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The respective contribution of conservation agriculture (CA) principles (no-tillage, permanent soil cover/mulch and crop rotations) on greenhouse gas (GHG) emissions is still unclear. This study was conducted at two long-term experimental sites established in 2013 in Zimbabwe, on an abruptic Lixisol at Domboshava Training Center (DTC) and on a xanthic Ferralsol at the University of Zimbabwe Farm (UZF). The purpose of the study was to unravel the individual and combined effects of tillage, mulching and rotation on N2O and CH4 emissions in low nitrogen (N) input maize-based cropping systems (< 60 kg N ha−1) and to compare emissions within maize rows and between maize rows. We hypothesised that integrating no tillage, mulch and cereal-legume rotation would enhance N2O emissions. Six treatments, replicated four times were investigated: conventional tillage, conventional tillage with rotation, no-tillage, no-tillage with mulch, no-tillage with rotation, no-tillage with mulch and rotation. The main crop was maize (Zea mays L.) and treatments with rotation included cowpea (Vigna unguiculate L. Walp.). Gas samples were regularly collected using the static chamber method in the maize row and inter-row spaces during the 2019/20 and 2020/21 cropping seasons and during the 2020/21 dry season. Soil moisture and mineral N were measured in the 0–20 cm soil depth. In 2019/20, cumulative total N2O emissions were significantly higher in mulch treatments at DTC, while at UZF N2O emissions were higher with cowpea rotation. Cumulative total N2O emissions ranged from 215 to 496 g N2O-N ha−1 yr−1 and from 226 to 395 g N2O-N ha−1 yr−1, at DTC and UZF, respectively. In 2020/21, N2O emissions were much lower and no differences were found between treatments on both sites (145 to 179 g N2O-N ha−1 yr−1 and 83 to 136 g N2O-N ha−1 yr−1 at DTC and UZF, respectively). A significant relationship was found between soil nitrate and daily N2O emissions. At UZF, highest N2O emissions were observed at a water-filled pore space of 60–70%. There were no significant differences in yield-scaled N2O emissions between treatments at both sites for the two seasons. DTC was a net source of CH4 (694 g CH4-C ha−1 yr−1 on average), while UZF was a net sink of CH4 (−494 g CH4-C ha−1 yr−1 on average). No evidence was found for in situ CH4 production at DTC, and an external source is most likely. Our study indicates that for low N input cropping systems in the sub-humid tropics, N loss through N2O is low.

Transitioning toward minimum or no tillage is challenging for smallholder farmers in sub-Saharan Africa (SSA), due to the possible yield penalties during the initial years of a transition. Understanding the early impacts of such transitions is crucial in a cash crop such as cotton, on which farmers rely for their income, and is necessary to inform agroecological strategies to cope with both these challenges. This study explores the combined impact of minimum or no tillage and fertilizer regimes on agronomic parameters of cotton–cereal rotations, as practiced by smallholder farmers in Benin. A multilocation experiment was set up in three different agroclimatic zones, namely, Savalou (7°55′41″, 1°58′32″), Okpara (2°48′15″, 7°72′07″), and Soaodou (10°28′33″, 1°98′33″). In each area, the experiment was laid out as a split-plot design with four replications (main plot = soil preparation; subplot = fertilizers regimes). The treatments consisted of three different forms of soil preparation, namely, tillage, strip tillage, and no tillage or direct seeding, and four fertilization regimes, namely, basal mineral fertilizers (BMF, 200 kg ha1 of N14P18K18S6B1 + 50 kg ha1 of urea), BMF + A (200 kg ha1 of calcium phosphate amendment, 22P2O5-43CaO−4S), BMF + C (400 kg ha1 of compost), and BMF + A + C. At all sites, direct seeding led to lower below-ground biomass growth and seed cotton yields compared with conventional tillage in an early transition to conservation agriculture starting from degraded soils (2% to 25%). Weak rooting under direct seeding resulted in lower cotton yields compared with that under tillage (−12%) and strip tillage (−15%). At 45 and 90 days after emergence, cotton plants were shorter under direct seeding compared with tillage (−9% and −13%, respectively) and strip tillage (−23% and −6%, respectively). Fertilizer regimes affected seed cotton yields differently across sites and treatments, with marginal responses within soil preparation methods, but they contributed to increase yield differences between conventional and no tillage. Considering the need for sustainable practices, in the context of degraded soils and poor productivity, such limited yield penalties under CA appear to be a reasonable trade-off in the first year of a transition. Alternatively, the results from the first year of this experiment, which is meant to continue for another 5 years, suggest that strip tillage could be a sensible way to initialize a transition, without initial yield penalties, toward more sustainable soil management.

International audience; Conservation agriculture (CA) has been promoted to mitigate climate change, reduce soil erosion, and provide a variety of ecosystem services. Yet, its impacts on crop yields remains controversial. To gain further insight, we mapped the probability of yield gain when switching from conventional tillage systems (CT) to CA worldwide. Relative yield changes were estimated with machine learning algorithms trained by 4403 paired yield observations on 8 crop species extracted from 413 publications. CA has better productive performance than no-till system (NT), and it stands a more than 50% chance to outperform CT in dryer regions of the world, especially with proper agricultural management practices. Residue retention has the largest positive impact on CA productivity comparing to other management practices. The variations in the productivity of CA and NT across geographical and climatical regions were illustrated on global maps. CA appears as a sustainable agricultural practice if targeted at specific climatic regions and crop species.

Meloidogyne spp. and Hirschmanniella spp. are among the most damaging plant-parasitic nematodes (PPNs). They threaten rice production, the main staple food in Asia. Cropping systems that promote natural biocontrol and plant tolerance to diseases are put forward as sustainable solutions to protect rice from these pests. In particular, cropping systems managed under conservation agriculture (CA) are promising because they improve soil health and functioning. We investigated the effects of two cropping system components in a Cambodian field, (i) CA practices, i.e., no-tillage with a cover crop Stylosanthes guianensis (cv. Nina), versus conventional plow-based tillage with no cover crop, and (ii) using IR504, IR64, Azucena and Zhonghua 11 rice varieties, on PPNs in roots and on communities (bacteria, fungi and nematodes) in the rhizosphere. We used a sequencing approach via amplicon barcoding to target microbial marker genes (16 S and ITS rRNA gene) and a microscopic approach to identify and quantify nematodes in the rhizosphere compartment. The variety had less effect than agricultural practices on the infection by PPNs and on the assembly of the three rhizosphere communities. Under CA, the abundance of PPNs extracted from the roots was reduced by 88%. Soil quality was substantially improved (+83% of total Kjeldahl nitrogen, +34% of available phosphorus, +10% of exchangeable potassium, +110% of soil organic carbon, +30% for the cation exchange capacity), thus providing more basal resources for microbial decomposers, especially fungi (+164% putative saprotrophs). Characterization of the three rhizosphere communities revealed a shift in the structure associated with soil enrichment. Both microbial richness (+3% for bacteria and +38% for fungi) and diversity (Shannon index, +11% for fungi and +5% for nematodes) increased. The relative abundance of taxa was modified by CA with notably more mycorrhizal fungi (+329% Glomeromycota spp.) and fewer Pratylenchidae nematodes (−92% Hirschmanniella spp.) in the rhizosphere. The reassembly of the communities using CA was associated with regulation of PPN populations. The reduction in Meloidogyne spp. abundance in roots (−64%) was correlated with the maturity of the food web (maturity index, +10% under CA) and with the increase in the relative abundance of omnivorous nematodes in the rhizosphere (+68% under CA). Seven years of CA in this field enabled the whole soil food web to mature thus creating a favorable niche for potentially predatory nematodes and microbes antagonistic against PPNs. This study confirms that CA is an alternative to nematicides to limit infection by PPNs in rice cropping systems.

Climate change models predict an increase in climate variability in the future, with more rainfall extremes and greater risks, causing a negative impact on crops produced by smallholders in West Africa. Conservation Agriculture (CA) systems can be effective in mitigating yield loss in environments with increased weather risk. This study aimed to evaluate CA cropping systems that can minimize both economic and climatic risks under erratic climatic conditions in West Africa. We tested upland rice-based CA systems and conventional systems with tillage (CT), in rotation with maize in some of the cases, without and with fertilization, at different sowing windows in the Bouaké region, Côte d'Ivoire, from 2015 to 2020. Sowing in June showed in a higher rice yield (1183 kg ha-1 and 1370 kg ha-1 without and with fertilization, on average over the 2017–2020 period) than in March (521 kg ha-1 and 495 kg ha-1 without and with fertilization) or in July or August (335 kg ha-1 and 498 kg ha-1 without and with fertilization). During the first four years, rice yields tended to be lower under the CA systems than under the CT systems, especially when water availability was not a major constraint. However, after this transition period, and especially when water stress occurred, as in 2020, rice yields under CA systems (1835–2021 and 2147–2254 kg ha-1 without and with fertilization) were higher than under CT systems (1350 kg ha-1 and 1435 kg ha-1 without and with fertilization). CA systems having relatively longer duration for growing cover crops tended to produce higher upland rice yield grown in the subsequent season. In both CT and CA systems, the impact of fertilization on rice yield was small over the study period, and the mean rice yield increase due to fertilization was on average 451 kg ha-1 even when rice was sown in the summer season, resulting in negative economic return. These results indicate that whereas low-input CA upland rice-based systems together with optimizing sowing window for rice could be promising options for sustaining rice yield and mitigating yield loss in environments with increased weather risk, further research is needed for reducing transition period to CA systems in order to enhance their adoption by smallholder farmers. Desirable cover crops should be less labor-demanding, generate incomes from their products, and produce large biomass under erratic climatic conditions.

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.

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

International audience; In West Africa, new management practices such as conservation agriculture with crop residue mulching can improve crop yields for individual farmers. However, in a context of complex social interactions between farmers, the introduction of such practices can also lead to conflicts between private interests and communal use of resources, for example the free grazing of crop residues. The objective of this paper was to assess ex-ante the impacts of the practice of crop residue mulching on crop productivity in a village of central Burkina Faso using an agent-based model, AMBAWA, that simulates the flows of biomass and nutrients between crop and livestock systems at the village scale. The model considers the interactions between four types of farmers that were identified in the study site: subsistence-oriented crop farmers, market-oriented crop farmers, agro-pastoralists and pastoralists. The model simulated increased cattle migration outside the village due to increased crop residue scarcity during the dry season with increased proportions of cropland under the practice of conservation agriculture, decreasing the manure availability at village scale. Consequently, the assumed direct yield increases due to soil moisture conservation as a result of mulching did not compensate for the yield losses resulting from lesser amounts of manure available. This effect was felt most strongly by farmers who own relatively large numbers of cattle (agro-pastoralists and pastoralists). The total maize production at village level depended more on the proportion of cropping land that was available for grazing by cattle, and thus not mulched, than on a possible direct effect of mulching on yield per se. The AMBAWA model can support discussion among stakeholders (farmers, traditional and administrative authorities) who are involved in the private and communal management of crop residues and other biomass resources, in order to co-design effective arrangements and practices for their sustainable use.

International audience; Purpose Phosphorus (P) is often the main limiting factor for plant growth in highly weathered tropical soils. Phosphate use efficiency and crop yields could be increased in low-input agroecosystems through cropping systems that favor organic matter accumulation or regular additions of composts and manure. Our objective was to determine the amounts and forms of P according to companion crops (Brachiaria ruziziensis-a grass species-or Cajanus cajan-a leguminous species) and tillage systems (conventional or no-tillage). Materials and methods Soil P pools were determined (P-resin, P-Olsen, PNaOH-EDTA, and P-total) and P species were characterized by P-31 NMR spectroscopy. Results and discussion The concentrations of available and labile inorganic P (P-resin, Pi(Olsen), and Pi(NaOH-EDTA)) were greater in soil samples where companion crops (Brachiaria ruziziensis or Cajanus cajan) and maize were planted on the same row, with a more significant effect with the legume species. According to the P-31 NMR, it is mostly the proportion and amount of P-Orthophosphate that was increased, with a slight increase of the content of P-Monoester. Overall, there was a decrease of the proportion of organic P (Po-NMR/P-NMR) from 32 to 16% when the legume companion crop was associated with maize. Conclusions The tillage systems did not lead to any change in the amounts and forms of P. Companion crops are thought to increase available P through mineralization of Po from plant residues and soil organic matter, leading to an increase of fluxes between active P pools.

International audience; Biodiversity-based agriculture is the main form of agriculture practiced by smallholder farmers, who produce half the world's food, especially in the Global South. This form of agriculture relies on planned biodiversity intentionally managed by farmers and on the associated biodiversity that spontaneously colonizes the agroecosystem. In recent decades, there have been increasing calls from researchers and society to support biodiversity-based agriculture as an alternative paradigm to today's industrial agriculture. Building adapted governance and management systems for enhancing farmers' access to agrobiodiversity is a key challenge for the development of biodiversity-based agriculture. To achieve this, a better understanding of how farmer's access agrobiodiversity is needed, and in particular, how this access is affected by interactions between farmers and with institutions, i.e., social networks. In this article, we first review the literature on the role of social networks in farmers' access to agrobiodiversity, in the form of crop diversity and associated biodiversity, and the related knowledge to manage this diversity. This review points at a major knowledge gap concerning how the composition and structure of these networks affect farmers' access to agrobiodiversity. Then, we review literature on social-ecological networks to identify how this framework developed for environmental management could contribute in getting a better understanding of the role of social networks' structure and composition in farmers' access to agrobiodiversity. Based on this review, we propose a social-ecological network framework dedicated to crop diversity. Finally, we present potential applications of this framework to develop new participatory approaches for agrobiodiversity management and governance, adapted to biodiversity-based agriculture.

Le Moyen-Ouest est une vaste région du centre de Madagascar située à l'ouest de l'Itasy et du Vakinankaratra et limité à l'est par la falaise du Bongo Lava et le fleuve Manambolo. La superficie du Moyen-Ouest est de 50 000 km2 environ, près du 1/5 de la superficie du pays. Nous avons choisi de considérer deux périodes dans le développement du Moyen-Ouest, depuis les années 1950. Le présent document a pour objet de faire le point sur l'histoire, les réussites, les difficultés et les évolutions de ce développement très innovant dans les deux périodes. Le référentiel de développement territorial du Moyen-Ouest fut d'abord élaboré et vécu entre 1950 et les années 1990, essentiellement grâce au Projet Sakay (dans sa partie technique) puis ODEMO (Opération de Développement du Moyen-Ouest) qui constitue une référence majeure pour le développement du Moyen-Ouest. La seconde période, après 2000, est surtout marquée par l'introduction concluante des SCV (ou Agriculture de conservation) dans la partie sud.

International audience

The conversion of native vegetation (NV) into agricultural land by clearing and tillage disrupts the soil structure, and depletes soil organic carbon (SOC) pool. Data on changes in SOC pools are needed to enhance scientific knowledge regarding the effects of land use and Conservation Agriculture (CA) on soil fertility, agronomic productivity, and soil C sink capacity. The objective of this study was to quantify changes in SOC fractions due to conversion of NV to agricultural land, and to assess the rate of recovery of SOC fractions and the resilience index of CA cropping systems under sub-tropical (Ponta Grossa/PR — PG) and tropical (Lucas do Rio Verde/MT — LRV) regions of Brazil.

The adoption of Conservation Agriculture (CA) and the maintenance of crop residues on the soil surface result in the long-term increase of carbon (C) in the system, promoting C sequestration and reducing C-CO2 emissions to the atmosphere. The present study conducted in subtropical and tropical regions in Brazil aimed to assess the impact of the continuous plow-based conventional tillage (CT) on soil organic carbon (SOC) stock vis-a-vis native vegetation (NV) as baseline, compare SOC balance among CT, CA cropping systems, and NV; and evaluate the redistribution of SOC stock in soil profile in relation to soil resilience.

Nutrient cycling is considered as a key agroecosystem service of Conservation Agriculture (CA). CA brings together major nutrients and organic matter fluxes within the soil-micro-organism-plant system. It also generates organic and inorganic nutrient pools accessible through new biological pathways. This chapter addresses nutrient management practices and benefits in CA systems. Current trends in CA systems design are discussed, as is integrated nutrient management. The concept of the “forest model” is introduced and discussed in detail. Sections on nutrient pools, bioavailability of elements, and mineral use efficiency in CA systems are also included. The chapter concludes with two case studies from contrasting agroecosystems: one from a Brazilian Fazenda transitioning from "generic" CA to CA based on multifunctional mix species cover, and one from a French dairy farm, illustrating how CA, associated with important and diversified organic matter inputs from cover crops and crop residues, impacts and modifies plant nutrition management.

Conservation agriculture (CA) is recognized as a promising crop management strategy for sustainable agricultural intensification. The objective of this study was to evaluate CA cropping systems for rainfed maize as an alternative to the traditional tillage-based cropping systems (CT) in the context of family farms, using a multi-criteria model that represents the point of view of farmers. Farmers considered several aspects for evaluating the cropping systems, thatwere systematized in the model through five criteria (with sub-criteria): (a) costs; (b) yield; (c) labour; (d) human health and environment; and (e) production risks. CA did not differ from CT for the 'costs' criterion but was superior for the 'yield' and 'labour' criteria. In contrast, CT obtained better ratings for the criteria 'human health and environment' and 'production risks'. Considering all criteria, CA was better appraised than CT. However, a new local policy measure that subsidizes the hiring of mechanized tillage services overturns this outcome, indicating the importance of exogenous factors. Overall, the participatory processes in building the model allowed us to better understand the reasons of adoption or non-adoption of CA by small-scale farmers in the tropics.

In response to the extensive development of upland rice on the hillsides of the Malagasy highlands, alternative cropping systems have been designed based on conservation agriculture (CA). As the promotion of CA in smallholder farming systems is still the subject of debate, its potential benefits for smallholder farmers require further assessment. In the context of resource-poor farmers and low-input production systems, nitrogen (N) is a major limiting nutrient. The effects of contrasted cropping systems have been studied on upland rice yield and N uptake in rainfed conditions: conventional tillage (CT) and CA with a mulch of maize or a legume (Stylosanthes or velvet bean). Decision Support Systems for Agrotechnology Transfer (DSSAT) crop growth model was used to quantify the soil N balance according to the season and the cropping system. The lowest yields were obtained in CA with a mulch of maize and were also associated with the lowest crop N uptake. Upland rice yields were higher or equivalent under CA with a legume mulch than under CT cropping systems. The supply of N was considerably higher in CA with a legume mulch than in CT, but due to higher leaching and immobilization in CA, the final contribution of N from the mulch to the crop was reduced although not negligible. DSSAT has been shown to be sufficiently robust and flexible to simulate the soil N balance in contrasting cropping systems. The challenge is now to evaluate the model in less contrasted experimental conditions in order to validate its use for N uptake and yield prediction in support to the optimization and design of new cropping systems.

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.

Conservation agriculture (CA) has become a dominant paradigm in scientific and policy thinking about the sustainable intensification of food production in sub-Saharan Africa. Yet claims that CA leads to increasing crop yields in African smallholder farming systems remain controversial. Through a meta-analysis of 933 observations from 16 different countries in sub-Saharan African studies, we show that average yields under CA are only slightly higher than those of conventional tillage systems (3.7% for six major crop species and 4.0% for maize). Larger yield responses for maize result from mulching and crop rotations/intercropping. When CA principles are implemented concomitantly, maize yield increases by 8.4%. The largest yield benefits from CA occur in combination with low rainfall and herbicides. We conclude that although CA may bring soil conservation benefits, it is not a technology for African smallholder farmers to overcome low crop productivity and food insecurity in the short term.

National audience; Notre système alimentaire n’est ni sain ni durable : l’agriculture et l’alimentation sont au cœur des enjeux environnementaux (dérèglement climatique, effondrement de la biodiversité) et de santé (développement des maladies chroniques). De nouveaux modèles d’agriculture cherchent à prendre en compte ces enjeux en développant des pratiques pour améliorer la santé du sol, des écosystèmes, de la planète, mais aussi humaine, en mettant sur le marché des produits permettant de se rapprocher des recommandations alimentaires. Nous comparons ici les forces et faiblesses de quatre modèles d’agriculture alternatifs : agriculture biologique (AB, cahier des charges spécifiant entre autres qu’engrais et biocides de synthèse ne sont pas autorisés), agriculture de conservation des sols (ACS, sans cahier des charges mais reposant sur trois principes : rotation longue, couverture permanente du sol, arrêt du labour voire suppression de tout travail du sol), agriculture paysanne (AP : charte pour une agriculture autonome et économe à bas niveau d’intrants) et Bleu Blanc Cœur (BBC, une démarche agricole et commerciale d’intérêt nutritionnel et environnemental, basée sur la complémentation des animaux avec du lin pour une haute valeur nutritionnelle des produits animaux et un apport en protéines issues de légumineuses cultivées en France). En ayant ou recherchant une traçabilité pour les consommateurs, ces modèles s’inscrivent dans la transition agroécologique des systèmes alimentaires. Leur analyse au prisme de la « santé unique » permet de déterminer dans quelle mesure ils permettent une amélioration de la santé dans plusieurs domaines (sol, plante, animal, écosystème, planète, Homme) via (i) l’augmentation des services écosystémiques, (ii) le bouclage des cycles biogéochimiques et (iii) la modification des modes de transformation et distribution des aliments. Certains de ces modèles ont un effet bénéfique démontré sur la santé, tels l’AB et BBC. L’AP est fortement engagée dans des projets de relocalisation alimentaire, en vente directe ou en circuits courts. L’ACS vise quant à elle le développement des services écosystémiques liés à un sol en bonne santé et est en voie de proposer un label. Cependant, nous pointons qu’aucun des quatre modèles ne fait référence explicitement à l’intérêt d’un paysage en mosaïque pour développer les services ni à la moindre consommation de produits animaux pour réduire l’empreinte environnementale de notre alimentation. Cette analyse montre qu’il doit être possible d’atteindre des objectifs encore plus ambitieux dans les différents domaines de santé en combinant les atouts des différents modèles et en tenant compte des deux leviers non considérés.

Pests, diseases and weeds are major constraints to cropping system intensification in sub-Saharan Africa. Four major intensification systems to achieve sustainable agriculture have been identified: conventional with high input, organic, agroecological and eco-technical 'sustainable intensive'. Those systems display advanced crop protection. Here we review the performance of those systems in the context of sub-Saharan Africa. The major points are: (1) Unlike economies of Europe and North America following World War 2, and of Asia and Latin America following the Green Revolution, sub-Saharan Africa rural economies were not transformed by conventional intensification involving cultivation of cash crops for export and over-reliance on pesticides. Genetically modified crops were used only to a limited extent at the regional level. (2) Most staple food-based cropping systems are de facto organic due to the unavailability of synthetic inputs. Organic systems are thus developing for some export cash crop sectors, with synthetic pesticides are being substituted by non-chemical pesticides. (3) Agroecological crop protection focuses on biological pest regulations such as the replacement of chemical inputs, thus implying the re-design of cropping systems. (4) For crop protection, the eco-technical pathway, which is based on principles of integrated pest management and ecological intensification, is more flexible and pragmatic than the other systems. In this review we compare the different systems, notably their contribution to six ecosystem services connected with crop protection issues: biomass production, pest and disease regulation, maintenance of water quality, biodiversity conservation, pollination and climate change mitigation. We then identify research needs in the context of food security, urbanization, trade globalization and climate change.

Soil organic carbon (SOC) pools, particularly labile pools, and soil enzymes are good indicators of short-term impacts of soil management. We hypothesized that labile SOC pools drives C accumulation and enzyme activity can be an efficient indicator for C build up in short-term conservation agriculture. The aims of this study were to quantify the impacts of tillage and crop rotations with diverse crop residue inputs on changes in SOC labile pools and enzymatic activities in rice-, soybean- and cassava-based cropping systems designated as RcCS, SbCS and CsCS, respectively. The four treatments in each cropping system consisted of: conventional tillage (CT), no-till in which main crops (rice, soybean and cassava) were grown in a one-year frequency pattern (NT1) and, no-till in which the main crops were grown in bi-annual rotations with maize (NT2 and NT3). After 5 years experiment period, greater hot-water extractable organic C (HWEO-C) stocks of 61%, 55% and 53%, and permanganate oxidizable C (POX-C) stocks of 23%, 21% and 32% were attributed to NT than those in CT soils under RcCS, SbCS and CsCS, respectively, at 0–5 cm soil layer. The pyrophosphate extractable organic C (PEO-C) and chemically stabilized organic C (CSO-C) stocks were almost constant in each depth among treatments, except 0–5 cm in CsCS. The β-glucosidase activity was 18%, 28% and 49% greater in NT than those in CT soils at 0–5 cm under RcCS, SbCS, CsCS, respectively. Arylsulfatase activity was 36% and 39% greater in NT than in CT under SbCS and CsCS, respectively but no significant differences in RcCS. A strong and positive correlation (P

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

Nous nous intéressons dans cet article aux pratiques de travail du sol d’agriculteurs engagés dans trois modèles d’agriculture aux degrés d’institutionnalisation différents (agriculture de conservation, agriculture biologique et agriculture raisonnée). Nous faisons apparaître comment, sur cette question du changement dans la façon de travailler le sol, un conflit des normes divise les agriculteurs selon leur engagement dans l’un ou l’autre modèle d’agriculture. Ce conflit est particulièrement visible dans la façon dont ces agriculteurs entre-définissent leur façon de produire., In this article we focus on tillage practices carried out by farmers engaged in three types of agriculture that have not the same institutionalization degree (conservation agriculture, organic agriculture and « agriculture raisonnée »). We show how a conflict of norms about no-till practices divides farmers, according to their position in one or other type of agriculture. This conflict is especially identifiable in the way farmers definite their type of agriculture relating to that of other farmers.

Conservation Agriculture aims for an environmental respect concerning water and soil biodiversity, optimizing quality and quantity for the food production. This agriculture is based on three principles: little soil disturbance, permanent soil cover and a diversity in the crop rotation. We focused on the effects produced by the adoption of Conservation Agriculture on crop and farm level. In addition to that we wanted to study the structure of the farmers groups focusing on Agriculture Conservation practices. For this we worked with the Group Manche Agriculture de Conservation accompanying by the Chambre d’Agriculture de la Manche. We noticed that these farmers groups are communities of practices. Members’ are trying to solve the problem of solitude and the lack of knowledge around the Conservation Agriculture. Thus the members generally have and innovating spirit. We built three ideal-types representing the diversity of effects caused by Agriculture Conservation adoption on the farms, for the three level studied. We underlined the differences between Conservation Agriculture practices depending especially on the famer’s values and its social environment. We summarized the complexity of the functioning of the Conservation Agriculture’s farms between the three topics (environmental, economic and social).; L’Agriculture de Conservation (AC) a pour principe d’optimiser la gestion de l’eau, du sol et de sa microfaune tout en répondant aux objectifs d’une production de qualité et de quantité. Cette agriculture est basée sur trois volets : réduction du travail du sol, couverture constante du sol et diversité des cultures. Nous nous sommes intéressés aux effets engendrés par l’adoption des pratiques de l’Agriculture de Conservation aux échelles système de culture et système d’exploitation. Puis nous avons essayé de comprendre la dynamique des groupements d’agriculteurs se formant autour de ces pratiques. Pour cela nous avons travaillé avec le groupement Manche Agriculture de Conservation animé par la Chambre d’Agriculture de la Manche. Nous notons que ces groupements sont des communautés de pratiques. Ses adhérents se regroupent pour lutter contre l’isolement social et contre le manque de connaissances dû à un retrait des organismes de recherche. Les agriculteurs allant vers ces pratiques ont donc une envie d’innovation. Nous avons construit trois idéaux-types permettant de comprendre la diversité des effets de l’Agriculture de Conservation sur une exploitation agricole, et cela aux trois échelles d’étude. Il en ressort que la mise en place de ces pratiques ne va pas être la même selon, entre autres, la situation pédoclimatique mais surtout les valeurs de l’agriculteur et son environnement social. Nous avons ici résumé la complexité des rouages d’une exploitation agricole en Agriculture de Conservation, et leur dynamique entre les volets économique, social et environnemental.

Since the early 2000s conservation agriculture (CA) has been promoted in the Lake Alaotra region of Madagascar for a more sustainable and profitable agriculture. There is, however, little known about its performance in low-input rainfed rice-based cropping systems. We conducted a study during two growing seasons (2013/14 and 2014/15) on an experiment that was established in 2009 at the agricultural research station of the National Center for Applied Research and Rural Development (FOFIFA) in the Lake Alaotra region of Madagascar. The experimental setup was a randomized block design with four replications. Two soil/residue management treatments were studied, conventional tillage without residue retention (CT) and no-tillage with residue retention (NT). These two treatments were tested for a 2-year rotation of maize + Dolichos lablab followed by rice (MD//R) and a 3-year rotation of maize + Stylosanthes guianensis, followed by S. guianensis in the second year, and rice in the third year (MS//S//R). During the 2013/14 and 2014/15 seasons, two levels of weed pressure: 'high' and 'low' were introduced as a split-plot design on the rice plots. The main determining factors of rice yield in the study region were studied: radiation interception, weed infestation, soil moisture and soil mineral nitrogen (N). Our results showed that five to six years of continuous practice of NT with retention of high amounts of crop residues (more than 5 Mg DM ha−1) on the soil surface had a significant (p = 0.02) positive effect on rice yield, irrespective of the level of weed pressure and type of crop rotation. CA systems significantly (p