Search

International audience; The growing world population and global increases in the standard of living both result in an increasing demand for food, feed and other plant- derived products. In the coming years, plant- based research will be among the major drivers ensuring food security and the expansion of the bio- based economy. Crop productivity is determined by several factors, including the available physical and agricultural resources, crop management, and the resource use efficiency, quality and intrinsic yield potential of the chosen crop. This review focuses on intrinsic yield potential, since understanding its determinants and their biological basis will allow to maximize the plant's potential in food and energy production. Yield potential is determined by a variety of complex traits that integrate strictly regulated processes and their underlying gene regulatory networks. Due to this inherent complexity, numerous potential targets have been identified that could be exploited to increase crop yield. These encompass diverse metabolic and physical processes at the cellular, organ and canopy level. We present an overview of some of the distinct biological processes considered to be crucial for yield determination that could further be exploited to improve future crop productivity.

Climate change will affect the yield potential of crops in different ways in different regions of Europe. In much of Europe there will be increased yield potential for crops. However, in southern and eastern regions there will be a strong decline in yield potential. To maximise yield potential and mitigate against yield declines both irrigating and maintaining nitrogen input is important. There are also some positive benefits of cultivar selection and rotation, but these are less significant. To mitigate against the impact of climate change the main policy recommendation is to identify and promote sustainable sources of both water and nitrogen for crop production for future cropping systems.

National audience

Ce numéro comprend les articles correspondant aux présentations du Colloque Casdar 2018; Dans un objectif d’atténuation du réchauffement climatique, la mise en place de systèmes de cultureplus autonomes vis-à-vis des engrais minéraux devient incontournable pour réduire les émissions degaz à effet de serre (GES) tout en diminuant le coût de la fertilisation. L’insertion de légumineuses dansces systèmes semble être un levier prometteur pour y parvenir. Les économies d’azote permises pardifférents modes d’introduction de légumineuses et leur impact sur les émissions de GES ont étéestimés et évalués en quantifiant au préalable les flux d’azote dans les systèmes avec ou sanslégumineuses à partir de données issues de dispositifs expérimentaux préexistants, disponibles dans labibliographie ou acquises dans de nouveaux essais. L’introduction de légumineuses présenterégulièrement un impact positif sur la réduction de l’emploi des engrais azotés. Le risqued’augmentation de la lixiviation du nitrate dépend de leur mode d’introduction et de leur place dans lesrotations. Enfin, les émissions mesurées en cultures principales de légumineuses sont généralementtrès significativement réduites en comparaison des cultures fertilisées, cependant la dégradation desrésidus des légumineuses (en culture ou en couverts) peut générer des émissions de N2O corrélées àleur impact sur les flux d’azote, variable selon les conditions pédoclimatiques. Ces résultats devraientpermettre d’élaborer des recommandations pour mieux prendre en compte les légumineuses dans laconception de systèmes de culture plus autonomes vis-à-vis des engrais azotés de synthèse et moinsémetteurs de N2O.

Dans un objectif d’atténuation du réchauffement climatique, la mise en place de systèmes de culture plus autonomes vis-à-vis des engrais minéraux devient incontournable pour réduire les émissions de gaz à effet de serre (GES) tout en diminuant le coût de la fertilisation. L’insertion de légumineuses dans ces systèmes semble être un levier prometteur pour y parvenir. Les économies d’azote permises par différents modes d’introduction de légumineuses et leur impact sur les émissions de GES ont été estimés et évalués en quantifiant au préalable les flux d’azote dans les systèmes avec ou sans légumineuses à partir de données issues de dispositifs expérimentaux préexistants, disponibles dans la bibliographie ou acquises dans de nouveaux essais. L’introduction de légumineuses présente régulièrement un impact positif sur la réduction de l’emploi des engrais azotés. Le risque d’augmentation de la lixiviation du nitrate dépend de leur mode d’introduction et de leur place dans les rotations. Enfin, les émissions mesurées en cultures principales de légumineuses sont généralement très significativement réduites en comparaison des cultures fertilisées, cependant la dégradation des résidus des légumineuses (en culture ou en couverts) peut générer des émissions de N2O corrélées à leur impact sur les flux d’azote, variable selon les conditions pédoclimatiques. Ces résultats devraient permettre d’élaborer des recommandations pour mieux prendre en compte les légumineuses dans la conception de systèmes de culture plus autonomes vis-à-vis des engrais azotés de synthèse et moins émetteurs de N2O., Promoting less dependent cropping systems on mineral fertilizers is necessary to reduce greenhouse gas emissions in order to mitigate their effects on global warming while reducing the cost of fertilization. The insertion of legumes into these systems seems to be a promising mean for achieving this objective. The nitrogen savings allowed by different ways of legumes insertion and their impact on greenhouse gas emissions were estimated and evaluated after quantifying nitrogen fluxes in cropping-systems with and without legumes using data from pre-existing experimental devices, available in the literature or collected in new trials. The introduction of legumes has often a positive impact on reducing the use of nitrogen fertilizers. The risk to increase nitrate leaching depends on the mode of introduction of legumes and their position in crops successions. Finally, measured emissions during legumes main crops are generally very significantly reduced compared to fertilized crops; however the degradation of legumes residues (grown as main crops or cover crops) can generate N2O emissions correlated with their impact on nitrogen fluxes depending on climatic conditions. These results should enable to deliver advices to better take into account legumes in designing cropping systems less dependent on synthetic nitrogen fertilizers and emitting less N2O.

809 ISBN: 978-0-85310-446-9Abstract 809ISBN: 978-0-85310-446-9; Optimising bread-wheat Nitrogen Use Efficiency (NUE) in most Western European countries pursues three objectives: reaching a high yield, obtaining enough grain protein concentration to satisfy market requirements and preventing nitrogen losses into the environment. One of the ways in which French farmers can improve their NUE is to grow varieties with improved NUE performance – if genetic progress is sufficiently marked and if farmers have relevant NUE characterisation information on the varieties that are available. This paper describes the recent progress being made in France to characterise the NUE of different genotypes, along the continuum from breeding programs to practical information provided to farmers, including changes in the variety registration process. It will demonstrate that we have built a strong research continuum from breeding program to ‘farmer’s real life’, to better characterise the impact of bread-wheat variety on NUE. Along with other projects aimed at finding new traits and new genomic sequences related to a better NUE and building new tools to phenotype crops more rapidly, we think that the results will significantly contribute to new agricultural systems combining high production performance and rational use of inputs.

National audience

Book of abstracts, ISBN: 978-3-900932-48-0 Abstract p. 73Book of abstracts, ISBN: 978-3-900932-48-0Abstract p. 73; Improving nitrogen use efficiency in wheat by genome wide and candidate genes targeted association studies. 13. IWGS

Proceedings: Book of abstracts, ISBN: 978-3-900932-48-0 Poster 297, p.478Proceedings: Book of abstracts, ISBN: 978-3-900932-48-0Poster 297, p.478; Assessing nitrogen deficiency tolerance of wheat varieties in registration process and breeding programs in France. 13. IWGS

National audience; Depuis plus de 40 ans, le pilotage de la fertilisation azotée des céréales est basé sur le calcul d’une dose totale prévisionnelle par la méthode du bilan, mais sa mise en œuvre est difficile. Un travail de thèse, co-financé et co-encadré par Arvalis et l’INRA, a permis de concevoir une nouvelle approche de la fertilisation azotée du blé.

Les pertes de nitrate par lixiviation sur la période hivernale qui suit la récolte d’une culture ont été largement étudiées dans les années 1990 et 2000 dans différents dispositifs en France et à l’étranger. Cette étude quantifie les stocks d’azote minéral du sol et la lixiviation du nitrate lors du deuxième automne-hiver après la récolte d’une culture de pois, de colza, ou de blé. La lixiviation pluri-annuelle pour des successions céréalières comprenant du pois ou du colza a également été analysée à partir de simulations basées sur des mesures de stock d’azote en entrée hiver. Pendant l’automne qui suit un pois ou un colza, la lixiviation est augmentée, par rapport à un blé. Au contraire, pendant l’automne qui suit un blé de pois ou un blé de colza, la lixiviation de nitrate est réduite, par rapport à un blé de blé, grâce à une meilleure utilisation de l’azote disponible par le second blé. Grâce à cette compensation inter-annuelle, la diversification des rotations céréalières, par l’introduction de pois ou de colza, n’augmente pas les risques de lixiviation par rapport à des successions à base de céréales. En outre, la culture de pois réduit les pertes ponctuelles d’azote liées à l’usage d’engrais (sur la culture elle-même et la culture suivante sur laquelle la fertilisation est réduite), celles liées à la volatilisation de composés azotés et à leur redéposition partielle, et les émissions de gaz à effet de serre comme le protoxyde d’azote, conduisant à un bilan azoté globalement positif pour les successions intégrant cette légumineuse., During the 90s and 2000s, the nitrate losses through leaching during the winter period following a given crop have been widely studied in France and abroad. This study quantifies soil mineral nitrogen contents and nitrate leaching during the second autumn-winter period after harvest of a pea, a rapeseed or a wheat. Nitrate leaching during successive years for cereal-based sequences including pea or rapeseed has also been studied from simulations based on measurements of soil nitrogen content at the beginning of winter in various crop sequences. During the autumn following a pea or an rapeseed, nitrate leaching is increased, compared to a wheat crop. On the opposite, during the autumn following a pea-wheat sequence or an rapeseed-wheat sequence, nitrate leaching is reduced, compared to a wheat-wheat sequence, due to a higher use efficiency of the available soil inorganic N by the 2nd wheat crop. Thanks to this inter-annual compensation, the diversification of cereal-based crop sequences by the introduction of a pea or a rapeseed does not increase the risk of nitrate leaching compared to cereal-based crop sequences. In addition, a pea crop allows to decrease N losses linked to the use of fertilizers (both on the crop itself and on the following crop, where N fertilisation is lowered), and thus N losses linked to ammonium volatilization and its partial redeposition, and greenhouse gas emissions such as nitrogen protoxide.

National audience

International audience; Agricultural management practices including soil tillage exert strong control on soil organic matter (SOM) turnover and its interactions with global C cycle through different mechanisms. One control mechanism is the priming effect (PE) which consists in stimulating SOM mineralization with the addition of fresh, energetic plant material. In this study, we quantified C mineralization and PE in soils sampled in two contrasted long-term (40 years) tillage treatments which deeply modified soil properties (e.g. organic C concentration, microbial biomass, pH). We hypothesized that soil tillage might affect these processes through changes in C addition rates, nutrient availability, and long-term variations in SOM content and microbial communities. We investigated the relationship between PE intensity, tillage and nutrients availability in soil samples taken in no till (NT) and full inversion tillage (FIT) in two layers (0-5 and 15-20 cm). Soils were incubated with or without addition of 13C labeled cellulose and mineral nutrients. Potential C mineralization and primed C were measured during 262 days. Unlabeled soil microbial biomass C was determined at the end of the experiment to separate apparent and real priming effect. Basal cumulative C mineralization in the control soil ranged from 363 to1490 mg kg-1 35 soil at day 262. It was strongly correlated with soil organic carbon (SOC) concentration. Specific mineralization rates were 44.8 and 68.8 g kg-1 SOC in the 0-5 cm layer for the FIT and NT treatments, respectively and were strongly linked with the particulate organic matter content (r = 0.99***). These results suggest that SOC was more active in the upper layer of the NT treatment due to the high concentration of readily-decomposable, particulate organic matter. The cellulose was entirely metabolized after 60 days and its kinetics of mineralization was affected neither by tillage, depth nor nutrients. The percentage of cellulose C released as CO2 represented 55-61% of the added cellulose-C at day 262. A positive PE was found in all treatments and its kinetics was parallel to that of cellulose mineralization. The cumulative PE significantly varied with nutrients level but not tillage, ranging from 73 to 78 mg kg-1 under high nutrients level and from 116 to 136 mg kg-1 in low nutrients level. No significant differences were found in unlabeled microbial biomass C between control and amended soil, suggesting no apparent priming effect. We conclude that the priming was mainly controlled by nutrient availability but not tillage, in spite of strong tillage-induced changes in SOC concentration and microbial biomass. Since PE is known to depend on C addition rate, tillage is expected to affect in situ PE through variations in the ratio of fresh carbon to nutrient concentration along the soil profile.

National audience; Human activities are currently considered to emit 5.3 Tg N-N2O per year, mainly from agriculture that accounts for around two-thirds of these emissions (UNEP, 2013). The atmospheric gas N2O is involved both in the greenhouse effect with a contribution on a molar basis of around 300 in relation to CO2 (Rodhe, 1990) and in ozone depletion (Ravishankara et al., 2009). The development of new approaches to increase agricultural efficiency and potential mitigation pathways are required in particular in the context of the continuing population growth. In soils, N2O is mainly produced through the microbial processes of denitrification and of nitrification. The last step of the denitrification process (N2O → N2) is currently the only known pathway for the terrestrial removal of N2O. N2O reduction is catalysed by the N2O reductase enzyme encoded by the nosZ gene (Viebrock and Zumft, 1988). The efficiency of soils to reduce N2O to N2 is highly variable. Soils with low N2O reduction potential have also been observed to emit high levels of N2O on a field scale (Hénault et al. 2005). We developed strategies to mitigate N2O emissions from agricultural soils based on the stimulation of the microbial process of reduction of N2O to N2. We therefore developed two different approaches for promoting the biological reduction of N2O in soils. The first one, is based on the results previously obtained by Sameshima-Saito et al., 2006 who had observed that Soybean roots nodulated with Bradyrhizobium japonicum USDA110, carrying the nosZ gene, were able to remove low concentrations of N2O. We studied the consumption of N2O by strains of Bradyrhizobium japonicum (USDA110 and MSDJ G49) on inoculated soybean plants cultivated in soil pots during a greenhouse experiment. During this experiment, we switched from a system acting as an N2O source (soil + soybean inoculated with a nosZ gene depleted strain) to a system acting as an N2O sink (soil + soybean inoculated with strains carrying the nosZ gene). Calculations using the obtained quantitative results clearly suggest an environmental benefit of nosZ+-nodulated leguminous on the field scale, with an assessed abatement of field emission of 60 % during the investigated period, (Hénault and Revellin, 2011). The principle of the second approach is to understand the physico-chemical determinism of the N2O reduction in soils and then to manage these conditions to promote N2O reduction. Around 100 soil samples of the RMQS, the French Soil Quality Monitoring Network, were sampled and analysed for determining their physico-chemical conditions associated to their capacity to reduce N2O into N2. Soil pH was observed as an essential determinant of the capacity of soil to reduce N2O, this capacity increasing with soil pH. A field experiment was then set up on an acidic soil, receiving calcareous amendment. We observed a pH increase followed by an increase of the soil capacity to reduce N2O and at the same time a reduction of soil N2O emissions at the field scale, with an observed abatement of field emission up to 50 % during the investigated period. The management of the biological reduction of N2O into N2 appears possible both by biological (inoculation of leguminous crops by strains having a functional nosZ gene) or physico-chemical (pH management) actions. A stimulation of the N2O reduction function in soil allows mitigating soil N2O emissions. These both approaches are very interesting because they don’t create any transfer of nitrogen pollution in environment and because they do not compromise agricultural production of proteins. Their economic aspects are currently investigated. These studies are supported by the ADEME (SOLGES project), the Conseil Regional Centre Val de Loire (PUIGES project) and the Labex Voltaire (ANR-10-LaBX100-01).

Effets du travail du sol sur les cycles biogéochimiques de l'azote et du carbone : de la compréhension des mécanismes aux conséquences pour la gestion des pratiques agricoles