Search

International audience; Conservation agriculture (CA) is one strategy with which both sustainability and productivity can be achieved by improving soil health. However, linkages between practices, soil health and cropping system performance remain poorly disentangled. We assessed the relationships between soil health and cropping system performance for three maize-based cropping systems in New Caledonia. Two CA systems, one with direct seeding into a mixed species dead mulch (CA-DM) and one into a stylo living mulch (CA-LM), were compared to a conventional tillage (CT) system. CA vs. CT experiment started in 2011, whereas the differentiation between CA-DM and CA-LM was initiated in 2017 only. In 2018, soil health was evaluated using Biofunctool (R), a set of ten in-field tools that assess soil carbon transformation, structure maintenance and nutrient cycling functions. The performance of the three cropping systems were assessed by monitoring weeds, maize growth and yield components. Structural equation modelling (SEM) was used to disentangle the links between agricultural management, soil health and cropping system performance. Soil structure maintenance and nutrient cycling functions were higher under CA-DM and CA-LM than under CT, and carbon transformation function was higher under CA-DM than under CT and CA-LM. Overall, the soil health index (SHI) was 1.3-fold higher under CA systems than under CT. Cropping system management had both direct and indirect effects on soil functioning and crop productivity leading to a 1.3-fold higher yield under CA than under CT. The direct and indirect effects of CA systems on soil health had positive impacts on ecosystem services (i.e., productivity, weed regulation and soil ecosystem services). Such integrative approaches that account for the relationships and possible trade-offs between cropping system components enable a better understanding of the effects and the performance of practices, and support adaptive agricultural management.

Ecological theory suggests that biodiversity has a positive and stabilizing effect on the delivery of ecosystem services. Yet, the impacts of increasing the diversity of cultivated crop species or varieties in agroecosystems are still under scrutiny. The empirical evidence available is scattered in scope, agronomic and geographical contexts and impacts on ecosystem services may depend on the type of diversification strategy used. To robustly assess the effects of crop diversification in agroecosystems, we compiled the results of 95 meta-analyses integrating 5,156 experiments conducted over 84 experimental years and representing more than 54,500 paired observations on 120 crop species in 85 countries. Overall, our synthesis of experimental data from across the globe shows that crop diversification enhances not only crop production (median effect +14%), but also the associated biodiversity (+24%, i.e. the biodiversity of non-cultivated plants and animals), and several supporting and regulating ecosystem services including water quality (+51%), pest and disease control (+63%) and soil quality (+11%). However, there was substantial variability in the results for each individual ecosystem service between different diversification strategies like agroforestry, intercropping, cover-crops, crop rotation or variety mixtures. Agroforestry is particularly effective in delivering multiple ecosystem services, i.e. water use and quality, pest and diseases regulation, associated biodiversity, long-term soil productivity and quality. Variety mixtures, instead, provide the lowest benefits, while the other strategies show intermediate results. Our results highlight that while increasing the diversity of cultivated crop species or varieties in agroecosystems represents a very promising strategy for more sustainable land management, contributing to enhanced yields, enhanced biodiversity and ecosystem services, some crop diversification strategies are more effective than others in supporting key ecosystem services.

Cover plants have a high potential to manage weeds through competition for shared resources in tropical agrosystems. Assessing the abilities of a large number of different plant species to compete with weeds requires long-term experiments in different pedoclimatic environments. Our study was based on a set of 10 trials including 46 species of cover plants and performed from 2016 to 2018 in three sites in Reunion. Our aim was to identify and measure plant traits that optimize plant coverage and weed control by cover plants under tropical climate. We characterized two traits of interest (a soil coverage efficiency index and a coverage growth rate) using a hierarchical clustering analysis and compared them between plant area of origin, life cycle or growth habit. The ability for cover plant to cover efficiently and rapidly the soil increased with growth rate in height and leaf appearance rate while tends to decrease with thermal time for emergence. Accordingly, weed control efficiency (low weed coverage and dry mass) was strongly correlated and increasing with cover plant growth rate in coverage, height and biomass. The characterization of plant species using functional traits enabled to identify cover plants which could be used in tropical agrosystems as an alternative to herbicides. Assuming that the spatial and temporal combinations with the main crop will determine the performances of the system, we discussed a trait-based methodology to identify the cover plants adapted to sugarcane agrosystems in Reunion.

International audience; In Martinique or La Reunion, French authorities recently banned the use of pesticides for the management of "soil-borne pathogens" on pineapple after several decades of intensive monoculture where the natural balance between beneficial and harmful communities of soil organisms has disappeared. Today, increasing infestation of pineapple by the nematode R. reniformis and other "soil-borne pathogens" causes severe damage to the crop. New cropping systems with innovative ecological nematode management are needed. An eco-friendly cropping system, which comprised rotation of sunn hemp (C. juncea), pineapple, a natural grass fallow and another cash crop, eggplant, consistently reduced the inoculum of nematodes. Nematode populations were reduced by 86.4%, 82% and 46.5% respectively under pineapple, sunn hemp and grass fallow compared to infestations of eggplant (3456 nematodes .100g(-1) of soil) after several rotations. Integrating a chemical induction of systemic resistance or application of an endophytic bacteria recovered from pineapple roots, Bacillus sp. GVS2, helped maintain low populations of nematodes during the vegetative cycle. On two pineapple varieties, MD2 and Victoria (Queen), two different treatments were applied monthly in the field, methyl jasmonate (10(-4) M, 10 ml per plant), or a suspension of Bacillus sp. GVS2 (10(8) CFU ml(-1), 10 ml per plant) isolated from pineapple roots. After eight months, the nematode populations were reduced respectively on MD2 and Victoria (Queen) by 58.3% and 50.3% with the methyl jasmonate and by 59.6% and 54.3% with the Bacillus sp. GVS2 compared to controls. Because of the efficiency of sunn hemp in reducing the inoculum of nematodes, no significant differences in vegetative growth were observed using the D leaf weight and the estimated root length densities (RLD). The potential of pest management through eco-friendly cropping systems for pineapple with a biocontrol for nematodes with no pesticide is discussed.

National audience; The data presented in this article describe 21 species that can be found in banana cropping systems: 17 cover crops species, 2 spontaneous species and 2 cultivars of banana. The cover crop species belongs mainly to Fabaceae family, but also to Poaceae, Euphorbiacea and Asteraceae. Four repetition of each species were cultivated individually, in the field, under non-limiting conditions. 40 variables were measured on whole plant, leaves and roots, at flowering or after six months of growth for longer cycle species. This dataset is made available to provide data on these species, enable comparisons between datasets and meta-analysis on cover crop or on species presented in arable fields. The data presented in this article were used in the research articles entitled “Trait-based characterisation of cover plants' light competition strategies for weed control in banana cropping systems in the French West Indies” (Tardy et al. 2015) and “Trait-based characterization of soil exploitation strategies of banana, weeds and cover plant species” (Tardy et al. 2017).

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

International audience; Cover crops are a potential component of agroecological cropping systems, since they may render crop rotations more sustainable. They simultaneously provide multiple ecosystem services, such as decreasing nitrate leaching, decreasing erosion, and increasing soil organic matter. However, cover crops increase evapotranspiration and reduce drainage, which results in a potential disservice for groundwater recharge. Little attention has focused on management of cover crop residues after destruction or their influence on water flux dynamics, particularly in dry and temperate climates. The objective of our study was to analyze and quantify the impact of cover crop management on soil water content and water flux dynamics to understand the main mechanisms of system functioning. We combined a two-year field experiment with crop-model simulations. We performed the field experiment in southwestern France that compared three cover crop treatments, with bare soil as the control. The treatments included (1) living cover crops lasting ca. 9 months from August-April, (2) crushing cover crops in November and leaving them as mulch on the soil, and (3) plowing up cover crops in November to promote residue decomposition and the green manure effect. The STICS soil-crop model was used to predict water fluxes that were not measured and to perform a 20-year independent simulation study based on recent climate series for the experimental site. Our main results indicated that cover crops (1) always reduce water drainage by 20-60 mm compared to that under bare soil; and (2) could significantly reduce soil water content (0-120 cm deep) for the next cash crop by a mean of 20-50 mm, and up to 80 mm in dry spring conditions, but early destruction could decrease this negative impact. The simulations clearly showed that the interaction between climate variability, i.e., rainfall distribution during the fallow period, and cover crop management should be considered to explain the impact of inter-annual variability on the water balance. Thus, destroying cover crops mechanically in late autumn and retaining the residues as mulch could be a good compromise between the multiple services the cover crop provides during the fallow period and avoiding the negative impact on soil water availability for the next cash crop.

International audience; AbstractCover crops provide many ecosystem services, such as soil protection, nitrate pollution of water mitigation, and green manure effects. However, the impact of cover crops on soil water balance is poorly studied, despite its potential impact on groundwater recharge. Some studies reported a reduction of the water drainage due to an increase of the evapotranspiration by plant cover transpiration. However, there is no real consensus on the intensity of this phenomenon, which highlights the importance to quantify the impact of cover crops on drainage compared to that of bare soil. We performed a meta-analysis of published papers presenting studies on the impact of cover crops on drainage compared to that of bare soil under temperate climates. Of the 436 papers identified, 28 of them were included in the analysis based on criteria required for performing a relevant meta-analysis. The originality of our study lies in two following results: (1) the quantification of drainage reduction with cover crops by a mean effect size of 27 mm compared to that of bare soil and (2) within the large variability of soils, climates, and cropping systems, no main determining factor was found significant to explain the variability of water drainage reduction. The cover crops provide a service of nitrate pollution mitigation, but the drainage reduction could be considered as a disservice, because they can lead to a reduction in groundwater recharge due to a higher evapotranspiration in comparison to bare soil. This highlights the need of research for optimizing trade-offs between services and disservices of cover crops for water balance.

International audience; Service crops are crops grown with the aim of providing non-marketed ecosystem services, i.e. differing from food, fiber and fuel production. Vineyard soils face various agronomic issues such as poor organic carbon levels, erosion, fertility losses, and numerous studies have highlighted the ability of service crops to address these issues. In addition to their ability to increase soil organic matter and fertility, and reduce runoff and erosion processes, service crops provide a large variety of ecosystem services in vineyards such as weed control, pest and disease regulation, water supply, water purification, improvement of field trafficability and maintenance of soil biodiversity. However, associating service crops with grapevines may also generate disservices and impair grape production: competition for soil resources with the grapevine is often highlighted to reject such association. Consequently, vinegrowers have to find a balance between services and disservices, depending on local soil and climate conditions, on their objectives of grape production and on the nature and temporality of the ecosystem services they expect during the grapevine cycle. This study proposes a review of the services and disservices provided by service crops in vineyards, and a framework for their management. Vinegrowers' production objectives and pedoclimatic constraints form the preliminary stage to consider before defining a strategy of service crop management. This strategy assembles management options such as the choice of species, its spatial distribution within the vineyard, the timing of its installation, maintenance and destruction. These management options, defined for both annual and long-term time scales, form action levers which may impact cropping system functioning. Finally, we underline the importance of implementing an adaptive strategy at the seasonal time scale. Such tactical management allows adapting the cropping system to observed climate and state of the biophysical system during the grapevine cycle, in order to provide targeted services and achieve satisfactory production objectives.

Background and aims The use of summer cover crops (SCCs) as residue inputs in agricultural systems can lead to a potential environmental trade-off between the amount C and N retained and the emission of N as the potent greenhouse gas, nitrous oxide (N2O). Our objectives were to relate N2O fluxes to the quality of SCCs residues and to select SCCs species with high C and N addition and low N2O emissions.Methods We measured SCC biomass production and N2O fluxes after SCCs termination - velvet bean, pearl millet, dwarf pigeonpea, sunn hemp, showy rattlebox and jack bean - under subtropical no-till conditions.Results The N2O fluxes in the first 30 days after SCCs termination corresponded to 65% of cumulative N2O emissions measured during 165 days in 2010 and 150 days in 2011. The cumulative N2O emissions varied from 0.46 to 1.38 kg N ha(-1) and were not proportional to aboveground biomass N addition. Cumulative N2O emissions were positively correlated to water-soluble C and N and the N content of crop residues and negatively correlated to cellulose and hemicellulose content. The N2O emission factor values varied from 0.24 to 0.64% and did not differ among SCCs.Conclusions Sunn hemp and dwarf pigeonpea are the most suitable species for inclusion in crop systems because they combined high C and N input and low N2O emissions.

The noctuid Helicoverpa armigera is one of the key cotton pests in the Old World. One possible pest regulation method may be the management of host crop in the landscapes. For polyphagous pests such as H. armigera, crop diversity and rotations can offer sequential and alternate resources that may enhance abundance. We explore the impact of landscape composition and host crop diversity on the abundance and natal host plant use of H. armigera in northern Benin.Host plant diversity at the largest scale examined (500 m diameter) was positively correlated with H. armigera abundance. Host plant diversity and the cover of tomato crops were the most important variables in relation to high abundance of H. armigera. Host plant (cotton, maize, tomato, sorghum) proportions and C3 versus C4 plants did not consistently correlate positively with H. armigera abundance. Moth proportion derived from cotton-fed larvae was low, 15% in 2011 and 11% in 2012, and not significantly related to H. armigera abundance.Cotton crop cover was not significantly related to H. armigera abundance and may be considered as a sink crop. Landscape composition and sequential availability of host plants should be considered as keys factors for further studies on H. armigera regulation. © 2015 Society of Chemical Industry.

PLoS OneISI Document Delivery No.: AE6LCTimes Cited: 0Cited Reference Count: 50Mollot, Gregory Duyck, Pierre-Francois Lefeuvre, Pierre Lescourret, Francoise Martin, Jean-Francois Piry, Sylvain Canard, Elsa Tixier, PhilippeCirad; e.u. fefer [30411]This research is a part of a PhD funded by the CIRAD and funded by the project "sustainable cropping systems design'' from E.U. FEFER (grant PRESAGE no 30411). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Public library scienceSan francisco; Plant diversification using cover crops may promote natural regulation of agricultural pests by supporting alternative prey that enable the increase of arthropod predator densities. However, the changes in the specific composition of predator diet induced by cover cropping are poorly understood. Here, we hypothesized that the cover crop can significantly alter the diet of predators in agroecosystems. The cover crop Brachiaria decumbens is increasingly used in banana plantations to control weeds and improve physical soil properties. In this paper, we used a DNA metabarcoding approach for the molecular analysis of the gut contents of predators (based on mini-COI) to identify 1) the DNA sequences of their prey, 2) the predators of Cosmopolites sordidus (a major pest of banana crops), and 3) the difference in the specific composition of predator diets between a bare soil plot (BSP) and a cover cropped plot (CCP) in a banana plantation. The earwig Euborellia caraibea, the carpenter ant Camponotus sexguttatus, and the fire ant Solenopsis geminata were found to contain C. sordidus DNA at frequencies ranging from 1 to 7%. While the frequencies of predators positive for C. sordidus DNA did not significantly differ between BSP and CCP, the frequency at which E. caraibea was positive for Diptera was 26% in BSP and 80% in CCP; the frequency at which C. sexguttatus was positive for Jalysus spinosus was 14% in BSP and 0% in CCP; and the frequency at which S. geminata was positive for Polytus mellerborgi was 21% in BSP and 3% in CCP. E. caraibea, C. sexguttatus and S. geminata were identified as possible biological agents for the regulation of C. sordidus. The detection of the diet changes of these predators when a cover crop is planted indicates the possible negative effects on pest regulation if predators switch to forage on alternative prey.

The effects of biofumigation using a Brassica juncea (mustard) cover crop on the dynamics of rhizoctonia root rot of sugar beet were recorded in two field trials in 2007 and 2008, and analysed using epidemiological modelling. Differences between partial biofumigation, involving the pulling up of mustard plants, and complete biofumigation, involving the crushing and incorporation of mustard residues into the soil, were compared with bare soil treatment. An epidemiological model was used that includes rates of transmission of primary and secondary infection, pre-emergence damping off, and expression of wilting symptoms (above-ground disease) due to infected roots (below-ground disease). The model indicated that biofumigation reduces the transmission of primary infections but affects secondary infections in a variable pattern between field trials. Likewise, the proportion of infected plants expressing wilting was significantly reduced, by 28%, in the partial and complete biofumigation treatments compared with bare soil in the trial of 2007 but not in 2008. It is suggested that the effects of biofumigation on secondary infection and the expression of disease are more variable than those on primary infection, and that this is probably due to an interplay between pathogen, antagonists, host, and environmental factors. These interactions may or may not offset the benefits afforded by a reduction in primary infection and account for the overall variable success of biofumigation to control disease.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; 1 Primary resources may affect the structure of species assemblages in upper trophic levels of food webs. These bottom-up effects may involve important ecological processes that affect pest control. For example, population densities of natural enemies may increase when alternative preys are favoured by a new resource. 2 Ants, particularly Solenopsis geminata Forel (Myrmicinae), are recognized as effective predators of herbivores eggs. In the present study, we tested the hypothesis that the addition of a primary resource in a banana agroecosystem will increase pest control of the banana weevil Cosmopolites sordidus Germar (Coleoptera, Curculionidae) by ants. 3 Using stable isotope analyses, we showed that S. geminata used the new resource pathway provided by the addition of a cover crop. This change was revealed by increased d13C values (13C/12C) in a cover crop treatment (C4 plant) compared with a banana (C3 plant) in bare soil treatment. 4 We also showed that the abundance of S. geminata, as measured with pitfall traps, was 4.85.4-fold higher in the cover crop treatment than in the bare soil treatment. Estimation of egg predation rates was in the range 7.870.3%, which occurred in plots with the lowest and highest S. geminata numbers, respectively. 5 The addition of a new primary resource in this system changed the origin of the carbon consumed by predators and increased their densities. The increased ant abundance resulted in increased predation of weevil eggs, which was consistent with our hypothesis. These results will be useful for the design of cropping systems that enhance the biological regulation of pests.

SUMMARYFarmers in the Lake Alaotra region of Madagascar are currently evaluating a range of conservation agriculture (CA) cropping systems. Most of the expected agroecological functions of CA (weed control, erosion control and water retention) are related to the degree of soil cover. Under farmers’ conditions, the grain and biomass productivity of these systems is highly variable and the biomass is used for several purposes. In this study, we measured biomass production of cover crops and crops in farmers’ fields. Further, we derived relationships to predict the soil cover that can be generated for a particular quantity of mulch. We used these relationships to explore the variability of soil cover that can be generated in farmers’ fields, and to estimate how much of the biomass can be removed for use as livestock feed, while retaining sufficient soil cover. Three different kinds of cropping systems were investigated in 91 farmers’ fields. The first two cropping sequences were on the hillsides: (i) maize + pulse (Vigna unguiculata or Dolichos lablab) in year 1, followed by upland rice in year 2; (ii) the second crop sequence included several years of Stylosanthes guianensis followed by upland rice; (iii) the third crop sequence was in lowland paddy fields: Vicia villosa or D. lablab, which was followed by rice within the same year and repeated every year. The biomass available prior to rice sowing varied from 3.6 t ha−1 with S. guianensis to 7.3 t ha−1 with V. villosa. The relationship between the mulch quantity (M) and soil cover (C) was measured using digital imaging and was well described by the following equation: C = 1 − exp(−Am × M), where Am is an area-to-mass ratio with R2 > 0.99 in all cases. The calculated average soil cover varied from 56 to 97% for maize + V. unguiculata and V. villosa, respectively. In order to maintain 90% soil cover at rice sowing, the average amount of biomass of V. villosa that could be removed was at least 3 t ha−1 for three quarters of the fields. This quantity was less for other annual or biennial cropping systems. On average the V. villosa aboveground biomass contained 236 kg N ha−1. The study showed that for the conditions of farmers of Malagasy, the production and conservation of biomass is not always sufficient to fulfil all the above-cited agroecological functions of mulch. Inventory of the soil cover capacity for different types of mulch may help farmers to decide how much biomass they can remove from the field.

International audience

Re-designing and assessing sustainable cropping systems has become a major challenge for agricultural researchers and farmers. In most prototyping methods, researchers are the main, or sometimes the only designers. However, more and more attempts for involving different kinds of stakeholders in participatory approaches have been accounted for. Besides, multi-criteria assessment tools are generally accepted as the solution to evaluating the overall sustainability of new cropping systems. The new method described in this thesis (DISCS for 're-Design and assessment of Innovative Sustainable Cropping Systems') implements a participatory re-designing process, while developing at the same time specific multi-criteria assessment tools for each category of stakeholders involved. Though founded on the common structure of prototyping methods, this five-step-method differs first by implementing three progress loops, at experimental field, farm then regional scale. Besides, an ongoing progress dynamic is set between research at the experimental station and crop management in farms, in order to ensure that innovative techniques actually match the farmers' expectations. Assessment at each step is performed using a scale-specific set of indicators. The DISCS method was tested on citrus production in Guadeloupe (French West Indies), to develop lower-pesticide sustainable cropping systems. Five weed management prototypes were collectively designed then tested at an experimental station based on the principles of a systematic approach. We show here that, contrary to other prototyping methods, innovative cropping systems can be the product of a farmer-researcher collaborative design. It was also verified that the innovation process benefited from involving non-agricultural stakeholders in the definition of the objectives for sustainable cropping systems. Such step by step improvement is well suited to perennial cropping systems. Using the DISCS framework should enable stakeholders to target precisely the decision-aid tools that need to be designed for a specific issue, thus ensuring a direct link between research and application. In this thesis, we present the first stages of citrus cropping system redesigning based on DISCS method; namely from the initial diagnosis, for to identify targets for improvement of the cropping system in collaboration with the stakeholders, to the multi-criteria assessment of weed management prototypes based on a set of appropriate indicators. Our work enables us to recommend sustainable weed management techniques for young orchards that correspond to the current constraints facing orchards in Guadeloupe., Les objectifs de développement de systèmes de culture durables imposent aux acteurs du développement rural une conception (ou reconception) et une évaluation de ces systèmes. Le prototypage peut être une méthodologie efficace de conception. Cependant, cette méthode conduit souvent les chercheurs à être seuls concepteurs alors que parallèlement l'appropriation des innovations dépend fortement de l'implication des autres acteurs dans les différentes étapes de conception et d'évaluation des nouveaux systèmes. En réponse, des approches participatives sont de plus en plus fréquentes pour pallier à cette difficulté d'appropriation tandis qu'une évaluation multicritère apporte une réponse aux objectifs d'évaluation de la durabilité des systèmes. La méthode développée dans cette thèse -nommée DISCS pour 're-Design and assessment of Innovative Sustainable Cropping Systems' - met en œuvre un processus de reconception des systèmes de culture par une approche participative tout en développant des outils d'évaluation multicritère spécifiques à chaque catégorie d'acteurs impliqués. La méthode DISCS s'inscrit tout de même dans la lignée de la méthodologie du prototypage mais se différencie par une démarche itérative à trois échelles d'étude (parcelle expérimentale, exploitation agricole et territoire) afin de s'assurer que les innovations et les critères d'évaluation répondent bien aux attentes des acteurs. A chaque étape du processus de reconception une évaluation est réalisée à l'aide d'un jeu d'indicateurs et ce aux trois échelles d'étude. DISCS a été testée sur le système de culture agrumicole en Guadeloupe (Antilles Françaises) dans un but de réduire l'utilisation des pesticides. Cinq prototypes de gestion de l'enherbement ont été conçus collectivement puis testés sur une station expérimentale selon les principes d'une approche systémique et évalués à l'aide d'indicateurs. Nous montrons dans ce travail que des systèmes de culture innovants peuvent être les produits d'une co-conception entre les producteurs et les chercheurs. DISCS permet aussi de définir explicitement le rôle de tous les différents acteurs impliqués dans le processus de reconception du système de culture. DISCS est particulièrement adaptée à la reconception des systèmes de culture pérenne notamment grâce à son processus d'amélioration pas à pas et itératif. Les outils d'évaluation multicritère développés, et notamment les indicateurs, permettent quant à eux de fournir des outils d'aide à la décision directement utilisables par les acteurs assurant ainsi un lien étroit entre la recherche et le développement. Dans cette thèse, nous présentons les premières étapes de reconception du système agrumicole guadeloupéen basée sur la méthode DISCS, à savoir du diagnostic initial pour identifier les objectifs d'amélioration du système en collaboration avec les acteurs, jusqu'à l'évaluation multicritère des prototypes de gestion de l'enherbement basée sur un jeu d'indicateurs approprié. Notre travail nous permet aujourd'hui de recommander des techniques de gestion de l'enherbement en jeunes vergers d'agrumes répondant aux contraintes actuelles de développement de systèmes de culture durable.

Generalist predators can play an important role in agroecosystems by controlling herbivores via top-down effects. As cover crops are increasingly used in agroecosystems, the effects of this resource on generalist predator diet need to be evaluated. We studied the effect of adding a cover crop, Brachiaria decumbens, on trophic niches of generalist predators in a banana agroecosystem by analysing stable isotope variation in C and N for Cosmopolites sordidus, a major banana pest, and its potential predators (spiders, ants, centipedes, and earwigs). While addition of the new resource did not change the trophic niche of the banana pestC.sordidus, the trophic position of the generalist predators was changed as indicated by 13 C signature. Cover crop provided resources that are likely to support a community of insect herbivores, which are alternative preys for generalist predators. The failure of the cover crop to increase 15 N signature is inconsistent with the hypothesis that the cover crop would increase intraguild predation. By providing alternative preys, the addition of a new resource in agroecosystems has the potential to increase populations of generalist predators and therefore pest control. Zusammenfassung Generalistische Pradatoren konnen in Agrarokosystemen eine wichtige Rolle spielen, indem sie eine top-down-Kontrolle auf Pflanzenfresser ausuben. Da zunehmend Grundungungspflanzen in Agrarokosystemen angebaut werden, mussen die Effekte dieser Ressource auf die Nahrung der generalistischen Pradatoren bewertet werden. Wir untersuchten den Effekt der Grundungungspflanze Brachiaria decumbens auf die trophischen Nischen von generalistischen Pradatoren in einem Bananen-Agrookosystem. Hierzu analysierten wir die Variation der stabilen Isotope von Kohlenund Stickstoff bei Cosmopolites sordidus, einem bedeutenden Bananenschadling, und seinen potentiellen Pradatoren (Spinnen, Ameisen, Hundertfuser und Ohrwurmer). Wahrend die angebaute Grundungung die trophische Position von C. sordidus nicht veranderte, anderten sich die 13 CSignaturen bei den generalistischen Pradatoren. Die Grundungspflanze bot Ressourcen,von denen vermutlich eine Gemeinschaft von herbivoren Insekten leben kann, die als alternative Beute fur generalistische Pradatoren konnen. Deren 15 N-Signatur

Les plantes de couverture, de plus en plus utilisées en zone tropicale en raison de leur intérêt pour la durabilité des systèmes de culture, le sont très peu en zone tempérée. C'est pourtant un moyen efficace de développer les services écosystémiques à cette échelle. L'objet de ce travail est triple : i) analyser la possibilité de les implanter en même temps qu'une culture commerciale sans entraîner de trop forte baisse de rendement ; ii) mesurer le supplément de matière organique susceptible de retourner au sol par l'allongement de la période d'utilisation du rayonnement photosynthétiquement actif ; iii) mesurer leur effet sur les risques de pollution des eaux par l'azote minéral. Un essai a été mis en place à Grignon en 1999-2001 (E1) et 2000-2002 (E2) pour étudier l'association d'une fétuque rouge (Festuca rubra L.) et d'un blé (Triticum aestivum L.), avec plusieurs modalités de compétition, obtenues en associant deux variétés de blé, à deux densités de semis, et deux de fétuque. Les blés ont été conduits avec un objectif de rendement en grains de 9 t/ha. Ces rendements (moyenne de E1 et E2) ont été plus affectés par le choix de la variété de blé (Isengrain : 8,8 t/ha, Scipion : 7,2 t/ha) que par la présence de la fétuque (blé seul : 8,6 t/ha ; blé associé : 7,8 t/ha). La fétuque a un effet dépressif sur l'élaboration du nombre de grains mais cet effet a été partiellement compensé par le poids d'un grain. La variété de fétuque n'a pas eu d'effet, ni la densité de semis du blé. Dans la période entre la récolte du blé et le semis de la culture suivante, les fétuques antérieurement associées ont produit 3,3 t/ha de biomasse en E1 et 2,7 t/ha en E2. Elles ont fait baisser la quantité d'azote minéral du sol dans la couche 0-0,9 m sous le seuil de 2 g/m 2., Cover crops, which have proven to be efficient in increasing the sustainability of tropical cropping systems, are much less used in temperate ones. The aim of this work is triple: i) to study the way to undersow a cover crop simultaneously with a cash crop in temperate areas without impacting too strongly the yield of the cash crop ; ii) to measure the overproduction of organic matter to be buried into the soil due to the lengthening of the period of the PAR use in such systems ; iii) to measure their impact on the risk of pollution of the ground water by nitrogen. Two two-year cycles of experimentation were carried out at Grignon in 1999-2001 (E1) and 2000-2002 (E2) to analyze the effect of red fescue (Festuca rubra L.), a turf grass selected as cover crop, on the wheat (Triticum aestivum L.) yield and its components and to observe its role during the following inter-crop. Several conditions of competition between the two species were analyzed: undersowing two wheat varieties at two sowing rates, two red fescue varieties, sole crops being compared with undersown ones. The wheat yield target was 9 t/ha. Wheat yields depended more on the wheat variety (Isengrain: 8.8 t/ha, Scipion: 7.0 t/ha) than on the red fescue undersowing (sole wheat: 8.6 t/ha ; undersown wheat: 7.8 t/ha). Undersowing had statistically significant effects for the lower wheat sowing rate. Yield component analysis showed that the undersowing had a depressive effect on the number of kernels per m 2. This effect was partially compensated for by a higher kernel weight in undersown wheat than in sole wheat. The red fescue variety and wheat sowing rate had no effect. During the time period between the wheat harvest and the sowing of the next cash crop, previously undersown fescue produced 3.3 t/ha in E1 and 2.7 t/ha in E2. The amount of soil mineral nitrogen in the 0-0.9 m layer decreased under the 2 g/m 2 threshold.

Biofumigation, as originally defined, is the use, in agriculture, of the toxicity of Brassica crop residues to control soilborne plant pathogens. This toxicity is specifically attributed to the release of toxic isothiocyanates, through the hydrolysis of glucosinolates present in the crop residues. This technique is considered a possible alternative to the use of pesticides, but field studies have generated conflicting data concerning the efficacy of biofumigation at field scale, limiting the use of this technique. Analytical studies based on a systematic approach involving evaluation of the potential effects of isothiocyanates can be used to address this problem in a rigorous manner. However, many recent studies have indicated that the mechanisms underlying biofumigation are much more complex than a simple toxic effect of residues. In this review, we dissect and discuss the problems encountered when trying to understand the variability in biofumigation efficacy and propose an integrative epidemiological approach to overcome these problems. This approach involves separating the effects of the different parameters of the system, such as the effects of different management phases of the biofumigant crop (i.e. the period of biofumigant crop growth and the phase during which crop residues are pulverised and incorporated into the soil) on the epidemiological mechanisms driving the development of an epidemic (density of primary inoculum and dynamics of disease progression). Finally, we propose new avenues of research into biofumigation in which the use of epidemiological tools and methods may improve our understanding of the factors underlying variation in the efficacy of biofumigant crops.

National audience; La présentation fait une revue des enjeux de gestion de la végétation dans les plantations à vocation de bois énergie ainsi que des techniques possibles pour la contrôler.

International audience; In many circumstances in afforestation, the quick development of very competitive herbaceous and shrubby species can compromise tree establishment. At present, this vegetation is often controlled by chemical and mechanical operations, whereas they are criticized from environmental points of view; some alternatives are under study. The cover crop technique, i.e. sowing in place of the spontaneous competitive vegetation a cover plant mixture assumed to be less competitive, is an example of potential ecological engineering. In addition with the control of competition for resources, the cover plants are thought to offer protection against frost and scorching temperatures to the young trees, or to avoid the water run-off encountered on bare soil. Despite promising results obtained in some experiments, there are also a lot of negative data. In fact the fundamental basis of the technique, i.e. a less competitiveness of the cover crops relative to young trees, and an improvement of microclimate, were relatively little or not assessed. Based on some recent data recorded in some experimental sites in France, we will discuss these issues and the potential of the technique as an alternative to herbicides in afforestation.

Biofumigation is increasingly viewed as a potentially useful technique for controlling soil-borne crop pathogens, but its efficacy has not systematically been demonstrated at field scale. We investigated the differences in efficacy observed in the field, by analysing the mechanisms by which a Brassica cover crop can act as a biofumigant crop in the prevention of soil-borne disease development. We hypothesised that the biofumigant crop might have a negative effect on soil-borne pathogens whilst growing, and that the pulverisation of this crop and the incorporation of its residues into the soil may enhance this effect. We tested this hypothesis by carrying out three field experiments in 2006, 2007 and 2008 in which Brassica juncea (brown mustard) was managed in different ways within a sugar beet–winter wheat rotation and analysing effects on sugar beet root rot caused by Rhizoctonia solani. Three treatments were studied: mustard pulled out at flowering (MP), mustard crushed at flowering and incorporated into the soil (MC) and bare soil (BS) as a control. Weassessed the effect of each treatment on root rot incidence and severity at harvest. Over the 3 years of the experiment, disease incidence was significantly higher on BS plots than on the other plots and was significantly higher on MP plots than on MC plots. MC treatment gave a significantly lower mean conditional severity (severity calculated for diseased beets only) than the BS and MP treatments. Mustard residue incorporation was consistently effective at decreasing disease incidence from year to year (43, 44 and 47% efficacy, as determined by comparison with the disease incidence on BS plots, in 2006, 2007 and 2008, respectively), but the efficacy of growing mustard was variable (36, 16 and 39% efficacy in 2006, 2007 and 2008, respectively). These findings provide insight into the mechanisms by which biofumigant crops may affect soil-borne diseases. These findings have implications for the possible use of biofumigant crops as a biological method for controlling soil-borne diseases at the field scale.

National audience

Past and recent development of perennial grasses is reviewed across environments and under the main types of farming systems. Few adapted cultivars (cvs) are registered and only seeds from French and Australian cys are available. As a result, there is insufficient use of these grasses. In future developments, a perennial grass-Iegume mixture is the best model to optimise both livestock nutrition and environ mental impacts. ln Europe both roles contribute to farm income either via the market or public subsidies. Adapted cys exist for c1imates with annual rainfall >500 mm and accumulated water deficit from May to September (Iate spring to end of summer), Cette revue présente un bilan du développement récent des graminées pérennes dans les régions méditerranéennes sèches, par type de système agraire. Peu de cultivars (cvs) sont inscrits et seuls ceux inscrits en France et en Australie ont des semences commercialisées. I/s ne sont significativement utilisés qu'en zones sub-tempérées. A l'avenir, les mélanges graminée-légumineuse à deux ou plusieurs composants s'imposent pour optimiser la production animale et les bénéfices environnementaux, tous deux contribuant au revenu des exploitations. Les cvs existants sont adaptés à une pluviométrie annuelle > 500 mm avec déficit climatique cumulé Mai-Septembre < 700 mm. L'utilisation croissante des pérennes fourragères en couverture dans des systèmes culturaux intensifs pour améliorer leur bilan environnemental va stimuler la sélection de nouveaux cvs pour cet usage. Ces variétés doivent être plus facilement accessibles. Les objectifs prioritaires de la recherche sont l'analyse du comportement en association et la tolérance à la sécheresse, en exploitant la dormance estivale rencontrée chez certains écotypes de dactyle du Maroc, ainsi que la tolérance à la déshydratation d'espèces comme Poa bulbosa. 1/ est recommandé de renforcer la coordination au sein du Bassin méditerranéen et de structurer les relations avec l'Australie, où la recherche et l'industrie semencière travaillent le matériel végétal méditerranéen sous les mêmes climats

National audience; Significant efforts are being pursued in the tropical world to develop and promote cropping systems based on mulch or cover crops (SCV, système de culture sous couverture végétale, cover crop systems), in order to reduce soil erosion and improve both nutrients and water balances. However, adoption of SCV by smallholders is often limited due to the important change induced by these techniques in the management of farm’s resources. The objective of this study conducted in Vietnam was to assess the feasibility of SCV that had been previously elaborated at field scale for several farm types. The method was based on the simulation of rational households optimizing the use of their resources for food-security and income. We showed that the proposed SCV were not economically attractive because of the extra labour and inputs that these techniques require during the first years of implementation. We also showed that improving the attractiveness of those SCV would require both technical adjustments, such as the use of herbicides combined with the reduction of the amount of biomass in mulches, and subsidies. More research is needed in order to better quantify the environmental services that could legitimate such subsidies. It is also necessary to better understand the causes of spatial and temporal variations of the agronomic and economic performances of the SCV and of the currently practised cropping systems. Lastly, SCV should be compared to other soil conserving techniques, especially cultivation on dry terraces that is tends tending to spread out in the region.; Cahier de l'agriculture 17, n° 3, 289-296 D’importants efforts sont menés dans le monde tropical pour mettre au point et promouvoir des systèmes de culture sous couverture végétale (SCV) en vue de réduire l’érosion des sols et d’améliorer les bilans minéraux et hydriques. En agriculture familiale, l’adoption des SCV reste cependant limitée par les profonds changements que ces systèmes induisent dans la gestion des ressources de l’exploitation. L’objectif de cette étude menée au Vietnam est d’évaluer la faisabilité, pour différents types d’exploitations, de SCV préalablement mis au point à l’échelle de la parcelle. La méthode repose sur la simulation de ménages rationnels optimisant l’usage des ressources en vue d’objectifs de sécurité alimentaire et de revenu. Elle révèle la faible attractivité économique des SCV proposés en raison du surcroît de travail et d’intrants que ces nouveaux systèmes requièrent la première année de mise en oeuvre. L’étude montre aussi que pour rendre les SCV plus attractifs, il serait nécessaire de combiner des adaptations de la technique, telles que la diminution des quantités de biomasse dans les paillis associée à un recours aux herbicides, avec des subventions. Des recherches complémentaires sont nécessaires pour mieux quantifier les services environnementaux qui justifieraient de telles subven- tions. Il est également nécessaire de comprendre les causes de variations spatiales et temporelles des performances agronomiques et économiques des SCV et des systèmes actuellement pratiqués. Enfin, il faudrait comparer les SCV à d’autres techniques de conservation des sols, dont en particulier la culture en terrasse qui se répand actuellement dans la région.

The nematofauna soil consists of plant parasitic nematodes (well known for the damage they cause to crops), as well as free-living nematodes which are for a large part microbivore. Because of the abundance and diversity of soil nematodes and of their biological characteristics, these organisms are good candidates to be use as bioindicators of soil conditions. The soil nematofauna was studied during 3 years in a long-term experiment with contrasting treatments (conventional tillage or notillage with or without permanent cover crops) in Madagascar (Antsirabé). The composition and structure of the nematofauna was clearly different between traitments according to tillage and cover crops. The structure of the nematofauna was stable over time for the period of study and was characteristic of the farming practices., La nématofaune des sols est constituée de nématodes phytoparasites, bien connus pour les dégâts qu’ils peuvent occasionner sur les cultures, ainsi que de nématodes libres dont une grande part est microbivore. Du fait de l’abondance et de la diversité des nématodes dans les sols ainsi que de leurs caractéristiques biologiques, ces organismes sont de bons candidats à leur utilisation comme bioindicateurs de l’état du sol. La nématofaune du sol a été étudiée 3 années successivement dans des systèmes SCV mis en place depuis plus de 10 ans à Madagascar (Antsirabé). La composition et la structure de la nématofaune est clairement différente en fonction du travail du sol et de la couverture végétale dans les systèmes étudiés. La structure de la nématofaune est stable au cours du temps pour la période d’étude et est caractéristique des pratiques culturales.

National audience; Significant efforts are being pursued in the tropical world to develop and promote cropping systems based on mulch or cover crops (SCV, système de culture sous couverture végétale, cover crop systems), in order to reduce soil erosion and improve both nutrients and water balances. However, adoption of SCV by smallholders is often limited due to the important change induced by these techniques in the management of farm’s resources. The objective of this study conducted in Vietnam was to assess the feasibility of SCV that had been previously elaborated at field scale for several farm types. The method was based on the simulation of rational households optimizing the use of their resources for food-security and income. We showed that the proposed SCV were not economically attractive because of the extra labour and inputs that these techniques require during the first years of implementation. We also showed that improving the attractiveness of those SCV would require both technical adjustments, such as the use of herbicides combined with the reduction of the amount of biomass in mulches, and subsidies. More research is needed in order to better quantify the environmental services that could legitimate such subsidies. It is also necessary to better understand the causes of spatial and temporal variations of the agronomic and economic performances of the SCV and of the currently practised cropping systems. Lastly, SCV should be compared to other soil conserving techniques, especially cultivation on dry terraces that is tends tending to spread out in the region.; Cahier de l'agriculture 17, n° 3, 289-296 D’importants efforts sont menés dans le monde tropical pour mettre au point et promouvoir des systèmes de culture sous couverture végétale (SCV) en vue de réduire l’érosion des sols et d’améliorer les bilans minéraux et hydriques. En agriculture familiale, l’adoption des SCV reste cependant limitée par les profonds changements que ces systèmes induisent dans la gestion des ressources de l’exploitation. L’objectif de cette étude menée au Vietnam est d’évaluer la faisabilité, pour différents types d’exploitations, de SCV préalablement mis au point à l’échelle de la parcelle. La méthode repose sur la simulation de ménages rationnels optimisant l’usage des ressources en vue d’objectifs de sécurité alimentaire et de revenu. Elle révèle la faible attractivité économique des SCV proposés en raison du surcroît de travail et d’intrants que ces nouveaux systèmes requièrent la première année de mise en oeuvre. L’étude montre aussi que pour rendre les SCV plus attractifs, il serait nécessaire de combiner des adaptations de la technique, telles que la diminution des quantités de biomasse dans les paillis associée à un recours aux herbicides, avec des subventions. Des recherches complémentaires sont nécessaires pour mieux quantifier les services environnementaux qui justifieraient de telles subven- tions. Il est également nécessaire de comprendre les causes de variations spatiales et temporelles des performances agronomiques et économiques des SCV et des systèmes actuellement pratiqués. Enfin, il faudrait comparer les SCV à d’autres techniques de conservation des sols, dont en particulier la culture en terrasse qui se répand actuellement dans la région.

The objective of this study was to investigate the impact of soil management on soil biofunctioning in the highlands of Madagascar. Direct seeding Mulch-based Cropping systems (DMC) were compared to conventional tillage (CT) and the natural fallow (NF) on the rate of decomposition and mineralization of residues as well as on the abundance, biomass and activity of litter- and soilmicroorganisms and macrofauna. Long term experimentation was used in Bemasoandro and Andranomanelatra. Contrasted cropping systems were studied, DMC on crop residues and on living mulches, CT and the NF. Results showed that the NF soil had the highest C and N content, however DMCs increased microbial biomass, soil respiration and nutrient cycling except for urease activity which was very high in NF (P, L'impact du mode de gestion du sol sur son biofonctionnement a été étudié sur les hauts plateaux de Madagascar. Le semis direct sur couverture végétale (SCV) est comparé au labour traditionnel (LB) et à la jachère naturelle (JN) concernant la minéralisation des résidus, l'abondance et les activités des microorganismes et de la macrofaune de la litière et du sol. L’étude a été menée à Bemasoandro et Andranomanelatra sur des systèmes contrastés de longue durée, SCV sur résidus et couverture vive, LB et la JN. Le sol sous la JN a les teneurs en C et N les plus élevées. Mais les SCV augmentent la biomasse microbienne, la respiration du sol et certaines activités enzymatiques du sol plus que la JN (P

Colloque du 2 décembre 2008 à Dijon; Living mulches are cover crops grown with a cash crop to provide ecological and agronomical benefits including protecting soils from erosion, improving soil fertility and biodiversity and suppressing weeds. Intercropping living mulches into cropping systems is a possible way to suppress weeds because weed and living mulch plants compete for the same resources. The major hurdle to the adoption and use of living mulches is lack of selectivity: a living mulch that is competitive enough to suppress weeds will often suppress crop growth and yield. Creative management approaches are required to reduce competition between the living mulch and cash crop species without eliminating the benefits to weed management.; Les mulchs vivants sont des plantes de couverture cultivées en association avec une culture commerciale de manière à fournir des services écologiques et agronomiques comme la protection contre l’érosion, l’accroissement de la fertilité des sols et de la biodiversité ou l’étouffement des adventices. Utiliser des mulchs vivants en association avec une culture commerciale peut permettre de diminuer les infestations d’adventices grâce à des processus de compétition sur les ressources. La principale difficulté dans l’utilisation des mulchs vivants est leur manque de sélectivité : une plante de couverture assez compétitive pour maîtriser les adventices a souvent un impact négatif sur la croissance et le rendement de la culture commerciale. Il est nécessaire de concevoir des modalités de conduites innovantes pour réduire la compétition entre le mulch vivant et la culture commerciale sans perdre les bénéfices en termes de contrôle des adventices.

National audience

Stage effectué au CIRAD Unité Propre de Recherche Production Fruitière Intégrée Le Bouchu 97119 VIEUX-HABITANTS Diffusion du document : INRA Antilles-Guyane, Documentation, Domaine de Duclos, 97170 Petit-Bourg, Guadeloupe (France) Diplôme : Licence Professionnelle; Une des problématiques de la filière agrumicole en Guadeloupe réside en une utilisation importante d’intrants chimiques, en particulier l’usage de l’herbicide (5 à 6 par an). Face au défi que représente la réduction de ces intrants, l’UPR-PFI s’est engagé aux cotés des agrumiculteurs de la région de la Côte sous le vent dans l’étude d’une pratique innovante : l’association culturale Agrumes - Plante de Couverture. Notre équipe s’est investie dans deux travaux liés (i) à la typologie des exploitations à base de vergers d’agrumes et (ii) à une expérimentation en milieu réel sur l’introduction d’une plante de couverture : le Macroptilium atropurpureum comme mode de gestion de l’enherbement. Le premier travail commencé en 2006 porte sur une typologie visant à analyser le fonctionnement et les pratiques des agrumiculteurs. Ensuite en 2007, ce présent rapport met l’accent l’identification des déterminants de la gestion de l’enherbement. Trois variables identifiées déterminent le choix des agrumiculteurs à la pratique de l’herbicide: la mécanisation des parcelles, la topographie des parcelles, la main d’œuvre affectée à la production d’agrumes. Le deuxième travail consiste en un bilan agronomique et économique d’une expérimentation en cours chez un agrumiculteur de la Côte sous le Vent. Cette région est caractérisée par de fortes contraintes : climatique (saison sèche très marquée), topographique et pierrosité. Cette évaluation montre l’intérêt agronomique, économique et d’appropriation de cette pratique. Sur le plan agronomique, cette pratique est efficace dans la gestion de l’enherbement et sans conséquence sur les rendements. Economiquement, nous constatons un surcoût d’investissement par rapport à l’usage d’herbicide. Enfin, nous retiendrons de l’enquête réalisée des réponses assez diversifiées.

Field experiment was conducted from 1988 to 1999 at an experimental farm at Agonkanmey, near Cotonou in southern Benin, to study the effect of relay-cropping maize through Mucuna pruriens (var. utilis). The relay-cropping system was compared with traditional maize cropping system without any input, and with a maize cropping system with mineral fertilizers (NPK). Special attention was given on the changes in soil C during the period of the experiment in relation to residue biomass C returned to the soil, runoff and soil erosion losses, and loss of C with erosion. The soils are classified as sandy loam Typic Kandiustult. The general properties of these soils are given. For this soil type, relay cropping of maize and mucuna was very effective in enhancing C sequestration: change in Ct (total C content) stock for 0 to 40 cm depth was 1.3 t C/ha per year over the 12-year period of the experiment, ranging among the highest rates recorded for the eco-region. This increase resulted first from the high amount of residue biomass provided by mucuna, which amounted to 10 t DM/ha per year (83% aboveground). Mucuna residues, supplying the soil with N, also favoured the production of maize biomass, and total mucuna plus maize residue biomass returned to the soil was approximately 20 t/ha per year. In contrast, non-fertilized and fertilized continuous maize cultivation resulted in -0.2 and 0.2 t C/ha per year change in Ct stock for 0 to 40 cm depth, respectively. Total residue biomass was 8 and 13 t/ha per year, including 77 and 29% by weeds, respectively. Thick mulch produced by mucuna decreased losses by runoff and erosion, which were 0.28, 0.12 and 0.08 mm/mm and 34.0, 9.0 and 3.0 t/ha per year in unfertilized, fertilized with NPK and mucuna treatments, respectively. Eroded C was estimated at 0.3, 0.1 and 1.0 t C/ha per year in unfertilized, fertilized with NPK and mucuna treatments, respectively. Through its benefits on soil organic matter management, weed suppression and erosion control, cropping systems including a legume crop may have an adverse impact from a global change standpoint.

International audience; The influence of biochemical characteristics of 15 crop residues on C and N mineralisation in soil was investigated by following the decomposition of roots, stems and leaves of four subtropical species and one temperate species buried into the soil. The C, N and polyphenols contents were measured in different biochemical pools obtained from residues of the different organs. The mineralisation of root C was significantly lower than that of leaves and stems. Chemical analysis showed a higher polyphenol content in the leaves and a higher ligninlike content in the roots. Carbon and N mineralisation were simulated with the STICS decomposition submodel and tested against the data set. The model predicted leaf and stem C mineralisation for all five species fairly accurately, but failed to predict root C mineralisation, indirectly revealing the more complex composition of the root tissue. The results showed the interest of separately considering the different plant parts when studying plant residue decomposition and the need to develop other methods of residue quality characterisation to improve the prediction of residue decomposition.

L`installation de jeunes ligneux en plantation forestière est souvent compromise par une forte concurrence avec la végétation herbacée. Les techniques classiques de gestion de cette compétition telles que l`utilisation d`herbicides ou l`entretien mécanique sont actuellement remises en question pour des raisons environnementales ou pour leur efficacité. Dans ce contexte, le semis de plantes de couverture permettant de contrôler la végétation représente une méthode alternative intéressante d`ingénierie écologique. Cet article présente les premiers résultats de la modification du couvert herbacé sur les variables micro-environnementales et la disponibilité en ressources dans deux expérimentations d`arbres plantés et semés. Le développement des arbres est encourageant, mais les résultats montrent cependant que des études sur la dynamique et la composition des mélanges semés sont encore nécessaires pour l`application plus générale de la technique. / Young tree establishment in forest plantation is often compromised by herbaceous vegetation competition. At present, this vegetation is generally controlled by chemical or mechanical operations but they are criticized either from environmental points of view either for their efficiency. In this prospect, an alternative method consists of sowing cover plants in order to control vegetation. This paper presents first results on the consequences of vegetation cover modification on micro-environmental variables and resources availability in two experiments of planted and seeded trees. Tree development is encouraging but results show that further studies on plants dynamics and seed mixture composition are needed before spreading the technique.

Fiche technique sur un système de culture du maïs en utilisant une légumineuse de couverure, Pueraria phaseoloïdes. Pour inverser la tendance à la dégradation du système agricole en Côte d'Ivoire, des techniques de gestion de la fertilité des sols et de lutte contre les adventices ont été mises au point. Parmi celles-ci, il en est une qui mérite d'être largement vulgarisée car elle permet de stabiliser durablement la culture du maïs ; c'est l'utilisation de Pueraria phaseolïdes, une légumineuse de couverture, qui couvre le sol, le protège du soleil et de la pluie et l'enrichit en azote et en matière organique

International audience; En régions semi-arides, la saison sèche est une période difficile pour l'entretien des animaux, du fait de la rareté des ressources alimentaires. Les animaux sont maintenus sur des résidus de fourrage de pauvre qualité, nécessitant une complémentation protéique si l'on veut assurer leur productivité. Dans cette étude, Calopogonium mucunoides a été distribué à des ânes de trait au repos pendant la saison sèche pour tester son appétibilité et ses valeurs nutritionnelles: 12 ânes adultes ont été repartis en 3 groupes alimentés comme suit: Groupe A = tiges de maïs + 0.5 kg d'une provende domestique constituée d'un mélange de son de maïs et de tourteau de coton en quantités égales; Groupe B = C. mucunoides + 0.25 kg de provende; Groupe C = C. mucunoides + 0.5 kg de provende. La consommation de fourrage, d'eau et le poids vif des animaux ont été enregistrés. Des échantillons de fourrage et de fèces ont été analysés. Les résultats n'ont montré aucune différence significative dans la consommation de fourrage. Une différence hautement significative a été observée pour la digestibilité des rations proposées, la meilleure étant pour le groupe B. Quel que soit le groupe, la consommation d'eau augmente et l'ingestion de fourrage diminue lorsque la température ambiante s'élève. La forte digestibilité de C. mucunoides confirme sa qualité supérieure aux autres ressources alimentaires. En dépit de sa faible appétibilité ou acceptabilité par d'autres espèces, C. mucunoides présente un taux élevé de protéines brutes intéressant pour tous les animaux. Elle pourrait effectivement remplacer les sources agro-industrielles de compléments protéiques, difficiles d'accès pour les petits exploitants. (Résumé d'auteur)

An agronomic device was conduced between 1995 and 1999 with maize cropping systems in the ecological zone of the semi-deciduous forest of Ivory Coast. We compared the supply of organic origin N to the maize with two fallow periods, 6 months (SC6MJ) and 18 months (SC18MJ). The fallows are occupied either by Chromolaena odorata (subspontaneous) or Pueraria phaseoloides (introduced). These four systems are compared to two controls, a non-Chromolaena fallow (artificially) for SC6MJ and with burning of Chromolaena for SC18MJ. Systems cover crops are managed as live-mulch with herbicides. Systems SC6MJ received moderate phosphorus fertilization. The study poses as assumptions that (i) determinants of short-term supply (crop cycle) and medium term (cumulative effects) mainly depend on quantities and litter quality original surface fallow (ii) these effects will concentrate on the surface of the soil. Mineralization potential litter is correlated with the laboratory / N, lower their report Pueraria C (C / N between 20 to 23) for Chromolaena (C / N of 25 to 43). In 1998 the rate of disappearance of litter followed with litterbags is much faster than in 1999 in relation the rainfall pattern. Two years the amount of litter present after cutting determines the rate of decomposition of litter in the medium term. These dynamics, modeled for two years, used to distinguish a litter compartment that disappeared rapidly and another one that disappeared slowly. Comparisons of losses in C in the litterbags with different mesh sizes showed that the activity of mesofauna and soil macrofauna could be responsible for the disappearance of 50% of the litter at the beginning of the decomposition process and 35% at the end of decomposition process. Their action of fragmentation and soil incorporation of litter (fungus growing termites) allowed a comparatively rapid loss of both litters, Chromolaena and Pueraria. The application of models to the data obtained on the mobilization of N fallow in relation to the needs of culture N indicates (i) a risk of "asynchrony" early cycle (ii) insufficient supply at end of cycle for SC6MJ (iii) little differentiation between the supply of Chromolaena and Pueraria. The supply of in situ mineral N in situ at soil surface (0-10 cm) in 1998 and 1999, estimated for periods of 90 days during the maize cycle was evaluated by measurement and incubations. With SC6MJ the mobilization of N in corn is greater with Pueraria the two years and this N offer is comparable to SC18MJ. The supply of N varies little SC18MJ treatments. The rainfall occurs (i) a multi-level, by determining the peak intensity of N mineralization soil mineral N and accumulation in the aerial parts of fallow (ii) the scale of the campaign interaction with the surface litter and activity of root systems of vegetation cover. Litter Pueraria seemed to conserve better the soil moisture. In limiting water situations, the net mineralization is correlated with soil moistures. Litters increased microbial biomass of the soil surface thus creating a potential source of temporary immobilization of N. In 1998 the supply of estimated net N mineralization indicates a better synchrony with the needs of the crop despite a more abundant rainfall cycle start over in 1999. A study using the 15N natural abundance to estimate the litter Pueraria can contribute significantly to the nitrogen nutrition culture, 30 to 41% in 1998 and 64 to 87% in 1999 in the culture system fallow 6 months. Differentiations on soil organic matter (SOM) indicate early effect on stocks valued at 0-10 cm averaged 2.34 t ha-1 N for SC6MJ and averaged 2.83 t ha-1 N for SC18MJ. For difference SC6MJ obtained between inputs and losses over four years suggests that Chromolaena best preserved stocks of C and N that Pueraria. The comparison with forest fallow located outside the device indicates that the availability of materials easily mineralizable in our agroecosystems (i) is reduced at the end of the rainy season (ii) reduced by the practice of burning (iii) slightly increased by fallowing. Studies on long-term incubations (106 and 85 days) show significant effects on the models made by fitting the experimental points on the kinetics of respiration and cumulative net mineralization (expressed in proportion to the total C and N soil). They identify important factors of differentiation in compartment MOS rate high turnover. For SC6JM this compartment represents a larger part with Pueraria certainly directly related to a better biochemical quality (ratio lignin / N). The duration of the fallow does not improve the availability of easily mineralizable N indicating a block of C and N in the soil physical and / or biochemical nature, Un dispositif agronomique pérennisé entre 1995 et 1999 avec des systèmes de culture de maïs à couvertures végétales a été installé dans la zone écologique à forêt semi-décidue de Côte d'Ivoire. L'offre en N d'origine organique est étudiée dans le cadre de systèmes de culture de maïs, avec une durée de jachère de 6 mois (SC6MJ) et 18 mois (SC18MJ). Les jachères sont occupées soit par Chromolaena odorata (subspontanée), soit par Pueraria phaseoloides (introduite). Ces quatre systèmes sont comparés à deux témoins, un sans Chromolaena pour les SC6MJ et un avec brûlis de Chromolaena pour les SC18MJ. Les systèmes à couvertures végétales sont gérés en couvertures vivantes avec des herbicides et leur pérennité est assurée par une reprise de croissance des espèces avant la récolte de la céréale. Les systèmes à SC6MJ bénéficient d'une fertilisation modérée en phosphore. L'étude réalisée pose comme hypothèses de départ que (i) les déterminants de l'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 (ii) ces effets se concentreront à la surface du sol. Le potentiel de minéralisation des litières au laboratoire est corrélé avec leur rapport C/N, plus faible pour Pueraria (C/N entre 20 à 23) que pour Chromolaena (C/N entre 25 à 43). En 1998 la vitesse de disparition des litières suivie avec des " sacs de décomposition " est beaucoup plus rapide qu'en 1999 en relation au début du cycle de décomposition avec le régime pluviométrique. Les deux années la quantité de litières présentes après la coupe détermine le taux de décomposition à moyen terme des litières. Ces dynamiques, modélisées sur deux années, permettent de distinguer un compartiment de litières à disparition rapide et un compartiment à disparition lente. La comparaison des pertes en C dans des " sacs de décomposition " à maille différente montre que l'activité de la mésofaune et de la macrofaune du sol pourrait être responsable de la disparition de 50 % des litières au début du processus de décomposition et de 35% à la fin du processus de décomposition. Leur action de fragmentation et d'incorporation au sol des litières (meules des termites champignonnistes situées à la surface du sol) permet une disparition comparativement plus rapide des litières de Chromolaena que celles de Pueraria. L'application des modèles aux données obtenues sur les mobilisations en N des jachères en relation avec les besoins de la culture en N indique (i) un risque " d'asynchronie " en début de cycle (ii) une offre insuffisante en fin de cycle pour les SC6MJ (iii) peu de différenciation entre l'offre de Chromolaena et celle de Pueraria. L'offre en N in situ du sol en surface (0-10 cm) en 1998 et 1999, estimée pendant des périodes de 90 jours durant le cycle du maïs par des mesures et des incubations de sol, est corrélée pour les SC6MJ avec les mobilisations en N du maïs dans les parties aériennes. C'est le traitement avec Pueraria qui les deux années satisfait le mieux les besoins en N de la culture et cette offre est comparable à celle des SC18MJ. L'offre en N varie peu selon les traitements des SC18MJ. Le régime pluviométrique intervient (i) à une échelle pluriannuelle, en déterminant, l'intensité du pic de minéralisation en N minéral du sol et les accumulations en N dans les parties aériennes des jachères (ii) à l'échelle de la campagne en interaction avec les litières en surface et l'activité des systèmes racinaires des couvertures végétales. La litière de Pueraria semble mieux conserver l'humidité du sol et le système racinaire de Chromolaena mobiliser de plus fortes quantités d'eau. En situations hydriques limitantes, la minéralisation nette est corrélée aux humidités de sol. Les litières semblent être à l'origine en 1998 de l'augmentation de la biomasse microbienne du sol en surface créant ainsi une source potentielle d'immobilisation temporaire de N. En 1998 l'offre en N estimée par minéralisation nette indique une meilleure synchronie avec les besoins de la culture malgré une pluviométrie plus abondante en début de cycle par rapport en 1999. Une étude utilisant l'abondance naturelle 15N permet d'estimer que la litière de Pueraria peut contribuer fortement à la nutrition azotée de la culture, de 30 à 41% en 1998 et de 64 à 87% en 1999 dans le cadre du système de culture à jachère de 6 mois. Les différenciations sur les matières organiques du sol (MOS) indiquent un début d'effet sur les stocks évalués sur 0-10 cm en moyenne à 2.34 t ha-1 N pour les SC6MJ et en moyenne à 2.83 t ha-1 N pour les SC18MJ. Pour les SC6MJ la différence obtenue entre les apports et les pertes sur quatre années suggère que Chromolaena conserve mieux les stocks en C et N que Pueraria. La comparaison avec une jachère forestière située hors dispositif indique que la disponibilité en matériaux facilement minéralisables dans nos agrosystèmes est (i) réduite en fin de saison des pluies (ii) diminuée par la pratique du brûlis (iii) peu augmentée par la pratique de la jachère. Les études sur des incubations de longue durée (106 et 85 jours) montrent des effets significatifs sur les modélisations faites par ajustement aux points expérimentaux sur les cinétiques de respiration et de minéralisation nette cumulées (exprimées en proportion par rapport au C et N total du sol). Elles permettent d'identifier d'importants facteurs de différenciation au niveau du compartiment des MOS à taux de renouvellement élevé. Pour les SC6JM ce compartiment représente une part plus importante avec Pueraria, certainement en relation directe avec des apports cumulés de plus grande qualité biochimique (rapport lignine / N). La durée de la jachère n'améliore pas la disponibilité en N facilement minéralisable indiquant ainsi un blocage de C et N au niveau du sol de nature physique et/ou biochimique.