of degradation of the rural environment. In these conditions it is possible to interest the peasants to modify their crop system and improve their farming methods to better conserve water and soil fertility.

Dans l'Ouest du Burkina Faso, la pression démographique a conduit à l'abandon de la jachère. Avec la culture continue du coton et du maïs, la fertilité des sols est mise à rude épreuve. Pour accroître la productivité des systèmes de culture et contribuer au relèvement de la fertilité des sols, des producteurs du Tuy participant au projet Fertipartenaires ont décidé de tester des associations culturales maïs/légumineuse. L'objectif de l'étude était de concevoir avec les producteurs des systèmes de cultures associées maïs/légumineuse économiquement performants et techniquement acceptables en réalisant des expérimentations en conditions réelles de culture. Des producteurs volontaires ont expérimenté l'association maïs/niébé (13 producteurs) et l'association maïs/ mucuna (10 producteurs). Pour chaque essai, l'association était comparée à la monoculture du maïs (témoin). Le niébé était déjà une culture pratiquée par les agriculteurs à une petite échelle à des fins alimentaires ou comme source de revenus, alors que le mucuna avait été récemment introduit comme ressource fourragère pour les bovins. La pratique des cultures associées maïs/légumineuse était nouvelle pour l'ensemble des agriculteurs. Les itinéraires techniques (ITC) ont fait l'objet d'un suivi complet jusqu'à la mesure des rendements. Pour les deux associations, les ITC homogènes ont été définis par analyse en composantes principales (ACP) et par classification ascendante hiérarchique (CAH) et les plus performants sur le plan technique et économique ont été comparés à la monoculture du maïs par analyse de variance (ANOVA). Il est ressorti que les dates de labour et de semis, la densité de peuplement, la date de sarclage et le niveau de fertilité des sols sont des facteurs de performance pour les associations maïs/ légumineuse. Les associations maïs/légumineuse produisent significativement (au seuil de 10%) plus de biomasses, de 22 à 29%, par rapport à la monoculture du maïs, sans pour autant augmenter significativement les temps de travaux. L'association maïs/niébé présente plus d'intérêt économique que l'association maïs/mucuna. Les études doivent se poursuivre pour améliorer les itinéraires techniques, estimer la pénibilité du travail au moment des récoltes et les arrières-effets des légumineuses sur les cultures de coton et maïs à moyens termes.

Despite huge gains in productivity, environmental impacts of industrial agriculture based on a few high-yielding crop cultivars and the massive use of chemical fertilisers and pesticides have led to a search for new pathways leading to more sustainable agriculture in both temperate and tropical regions. New strategies incorporating ecological knowledge gained from the observation of natural ecosystems is an alternative to design “ecologically intensive” agroecosystems. Such systems are indeed both ecological and productive. Designing ecologically intensive agroecosystems calls for in-depth knowledge of biological regulations in ecosystems, and for the integration of traditional agricultural knowledge held by local farmers. This article reviews the main initiatives underlying ecologically intensive agroecosystems, analyses basic concepts, and proposes a framework for action. The rainforest model, the dry forest model, and the American Prairie are exemplified as three main natural systems at the basis of the mimicry concept. The link between biodiversity and the mimicry hypotheses, and the use of the concepts of productivity, efficiency, stability, and resilience for agroecosystems are discussed. Six main principles for cropping system design based on natural ecosystem mimicry are identified. A three-step framework for action is proposed, including nature observation, experimental design, and participatory design. Although far from being a panacea, the mimicry approach can provide new ways for agroecosystem design both in temperate and tropical countries.

La dégradation des terres en Afrique subsaharienne accentue l'effet de la sécheresse et de la faible fertilité des sols sur la production agricole, aggrave l'insécurité alimentaire et accroît la vulnérabilité des populations et des ressources de base. En réponse, les paysans ont développé des pratiques qui, pour certaines, ont bénéficié du support de la recherche et du développement. Le zaï et le mulch, c'est-à-dire la couverture du sol par des ressources organiques mortes, permettent de récupérer rapidement les propriétés hydrophysiques des sols dégradés en stimulant l'activité biologique. L'amélioration subséquente de la fertilité conduit à la restauration des fonctions du sol, la production primaire est augmentée. Cependant, malgré leur efficacité, la diffusion de ces deux pratiques reste limitée du fait de la faible disponibilité des ressources organiques : fumier, compost ou encore les résidus de cultures qui sont prioritairement destinés A l'élevage. Le mulch peut être dérivé de la strate ligneuse mais bien souvent s'y opposent la faible disponibilité sur site et l'investissement nécessaire en travail ou pour le transport à partir des sites avoisinants. Une autre alternative moins connue et peu investiguée consiste en l'intégration d'arbustes natifs, particulièrement Piliostogma reticulatum et Guiera senegalensis, dans le système de culture. Dans certaines localités, les paysans maintiennent ces deux arbustes dans les champs cultivés et les gèrent annuellement, de façon ingénieuse. Pendant la saison sèche les arbustes se développent en touffes multitiges, ils réduisent l'érosion éolienne, interceptent les particules minérales et les matières organiques déplacées par le vent et, piègent les poussières transportées par l'harmattan. A l'entrée de la saison humide, ils sont coupés au ras du sol pour faire place aux cultures, les branches sont étalées en mulch sur le sol. La culture qui est généralement une céréale à laquelle est associé ultérieurement le niébé est installée par semis direct manuel au travers du mulch. À la montée de la céréale, les branches effeuillées sont ramassées pour servir de combustible. Les premiers rejets des souches sont gérés comme des adventices, ceux arrivant après le second désherbage sont laissés croître. À la récolte de la céréale, l'arbuste repart et ainsi de suite. Ce système ingénieux associant cultures annuelles et plantes pérennes dans lequel l'arbuste joue un rôle central de facilitation pour la culture peut conduire à l'amélioration de la fertilité du sol et de la production agricole, voire à. l'intensification écologique des systèmes de culture actuels. Par ailleurs, Piliostigma reticulatum et Guiera senegalensis sont sempervirents et se développent tout au long de la bande sahélienne, de l'Atlantique la mer Rouge et, ils sont connus des paysans pour leurs usages multiples. Un effort de recherche est nécessaire pour mieux connaître ces systèmes afin d'en améliorer les performances.

Limited information is available on the potential performance of introduced dual purpose varieties across different Kenyan soils and agro-ecological environments and consistency across sites and seasons. Crop simulation modeling offers an opportunity to explore the potential of and select introduced cultivars for new areas before establishing costly and time-consuming field trials. Dual purpose soybeans were introduced due to their ability to improve soils and at the same time provide substantial grain yields. The objective of this study was to derive genetic coefficients of recently introduced dual purpose soybean varieties and to explore the reliability of the Cropping System Model (CSM)-CROPGRO-Soybean model in simulating phenology and yield of the dual purpose varieties under different environments. Field trials for seven varieties were conducted across three sites in two seasons and data on phenology and management, soil characteristics and weather was collected and used in the CROPGRO model. A stepwise procedure was used in the calibration of the model to derive the genetic coefficients. Two sets of data from Kakamega and Kitale were used in calibration process while 2006 data for Kakamega and Msabaha, were used for evaluation of the model. The derived genetic coefficients provided simulated values of various development and growth parameters that were in good agreement with their corresponding observed values for most parameters. Model evaluation with independent data sets gave similar results. The differences among the cultivars were also expressed through the differences in the derived genetic coefficients. CROPGRO was able to accurately predict growth, phenology and yield. The model predicted the first flowering dates to within 2¿3 days of the observed values, the first pod dates within 3 days of the observed values and yields within 5¿300 kg ha-1 of the observed yields. The genetic coefficients derived in CROPGRO model can, therefore, be used to predict soybean yield and phenology of the dual purpose soybean varieties across different agro-ecological zones.

La zone Ouest du Burkina Faso se caractérise principalement par les rotations coton-céréale et un élevage extensif. Les légumineuses, malgré leur rôle reconnu en termes d'amélioration de la performance des systèmes de culture à base de céréales, occupent une place marginale dans les assolements. Les objectifs de cette thèse étaie nt de faire l'état de l'évolution de la fertilité des sols et de déterminer les facteurs de variabilité des performances du maïs et des légumineuses (niébé, mucuna) en fonction des systèmes de culture par des expérimentations conduites chez et par le paysan (ECPP). L'étude a é té conduite en 2010 avec 94 paysans et en 2011 avec 88 paysans suivant une démarche de recherche action incluant l'expérimentation chez et par les paysans (ECPP) dans 7 villages de la province du Tuy. Un diagnostic de la fertilité des sols a été réalisé et des indicateurs de fertilité ont été reliés aux productions du maïs, du niébé et du mucuna. Des expérimentations sur les cultures pures du niébé et du mucuna et sur les associations maïs/niébé et maïs/mucuna ont été conduites par les paysans en vrai grandeur. Les variables liées aux caractéristiques des exploitations, les variables agronomiques et les variables économiques ont été déterminées. Les résultats indiquent que la démarche d'analyse de données associant successivement une analyse en composantes principales (ACP), une classification ascendante hiérarchique (CAH), une analyse factorielle discriminante (AFD) et une analyse de variance (ANOVA), permet de prendre en compte la diversité des pratiques dans le cadre d'ECPP et de tirer les enseignements utiles pour concevoir dans des condit ions d'incertitudes, des innovations plus productives, écologiquement durables et acceptables par les paysans. Les données du diagnostic de fertilité confirment la baisse organique des sols suite à une exploitation continue des terres (avec des teneur en C de 3,41 % pour les sols non cultivés contre 0,79 % pour les sols dont l'âge de mise en culture varie entre 1 et 10 ans et 0,48 % pour les sols dont l'âge de mise en culture est supérieur à 30 ans). Toutefois, elles suggèrent comme résultat nouveau, un relèvement de la teneur en phosphore (P) assimilable des sols suite aux apports continus d'engrais chimique. La dégradation organique et l'enrichissement en P assimilable qui pourraient aller de pair, rendent complexe la notion de fertilité des sols. Ainsi, la baisse organique du sol ne serait pas automatiquement suivie de la baisse de rendement de certaines cultures (maïs, légumineuses) sensibles au phosphore. Nos recherches révèlent que les facteurs de variabilité des performances agronomiques et économiques des cultures pure des légumineuses et des cultures associées maïs/légumineuses, sont : les dates de semis, les conditions d'humidité du sol pendant le semis, les densités de peuplement, les dates de sarclage, les apports d'engrais (NPK et urée) dans les meilleurs délais et l'effet résiduel des précédentes fertilisations minérales. Les données sur les cultures pures de légumineuses indiquent que le niébé (légumineuse locale) est sensible à l'arrière effet de la précédente fertilisation contrairement au mucuna (légumineuse introduite) qui aurait plus de capacité à améliorer la fertilité des sols avec une quantité d e N accumulé plus élevée que celle des autres systèmes de culture. Les cultures pures de légumineuses peuvent constituer des sources de revenus pour les exploitations agricoles avec des marges brutes pouvant atteindre 156 479 ± 41 828 FCFA/ha pour le niébé et 64 918 ± 11 937 FCF A/ha pour le mucuna. Cette modalité d'insertion des légumineuses se trouve limitée par le problème d'espace cultivable et d'opportunité de marché dans la zone. La modalité associant les légumineuses au maïs, sans entrainer une augmentation significative du temps de travail, présentent l'avantage de faire des économies de l'espace (LER variant entre 1 et 1 ,46) par rapport aux cultures pures du maïs (LER < 1) et de légumineuses (LER < 1), de diversifier les produits agricoles sur la même parcelle et d'assurer une gestion durable de la fertilité du sol par la fixation de N atmosphérique par les légumineuses. Pour soutenir ces performances agronomiques et économiques de ces associations maïs/légumineuse et faciliter leur adoption et appropriation par les paysans, il conviendrait d'insérer les légumineuses dans des chaines de valeur pour lever les contraintes d'acquisition des intrants et pour créer des opportunités de marché.

Dans la zone à forêt semi-décidue de Côte d'Ivoire, un dispositif expérimental pérennisé entre 1995 et 1999 sur environ un hectare avec des systèmes de culture de maïs à couvertures végétales, a fait l'objet d'études associant agronomie et écologie du sol. L'offre en azote d'origine organique est étudiée dans le cadre de systèmes de culture de maïs, avec une durée de jachère de 6 mois et 18 mois. Les jachères sont occupées soit par Chromolaena odorata (subspontanée), soit par Pueraria phaseoloïdes (légumineuse introduite). L'étude réalisée pose comme hypothèses de départ que: (i) les déterminants de cette offre à court terme (cycle cultural) et à moyen terme (effets cumulés) dépendront principalement des quantités et de la qualité des litières de surface d'origine des jachères; et (ii) ces effets se concentreront à la surface du sol. Les résultats obtenus permettent de comprendre les bases de fonctionnement des systèmes à couvertures végétales, qui connaissent un réel développement. Plus globalement, ces systèmes intéresseront tous les praticiens, écologues et agronomes, concernés par la promotion d'une agriculture à la fois productrice et respectueuse de l'environnement.

Préambule En ce qui concerne le thème de « la jachère et la fertilité des sols », les différentes équipes du programme « jachère » ont eu pour but de clarifier les processus de changements d’états physiques, biologiques, chimiques qui modifient le milieu cultivé au cours du cycle culture-jachère et de déterminer les conséquences de ces modifications au niveau de la production à long terme. D’autre part, ils ont tenté diverses manipulations sur le cycle jachère-culture tentant de « simuler » l...

Présentation de l'éditeur : Agriculture in whatever age, under whatever natural, economic and social conditions, has to feed the human being. To fulfil this mission, the sector has to overcome continuous and changing challenges to achieve notable developments. The Green Revolution, through developing and introducing high-yielding crop varieties and advanced crop management techniques, saved billions people from starvation. The advent of biotechnology, in its turn, has speed up the agricultural growth to meet food demands of the world's booming population. Continuous demographic pressure and rapid market integration have created necessity to further agricultural developments to meet not only food security, but also the increased demands for nutrition security, food safety, energy, etc., while the global climate change has created needs for capturing synergies between agricultural production and environmental protection. New breakthroughs to trigger the second Green Revolution have therefore become necessary. Thus, it is now the right time for us to consider the means to make "the Double-Green Revolution" to become a reality. Conservation Agriculture (CA) has demonstrated potential to meet this goal through designing and promoting the adoption of environment-sound and climate-resilient agricultural production systems. Increasing interests and efforts have been given to CA research for development in the Southeast Asia during the last 15 years. As a result, a new stage has been reached with the formation of the Conservation Agriculture Network for Southeast Asia (CANSEA) in 2009, in which efforts have been maintained to adapt concepts of CA to small scale farmers dealing with a great diversity of climate, land, topography and economy conditions. Enormous inputs are needed for the Southeast Asia to design specific and diverse CA innovations appropriate for local farmers and to promote their large scale adoption. This requires involvement of a wide range of stakeholders from both private and public sectors. This is the reason for us to gather together at the 3rd International Conference on Conservation Agriculture in Southeast Asia. At this conference, the results of a tremendous amount of creative work dedicated to CA development worldwide will be presented. The methods and tools for designing relevant CA innovations and the experience and proposals for their adoption will be shared. This volume compiles a picture portfolio of abstracts selected through a peerreview process for oral and poster presentations at the conference. Main topics addressed in this volume include (1) Agrarian transitions in the Southeast Asian uplands and highlands; (2) Impacts of agricultural systems on agricultural ecosystem sustainability; (3) Farming and cropping system design to sustainably intensify production; (4) Synergizing concepts of CA and Agroforestry; (5) Potentials and constraints of CA for rural development, and (6) Conditions, strategies, barriers and opportunities for scaling-up CA. This compilation represents a state and the art of CA research for development worldwide and the possible applications for the Southeast Asia

International audience; This paper analyses the Organic Food & Farming (OF&F) scientific domain dynamic throught a "progressive document co-citation analysis" based on peer-reviewed papers from Web of Science. The dataset of OF&F domain displayed an exponential growth and a thematic diversification pattern. Both dominant and marginal clusters in association with their main cited articles were identified. This study enables to pinpoint major themes addressed or emerging. It can feed further research work and projects, namely with the definition of information system and research policy

One of the most serious problems of farming systems in West Africa is the excessive reduction of agricultural productivity related to the "slash and burn" and shifting cultivation systems. With the aim of designing more sustainable yam cropping systems, the agronomic research organization in Benin implemented alternative systems including herbaceous legumes (Aeschynomene histrix and Mucuna pruriens var utilis). This study examines with end-users in the framework of focus group and individual surveys in 306 farm households, constraints degree of severity of yam-based cropping systems and participatory solutions in order to improve policy transacting in rural areas for sustainable yam-production. The results showed significantly high constraint degree of severity for herbaceous legumes biomass incorporation (52% and 46%) for Mucuna and Aeschynomene respectively during individual survey and 82% during focus group for both legumes. Crop competitions, field access (with Mucuna), animal divagation, fertilizer cost, biomass burn, seed consumption, market and grains harvest (with Aeschynomene) were additional constraints as well as in low and relatively high population density zone. On the seed production plot, the biomass of Aeschynomene at senescence could be shaken within basins to collect easily the seeds and avoid lost. The mixture of Aeschynomene seeds with dry sand (3/4 sand - 1/4 seeds) solves the problem of planting small seeds. Before the legumes reach the physiological maturity, three-quarters of biomass could be manually incorporated into the soil before the dry season during ridging and the remaining biomass could be left on the surface as mulch in order to reduce the workload related to the biomass incorporation into the soil. The practice of fire wall and fire of reference around the plot is necessary to avoid the burn of the mulch in the dry period. Mucuna seeds valorisation occurred to generate additional incomes for smallholders' households. The animal nutrition with Mucuna grains deserves to be more investigated. The crop-livestock integration with these herbaceous should be an opportunity for yam production because of agro pastoral potential in the Guinea- Sudan transition zone of Benin.