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In West Africa, weeds are major production constraints in rain-fed lowland rice systems — often located in the inland valleys. Weed management technologies have been developed and promoted in such rice systems, but adoption by farmers lags behind, probably because of insufficient considerations of the system diversity or the farm-specific characteristics during technology development or promotion. This study aimed to identify farm-type specific entry points for innovations in weed management practices of smallholders in rice-based systems in inland valleys. We conducted farm surveys in the Mono Couffo region of Benin in 66 fields in 2010 and 2011 in a range of socio-economic settings typical for smallholder farms. A combination of multivariate analyses using Principal Component Analysis and Agglomerative Hierarchical Cluster is helpful in constructing farm typologies. This categorization, in turn, enables the assessment of farm-type specific weed management strategies and consequently the identification of entry points for innovation. Specific entry points for innovations in weed management include: (i) complementing the existing range of curative options by more preventive measures, (ii) diversifying the existing range of curative measures (mainly hand weeding and herbicide application) by measures that are both non-chemical and labor-saving, and (iii) improving women farmers’ access to information and inputs by targeted training endeavors and conducive credit systems.

Numerous studies have highlighted the merits of grafting to improve the performance of vegetable crops. However, the technique is hindered by several obstacles, including the synchronization of seedlings used as scions and rootstocks, and the effects of rootstocks and climatic conditions on grafting success rates. This study sought to gain insights into how such technical obstacles affect tomato grafting. An initial experiment conducted in a greenhouse set out to assess the relevance of using degree-days to predict the growth rates of seedlings used for grafting (i.e., stem diameters above cotyledons). The success rate for grafting a tomato variety (Tanya) on 10 different rootstocks from different species—namely tomato, eggplant, african eggplant, and a wild species—was assessed at different temperatures (i.e., 15, 20, 25, 30, 35, and 40 °C). The effects of grafting on plant vigor (i.e., fresh biomass), number of leaves, and plant height, and on the hydraulic conductivity of xylem vessels in the plant stem were assessed 2 weeks after grafting. The results show the advantage of using degree-days to predict the ready-to-graft stage of seedlings, as it reduced the discrepancy among trials. The grafting success rate was more than 90% at 15 and 20 °C, but decreased significantly with higher temperatures, down to 20% at 40 °C. Larger variations in growth rate for seedlings used as scions and rootstocks, a lower grafting success rate, and less vigor were recorded for heterografted plants than for homografted plants. The lower hydraulic conductivity measured in the stems of grafted plants, especially heterografted plants, was consistent with the lower plant vigor observed. Further studies are needed to investigate how grafting affects the hydraulic conductivity of xylem vessels in later developmental stages of grafted plants.

In the last 40 years in sub-Saharan Africa, huge investments have been made in inland valley (IV) development for agricultural production. Understanding the agricultural and socioeconomic impacts of IV development may help develop strategies for modernization and optimization of irrigation systems. A farmers’ perception approach was used to analyze the impacts of IV development on agricultural and hydraulic performances and on farmers’ socioeconomic conditions in the circle of Sikasso, Mali. Data were collected through focus group discussions, field visits and participatory observations in 37 inland valleys of which 17 were developed. The two main water control systems observed in developed inland valleys were (1) controlled submersion with bunded plots dedicated to rice and (2) spate irrigation regulated by weirs and cofferdams. Compared to undeveloped inland valleys, controlled submersion and spate irrigation expanded the cultivated area in the rainy season. In the dry season, crop extension was observed only in spate irrigation schemes. Higher crop productivity was observed in inland valleys located close to an urban market and in valleys cultivated during the off-season. Spate irrigation is widespread in bigger inland valleys with more water resources and is often associated with the cultivation of higher value off-season crops. Consequently, we observed farmers had individual and collective investment capacity in spate irrigation schemes than in controlled submersion and undeveloped inland valleys. The study highlighted the importance of re-thinking the design of water control facilities to enable crop diversification to improve the livelihoods of inland valley-dependent communities.

SUMMARYIndigenous crops, such as jute mallow (Corchorus olitoriusL.) have high potential for improving nutrient efficiency and income source diversification of farmers in sub-Saharan Africa. A better understanding of plant responses to nitrogen (N) is essential in shedding light on the trend towards increasing fertilizer applications for commercially grown jute mallow. The aim of this study was to determine the critical N dilution curve in order to assess the N nutrition index (NNI) in jute mallow in southern Benin. Above-ground dry matter (DM) and N concentration were determined weekly during the 2010 and 2011 growing seasons and six N treatments of 0, 30, 60, 120, 180 or 240 kg N ha−1were tested under irrigated conditions. A critical N curve (Nc= 3.35 W−0.18), where W is the DM in Mg per ha, was plotted based on the N concentration in the whole plant. The critical N concentration (Nc) represents the minimal N concentration required to achieve maximum growth. According to significant differences in DM at each sampling date, data points were divided into two groups representing either N deficient or N excess conditions. All data points in the N deficient group were under the critical N curve and most data points in the N excess group were on or above the critical N curve, therefore confirming the validity of the critical N curve determined in southern Benin. The NNI calculated as the ratio between the measured N concentration and predictedNc, ranged from 0.55 to 1.30. The equation for the critical N curve and NNI determined in this study for jute mallow could potentially be used as a parameter for N application under non-deficient water conditions in southern Benin.

Agricultural management practices are frequently non conservative and can lead to substantial loss of soil organic carbon and soil fertility, but for many regions in Africa the knowledge is very limited. To study the effect of local agricultural practices on soil organic carbon content and to explore effective ways to increase soil carbon storage, field experiments were conducted on an upland rice soil (Lixisol) in northern Benin in West Africa. The treatments comprised two tillage systems (no-tillage, and manual tillage), two rice straw managements (no rice straw, and rice straw mulch at 3 Mg ha ⿿1 ) and three nitrogen fertilizer levels (no nitrogen, 60 kg ha ⿿1 , 120 kg ha ⿿1 ). Phosphorus and potassium fertilizers were applied to be non-limiting at 40 kg P 2 O 5 ha ⿿1 and 40 kg K 2 O ha ⿿1 per cropping season. Heterotrophic respiration was higher in manual tillage than no-tillage, and higher in mulched than in non-mulched treatments. Under the current management practices (manual tillage, with no residue and no nitrogen fertilization) in upland rice fields in northern Benin, the carbon added as aboveground biomass and root biomass was not enough to compensate for the loss of carbon from organic matter decomposition, rendering the upland rice fields as net sources of atmospheric CO 2 . With no-tillage, 3 Mg ha ⿿1 of rice straw mulch and 60 kg N ha ⿿1 , the soil carbon balance was approximately zero. With no other changes in management practices, an increase in nitrogen level from 60 kg N ha ⿿1 to 120 kg N ha ⿿1 resulted in a positive soil carbon balance. Considering the high cost of inorganic nitrogen fertilizer and the potential risk of soil and air pollution often associated with intensive fertilizer use, implementation of no-tillage combined with application of 3 Mg ha ⿿1 of rice straw mulch and 60 kg N ha ⿿1 could be recommended to the smallholder farmers to compensate for the loss of carbon from organic matter decomposition in upland rice fields in northern Benin.

In a context of greater climate variability and increasing population pressure, inland valleys are considered as high potential agricultural area. This agricultural potential has been subject to multiple initiatives for characterization which were generally based on the physical characteristics. However, support strategies based on such inventories often fail to fit with the promoters’ expectations. One of the reasons is that approaches used to classify inland valleys do not generally take into account socio-economic factors. This study aims to characterize the diversity of inland valleys in the departments of Mono and Couffo based on a joint consideration of biophysical, agronomic and socio-economic characteristics and to prioritize the factors affecting their agricultural use. Data were collected on 158 inland valleys and were related to biophysical characteristics, uses, management and economic productivity. Six types of inland valleys differentiated by the production systems, economic productivities and socioeconomic characteristics were identified. The production system based on rainfed rice and off-season vegetable with application of chemical fertilizer generated the highest economic productivity. Strengthening farmers’ technical abilities was important for a better capitalization on inland valleys. These results support the importance to combine several approaches in the classification of inland valleys and to fully understand the factors affecting their valorization by rural populations. Key words: Diversification, inland valleys, intensification, performance, typology, uses.

Improvements in agricultural land and labour productivity are needed to meet the growing food demand and reduce farmer poverty in sub-Saharan Africa. The objectives of this study were to (i) quantify variation in labour inputs, yield and labour productivity among rice fields; (ii) elicit factors associated with this variation; and (iii) identify opportunities for improving yield and labour productivity. The study was carried out in two contrasting Beninese villages: Zonmon in the south and Pelebina in the north-west. In Zonmon 82 irrigated rice fields were surveyed during the 2013 and 2014 dry seasons. In Pelebina 50 rainfed lowland rice fields were surveyed over three rainy seasons (2012–2014). Data on farmer field management practices and field conditions were recorded through interviews with farmers, on-farm observations and measurements. Stepwise regression analyses were used to identify variables associated with variation in yield, labour inputs and labour productivity. Average yields were 4.8 ± 2.0 t ha−1 in Zonmon and 2.3 ± 1.2 t ha−1 in Pelebina. Average labour productivity, however, was larger in Pelebina (17 kg of paddy rice person-day−1) than in Zonmon (8 kg of paddy rice person-day−1). Relative yield gaps (43–48%) and labour productivity gaps (59–63%) were similar in the villages. There was no trade-off between yield and labour or labour productivity within the villages, suggesting that in many cases rice yields can be increased without additional labour inputs. The major labour-demanding farming operations were bird scaring in Zonmon and harvesting and threshing in Pelebina. We identified opportunities to improve rice yield and labour productivity, given current farmer knowledge and resource endowment. Based on the statistical models fitted per village, increasing the average hill density would result in up to 1.2 t ha−1 more yield, and up to 4 kg person-day−1 greater labour productivity for Zonmon. Increasing the average field size and avoiding rice shading would result in up to 0.8 t ha−1 more yield, and up to 17.1 kg person-day−1 greater labour productivity for Pelebina. Further enhancing yield and labour productivity will require (i) introducing small-scale mechanisation and other labour-saving innovations, in particular for labour-demanding farming operations such as bird scaring in Zonmon and harvesting and threshing in Pelebina; and (ii) combining analyses of yields and labour productivities at field level with detailed analyses of labour use and labour productivity at farm level. We found that, on average, one hectare in Zonmon contributed twice as much to Beninese rice production than one hectare in Pelebina but with a two times smaller reward for farmer labour. This paradox of higher yields but lower labour productivity in such different rice growing environments and farming systems should be addressed in elaborating development policies.

In sub-Saharan Africa, unexploited land and water resources in wetlands represent an important potential for intensified, sustainable and food-secure farms through rice production and market gardening. The lack of uptake of cropping in wetlands may be related to the ways in which resources are divided between family fields and individual fields. The management system on sub-Saharan African farms comprises a family management unit or a combination of a family management unit and one or more individual management units. The family management unit or the farm head controls production in family fields to satisfy family needs while the individual management units control production in individual fields to satisfy individual needs. Our objective was to investigate the diversity in farm management systems and the resulting uptake of cropping in wetlands for different farm types, as the first step towards suggestions for enhancing rice production and market gardening in wetlands. We studied farms in two case-study villages in Benin: Zonmon in the southern part and Pelebina in the north-western part. Farm typologies were developed based on random samples of 51 out of 134 farms (38%) from Zonmon and 50 out of 146 farms (34%) from Pelebina by combining principal component analysis and Ward's minimum variance clustering. Variables included in the PCA were related to levels of resource endowment (e.g., amounts of land, family labour, cash for purchasing chemical inputs and hiring labour) and to resource-use strategies including resource division between family fields and individual fields, and between uplands and wetlands. We identified 3 farm types in Zonmon and 5 farm types in Pelebina based on differences in resource-use strategies and in resource endowment. We found no trade-off between the existence of individual fields and the area under rice and market garden crops in wetlands. Labour abundance was the main factor driving both the occurrence of individual fields and the expansion of cropping in wetlands. Differences in labour division strategies between family and individual fields among farm types reflected differences in food and cash division strategies. Land use appeared strongly motivated by food self-sufficiency objectives and labour productivity, leading to prioritisation of upland over wetland areas. In wetlands, most farm types opted for cultivating market garden crops during the dry season when labour demand for upland fields was low. Our results indicate that increasing labour productivity in food crops and in rice and market garden crops would enhance the uptake of rice and market garden crops in wetlands. Creating credit facilities would increase the labour resource and allow farmers to hire labour, further contributing to wetland use. We discuss the relevance of a systemic farm analysis that enables distinguishing family and individual fields for understanding farm uptake of rice and market garden crops in wetlands.

National audience; Sanitary requirements are strengthening in response to consumers’ expectations, European regulations and private actor’s requirements, through retailers, in particular. Farmers are directly concerned by the dynamic, which has emerged for the last twenty years, since specifically the “mad cow” crisis. Mayotte is a French overseas department since 2011 and an ultraperipherial region of Europe since 2014. It is supposed to comply to European requirements. However, numerous studies highlight that the retrofit between practices and sanitary expectations is not already achieved. In order to answer this inadequacy in a context where almost 80% of the total production is informal, we have surveyed 47 tomatoes producers. This production is very sensitive to pests and particularly to tomatoes fly during the dry season, which can destroy all or some parts of the harvest. We demonstrate that more than producers’ individual characteristics, numerous exogenous factor could help understand the inadequacy observed. Institutional environment could be a brake as well as a leverage to setting up more environmental friendly practices.

International audience; AbstractVegetable production in sub-Saharan Africa faces numerous agronomic constraints that will have to be overcome to feed the increasing population and to fight malnutrition. Technology transfer and the adoption of low-tech protected cultivation techniques affordable for smallholders are believed to be able to meet this challenge. Protected cultivation techniques are a set of agricultural practices aimed at artificializing the crop environment through the use of soil covers and/or plant covers to control pests and climatic conditions. Although protected cultivation techniques may increase the yield and quality of vegetable crops and extend their production periods worldwide, the transfer of these techniques in sub-Saharan Africa raises questions about their agronomical performances, their profitability but also their environmental impacts. Are low-tech protected cultivation techniques adapted to the sustainable production of vegetables by smallholders in sub-Saharan Africa? To answer this question, we present an overview of the agronomic, economic, and environmental performances of low-tech protected cultivation techniques in sub-Saharan Africa as reported in the literature. The major conclusions that can be drawn from the review are (1) low-tech protected cultivation techniques are not suitable in all climatic conditions in sub-Saharan Africa and need to be combined with other methods to ensure adequate pest control, (2) the profitability of protected cultivation techniques relies on the capacity to offset increased production costs by higher yields and higher selling prices to be obtained with off-season and/or higher quality products, (3) breaking with existing cropping systems, the lack of technical support and skills, and the limited access to investment funding are major obstacles to the adoption of protected cultivation techniques by smallholders (4) life cycle assessments conducted in northern countries suggested that more efficient use of agricultural inputs would offset the negative impacts of protected cultivation techniques if they are properly managed, but further studies are required to be sure these results can be extrapolated to sub-Saharan Africa context.

This present study analyses gender and governance in the rice and vegetable-based value chain systems in 3 lowlands of southern Benin and 2 lowlands in Southern Mali. A sample of 243 farmers, 1 modern processing unit, 18 traditional processors, 76 traders and 8 national institutions were interviewed in Benin and Mali. Descriptive statistics and Harvard analytical framework were used for the analysis of governance and gender respectively in the value chains. The majority of farmers have access to the use of land. Women produce up to 80% of basic foods for household consumption and sale. However they don't have the control of these resources (capital and land). Decision making in relation to resources (land, water labor, credit) is under the control of men and natives. The governance analysis showed that the products of lowlands are not subject to quality control, with no public inspection for health and product quality. There is no input subsidy for actors in both countries. There are informal contracts between actors of the rice based systems in Mali and Benin. The markets are open for all the products and credit systems do exist. Some structures are involved in upstream and downstream chain components for training in various activities.

Urban agriculture, Life-cycle inventory,Typology,Cropping system data,Treatment frequency index,Nutrient budget; International audience; In sub-Saharan Africa, urban farmers have recently intensified the production of vegetables to cope with the increasing food demand. As a consequence, such an intensification may lead to potential risks for the environment and human health. There is therefore a need for an integrated evaluation of urban agricultural practices. Here, we studied tomato production in Benin cities. We measured performances and the environmental risks. We have monitored 12 cropping systems during 6 months and we calculated the pesticide treatment frequency index (TFI), the nutrient budgets, and the field emissions. Our results show that yields were low and variable, averaging at 9,533 kg.ha−1 and ranging from 0 to 21,163 kg.ha−1. The average TFI for pesticides was 8.9. The maximum TFI of 25 was observed for an insecticide applied weekly at 2.3 times the official rate. We observed an excess of the average nutrient budget of 120 kg N and 84 kg P. ha−1. In conclusion, our study of urban tomato production revealed poor practices and high risks for health and the environment.

While weeds generally are considered as the most important overarching production constraints in inland-valley cropping systems in West Africa, little is known about species' associations with environmental and crop management factors. Weed species' associations with seasonal and environmental factors, such as their position on the catena, soils and cropping systems, were studied during two seasons (dry and wet) in 45 arable fields of three inland valleys in south-western Benin, Africa. The three most dominant weed species were Dactyloctenium aegyptium, Commelina benghalensis and Digitaria horizontalis on the inland-valley crests (uplands), Ludwigia hyssopifolia, Corchorus aestuans and Ludwigia octovalvis on the sloping hydromorphic fringes and Leersia hexandra, Ipomoea aquatica and Fimbristylis ferruginea in the valley bottoms (lowlands). Echinochloa colona, Cleome viscosa and Talinum triangulare were the three most dominant species in the dry-season crops (maize or vegetables) and Leer. hexandra, I. aquatica and Sphenoclea zeylanica were the three most dominant species in the wet-season crop (rice). Ageratum conyzoides, Synedrella nodiflora and D. horizontalis were observed throughout the catena. Problem weeds in inland-valley agro-ecosystems are those that combine a high frequency with a high submergence tolerance and ecological plasticity, C4 grasses, perennial C3 species with persistent root structures and broad-leaved species with high propagation rates. Weed management strategies that are aimed at increasing the resilience of rice-based cropping systems in the inland valleys of the southern Guinea Savanna of Africa should address the categories of problem species that were identified in this study. This can be done best by following an integrated approach, including the use of more weed-competitive cultivars and rotation crops.

International audience; Chemical control has highly expanded over the last 30 years in sub-Saharan Africa to reduce bio-aggressors on all crops. Pest management of fruits and vegetables by small farmers in sub-Saharan Africa have developed anarchically in a fuzzy regulation framework. Pesticide toxicity and excessive application are often criticized both by farmers and consumers. Here, we review pesticide management in sub-Saharan Africa over the past 30 years. We then propose options to improve and reduce pesticide application, in order to decrease environmental and human hazards. The major points are as follows: (1) global changes in sub-Saharan Africa such as urbanization modify farmer practices and crop losses. (2) Pesticides are more and more used by small farmers in an unsustainable way. (3) The risk of pesticide application for human health and environment is poorly known. (4) We propose options to reduce pesticide application based upon integrated pest management (IPM) and agroecology. Moreover, IPM increases farmer economy, thus decreasing poverty.

To explore effective ways to decrease soil CO 2 emission and increase grain yield, field experiments were conducted on two upland rice soils (Lixisols and Gleyic Luvisols) in northern Benin in West Africa. The treatments were two tillage systems (no-tillage, and manual tillage), two rice straw managements (no rice straw, and rice straw mulch at 3 Mg ha −1 ) and three nitrogen fertilizers levels (no nitrogen, recommended level of nitrogen: 60 kg ha −1 , and high level of nitrogen: 120 kg ha −1 ). Potassium and phosphorus fertilizers were applied to be non-limiting at 40 kg K 2 O ha −1 and 40 kg P 2 O 5 ha −1 . Four replications of the twelve treatment combinations were arranged in a randomized complete block design. Soil CO 2 emission, soil moisture and soil temperature were measured at 5 cm depth in 6–10 days intervals during the rainy season and every two weeks during the dry season. Soil moisture was the main factor explaining the seasonal variability of soil CO 2 emission. Much larger soil CO 2 emissions were found in rainy than dry season. No-tillage significantly reduced soil CO 2 emissions compared with manual tillage. Higher soil CO 2 emissions were recorded in the mulched treatments. Soil CO 2 emissions were higher in fertilized treatments compared with non-fertilized treatments. Rice biomass and yield were not significantly different as a function of tillage systems. On the contrary, rice biomass and yield significantly increased with application of rice straw mulch and nitrogen fertilizer. The highest response of rice yield to nitrogen fertilizer addition was obtained for 60 kg N ha −1 in combination with 3 Mg ha −1 of rice straw for the two tillage systems. Soil CO 2 emission per unit grain yield was lower under no-tillage, rice straw mulch and nitrogen fertilizer treatments. No-tillage combined with rice straw mulch and 60 kg N ha −1 could be used by smallholder farmers to achieve higher grain yield and lower soil CO 2 emission in upland rice fields in northern Benin.

Weeds are a major constraint to rice production in labor-limited, upland rice-based systems in West Africa. The effects of weeding regimes and rice cultivars on weed growth and rice yield were investigated at two upland locations (Abomey-Calavi and Niaouli) in the degraded coastal savanna zone of Benin in 2005 and 2006 with below-average rainfall. Four weeding regimes (hoe weeding at 21 d after sowing [DAS], delayed hoe weeding at 31 DAS, hoe weeding at 21 and 42 DAS, and a no weeding control) were the main plot treatments. Cultivars comprising three interspecific upland rice cultivars (NERICA 1, NERICA 2, and NERICA 7) and the parents (Oryza sativaWAB56-104 andO. glaberrimaCG14) were tested in subplots. The most dominant weed species identified were Jamaican crabgrass,Mariscus, and silver spinach. Rice yield was generally low because of drought stress; none of the experiments had a higher mean yield than 1,400 kg ha−1across cultivars. Across cultivars, the best weeding regimes in terms of weed control and rice yields were single weeding at 31 DAS (W31) and double weeding at 21 and 42 DAS (W21+42). Under these weeding regimes, WAB56-104 out-yielded the three NERICA cultivars. CG14 showed the strongest weed suppressive ability (WSA) in Abomey-Calavi but did not have strong WSA in Niaouli because of lower biomass accumulation. WSA of WAB56-104 was similar to that of the three NERICA cultivars. Single weeding at 31 DAS, together with the use of cultivars with good adaptation to unfavorable rice growing conditions, would increase land and labor productivity of upland rice-based systems in West Africa.

Gboma (Solanum macrocarpon) is the major leafy vegetable cultivated in Benin, with many people depending on this crop for their livelihood. In March 2012, wilted Gboma plants without foliar yellowing were observed at three locations (Dogbo, Lokossa, and Athieme) in the southwestern districts. Longitudinal sections of most stems of Gboma showed brown vascular discoloration. The cut stems released whitish bacterial ooze in water. Bacterial colonies on modified semi-selective medium from South Africa SMSA (Engelbrecht 1994) were mucoid and round with red centers with beige peripheries, thus morphologically similar to Ralstonia solanacearum. To fulfill Koch's postulates, 19 different isolates were inoculated on susceptible Gboma cv. Kpinman, grown in sterilized field soil. Plants (10 per isolate) were inoculated by drenching the soil with 40 ml of a bacterial suspension containing 108 CFU/ml. Plants treated in a similar manner with sterile water served as a negative control. Inoculated plants were incubated under a protected shed at about 30°C. By 15 days after inoculation, 100% of the inoculated plants were wilted whereas all control plants remained healthy. R. solanacearum was recovered from all symptomatic plants on modified SMSA medium. In 2014, a survey throughout the Abomey-Calavi area (Atlantic District) identified bacterial wilt of Gboma within all cultivated farms, with incidences ranging from 15 to 75.2%. Thirty newly collected bacterial isolates were identified as Ralstonia solanacearum using ImmunoStrip assays (Agdia Inc., Elkhart, IN, USA), and diagnostic PCR with 759/760 primers (Opina et al. 1997). A phylotype-specific multiplex PCR (Fegan and Prior 2005) classified all strains in R. solanacearum Phylotype I. Partial sequences of the egl and mutS genes were deposited in GenBank under Accession Nos. KP730628 to KP730687. Alignment of these to R. solanacearum reference sequences confirmed that all strains from Abomey-Calavi and two from Dogbo belonged to one unique Sequence Type (ST) within Phylotype I (egl ST 43 (sequevar 31), mutS ST 22). This ST has also been reported to be widespread in the Ivory Coast (N'Guessan et al. 2012), and in South Africa, India, and Reunion Island (Wicker, unpublished data, 2015). This is the first report of R. solanacearum causing bacterial wilt on Gboma in Benin. Further surveys will help to assess the precise distribution of bacterial wilt disease on Gboma in Benin, and allow development of integrated management strategies combining currently available resistant cultivars and rotation with suppressive crops. (Texte integral)

Pests and diseases are one of the limiting factors that farmers have to control to obtain better yields. With a view to gaining a clear understanding of their cultivation practices and technical decisions in order to support farmers in a move toward environment-friendly practices, a two-year survey of tomato farmers was conducted in Mayotte. Thirty five farmers were interviewed several times about their crop management, and field observations were undertaken every two weeks. Results showed that the number of pesticide applications varied greatly (4–23) with a tendency toward over-application, and no relationship was found between the application rate and the health status of the crop. Inefficiency in protecting crop health also reflected a problem of access to pesticide information and a poor control of crop protection methods. Over-application of pesticide has long term impacts on marine health and biodiversity. The planting bed and the individual plant were found to be appropriate units for technical decision making and applying market gardening techniques. However, current agricultural advice does not apply to these units, suggesting that a redefinition of technical advice is needed.

Crop pests are a major constraint to the intensification of agricultural production in the tropics, with novel issues related to global change (climate, land use, biological invasions, etc.), food security and preservation of natural resources and biodiversity. A research, extension and education network called DIVECOSYS (Diversity of cropping systems and ecologically-based pest management in West Africa) was launched in 2010 to synergize applied research actions in response to growing concerns on the vulnerability of agricultural systems to pest management in West Africa. This scientific network brings together research and academic institutions, with expertise spanning a multidisciplinary perspective from biology and ecology to remote sensing, agronomy and integrated pest management. Its main scientific objective is to explore the potential of biodiversity and ecological processes such as pest regulation, enabling novel ecologically-based models for productive systems, reduction of pesticide use, and adaptation or resilience of farming systems in the face of environmental disruptions. From Northern Senegal to Southern Benin, the research group explores a wide range of ecoregions and socio-ecological contexts, including stakeholders and their objectives, land use and agricultural practices, and management of biodiversity for enhancing biological control. Main challenges to be turned into opportunities include (i) encouraging collaborations amongst researchers from different scientific fields, (ii) fostering interactive research and synergies among research institutions and among countries, and (iii) developing an ecological engineering approach for the design of sustainable agricultural systems for smallholder farmers.

Because of the limiting efficacy of common weed control methods onCyperusspp. andImperata cylindricatheir occurrences in tropical agroecologies and the effect of soil properties in suppressing these species were investigated in south Benin (Cotonou), a typical ecology of the Dahomey gap. Weeds and soil samples were collected twice early and later in the rainy season in 2009 at four topographic positions (summit, upper slope, middle slope, and foot slope). Sampling was done according to Braun-Blanquet abundance indices (3 and 5) and the absence (0) ofCyperusandImperatain a quadrat, respectively. The relationship between their respective abundances and soil parameters (texture, C, N, P, K, Na, Ca, Mg, and Fe) was explored. Weed occurrence was less related to soil texture, andImperatagrowth was more influenced by soil nutrients (K, Ca, and Fe) thanCyperusspp. Soil cation ratios of K : Mg and Ca : Mg were the main factors that could be changed by applying K and/or Mg fertilizers to reduceCyperusand/orImperataoccurrence. Maintaining high Fe concentration in soil at hillside positions can also reduceImperataabundance, especially in the Dahomey gap.

Tomatoes are widely cultivated in developing countries and are a major source of income for small-scale farmers. Yields of field-grown tomatoes vary considerably under tropical conditions but the main factors that limit yields remain to be identified. To this end, we conducted an on-farm survey in 22 fields in 2003 and in 28 fields in 2005 in a range of socio-economic settings typical of smallholder farms on the island of Mayotte (Indian Ocean). Data on crop management, fulfilment of water requirements, weed density, nitrogen absorption by the crop and nutrient availability in the soil, as well as the sanitary status of the crop were recorded at two-week intervals throughout the crop cycle. The data were analysed by principal component analysis, and multiple linear regression. Yields varied between years and sites from 0.7 to 45.3 t ha−1 in 2003 and from 8.1 to 89.1 t ha−1 in 2005. In 2003, the number of fruits per m2, fruit weight, the health status of the crop, and the cation exchange capacity of the soil explained 84.7% of yield variability among fields. In 2005, the number of fruits per m2 and the health status of the crop explained 84% of yield variability. In 2003, 61.8% of the variability of the number of fruits per m2 was explained by health status and the number of plants per m2, whereas in 2005, 65.6% of the variability was explained by health status, the number of pesticide applications, and planting density. The results of this study indicate that tomato yield could be increased by improving the health status of the crop by improving the efficiency of crop protection practices and by increasing planting density.

Sur un Acrisol (nomme terre de barre en Republique du Benin), nous avons echantillonne les herbes et le sol (de 0 a 20 cm de profondeur) au debut et a la fin de la periode de culture en 2009 pour mieux connaitre l'interaction entre l'occurrence d'essence a noix et les parametres du sol. Les echantillons furent preleves le long d'une toposequence a la station experimentale du Centre du riz pour l'Afrique en fonction des positions topographiques, du sommet, du haut de versant, de la mi-versant et du bas de versant. Pour chaque position topographique, un quadrat de1m x 1m fut delimite pour etudier l'abondance de Cyperus selon les indices d'abondance 0, 3 et 5. Les especes d'herbes prelevees ont ete identifiees, sechees et pesees. La granulometrie du sol ainsi que les teneurs du sol en C organique, N-total, P disponible, K, Ca, Mg et Fe-extractible ont ete determines. Parmi les trois especes de Cyperus observees, C. rotundus etait le plus frequent sur toute la toposequence alors que C. esculentus et C. sphacelatus se limitaient respectivement au sommet et haut de versant. Les teneurs du sol en sable, Fe et Pa influencaient positivement la presence de Cyperus spp contrairement aux teneurs en C et Mg. Mais seuls ces derniers nutriments faisaient cela de facon continue et significative. Donc, l'apport de matiere organique et d'un engrais riche en Mg pourrait ameliorer le controle des Cyperus. (Resume d'auteur)

Reduction of pesticide use is one of the main objectives in tropical fruit and vegetable production. To meet this objective, CIRAD proposed solutions based on the agroecological approach. The hypothesis is that increasing biodiversity in the agro-horticultural system will allow reduction of pesticide use by favoring ecological regulation mechanisms. To organize the research, CIRAD has set up different networks in the tropics. The first initiative, ATP OMEGA 3, has developed activities on okra in Africa, tomato in the Caribbean, and cucurbits in the Indian Ocean, focused on insect trap cropping control and soil borne disease service plant-based sanitation. In 2009, an initiative emerged from West African institutions and universities in 5 countries. This network, DIVECOSYS, aims to develop research and education programs in Sub-Saharan Africa and France on bio-aggressor managements on cropping systems from savanna area. Fruit flies on mango, Plutella xylostella on cabbage, weeds in rice-vegetables systems and Helicoverpa armigera on cotton are the biological models studied in view of pest control. In 2009, DEVAG, a regional project funded by European Commission, Ministry of Foreign Affairs of France with institutions from Cuba, Haiti and French West Indies has begun with the general objective to improve the agroecological horticultural systems in the cases of tropical islands. In 2011, the ECOHORT project was launched. This platformprogram proposes innovative horticultural systems based on ecological intensification. It brings together universities and research institutions from Europe and developing countries to promote the system approach in designing ecologically intensified systems in higher education and research. Some results from these networks are presented. (Resume d'auteur)

Cette étude se propose d’évaluer la contamination métallique des légumes produits à Grand-Popo au Bénin en liaison avec le maraîchage très développé dans la région. De façon spécifique, l’évaluation a concerné la contamination métallique par les engrais minéraux et la fiente de volaille utilisés de façon intensive par les producteurs pour la fertilisation des cultures. La méthode adoptée est basée sur des essais agronomiques conduits pendant quatre campagnes de production de 2009 à 2010 sur les sites de Yodo-Condji et d’Ayi-Guinnou. Il a été procédé à des analyses de laboratoire pour la recherche de quatre métaux lourds (cuivre, plomb, cadmium et fer) dans les échantillons de légumes et de fiente de volaille. Les teneurs moyennes du plomb dans la carotte, la grande morelle et la tomate, dépassent respectivement de 41, 6 et 38 fois les normes béninoises tandis que celles du cadmium le sont respectivement de 25, 6 et 40 fois. Cependant, dans la fiente de volaille, seules les teneurs du fer ont dépassé les normes requises, au cours des campagnes 1, 2 et 3 tandis queles autres métaux n’ont donné que des traces. Ces différentes teneurs ont révélé l’existence d’une relation de causalité entre les activités humaines non agricoles au niveau des sites étudiés et les degrés de contamination obtenus. Les conséquences induites par cette contamination sont des risques sanitaires pour les consommateurs et producteurs. Pour remédier à cette situation, il urge que des dispositions soient prises pour identifier toutes les sources potentielles de contamination notamment les activités domestiques et commerciales afin d’y renoncer ou de les contrôler.Mots clés: Maraîchage, métaux lourds, légumes, risques sanitaires, Bénin

Mycosphaerella leaf spot diseases of banana caused by Mycosphaerella musicola (Sigatoka leaf spot, SLS) and M. fijiensis (black leaf streak, BLS) are very destructive. The cultivation of resistant banana clones appears to be the most appropriate means to combat disease because genetic resistance is usually more durable than chemical control. Since pathogen populations maintain a high level of genetic diversity and single gene resistances, such as is suspected in total or hypersensitive resistance situations, are easily overcome, the phenomenon of "partial resistance", which may be multigenic and hence more durable, is used in CIRAD breeding programmes. New hybrids of banana developed by CIRAD are routinely selected for resistance against Mycosphaerella leaf spot diseases. There are four steps in the evaluation process. Firstly, the level of resistance to M. musicola is assessed under field conditions in Guadeloupe. Secondly, the most resistant hybrids are selected for detached-leaf resistance tests to M. musicola and M. fijiensis under controlled conditions. Thirdly, the efficacy of partial resistance of selected hybrids against M. musicola is confirmed in the field in the French West Indies and against M. fijiensis in the field in Mayotte. Finally, the durability of the hybrids' partial resistance is assessed by measuring disease severity in experimental plots for several years. This complete 4-steps process allows, through experimental approaches, to select banana cultivars with durable resistance against Mycosphaerella leaf spot diseases. (Resume d'auteur)