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Voir la prépublication How reducing synthetic nitrogen in Europe affects ecosystem carbon and biodiversity: two perspectives of the same policy, hal-03763653,; International audience; Synthetic Nitrogen (N) usage in agriculture has greatly increased food supply over the past century. However, the intensive use of N fertilizer is nevertheless the source of numerous environmental issues and remains a major challenge for policymakers to understand, measure, and quantify the interactions and trade-offs between ecosystem carbon and terrestrial biodiversity loss. In this study, we investigate the impacts of a public policy scenario that aims to halve N fertilizer application across European Union (EU) agriculture on both carbon (C) sequestration and biodiversity changes. We quantify the impacts by integrating two economic models with an agricultural land surface model and a terrestrial biodiversity model (that uses data from a range of taxonomic groups, including plants, fungi, vertebrates and invertebrates). Here, we show that the two economic scenarios lead to different outcomes in terms of C sequestration potential and biodiversity. Land abandonment associated with increased fertilizer price scenario facilitates higher C sequestration in soils (+ 1014 MtC) and similar species richness levels (+ 1.9%) at the EU scale. On the other hand, the more extensive crop production scenario is associated with lower C sequestration potential in soils (− 97 MtC) and similar species richness levels (− 0.4%) because of a lower area of grazing land. Our results therefore highlight the complexity of the environmental consequences of a nitrogen reduction policy, which will depend fundamentally on how the economic models used to project consequences.; L'utilisation de l'azote synthétique (N) dans l'agriculture a permis d'accroître considérablement l'approvisionnement alimentaire au cours du siècle dernier. L'utilisation intensive d'engrais azotés est néanmoins à l'origine de nombreux problèmes environnementaux et reste un défi majeur pour les décideurs politiques pour comprendre, mesurer et quantifier les interactions et les compromis entre le carbone des écosystèmes et la perte de biodiversité terrestre. Dans cette étude, nous examinons les impacts d'un scénario de politique publique visant à réduire de moitié l'application d'engrais azotés dans l'agriculture de l'Union européenne (UE) sur la séquestration du carbone (C) et les changements de biodiversité. Nous quantifions les impacts en intégrant deux modèles économiques avec un modèle de surface des terres agricoles et un modèle de biodiversité terrestre (qui utilise les données d'une série de groupes taxonomiques, y compris les plantes, les champignons, les vertébrés et les invertébrés). Nous montrons ici que les deux scénarios économiques conduisent à des résultats différents en termes de potentiel de séquestration du carbone et de biodiversité. L'abandon des terres associé au scénario d'augmentation du prix des engrais facilite une plus grande séquestration de C dans les sols (+ 1014 MtC) et des niveaux de richesse des espèces similaires (+ 1,9 %) à l'échelle de l'UE. En revanche, le scénario de production végétale plus extensive est associé à un potentiel de séquestration de carbone plus faible dans les sols (- 97 MtC) et à des niveaux de richesse en espèces similaires (- 0,4 %) en raison d'une surface de pâturage plus faible. Nos résultats soulignent donc la complexité des conséquences environnementales d'une politique de réduction de l'azote, qui dépendra fondamentalement de la manière dont les modèles économiques utilisés pour projeter les conséquences.

Sustainable field crop management has been considered to reach the food security issue due to global warming and water scarcity. The effect of deficit irrigation and nitrogen rates on quinoa yield is a challenging issue in those areas. In this regard, the interaction effects of different N rates (0, 125, 250, and 375 kg N ha−1) and irrigation regimes [full irrigation (FI) and deficit irrigation at 0.75 FI and 0.5 FI] on quinoa yield and water and nitrogen efficiencies were evaluated with a two-year field experiment. Increasing nitrogen fertilizer application levels from 250 to 375 kg N ha−1 under FI and deficit irrigation did not cause a significant difference in seed yield and the total dry matter of quinoa. Furthermore, 20% and 34% reductions were observed for nitrogen use efficiency (NUE) and nitrogen yield efficiency with the application of 375 kg N ha−1 compared with that obtained in 250 kg N ha−1 nitrogen fertilizer, respectively. Therefore, a Nitrogen application rate of 250 kg ha−1 and applying 0.75 FI is suggested as the optimum rate to reach the highest seed water use efficiency (0.7 kg m−3) and NUE (0.28 kg m−3) to gain 4.12 Mg ha−1 quinoa seed yield. Under non–limited water resource conditions, an FI and N application rate of 375 kg ha−1 could be used for higher seed yield; however, under water-deficit regimes, an N application rate of 250 kg ha−1 could be adequate. However, questions about which environmental factors impressively restricted the quinoa growth for optimizing the potential yield need further investigation.

Most of the world's sugar is produced from a semi-perennial plant whose root system, although being one key to its success, remains poorly understood. In this study, we sought to describe how nitrogen fertilisation is likely to affect the development of the sugarcane root system and can have significant agronomic implications. We studied sugarcane root distribution, root biomass production and root N accumulation from soil cores sampled down to a depth of 1 m throughout the growth cycle of a ratoon crop in a 144 kgN ha−1 year fertilised plot and at crop harvest in six ratoon plots with fertilisation ranging from 0 to 330 kgN ha−1 year. The development of the root system in the fertilised sugarcane plot showed 1/homogeneous colonization of the topsoil by fine roots from the early phase, followed by 2/a progressive development of thicker roots mainly localised under the sugarcane row. The results suggested that nitrogen fertilisation could reduce root density in the topsoil layer. The root-to-shoot ratio of biomass and N mass decreased, respectively, from 2.1 to 0.3 and from 1.2 to 0.7 throughout an annual crop growth cycle in a fertilised plot. When sugarcane was not fertilised, an increase of 70% root biomass was observed as compared to fertilised sugarcane. In addition, approximately half of the cane N mass was found in the root compartment of the non-fertilised crop. The root system of sugarcane appeared to be a major pool of N that should be considered in studies dealing with fertiliser N use efficiency and N cycling in sugarcane agroecosystems.

Yam (Dioscorea spp.) is an important source of food for millions of people throughout the tropics. Yam yields are constrained by several factors such as low soil fertility and a poor response of the crop to nutrient supply. Here we present an experimental and modeling study performed to test the hypothesis that N leaching in the humid tropics is a key factor that explains the poor response of water yam (Dioscorea alata L.) to N fertilization. A field experiment was carried out to assess the impact of three levels of N supply (50, 125 and 200 kg N ha−1) on crop growth and soil N availability. The N fertilizer was split into two equal doses (i.e., 50%/50% split ratio), one applied just before emergence and the other a month after tuber initiation, which corresponds to the current management used by farmers. The CropSyst-Yam model was adapted to include a new soil-crop N component describing the effects of limiting N conditions on yam growth, and then to test different N fertilizer managements. The experimental results indicated that all variables linked to the soil-crop system were affected by the increase in N supply (soil N availability, crop biomass, leaf area and N uptake), and the model well described these impacts. Nitrogen leaching throughout the field experiment represented about one third of the total N supplied by each treatment. Observed and predicted data revealed that N leaching reduced yam growth under the N50 and N125 treatments by reducing soil N availability near the tuber initiation stage. This effect was not observed under the N200 treatment. Model results showed that N leaching and its negative impact near tuber initiation in N50 and N125 could be diminished by advancing the second N application by two or three weeks, and by using a split ratio of 70%/30%. Model results also indicated that this fertilizer strategy would even be suitable during very rainy growing seasons.

International audience; Nitrogen (N) fertilizer is commonly applied to wheat crops (Triticum aestivum L.) during the vegetative growth to meet crop requirements. Current decision rules for N application result in N losses to the environment, and thus to low N use efficiency, due to excess of N fertilizer and/or poor synchrony between soil supply and crop N demand. Despite existing tools and methods to manage N fertilization, combining maximum grain yield, high grain protein content, and minimum N losses to the environment remains challenging. There is thus a need to provide decision rules to apply N fertilizer at the time of optimal weather conditions and high crop N demand, without exceeding N crop requirements, thereby increasing N use efficiency and limiting N losses. Here we developed, for the first time, a modeling approach based on the Azodyn model and using the mathematical framework of the viability theory to build decision rules where 1) N is applied only if weather conditions are optimal and if there is a risk that a period of N deficiency becomes detrimental to grain yield and protein content, and 2) the N rate is the minimum sufficient to prevent from detrimental N deficiencies whilst minimizing N losses to the environment. We computed metric of robustness to build decision rules for timing and rates of N fertilizer in the view to manage crop N nutrition according to such targets. We showed that, comparing those decision rules with current recommendations, by simulations over 20 years, the average total N rate could be decreased by 50 kg N ha-1 and N losses by 42 kg N ha-1 whilst maintaining similar yield, and reaching grain protein content above 11.5% more often (17 years out of 20, compared to 10 years out of 20 with current recommendations). In respect of those theoretical results, the next step should be to experimentally assess performances in real situations and to assess to which extend the method could help farmers to change their practices.

International audience; Managing the nitrogen (N) supply in agroecosystems is a critical issue to ensure sufficient food production while preserving the environment. Intercropping is known to be a sustainable means of reducing the use of N-fertilizers. However, managing the N supplied to a crop while optimising the use of N by different species in a mixture remains a challenge. This is partly due to the difficulty of assessing the N requirements of each component in the mixture separately in order to correctly drive the performance of the whole system. The methods used to assessplant N nutrition status were initially developed for sole crops. In this review, i) we present different approaches adapted from these previous works to determine the N nutrition status of crops in intercrops; ii) we then compare the predictions of some of them, based on a European database of experimental results regarding cereal–grain legume and perennial grass–legume mixtures; and iii) we discuss the interests and limitations of current indices for mixed crops. We conclude that no single approach is currently valid to assess the N nutrition status of crops within the entire range of possible mixtures explored by farmers. However, some indices based on the N dilution theory perform well regarding the most common situations of balanced binary intercrops. Further research is now needed to properly address the cases of complex mixtures and severely shaded crops.

Background: Nitrogen fertilization is known to increase disease susceptibility, a phenomenon called Nitrogen-Induced Susceptibility (NIS). In rice, this phenomenon has been observed in infections with the blast fungus Magnaporthe oryzae. A previous classical genetic study revealed a locus (NIS1) that enhances susceptibility to rice blast under high nitrogen fertilization. In order to further address the underlying genetics of plasticity in susceptibility to rice blast after fertilization, we analyzed NIS under greenhouse-controlled conditions in a panel of 139 temperate japonica rice strains. A genome-wide association analysis was conducted to identify loci potentially involved in NIS by comparing susceptibility loci identified under high and low nitrogen conditions, an approach allowing for the identification of loci validated across different nitrogen environments. We also used a novel NIS Index to identify loci potentially contributing to plasticity in susceptibility under different nitrogen fertilization regimes.Results: A global NIS effect was observed in the population, with the density of lesions increasing by 8%, on average, under high nitrogen fertilization. Three new QTL, other than NIS1, were identified. A rare allele of the RRobN1 locus on chromosome 6 provides robust resistance in high and low nitrogen environments. A frequent allele of the NIS2 locus, on chromosome 5, exacerbates blast susceptibility under the high nitrogen condition. Finally, an allele of NIS3, on chromosome 10, buffers the increase of susceptibility arising from nitrogen fertilization but increases global levels of susceptibility. This allele is almost fixed in temperate japonicas, as a probable consequence of genetic hitchhiking with a locus involved in cold stress adaptation.Conclusions: Our results extend to an entire rice subspecies the initial finding that nitrogen increases rice blast susceptibility. We demonstrate the usefulness of estimating plasticity for the identification of novel loci involved in the response of rice to the blast fungus under different nitrogen regimes.

Cassava production requires nitrogen (N) inputs to drive processes such as protein synthesis. Nevertheless, N not taken up by cassava roots is subjected to microbial transformation resulting in nitrous oxide (N2O) production, a potent greenhouse gas. The temporal dynamics of soil N is partially influenced by the N source (i.e., organic or inorganic fertilizer) and the synchrony between N supply and demand. This study, which was conducted in Colombia on soils with high organic carbon and phosphorus contents, aimed at monitoring N2O emissions from cassava plots fertilized with organic (49.8 kg N ha-1 year-1) or inorganic fertilizers (22.7 kg N ha-1 year-1). Although the organic fertilizer (vermicompost) contained more than double the amount of N, cumulative N2O emissions from organic cassava production (1.28 kg N2O-N ha-1) were lower than those from inorganic fertilizer-based cassava production (1.74 kg N2O-N ha-1) system. This finding indicates that, if crop yields can be maintained, there is potential to reduce cassava production's environmental impact through organic fertilization on highly fertile soils. However, a transition to organic fertilization depends on the availability of sufficient amounts of organic fertilizers at the farm level. The N2O emissions in this study were higher than those predicted using the default IPCC emission factor, which confirmed the relevance of using country or regional specific emissions factors.

Les engrais azotés ont contribué de manière substantielle à la sécurité alimentaire et à la nutrition mondiales. Toutefois, l'azote qu'ils contiennent peut être accumulé en quantités excessives dans les écosystèmes ou dans l'atmosphère ; il entraîne alors des impacts environnementaux négatifs. Il existe souvent une grande disparité entre ce qui est fourni par la fertilisation et ce qui est utilisé par les cultures, ce qui entraîne de faibles rendements d'efficience de l'utilisation de l'azote (NUE) des engrais. Le recyclage des résidus organiques dans les agroécosystèmes pourrait être une alternative ou un complément prometteur aux engrais synthétiques, et un moyen de promouvoir une durabilité économique et agricole circulaire. L'objectif général de cette thèse de doctorat était dans un premier temps de dresser un bilan complet et dynamique des entrées et sorties d'azote dans un site expérimental fortement instrumenté cultivé en canne à sucre. Dans un second temps, il a s'agit d'étudier le devenir de l'azote apporté avec deux types d'engrais organiques (lisier de porc et boues d'épuration méthanisées chaulées séchées) dans ce système sol-plante en comparaison d'un apport d'engrais de référence (urée), pour la canne à sucre à la Réunion. L'évolution de la biomasse et de la minéralomasse de N a été mesurée au pas de temps mensuel au cours des 24 mois de l'étude dans les 4 traitements distincts (non fertilisé, urée, lisier de porc, boues de STEU). Les résultats a révélé que la part de l'azote de la plante contenu dans les racines pouvait être considérable et représenter jusqu'à 65 % et 104 % de l'azote mesurée dans la biomasse aérienne des traitements non-fertilisé et fertilisé. Un ensemble de méthodes peu destructives a été proposé afin d'estimer le NUE tout au long du cycle de croissance de la canne à sucre. Les contributions respectives de différentes sources de N pour la nutrition de la canne ont été déterminées à l'aide de microplacettes enrichis en 15N. Le paillis et les apports précédents d'engrais présentaient une contribution constante mais inférieure à 5 %, les engrais, qu'ils soient minéraux ou organiques, représentaient environ 4.4-17.8 % ; c'est donc le sol qui représentait de loin (>74 %) la principale source de N. Des calculs de NUE ont été élaborés avec deux méthodes, par différence et isotopique, mettant en évidence 1/ un écart de résultats entre méthodes, 2/ une baisse au cours des 6 derniers mois avec l'approche isotopique uniquement suggérant un déficit de 15N qu'il reste à élucider, 3/ une efficience faible autour de 9.2 – 16.1% pour l'engrais de référence en raison notamment d'un fort niveau de volatilisation. La lixiviation de l'azote apporté avec les engrais a été étudiée grâce à un dispositif de bougies poreuses à trois profondeurs du sol et dans les 4 traitements, et des sondes TDR pour la modélisation des flux hydriques. Les pertes estimées à 100 cm n'ont pas dépassé 18.3 kgN/ha quel que soit le traitement. Ce résultat est probablement à mettre au compte d'une capacité des sols à retenir les nitrates mais surtout à la dynamique de croissance de la canne. Un bilan complet des flux d'azote à l'échelle de l'agroécosystème a été établi pour chaque traitement fertilisant, et a montré des niveaux élevés de perte d'azote pour l'urée et le lisier de porc par volatilisation (36 % et 63 % respectivement), ainsi qu'un niveau élevé d'immobilisation pour les boues de STEU (70 % de l'azote apporté). En conclusion, ces travaux ont mis en évidence le rôle central du sol en tant que pourvoyeur de N. Ils ont mis en lumière le rôle de premier plan du compartiment racinaire ainsi que la nécessité d'améliorer l'efficience d'utilisation des fertilisants en abaissant le niveau de volatilisation à la Réunion. Le recours à des engrais organiques en substitution partielle des engrais minéraux apparait comme un bon moyen de nourrir les cultures et d'amender les sols, tout en limitant les pollutions environnementales.

International audience; Smallholder farmers in sub-Saharan Africa (SSA) currently grow rainfed maize with limited inputs including fertilizer. Climate change may exacerbate current production constraints. Crop models can help quantify the potential impact of climate change on maize yields, but a comprehensive multimodel assessment of simulation accuracy and uncertainty in these low-input systems is currently lacking. We evaluated the impact of varying [CO2], temperature and rainfall conditions on maize yield, for different nitrogen (N) inputs (0, 80, 160 kg N/ha) for five environments in SSA, including cool subhumid Ethiopia, cool semi-arid Rwanda, hot subhumid Ghana and hot semi-arid Mali and Benin using an ensemble of 25 maize models. Models were calibrated with measured grain yield, plant biomass, plant N, leaf area index, harvest index and in-season soil water content from 2-year experiments in each country to assess their ability to simulate observed yield. Simulated responses to climate change factors were explored and compared between models. Calibrated models reproduced measured grain yield variations well with average relative root mean square error of 26%, although uncertainty in model prediction was substantial (CV = 28%). Model ensembles gave greater accuracy than any model taken at random. Nitrogen fertilization controlled the response to variations in [CO2], temperature and rainfall. Without N fertilizer input, maize (a) benefited less from an increase in atmospheric [CO2]; (b) was less affected by higher temperature or decreasing rainfall; and (c) was more affected by increased rainfall because N leaching was more critical. The model intercomparison revealed that simulation of daily soil N supply and N leaching plays a crucial role in simulating climate change impacts for low-input systems. Climate change and N input interactions have strong implications for the design of robust adaptation approaches across SSA, because the impact of climate change in low input systems will be modified if farmers intensify maize production with balanced nutrient management.

Sustainable alternatives to slash-and-burn shifting cultivation in the (sub)humid tropics rely on the use of external nutrient inputs to address soil fertility decline. The use of organic inputs is widely accepted as a practice to improve soil fertility, in particular soil organic carbon (SOC). On the other hand, its combined use with mineral fertilizer has the potential to maintain or increase crop productivity through positive interactive effects between both resources. Few studies have investigated these effects in the long term. Therefore, the objective of this study was to investigate whether maize productivity and soil SOC can be sustained under permanent cropping with sole and combined use of compost and mineral nitrogen (N) fertilizer. Here, we report results from a long-term experiment carried out in Gagnoa, Ivory Coast, from 1971 to 1990. The experiment followed a randomized block design comprising eight replicates of 12 treatments. The two studied factors were compost (0 or 10 t DM ha−1 yr−1) and mineral N (0, 40, 80, 120, 160 or 200 kg N ha−1 yr−1) additions. Average maize grain yields of the first cropping cycles were significantly lower without compost (5.05 ± 1.57 t ha−1) than with compost addition (6.07 ± 1.31 t ha−1). The annual yield variability as shown by the standard deviation of the mean was reduced by 20% with compost addition. Without compost, 53% of the initial SOC stock in the 0–20 cm soil layer was lost, resulting in a SOC loss rate of − 0.62 t C ha−1 yr−1 compared to 21% with compost (−0.27 t C ha−1 yr−1). Compost addition therefore reduced SOC loss with an apparent SOC storage rate of 0.35 t C ha−1 yr−1. The conversion rate of organic carbon (OC) inputs to SOC was about 12%. The Introductory Carbon Balance Model (ICBM) reproduced well SOC dynamics, especially without compost. Without mineral N and without compost, maize grain yield decreased with decreasing SOC concentration until the introduction of leguminous crops in the second cropping cycle. We conclude that combined application of compost with mineral N fertilizers was effective at maintaining maize productivity but inadequate to prevent the decline of SOC stocks, despite large additions. Leguminous crops in the rotation were key for maize productivity, but probably due to effects non-related to supplementary N supply.

International audience; Cereal-legume intercropping has gained increased interest in Europe. Nevertheless, performance and especially the percentage of each species at harvest are often considered highly variable. Nitrogen (N) fertilisation can be a relevant driving factor affecting the percentage of each species at harvest. Soil N availability influences competition for light and nitrogen in cereal-legume intercrops. However, management of N fertilisation still remains unclear for intercrops. Few references on the effects of a range of strategies of N fertilisation are available to guide farmers with relevant decision rules considering their expectations. Here, a modelling approach was proposed to simulate interactions between light and N acquisition of a pea-wheat intercrop and to test different scenarios for the management of such intercrops. A model (Azodyn-IC) was built resulting from the combination of two existing individual-crop models (AZODYN and AFISOL) and by applying rules of light and soil inorganic nitrogen sharing between the intercropped pea and wheat. Evaluation of the model outputs with experimental data showed satisfactory predictions of the studied variables (N accumulation, LAI, and crop dry weight). The model validated both resource sharing and light-N interactions. Furthermore, the model was able to respond to increases in inorganic N availability based upon straightforward formalisms. Simulating unmeasured variables, such as root growth and light interception and use by each species, improved our understanding of the relative dominance of each species for acquiring resources. Eventually, the model was used to simulate different scenarios of N fertilisation over 26 years of climatic data to account for climatic variability. We demonstrated the interest of such a modelling approach to design decision rules of N fertilisation according to farmers’ expectations.

International audience; Oil palm (Elaeis guineensis Jacq.) is currently cultivated on 19 million ha, and palm oil represents more than one‐third of the global vegetable oil market. Addition of nitrogen (N) via legume cover crop and fertilizers is a common practice in industrial oil palm plantations, however, there is a tendency for N loss, thus contributing significantly to environmental effects. To improve the sustainability of palm oil production, it is crucial to determine which management practices minimize N losses. Continuous field measurements would be cost‐prohibiting as a monitoring tool, and in the case of oil palm, available models do not account for all the potential nitrogen inputs and losses or management practices. In this context, we developed IN‐Palm, a model to help managers and scientists estimate N losses to the environment and identify best management practices. The main challenge was to build the model in a context of knowledge scarcity. Given these objectives and constraints, we developed an agri‐environmental indicator, using the INDIGO method and fuzzy decision trees. We validated the N leaching module of IN‐Palm against field data from Sumatra, Indonesia. IN‐Palm is implemented in an Excel file and uses 21 readily available input variables to compute 17 modules. It estimates annual emissions and scores for each N‐loss pathway and provides recommendations to reduce N losses. IN‐Palm predictions of N leaching were acceptable according to several statistics, with a tendency to underestimate nitrogen leaching. Thus, we highlighted necessary improvements to increase IN‐Palm precision before use in plantations.

This work was conducted to study the performance of eight sorghum varieties that contrasted with intensified practices in the Sudano-Sahelian zone of Mali. Two experiments were carried out in 2018 and 2019 rainy seasons at Sotuba Agricultural Research Station in Mali. The experimental design used was a Split-split-plot with three replications and three factors including two plant densities (D1: 26666 plants ha-1 and D2: 53333 plants ha-1) as the main plot, three nitrogen levels (0, 41 and 82 kg N ha-1) as the subplot and varieties as the sub-subplot. Measurements focused on growth and physiological parameters, grain yield and yield components. The results showed that sorghum grain yield was positively correlated with straw yield, leaf area index, grain number per panicle, panicle number per m2, panicle weight per m2 in N0D1 (0 kg N ha-1 and 26666 plants ha-1) and N2D2 (178 kg N ha-1 and 53 333 plants ha-1). Furthermore, straw yield was positively correlated with the leaf area index and panicle weight m-² in N0D1 and in N2D2. Analysis of variance showed that plant density, nitrogen and variety effect on grain and straw yields were significant. The interaction density x nitrogen x variety effect was also significant on grain and straw yields. Grain and straw yields were high in the N2D2 treatment for eight varieties compared to the N0D1 treatment. GRINKAN, C2_075-15 and C2_007-03 varieties had the highest grain and straw yields in N0D1. These caudatum-type varieties could be recommended in less intensive sorghum production areas in Mali. The FADDA variety produced high grain and straw yields in N2D2. Guinea-type hybrid FADDA may be recommended for grain and straw production in intensive sorghum production areas in Mali.

SUMMARYFertilization of rubber plantations has been poorly documented despite the huge economic and ecological impact of this tropical perennial crop, especially in Southeast Asia. The main objective of this paper is to provide information on the fertilization practices of rubber smallholders in Thailand and to investigate the drivers of these practices. Data were sourced from individual interviews conducted with 414 rubber smallholders. The results showed that 99.4% of the mature rubber plantations were fertilized with either chemical or organic fertilizers, or both. The average dose of chemical fertilizers was 105/53/92 kg ha−1 of N/P/K that is consistent with the national recommendations. We estimated that almost two-thirds of the plantations had intensive or very intensive fertilization practices. Geographical location, especially the distinction between historical and new rubber-producing areas, appeared as a major factor explaining differences in fertilization practices. Several drivers commonly found in the literature did not affect the fertilization practices of the rubber farmers, highlighting some specificity of perennial crops and a context where access to fertilizer was not an issue. The high economic and environmental costs of intensive fertilization practices, while their benefit to the yield of rubber plantations continues to be debated, show the need to conduct research on sustainable fertilization practices in rubber smallholdings.

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

In the central highlands of Madagascar, blast, a serious fungal disease of rice caused by Magnaporthe oryzae, was shown to be less severe in conservation agriculture (CA) than in conventional tillage (CT) cropping systems. To assess the effects of CA cropping systems on rice susceptibility to blast and to understand the mechanisms involved, an experiment was conducted over three growing seasons in two sites (at high and mid-altitude). Two fertilization treatments, one with mineral nitrogen (N) fertilizer, and one without, were studied in interaction with two different cropping systems (CA/CT) and two rice varieties that differ in their susceptibility to blast. The performances of the two cropping systems were assessed, and results showed that yields were no higher in the CA or were lower than in CT cropping systems. The effects of the treatments on upland rice crop growth were measured by leaf N content as an indicator of N crop status, and leaf area index (LAI) as an indicator of canopy density. In all years at both sites, leaf N content during early growth stages was higher in the CT than in the CA cropping system. The LAI was lower in the CA than in the CT cropping system at the high altitude site in all three years, and in two out of three seasons at the middle altitude site. Overall, when the level of blast was high, blast was less severe in the CA cropping system and with no N fertilizer. Leaf N content and LAI were used as intermediate explanatory variables in the statistical analyses, and one or the other or both always masked the effect of the cropping system or of N fertilization. Our results show that leaf N content during early growth stages masks the effect of the cropping system on leaf blast severity. When the LAI is strongly affected by the cropping system, it also masks the effect of the cropping system on the severity of leaf and panicle blast. Very often both variables masked the effects of the cropping system and of N fertilization. These findings should help improve disease management by modifying fertilization practices and crop nutrition in conservation agriculture cropping systems.

Made available in DSpace on 2018-12-11T16:52:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-01-01 Functional specialization of fine roots was found for Eucalyptus grandis trees at harvesting age (6 years) on tropical soils. Aiming to elucidate whether functional specialization is a ubiquitous feature of eucalypts, we focused on its changes with ontogeny, tree nutrient status and soil depth. We studied the potential uptake of N, K and Ca by 2-year-old E. grandis trees, as a function of soil depth and NPK fertilization. We injected NO−3-15N, Rb+ (K+ analogue) and Sr2+ (Ca2+ analogue) tracers simultaneously in a solution at depths of 10, 50, 150 and 300 cm in a sandy Ferralsol soil. A complete randomized block design was set up with three replicates of paired trees per injection depth, in fertilized and non-fertilized plots. Recently expanded leaves were sampled at 70 days after tracer injection. Determination of foliar Rb, Sr concentrations and x(15N) allowed estimating the relative uptake potential (RUP) and the specific RUP (SRUP), defined as the ratio between RUP and fine root length density (RLD) in the corresponding soil layer. Various root traits were measured at each depth. Foliar N and K concentrations were higher in fertilized than in non-fertilized trees. The RUP of NO3 –-15N decreased sharply with soil depth and the highest values of the SRUP of NO3 –-15N were found at a depth of 50 cm. The RUP of Rb+ and Sr2+ did not change with soil depth, whilst the SRUP of Rb+ and Sr2+ were higher at the depth of 300 cm than in the topsoil, concomitant with an increase in root diameter and a decrease in root tissue density with depth. The SRUP of Rb+ and Sr2+ at a depth of 300 cm were on average 136 and 61% higher for fertilized trees than for non-fertilized trees, respectively. Fine roots of young E. grandis trees showed contrasting potential uptake rates with soil depth depending on the nutrient. Fertilization increased the uptake rate of Rb+ and Sr2+ by unit of root length in deep soil layers. Functional specialization of fine roots for cations of low mobility depending on depth previously shown at harvesting age also occurs in young E. grandis plantations and increases with fertilization application. This mechanism helps explaining very low amounts of cations lost by leaching in Eucalyptus plantations established in deep tropical soils, even in highly fertilized stands. USP-ESALQ CIRAD UMR Eco&Sols Eco&Sols Univ Montpellier CIRAD INRA IRD, Montpellier SupAgro UNESP Departamento de Solos e Recursos Ambientais Universidade Estadual Paulista ‘Júlio de Mesquita Filho’ USP-CENA INRA CIRAD IRD Montpellier SupAgro University of Montpellier UMR Eco&Sols UNESP Departamento de Solos e Recursos Ambientais Universidade Estadual Paulista ‘Júlio de Mesquita Filho’

Accurate estimations of ammonia (NH 3) emissions due to nitrogen (N) fertilization are required to identify efficient mitigation techniques and improve agricultural practices. Process-based models such as Volt'Air can be used for this purpose because they incorporate the effects of several key factors influencing NH 3 volatilization at fine spatio-temporal resolutions. However, these models require a large number of input variables and their implementation on a large scale requires long computation times that may restrict their use by public en- vironmental agencies. In this study, we assess the capabilities of various types of meta-models to emulate the complex process-based Volt'Air for estimating NH3 emission rates from N fertilizer and manure applications. Meta-models were developed for three types of fertilizer (N solution, cattle farmyard manure, and pig slurry) for four major agricultural French regions (Bretagne, Champagne-Ardenne, Ile-de-France, and Rhône-Alpes) and at the national (France) scale. The meta-models were developed from 106,092 NH3 emissions simulated by Volt'Air in France. Their performances were evaluated by cross-validation, and the meta-models providing the best approximation of the original model were selected. The results showed that random forest and ordinary linear regression models were more accurate than generalized additive models, partial least squares regressions, and least absolute shrinkage and selection operator regressions. Better approximations of Volt'Air simulations were obtained for cattle farmyard manure (3% < relative root mean square error of prediction (RRMSEP) < 8%) than for pig slurry (17% < RRMSEP < 19%) and N solution (21% < RRMSEP < 40%). The selected meta- models included between 6 and 15 input variables related to weather conditions, soil properties and cultural practices. Because of their simplicity and their short computation time, our meta-models offer a promising alternative to process-based models for NH3 emission inventories at both regional and national scales. Our approach could be implemented to emulate other process-based models in other countries.

L’impact du changement climatique sur la qualité et la pollution des milieux est souvent négligé par rapport à d’autres impacts plus médiatisés (e.g. événements climatiques et hydrologiques extrêmes, santé, trait de côtes, disponibilité des ressources en eau…). Les eaux et l’air de Nouvelle-Aquitaine, et à moindre mesure les sols, déjà significativement pollués, subiront pourtant plusieurs détériorations significatives, qui sont présentées et discutées dans ce chapitre. Certains de ces effets sont déjà visibles et vont s’aggraver dans le contexte climatique prévu. Il s’agit principalement, pour l’eau douce superficielle, de l’augmentation de la température, de la diminution des débits des cours d’eau, de l’évolution des espèces aquatiques et du développement accru de micro-organismes de type cyanophycées, ou pour l’air, de l’augmentation de l’index pollinique et des effets néfastes croissants sur la santé publique. Bien que non réellement démontrés in situ en région, d’autres effets sont fortement prévisibles, comme la diminution de la matière organique des sols et de leur fertilité, l’augmentation des teneurs en polluants dans toutes les masses d’eau, l’augmentation de l’écotoxicité des eaux de surface et l’augmentation de la concentration en ozone dans l’air et autres composés organiques volatils et aérosols. Les travaux de recherche et études sur cette problématique au niveau régional, comme national, sont rares et/ou peu publiés. Une recherche appliquée au « terrain » de la Nouvelle-Aquitaine, sur des sites d’observation scientifiquement et économiquement sélectionnés, est indispensable pour évaluer plus clairement ces impacts du changement climatique, mais également les adaptations à préconiser et les enjeux environnementaux et socio-économiques qui en découleront.

Humanity faces the challenges of urgently decreasing the environmental impact of agriculture, shifting diets and increasing food production. Oil palm is a tropical perennial crop emblematic of these challenges. While its cultivation can be associated with environmental impacts, oil palm can produce 3 to 7 t of edible oil ha-1 in optimal conditions, which is 7 to 10 fold higher than in annual oil crops. In this context, improving palm oil production sustainability is crucial for both reducing negative environmental impacts and ensuring food security. Application of synthetic nitrogen (N) fertilisers was identified as a major source of environmental impacts associated with the cultivation of oil palm. Life cycle assessments of palm oil have already been performed to help quantify impacts and identify potential improvements of management practices. However, the only available emission models to estimate N losses to environment are generally valid for annual crops and temperate climate conditions. The use of such general models in life cycle assessment may lead to very uncertain results or to low sensitivity of assessments to management practices. The overall objective of this research work was to help identify management practices to reduce N losses in the environment. The core of the work was hence to develop a model that estimates all N losses in oil palm plantations, while being sensitive to management practices. The study focused on N fluxes in industrial oil palm plantations on mineral soils. We performed four steps in order to complete the objectives of this research work. First, we conducted a literature review of all the existing knowledge about N fluxes and losses in plantations. Second, we compared 11 existing models that may be used to predict N losses in plantations. Third, we performed an in-depth Morris’s sensitivity analysis of one of the models, the APSIM-Oil palm process-based model. Fourth, we used all the information identified in the previous chapters, together with expert knowledge, to build IN-Palm, an agri-environmental indicator for N losses in oil palm plantations. We used the INDIGO® method and the fuzzy decision tree modelling approach to develop IN-Palm, and we validated this indicator using a field dataset of N leaching from a plantation in Sumatra, Indonesia. Our literature review and model comparison showed that oil palm peculiarities may impact significantly N dynamics and losses. We identified research gaps and uncertainties about N losses, their drivers and the modelling of oil palm peculiarities. We identified the main drivers of N losses and yield in the APSIM-Oil palm processbased model. We built IN-Palm, which uses 21 readily available input variables to estimate each N loss pathway. IN-Palm predictions of N leaching were acceptable, and IN-Palm has shown efficient to help testing management changes. This research constitutes a comprehensive synthesis of the available knowledge and models for N fluxes and losses in oil palm plantations. One of the main results is a novel agri-environmental indicator, IN-Palm, operationally-oriented, sensitive to local practices and environmental conditions, as well as potentially useable as an emission model for holistic approaches such as life cycle assessment. The INDIGO® method and fuzzy decision tree modelling approach were shown to be very well adapted for building agri-environmental indicators in contexts of knowledge scarcity. This indicator can be a useful base for further research about using agrienvironmental indicators to reduce uncertainty in life cycle assessment, and for future adaptations for other tropical perennial crops.; L’humanité fait face aux défis urgents de réduire l’impact environnemental de l’agriculture, de changer les régimes alimentaires et d’accroître la production alimentaire. Le palmier à huile est une plante pérenne tropicale emblématique de ces défis. Alors que sa culture peut être à l’origine d’impacts environnementaux, le palmier à huile peut produire, en conditions optimales, 7 à 10 fois plus d’huile alimentaire que les cultures oléagineuses annuelles. Dans ce contexte, améliorer la durabilité de la production d’huile de palme est crucial, tant pour réduire les impacts environnementaux négatifs que pour garantir la sécurité alimentaire. L’application de fertilisants azotés (N) a été identifiée comme une source majeure d’impacts environnementaux dus à la culture du palmier. Des analyses de cycle de vie de l’huile de palme ont été réalisées pour quantifier les impacts et identifier des améliorations de pratiques agricoles. Cependant, les seuls modèles d’émissions disponibles pour estimer les pertes de N dans l’environnement sont généralement valides pour les cultures annuelles et en climat tempéré. L’utilisation de tels modèles dans l’analyse de cycle de vie peut mener à des résultats très incertains ou à une faible sensibilité aux pratiques. L’objectif global de ce travail de recherche était d’aider à l’identification de pratiques pour réduire les pertes de N dans l’environnement. Le cœur du travail était le développement d’un modèle estimant toutes les pertes de N dans les plantations, tout en étant sensible aux pratiques. L’étude s’est concentrée sur les flux de N dans les plantations de palmiers sur sols minéraux. Nous avons réalisé quatre étapes pour mener à bien cette recherche. Premièrement, nous avons mené une revue de littérature de tout le savoir existant concernant les flux et pertes de N dans les plantations. Deuxièmement, nous avons comparé 11 modèles existants, pouvant être utilisés pour prédire les pertes de N dans les plantations. Troisièmement, nous avons réalisé une analyse de sensibilité de Morris approfondie du modèle mécaniste APSIM-Oil palm. Quatrièmement, nous avons construit IN-Palm, un indicateur agri-environnemental pour les pertes de N dans les plantations. Nous avons utilisé la méthode INDIGO® et l’approche de modélisation par arbres de décisions flous pour développer IN-Palm, et nous avons validé cet indicateur en utilisant des mesures de lixiviation de N d’une plantation à Sumatra, Indonésie. Notre revue de littérature et notre comparaison de modèles ont montré que les particularités du palmier à huile peuvent affecter significativement les dynamiques et pertes de N. Nous avons identifié des manques de recherche et des incertitudes sur les pertes de N, leurs déterminants et la modélisation des particularités du palmier. Nous avons identifié les déterminants des pertes de N et du rendement dans le modèle mécaniste APSIM-Oil palm. Nous avons développé IN-Palm, qui utilise 21 variables d’entré facilement accessibles pour estimer chaque voie de perte de N. Les prédictions de lixiviation de N par IN-Palm étaient acceptables, et IN-Palm s’est montré efficace pour tester des changements de pratiques agricoles. Cette recherche constitue une synthèse exhaustive des connaissances et modèles disponibles pour les flux et pertes de N dans les plantations. L’un des principaux résultats est un nouvel indicateur agri-environnemental, IN-Palm, sensible aux pratiques et conditions locales, de même qu’utilisable en tant que modèle d’émission dans des approches holistiques. Cet indicateur peut être une base utile pour de futures recherches sur l’utilisation d’indicateurs agri-environnementaux pour réduire l’incertitude des analyses cycle de vie, et pour de futures adaptations à d’autres plantes pérennes tropicales.

International audience; Global warming is a major threat to agriculture worldwide. Between 2008 and 2013, some coffee producing countries in South and Central America suffered from severe epidemics of coffee leaf rust (CLR), resulting in high economic losses with social implications for coffee growers. The climatic events not only favored the development of the pathogen but also affected the physiological status of the coffee plant. The main objectives of the study were to evaluate how the physiological status of the coffee plant modified by different environmental conditions impact on the pathogenesis of CLR and to identify indicators of the physiological status able to predict rust incidence. Three rust susceptible genotypes (one inbred line and two hybrids) were grown in controlled conditions with a combination of thermal regime (TR), nitrogen and light intensity close to the field situation before being inoculated with the rust fungus Hemileia vastatrix. It has been demonstrated that a TR of 27-22°C resulted in 2000 times higher sporulation than with a TR of 23–18°C. It has been also shown that high light intensity combined with low nitrogen fertilization modified the CLR pathogenesis resulting in huge sporulation. CLR sporulation was significantly lower in the F1 hybrids than in the inbred line. The hybrid vigor may have reduced disease incidence. Among the many parameters studied, parameters related to photosystem II and photosynthetic electron transport chain components appeared as indicators of the physiological status of the coffee plant able to predict rust sporulation intensity. Taken together, these results show that CLR sporulation not only depends on the TR but also on the physiological status of the coffee plant, which itself depends on agronomic conditions. Our work suggests that vigorous varieties combined with a shaded system and appropriate nitrogen fertilization should be part of an agro-ecological approach to disease control.