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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.

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; 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.

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.

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.

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

As a response to the worldwide challenge raised by soil degradation, Conservation Agriculture (CA) was proposed to help restoring the three main soil functions, i.e. carbon transformation, nutrient cycling and structure maintenance. However, there is still a lack of integrative studies that assess the overall impact of CA on soil health. To fill the gap, Biofunctooll (R), a set of in-field indicators, was developed to monitor changes in soil biological functioning. In this study, Biofunctool (R) was used to assess the impact of a conventional tillage (CT) and three CA annual-based cropping systems on soil health on a Cambodian Oxisol. Eight indicators related to the three soil functions were monitored and integrated into a Soil Quality index (SQI), i.e. the Biofunctool (R) Index. Overall, we found that soil health was twice higher under the CA treatments than under CT treatment. Although it was similar in the three CA treatments, the contribution of each soil function to the soil health diverged. An analysis of soil carbon dynamics also showed that CA support short-term soil organic carbon stabilization compared to CT. This study demonstrates that Biofunctool (R) is a robust, relevant, time-and cost-effective in-field assessment tool that can be used in multiple ways including cropping system management, capacity building of local stakeholders, and policy dialogue.

Today, crop residues are no longer considered as waste: their contributions to the agronomic and environmental balance of cropping systems are recognized In this context, knowing their quantity on the soil surface after harvest, becomes an important stake of the management of organic matter in the crop rotation. Generally, the quantitative estimation is carried out by taking samples, in order to determine the dry mass (DM) in the laboratory. The aim of this work is to propose a rapid method of quantification of soil residues, the assumption of which is based on a method for estimating standing grass biomass. This work has been carried out on farms practising conservation agriculture in a crop farming region. The residues were ground during the harvest or a subsequent specific operation. Biomass data were collected using 0.5 x 0.5 m frames, while thickness measurements were collected using an asperimeter. This work compares two methods of thickness measurement: either by random repetitions of positioning of the asperimeter along a transect perpendicular to the direction of progression of the harvester, or by side-by-side repetitions. A test of the number of thickness measurements was carried out to know the maximum spacing to keep making an accurate estimate. The results show that it is preferable to perform residue thickness measurements over the entire harvester transect to accurately estimate this information, and that 100 thickness measurements must be maintained to keep an estimate close to the reference thickness measurement; the spacing between two measurements must not exceed 6 cm. Moreover, this work shows that it possible to approximate the biomass left on the soil with a good quality of estimation by retaining that one millimeter of residue thickness represents 50 g DM.m(-2)., Aujourd’hui, les résidus de culture ne sont plus considérés comme des déchets : leurcontribution aux équilibres agronomiques et environnementaux des systèmes de culture est reconnue.Dans ce contexte, connaître leur quantité à la surface d’un sol, après une récolte, devient un enjeuimportant de la gestion des matières organiques dans la rotation des cultures. Généralement,l’estimation quantitative se réalise par prélèvement d’échantillons, afind’en déterminer la masse sèche(MS) au laboratoire. L’objectif de ce travail est de proposer une méthode rapide de quantification desrésidus au sol, dont l’hypothèse est basée sur une méthode d’estimation de biomasse prairiale sur pied.Ce travail a été réalisé sur des exploitations pratiquant l’agriculture de conservation en région degrandes cultures. Les résidus ont été broyés lors de la récolte ou lors d’une opération spécifiquesuivante. Les données de biomasse ont été collectées à l’aide de cadres de 0,5 0,5 m, tandis que lesmesures d’épaisseur ont été effectuées à l’aide d’un aspérimètre. Ce travail compare deux méthodes demesure d’épaisseur : soit par répétitions aléatoires de positionnement de l’aspérimètrelelongd’untransect perpendiculaire au sens de progression de la moissonneuse, soit par répétitions côte à côte. Untest du nombre de mesures d’épaisseur a été réalisé pour connaître l’espacement maximal à conserverpour réaliser une estimation précise. Les résultats montrent qu’il est préférable de réaliser les mesuresd’épaisseur des résidus sur l’intégralité d’un transect de moissonneuse pour estimer avec précision cetteinformation, et qu’il faut maintenir 100 mesures d’épaisseur pour conserver une estimation proche de lamesure d’épaisseur de référence, l’espacement entre deux mesures ne devant pas excéder 6 cm. Parailleurs, ce travail montre qu’il est possible d’obtenir une approximation de la biomasse présente auchamp avec une bonne qualité d’estimation, en retenant qu’un millimètre d’épaisseur de résidureprésente 50 g MS.m 2.

International audience; In a conservation agriculture system, crop residues are no longer mixed in a volume of ploughed soil, but maintained on the surface or partially buried. Their presence contributes to the sustainability of these systems by maintaining the agronomic and environmental balances. In this context, knowledge of the evolution of their quantity on the soil surface, from harvest to sowing of the next crop, becomes an important stake of soil management. Several authors have established a relationship between the soil cover ratio and biomass, specific to each plant species, from an identical formalism developed by Gregory (1982). The objectives of this work are to test its use in the pedoclimatic context of the Grand-Est region (France), after harvesting and during the residue degradation process, on several crops. This work has been carried out on farms practicing conservation agriculture for several years. The residues were ground during the harvest or a subsequent specific operation. Biomass data were collected using 0.5 m x 0.5 m frames, while ground cover were studied using digital photographs. The cover rates were calculated using an image analysis software. This work also compares two measurement periods: at the end of winter, several months after the harvest, and right after the summer harvest. The results show a very good correspondence between the soil cover ratio and the biomass measured on the ground, for all species and measurement periods, by adding a parameter to the Gregory (1982) formalism. The integration of spatial variability on the ground makes it possible to propose the use of a single linear adjustment that simplifies the prediction of soil cover ratio or the amount of biomass.; -En système d'agriculture de conservation, les résidus de cultures ne sont plus brassés dans un volume de sol labouré mais maintenus à la surface des sols ou partiellement enfouis. Leur présence contribue à la durabilité de ces systèmes par le maintien des équilibres agronomiques et environnementaux qu'ils induisent. Dans ce contexte, la connaissance de l'évolution de leur quantité à la surface d'un sol, de la récolte au semis de la culture suivante, devient un enjeu important de gestion des sols. Plusieurs auteurs ont établi une relation entre le taux de couverture du sol (TC) et la biomasse, propre à chaque espèce végétale, à partir d'un formalisme développé par Grégory (1982). Les objectifs de ce travail sont de tester sa validité dans le contexte pédoclimatique de la région GrandEst (France), après récolte et au cours du processus de décomposition des résidus. Ce travail a été réalisé sur des exploitations pratiquant l'agriculture de conservation depuis plusieurs années. Les résidus ont été broyés lors de la récolte ou d'une opération spécifique. Les données de biomasse ont été collectées à l'aide de cadres de 0,5 m  0,5 m, tandis que la couverture du sol a été étudiée à l'aide de photographies numériques. Le taux de couverture du sol a été calculé à l'aide d'un logiciel d'analyse d'images. Ce travail compare également deux périodes de mesure : en sortie d'hiver, plusieurs mois après la récolte, et juste après la récolte estivale. Les résultats montrent une très bonne correspondance entre le TC et la biomasse mesurée au sol, toutes espèces et période de mesures confondues, moyennant l'ajout d'un paramètre au formalisme de Grégory (1982). L'intégration de la variabilité spatiale au sol permet de proposer l'emploi d'un ajustement linéaire unique qui simplifie la prédiction du TC du sol ou « la prédiction » de la quantité de biomasse.

Limited field studies have been performed to evaluate the impacts of conservation agriculture (CA) on crop yields and soil organic carbon sequestration in tropical conditions. In this study, we used the Environmental Policy Integrated Climate (EPIC) model to evaluate the impact of CA and conservation tillage (CT) on crop yields in tropical conditions for unique upland rice, soybean, and cassava cropping systems in Cambodia. New crop parameters were developed and tested for cassava, sesame, banana, sunn hemp, stylo, and congo grass. The results show that EPIC successfully replicated crop yields of soybean, upland rice, maize, and cassava based on R2 statistics ranging from 0.62 to 0.88 and percent bias (PBIAS) values ≤10%. However, it cannot be concluded that the model can accurately capture the biomass for all the individual crops due to limitations in the observed biomass data. The cassava and maize biomass were simulated satisfactorily, resulting in R2 values of 0.81 and 0.75, respectively. However, the computed PBIAS for the biomass estimates of the two crops were >25%. In contrast, the predicted rice and soybean biomass met PBIAS criteria (≤23%) but resulted in weak R2 statistics of ≤0.20, indicating inaccurate replications of the measured biomass. Similarly, the cover crop mean biomass and PBIAS statistics were acceptable but the R2 values were not. Overall, the model tended to overestimate the measured crop biomass. No significant difference was found in the simulated crop yields between the CA and CT treatments. However, the predicted rice and soybean results reflect an increased yield trend over time for the CA treatments, versus no discernible trend for the cassava and maize yields.

Climate-smart cropping systems should be designed with three objectives: reducing greenhouse gas (GHG) emissions, adapting to changing and fluctuating climate and environment, and securing food production sustainably. Agriculture can improve the net GHG emissions balance via three levers: less N2O, CH4 and CO2 emissions, more carbon storage, and green energy production (agrifuels, biogas). Reducing the application of mineral N fertilizer is the main option for reducing N2O emissions either directly or by increasing the proportion of legumes in the rotation. The most promising options for mitigating CH4 emissions in paddy fields are based on mid-season drainage or intermittent irrigation. The second option is storing more carbon in soil and biomass by promoting no-tillage (less fuel, crop residues), sowing cover crops, introducing or maintaining grasslands and promoting agroforestry. Breeding for varieties better adapted to thermal shocks and drought is mainly suggested as long-term adaptation to climate change. Short-term strategies have been identified from current practices to take advantage of more favorable growing conditions or to offset negative impacts: shifting sowing dates, changing species, cultivars and crop rotations, modifying soil management and fertilization, introducing or expanding irrigation. Some crops could also move to more suitable locations. Model-based tools and site-specific technologies should be developed to optimize, support and secure farmer's decisions in a context of uncertainty and hazards. Most of the adaptation and mitigation options are going in the same way but tradeoffs will have to be addressed (e. g. increasing the part of legumes will be possible only with significant breeding efforts). This will be a challenge for designing cropping systems in a multifunctional perspective., Des systèmes de culture climato-intelligents doivent combiner (i) réduction des émissions de gaz à effet de serre (GES), (ii) adaptation au changement et à la variabilité climatique et (iii) sécurisation de la production alimentaire. L’agriculture peut améliorer le bilan des émissions de GES via trois leviers : (i) moins d’émissions de N2O, CH4 et CO2, (ii) plus de stockage du carbone, (iii) de la production d’énergie verte (biocarburants, biogaz). Réduire l’application d’engrais minéral ou augmenter la proportion de légumineuses dans la rotation permet de réduire les émissions de N2O. La réduction des émissions de CH4 en riziculture inondée impose de revoir la gestion de l’eau (drainage, irrigation). Stocker plus de carbone dans le sol et la biomasse passe par la culture sans labour (moins d’énergie, paillage avec les résidus de récolte), l’utilisation de plantes de couverture, l’introduction ou le maintien de prairies et la pratique de l’agroforesterie. La sélection de variétés mieux adaptées aux chocs thermiques et à la sécheresse est la principale adaptation à long terme au changement climatique. Des stratégies à court terme ont été identifiées à partir des pratiques actuelles, tirant profit de conditions de croissance plus favorables ou compensant les impacts négatifs par le décalage des dates de semis, l’introduction de nouvelles espèces et cultivars, la diversification des rotations, de nouvelles pratiques de gestion du sol et de la fertilisation, l’introduction ou l’expansion de l’irrigation. Certaines cultures pourraient également migrer vers des zones de culture plus appropriées. Des outils basés sur les modèles et l’agriculture de précision devraient être développés afin d’aider les agriculteurs face à un contexte plus incertain et plus risqué. La plupart des options d’adaptation et d’atténuation sont compatibles, mais des arbitrages devront être faits : ainsi augmenter la part des légumineuses ne sera possible que si des efforts de sélection importants sont conduits.

Avec les remerciements pour Jodie Thénard; Conventional agriculture strongly alters soil quality due to industrial practices that often have negative effects on soil life. Alternative systems such as conservation agriculture and organic farming could restore better conditions for soil organisms. Improving soil life should in turn improve soil quality and farming sustainability. Here, we have compared for the first time the long-term effects of conservation agriculture, organic farming, and conventional agriculture on major soil organisms such as microbes, nematofauna, and macrofauna. We have also analyzed functional groups. Soils were sampled at the 14-year-old experimental site of La Cage, near Versailles, France. The microbial community was analyzed using molecular biology techniques. Nematofauna and macrofauna were analyzed and classified into functional groups. Our results show that both conservation and organic systems increased the abundance and biomass of all soil organisms, except predaceous nematodes. For example, macrofauna increased from 100 to 2,500 %, nematodes from 100 to 700 %, and microorganisms from 30 to 70 %. Conservation agriculture showed a higher overall improvement than organic farming. Conservation agriculture increased the number of many organisms such as bacteria, fungi, anecic earthworms, and phytophagous and rhizophagous arthropods. Organic farming improved mainly the bacterial pathway of the soil food web and endogeic and anecic earthworms. Overall, our study shows that long-term, no-tillage, and cover crops are better for soil biota than periodic legume green manures, pesticides, and mineral fertilizers.

National audience; Direct seeding under cover meets three principles applied simultaneously and continuously: almost total reduction of tillage, maximum soil coverage and diversification of rotation. Its adoption started in France in the 2000s and today seems to convince more and more farmers. For farmers, the adoption of a new system means changing practices, by important ways or not. For direct seeding under cover, few is known about the required changes. The purpose of this article is to clarify the changes that can occur for farmers when adopting direct seeding under cover. An online survey was conducted: 425 French farmers responded. Results show that the adoption of direct seeding under cover has deeply changed the practices of 30% of farmers. For others, changes concern only one or two principles. The most important changes (for 96% of farmers) concern the almost total reduction of soil tillage principle. On the contrary, changes are less important for the diversification of rotation. Only 48% of farmer modify their crop rotation when adopting direct seeding under cover. Optimizing soil coverage represents a change for 67% of farmers. During first years, soil coverage is mainly achieved through multi-species temporary cover crops. By upsetting fundamentals of conventional farming, these farmers seems to minimize risks when adopting direct seeding under cover by a soft transition way and by sharing knowledge.Résumé – Le semis direct sous couvert repose sur l’application simultanée et continue de trois principes :la réduction quasi-totale du travail du sol, une couverture organique des sols et une rotation diversifiée. Cesystème agricole adopté en France à partir des années 2000 sous l’impulsion de groupes d’agriculteurs est enextension. Pour les agriculteurs, adopter un nouveau système agricole revient à modifier, de manière plus oumoins importante, leurs pratiques. Concernant le semis direct sous couvert végétal, peu d’informationsexistent. Cet article a pour objectif d’éclairer les modifications que peut induire sa mise en place. Pour cela, ils’appuie sur les réponses de 425 agriculteurs français à une enquête en ligne. Pour 30% des agriculteurs, lesemis direct sous couvert constitue une modification complète du système agricole. La réduction quasitotaledu travail du sol est le principe qui entraîne le plus de modifications (pour 96% des agriculteurs). Aucontraire, la diversification de la rotation connaît le moins de modifications (48% des agriculteurs).L’absence d’une modification de la rotation peut s’expliquer par une rotation déjà diversifiée en place oul’incapacité pour les agriculteurs d’ajouter de nouvelles cultures à leur rotation. L’optimisation de lacouverture végétale du sol entraîne une modification des pratiques pour 67% des agriculteurs. Durant lespremières années, les agriculteurs s’orientent majoritairement vers l’utilisation de couverts temporairesplurispécifiques. Bouleversant certains fondamentaux de l’agriculture, ces agriculteurs minimisent lesrisques encourus en favorisant une transition progressive et en partageant les connaissances acquises.