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HAL Id : hal-02471202, version 1 https://cel.archives-ouvertes.fr/METIS_UMR7619/hal-02471202 HAL Id : hal-02471202, version 1 https://cel.archives-ouvertes.fr/METIS_UMR7619/hal-02471202; National audience

International audience; Introduction Agriculture is the main source of terrestrial N2O emissions, a potent greenhouse gas and the main cause of ozone depletion ((Hu et al., 2015). The reduction of N2O into N2 by microorganisms carrying the nitrous oxide reductase gene (nosZ) is the only known biological process eliminating this greenhouse gas. Recent studies showed that a previously unknown clade of N2O-reducers (nosZII) was related to the potential capacity of the soil to act as a N2O sink (see Hallin et al., 2017 and references therein). However little is known about how this group responds to different agricultural practices. Here, we investigated how N2O-producers and N2O-reducers were affected by agricultural practices across a range of cropping systems in order to evaluate the consequences for N2O emissions Materials and Methods Soil samples were collected in spring 2014 from 4 experimental sites in France, which undergo a large range of agricultural practices. The abundance of both ammonia oxidizers and denitrifiers was quantified by real-time qPCR, and the diversity of both nosZ clades was determined by 454 pyrosequencing. Denitrification and nitrification potential activities as well as in situ N2O emissions were also assessed. The physical and chemical soil characteristics were measured for all samples (INRA Laboratory of Soil Analysis, Arras, France) Results and Discussion Overall, greatest differences in microbial activity, diversity and abundance were observed between sites rather than between agricultural practices at each site. To better understand the contribution of abiotic and biotic factors to the in situ N2O emissions, we subdivided more than 59.000 field measurements into fractions from low to high rates. We found that the low N2O emission rates were mainly explained by variation in soil properties (up to 59%), while the high rates were explained by variation in abundance and diversity of microbial communities (up to 68%). Notably, the diversity of the nosZII clade but not of the nosZI clade was important to explain the variation of in situ N2O emissions fractions (Figure 1). I. Landscape Functioning – Microbes in the Landscape 61 Figure 1. Variation partitioning of in situ N2O emissions. (a) Variance of in situ N2O emissions was partitioned into soil physicochemical properties (S), abundance of N2O-producers and abundance of N2O-reducers (A), diversity of N2O-reducers (D), and by combinations of predictors. Geometric areas are proportional to the respective percentages of explained variation. The edges of the triangles depict the variation explained by each factor alone, while percentages of variation explained by interactions of two or all factors are indicated on the sides and in the middle of the triangles, respectively. (b) Variance partitioning of basal in situ N2O emissions (25% fraction), (c) variance partitioning of median in situ N2O emissions (50% fraction), (d), (e), (f) and (g) correspond to the variation partitioning of high N2O emissions of 75%, 90%, 95% and 99%, respectively. All numbers represent percentages. Only variance fractions ≥ 0.05% are shown. Conclusions Our results highlight the higher sensitivity of the nosZII- than nosZI-community to environmental factors. However, despite significant variations in the nosZII community across the sites examined, only a few of the studied agricultural practices resulted in shifts on the diversity of this community. Nevertheless, comparison of all plots across the different sites showed for the first time that a higher diversity of the nosZII community was concomitant with lower in situ fluxes. Moreover, our work also indicates that microbial communities were more important for explaining variations in high than in low N2O emissions. This work emphasizes the consideration that the N2O-reducing community should have when addressing process-related N2O fluxes, particularly in studies aiming at mitigating emissions.

A multi-model assessment of C cycling and soil C sequestration in grasslands and croplands. 6th International Symposium on Soil Organic Matter ; Harpenden (Royaume Uni)

EA BIOmEEABIOmE; Promoting diverse and functional biological communities is an important objective of agroecology, with increasing attention given to the important role of soil biodiversity. In an experimental study conducted in actual field conditions, we followed over four years the dynamic of soil organisms from microorganisms to micro-, meso- and macro-fauna in a cropping system submitted to four different treatments that varied in tillage, residue management and N fertilization rate. Differentiation in taxonomic diversity, in the abundance and diversity of the multiple trophic groups and in food-web structure was evaluated. A co-statis analysis was used to investigate the joint dynamics of food-web structure and soil functions linked to C and N dynamics. Our study demonstrated a delayed but effective differentiation in soil biota diversity following implementation of the agricultural practices. Soil biodiversity varied throughout time with some groups responding more readily than others. While tillage appeared a main factor of influence, surprisingly little impact of residue management and nitrogen fertilization could be observed. Significant interactive effect of year and treatment was found on the mean trophic level and the bacterial to fungal path ratio, but not on the number of trophic groups and Shannon's link diversity. Finally, co-statis analysis revealed significant differences in co-dynamics between food-web structure and soil functions over four years, mainly drove by conventionally tilled vs reduced tilled treatments. Through its multi-taxonomic approach, the present study increases our understanding of the dynamic of soil communities in agricultural cropping systems and helps identify possible consequences for soil functioning.

BAP GEAPSI BAP GEAPSIBAPGEAPSI; Freezing is a major environmental limitation to crop productivity for a number of species including legumes. In the context of global climate change, winter crops will experiment milder autumn temperatures that could be detrimental to the achievement of cold acclimation, which is the ability for plants to increase their level of frost tolerance (FT) in response to low but non-freezing temperatures. For the pea crop, a modelling approach has shown that climate warming will increase the occurrence of freezing damage events, even if these latter will be less severe (Castel et al., 2014). Thus, breeding for frost tolerant winter peas requires not only to improve their FT threshold, but also to raise their cold acclimation rate. In order to evaluate the genetic variability of both traits, we are adjusting a protocol in controlled conditions, which provides an indirect evaluation of FT by the measurement of tissues’electrolyte leakage (EL). Pea stem samples have been collected after variable durations of cold acclimation at 4°C day/2°C night in a climatic chamber. They have been then progressively cooled at 2°C h-1 in a programmable temperature-test chamber to reach test temperatures ranging from +4°C to -36°C. After 14 days of cold acclimation, EL evaluation enabled the same ranking of genotypes according to their FT threshold as obtained in the Chaux-des-Prés field platform. Improvements of the protocol are however still needed to use it as a routine ranking test.

CT3 ; EnjS4 ; Département EA; Mitigation of N2O emissions in agroecosystems: the role of N2O-reducers. 16. International Symposium on Microbial Ecology - ISME16

cited By 3; International audience; This book contains 28 chapters with emphasis on the interactive nature of the relationships between the soil, plant, animal and environmental components of grassland systems, both natural and managed. It analyses the present knowledge and the future trends of research for combining the classical view of grasslands, as a resource for secure feeding of an increasing human population, with the more recent perspective of the contribution of grasslands to the mitigation of environmental impacts and biodiversity erosion as consequences of human society activities. The chapters are organized within five sections dealing with the different functions and the main ecosystem services expected from grasslands: (i) domestic herbivore feeding and animal production; (ii) the regulation of biogeochemical cycles and its consequences for the environment; (iii) dynamics of biodiversity hosted by grasslands; (iv) integration of grasslands within sustainable animal production systems; and (v) interactions of grassland areas with other land use systems at the landscape level.

cited By 96; International audience; no abstract

International audience; Despite their role in soil functioning, the ecology of nitrite-oxidizing bacteria, NOB, and their response to disturbances such as those generated by agricultural practices are scarcely known. Over the course of 17 months, we surveyed the potential nitrite oxidation, PNO, the abundance of the Nitrobacter- and Nitrospira-like NOB (by quantitative PCR) and the community structure of the Nitrobacter-like NOB (by PCR-DGGE and cloning-sequencing targeting the nxrA gene) in soils for four treatments: after establishment of tillage on a previously no-tillage system, after cessation of tillage on a previously tillage system, and on control tillage and no-tillage systems. Key soil variables (moisture, organic carbon content and gross mineralization – i.e. ammonification – measured by the 15N dilution technique) were also surveyed. PNO was always higher for the no-tillage than tillage treatments. Establishment of tillage led to a strong and rapid decrease in PNO whereas cessation of tillage did not change PNO even after 17 months. PNO was strongly and positively correlated to the abundance of Nitrobacter-like NOB and was also strongly related to gross mineralization, a proxy of N-availability; in contrast, PNO was weakly and negatively correlated to the abundance of Nitrospiralike NOB. Selection of a dominant population was observed under no-tillage, and PNO was loosely correlated to the community structure of Nitrobacter-like NOB. Our results demonstrate that Nitrobacter-like NOB are the key functional players within the NOB community in soils with high N availability and high activity level, and that changes in PNO are due to shifts between Nitrospira-like and Nitrobacter-like NOB and to a weaker extent by shifts of populations within Nitrobacter-like NOB.

En régions de climat tempéré, les terres cultivées ont un potentiel de stockage de carbone que l’on peut tenter d’utiliser pour réduire d’autant les émissions de CO2 atmosphérique par des pratiques culturales adaptées et notamment par les techniques culturales sans labour (TCSL). Cette capacité de stockage de carbone dans le sol a été évaluée sur l’essai de longue durée de Boigneville (Bassin de Paris, France) et a été comparée aux données de la littérature internationale. Le suivi du stock de carbone du sol sous une rotation maïs-blé indique une tendance à un stockage modéré tant en système labouré (0,10 t C ha-1 an-1 sur 28 ans) qu’en TCSL (respectivement 0,21 t et 0,19 t C ha-1 an-1 pour le travail superficiel et le semis direct sur cette même période). Avec une absence de différence significative entre le semis direct et le travail superficiel, l’effet spécifique moyen des TCSL évalué à 0,10 t C ha-1 an-1 sur 28 ans apparait sensiblement plus faible que celui mesuré sur les 20 premières années et évalué à 0,20 t C ha-1 an-1. Ces valeurs, inférieures à d’autres valeurs largement diffusées par ailleurs, et cette variation décroissante de la capacité de stockage avec la durée de TCSL sont cohérentes avec la tendance moyenne observée à partir d’un large échantillonnage de données de la littérature internationale. L’évolution de ce stockage de carbone est discutée en lien avec les indications sur l’évolution du stock de carbone des sols de cette même région, les indicateurs de stockage potentiel, et les implications liées à l’évolution du climat.Mots clés: Techniques de culture sans labour, travail superficiel, semis direct, stockage de carbone, séquestration, mitigation, gaz à effet de serre, essai de longue durée, climat tempéré

Straw residues may be accumulated in isolated zones in the plough layer after mouldboard ploughing. This may limit straw decomposition because of limited nitrogen availability depending on the prevalent water flow pathways induced by tillage. In this study, we used the food dye Brilliant Blue FCF (Color Index 42090) to make visible the flow pathways in the plough layer of a loamy soil after incorporation of 10 tonne of dry mass ha− 1, and to get a qualitative and quantitative interpretation of the small-scale flow behaviour. Approximately 1.3 L of a 4 g L− 1 Brilliant Blue solution was applied at a matric head of − 1 cm with an infiltrometer, equipped with a 25 cm-diameter disk. Horizontal cross-sections of 50 × 50 cm were photographed at 1.5 to 3.5 cm depth intervals. High-resolution spatial maps of Brilliant Blue concentration were derived from the scanned photographs, using separate calibration relationships between the measured Brilliant Blue concentrations and the color spectra and depth for the soil and the straw. Pronounced lateral dye movement was observed through the soil matrix owing to soil sorptivity. In cases of high sorptivity, the dye barely reached the depth of straw incorporation. Otherwise, enhanced preferential dye transport directed towards the incorporated straw was made visible and the stained water eventually ponded on the plough pan which induced lateral redistribution. Although the straw inclusions contributed to dye transport, they did not retain a substantial part of the applied dye mass, owing to the low density and surface area of straw. However, these inclusions may enhance the fast migration of potential pollutants such as nitrate or pesticides out of the tilled layer where much of the transformation occurs due to biological activity.

16 ref.; Une des fonctions assignées au travail du sol est la modification de la structure en vue de contrôler le fonctionnement hydrique du sol. L'étude que nous avons conduite avait pour but d'analyser l'effet de la structure sur le dessèchement d'un sol cultivé au printemps. Trois traitements se différenciant par leur niveau de compacité (fort/faible) et/ou par la date de travail du sol (automne/printemps) ont été créés dans un sol de craie (Rendoll Typic) et dans un sol de limon (Luvisol Orthic). Un suivi de la teneur en eau et du potentiel de l'eau a été réalisé, respectivement, à partir de prélèvements gravimétriques et de mesures par des tensiomètres. Le flux d'évaporation a été calculé par la méthode du plan de flux nul. Les propriétés hydrodynamiques ont été estimées par la méthode évaporative de Wind. Dans le sol de craie, le traitement compacté avait un flux d'évaporation supérieur à celui des traitements travaillés d'environ 1mm/jour. Les premiers centimètres du traitement compacté restaient humides tandis que ceux des traitements travaillés s'asséchaient rapidement. Au contraire, en profondeur, la teneur en eau du traitement compacté était inférieure à celle des traitements travaillés. Cet effet de la compacité du sol est à mettre en relation avec les variations de conductivité hydraulique du sol non saturé en fonction de la masse volumique du sol. La conductivité hydraulique était plus élevée dans le traitement compacté, probablement à cause d'une surface de contact entre fragments terreux plus grande, donc d'une meilleure continuité de la phase liquide du sol non saturé. L'augmentation de la conductivité hydraulique du traitement compacté a permis une meilleure ré-alimentation en eau de la surface du sol depuis les couches profondes, donc un flux d'évaporation plus élevé et un dessèchement de l'ensemble de la couche labourée. Cet effet n'a pas été observé dans le sol de limon pour lequel les variations de structure du sol n'ont pas eu de conséquences marquées sur le dessèchement du sol. La conductivité hydraulique était la même, à une teneur en eau donnée, quelle que soit la masse volumique. Ceci pourrait résulter de la formation de pores structuraux reliques par compactage. Il apparaît qu'un sol trop poreux en sortie d'hiver peut limiter le dessèchement de la couche labourée au printemps. La présence des pores reliques dans un sol pourrait permettre de caractériser les conditions de compactage qu'il a subies

International audience; La mise au point de règles d'aide à la décision en matière de travail du sol ou l'évaluation de l'effet des systèmes de culture sur l'évolu-tion de la composante physique de la fertilité des sols requièrent des modèles permettant d'évaluer l'effet des outils, de la circulation des engins et des agents naturels sur la structure du sol. L'objet de cet article est la présentation d'un tel modèle qui permet de simuler sur un pas de temps qui est celui de l'opération culturale, l'évolution d'un indicateur de l'effet des systèmes de culture sur la structure du sol : la proportion de volume de sol fortement compacté (d'état interne ∆) dans la couche labourée. Ce modèle, baptisé SISOL, repose sur des hypothèses d'évolution de la proportion de zones tassées dans les couches de sol travaillées sous l'effet combiné du retournement par la charrue, du tassement par les roues des engins et de la fragmentation par les outils de reprise du labour et le climat. Son évaluation sur un essai de longue durée a montré que si les courbes d'évolution de la teneur en ∆ étaient correctement prédites (sur une période de simulation de sept ans), le modèle pouvait être amélioré en prenant mieux en compte la disparition des zones ∆ sous l'effet du climat et de la faune du sol. Même si son extension à d'autres types de sol que les limons argileux du Bassin Parisien est souhaitable, ce modèle peut, en l'état, être utilisé pour comparer l'effet sur l'évolution de la structure du sol de différents choix techniques (dates d'interventions, types d'équipement, modalités de travail du sol, successions de cultures…).

International audience; STICS is a model that has been developed at INRA (France) since 1996. It simulates crop growth as well as soil water and nitrogen balances driven by daily climatic data. It calculates both agricultural variables (yield, input consumption) and environmental variables (water and nitrogen losses). From a conceptual point of view, STICS relies essentially on well-known relationships or on simplifications of existing models. One of the key elements of STICS is its adaptability to various crops. This is achieved by the use of generic parameters relevant for most crops and on options in the model formalisations concerning both physiology and management, that have to be chosen for each crop. All the users of the model form a group that participates in making the model and the software evolve, because STICS is not a fixed model but rather an interactive modelling platform. This article presents version 5.0 by giving details on the model formalisations concerning shoot ecophysiology, soil functioning in interaction with roots, and relationships between crop management and the soil-crop system. The data required to run the model relate to climate, soil (water and nitrogen initial profiles and permanent soil features) and crop management. The species and varietal parameters are provided by the specialists of each species. The data required to validate the model relate to the agronomic or environmental outputs at the end of the cropping season. Some examples of validation and application are given, demonstrating the generality of the STICS model and its ability to adapt to a wide range of agro-environmental issues. Finally, the conceptual limits of the model are discussed.

Dans les modèles de simulation du fonctionnement des cultures, l’interception du rayonnement est une variable cruciale pour la prévision de la productivité en biomasse. D’autre part, la connaissance de l’interception du rayonnement par une culture permet de mieux analyser la réponse à un traitement en autorisant la distinction entre les effets morphogénétique et physiologique du traitement. Par exemple, dans l’étude de la fertilisation azotée du colza [1] on a pu faire la part de l’effet morphogénétique (accroissement de l’indice foliaire, donc de l’interception) et de l’amélioration de la conversion photosynthétique du rayonnement absorbé. Dans un cas comme dans l’autre, une estimation correcte de l’interception du rayonnement est essentielle. Très souvent, un formalisme dérivé de la loi de Beer-Lambert est utilisé pour quantifier la part interceptée du rayonnement : PARi = epsiloni PAR (1) et epsiloni = 1 - e- k.IF (2), PAR représentant le rayonnement photosynthétiquement actif incident (exprimé en Joules ou en moles de photons), PARi la part de ce dernier interceptée par le couvert, epsiloni le coefficient (sans dimension) d’interception, IF l’indice foliaire et k le coefficient d’extinction du rayonnement. Un formalisme un peu plus complexe doit être utilisé si on veut considérer le rayonnement absorbé [1, 2]. Pour des cultures couvrantes, la sensibilité de ces modèles à la valeur de k est faible pour les IF élevés, c’est pourquoi ces modèles sont souvent utilisés avec succès. Mais aux faibles IF, les modèles sont sensibles à k, d’où l’importance de l’estimation de ce paramètre pour les cultures présentant une longue période de faible couverture du sol, tel le colza peu fertilisé en phase hivernale. De plus, pour les cultures discontinues, c’est-à-dire présentant des zones où le sol n’est pas du tout couvert par la végétation, comme les inter-rangs, on doit introduire dans l’équation 2 un paramètre représentant le taux de couverture du sol. Si l’estimation par mesure directe de epsiloni et donc l’estimation de k sont assez simples, au moins dans le principe pour un couvert développé en hauteur (colza après montaison) [3], une telle mesure devient beaucoup plus complexe dans le cas d’un couvert discontinu et bas. Dans ce milieu hétérogène (et souvent dans des conditions hivernales sévères), une distribution représentative des capteurs de rayonnement est difficile, les risques de perturbation de la mesure (salissure des capteurs, déréglages) sont élevés. Plusieurs études ont déjà traité de epsiloni et k dans le cas du colza [3-7]. Elles sont fondées sur des mesures d’interception du rayonnement et concernent des couverts fermés, après montaison. Une autre approche consiste à effectuer un calcul précis de PARi avec des modèles détaillés utilisant une description complète des paramètres (géométriques et radiatifs) du feuillage, et du rayonnement incident [8]. Mais les données nécessaires sont alors nombreuses, complexes à obtenir et donc généralement non disponibles en expérimentation. Pour répondre aux besoins de calcul de l’interception du rayonnement dans les phases d’installation du colza, cet article présente une méthode permettant de calculer epsiloni en tenant compte des principales caractéristiques de la morphologie du couvert et du régime radiatif auquel ce dernier est soumis. Les données nécessaires sont limitées : l’indice foliaire, les taux de couverture du sol (deux définitions), la latitude du lieu considéré, la date et le rayonnement incident quotidien. Ce calcul permet une estimation du coefficient moyen d’extinction k (équation 2). On verra que k peut être corrélé à l’IF, la période de l’année et la latitude du lieu, ce qui permet de proposer une estimation simple de k et donc un calcul simplifié de epsiloni, adapté au cas des faibles IF(colza entre levée et montaison).

International audience; The biochemical composition of stems, pod walls and roots of oilseed rape (Brassica napus L.) plants, grown in a growth chamber with two levels of N fertiliser, was assessed by two global methods, i.e., serial extraction with the Van Soest's technique and temperature-programmed pyroanalysis (TP-Py). Statistical analysis of the effect of various parameters on the proportion of soluble components, hemicellulose, cellulose and lignin-like components in oilseed rape organs showed that the composition of plant materials depended on the N nutrition conditions during plant growth. Contents of soluble and hemicellulose fractions were affected by the technique used. Elsewhere, both global techniques resulted in similar proportions of skeletal cellulose (respectively 41 and 36% in low and high N stems, 37 and 30% in low and high N pod walls, 32 and 29% in low and high N roots) and of lignin-like components which ranged from about 7% in high N stems and pod walls to 16% in low N roots. Spectroscopy by FTIR showed a significant band at 1650 cm(-1) (amide I in proteins) in the root material (organ with the lowest C/N ratio) and the absence of lignin-specific bands. Carbon distribution by C-13 NMR CP/MAS of labelled plants indicated that 60-64% was (cellulose + hemicellulose)-C, close to the values obtained by global methods. The proportion of aromatic-C (110-160 ppm) and phenolic ether was higher in roots than in stems and pod walls. Organs from oilseed rape plants with higher N contents exhibited a larger proportion of C in the 171 ppm chemical shift attributed to the peptide bond. The concomitance of a high level of aromatic and proteinaceous components in roots would reveal the presence of tannin-protein complexes in addition with true lignin.

International audience; C and N mineralisation kinetics obtained in laboratory incubations during decomposition of crop residues under non-limiting nitrogen conditions were simulated using a simple dynamic model. This model includes three compartments: the residues, microbial biomass and humified organic matter. Seven parameters are used to describe the C and N fluxes. The decomposed C is either mineralised as CO2 or assimilated by the soil microflora, microbial decay producing both C humification and secondary C mineralisation. The N dynamics are governed by the C rates and the C:N ratio of the compartments which remain constant in the absence of nitrogen limitation. The model was parameterised using apparent C and N mineralisation kinetics obtained for 27 different residues (organs of oilseed rape plants) that exhibited very wide variations in chemical composition and nitrogen content. Except for the C:N ratio of the residues and the soil organic matter, the other five parameters of the model were obtained by non-linear fitting and by minimising the differences between observed and simulated values of CO2 and mineral N.Three parameters, namely the decomposition rate constant of the residues, the biomass C:N ratio and humification rate, were strongly correlated with the residues C:N ratio. Hyperbolic relationships were established between these parameters and the residues C:N ratio. In contrast, the other two parameters, i.e. the decay rate of the microbial biomass and the assimilation yield of residue-C by the microbial biomass, were not correlated to the residues C:N ratio and were, therefore, fixed in themodel. Themodel thus parameterised against the residue C:N ratio as a unique criterion, was then evaluated on a set of 48 residues. An independent validation was obtained by taking into account 21 residues which had not been used for the parameterisation. The kinetics of apparent C and N mineralisation were reasonably well simulated by the model. The model tended to over-estimate carbon mineralisation which could limit its use for C predictions, but the kinetics of N immobilisation or mineralisation due to decomposition of residues in soil were well predicted. The model indicated that the C:N ratio of decomposers increased with theresidue C:N ratio. Higher humification was predicted for substrates with lower C:N ratios. This simple dynamic model effectively predicts N evolution during crop residue decomposition in soil.

National audience

The interactions occurring between biochemical composition and N content of crop residues while decomposing in soil, and the associated N dynamics were assessed by studying the kinetics of C and N biotransformations of different tissues of Brassica napus L. (roots, stems and pod walls). These residues were obtained by growing a rapeseed crop under low and high N nutrition, in a labeling growth chamber with enriched 13 CO 2 atmosphere and a 15 N nutritive solution. The resulting crop residues in which the C-to-N ratio varied between 22 and 135 were homogeneously labeled with 13 C and 15 N. Paired labeled residues ( 13 C 15 N labeled residues with unlabeled soil inorganic N; 13 C 14 N residues with 15 N labeled soil inorganic N) were used to determine net and gross fluxes of immobilization and mineralization. Decomposition was studied during laboratory incubations at 15°C, the initial soil N availability being non-limiting with regard to the rate of C decomposition. The rate of 13 C mineralization from the residues was influenced by the biochemical composition of the tissues and particularly by their soluble C content. The N content of the tissues did not significantly affect the kinetics or the amount of C mineralized, except in the very short-term. Decomposition was rapid and after 168 days of incubation at 15°C, 82% of the C from the stems and pod walls and 69% from the roots at both low and high N contents had disappeared from the soil coarse fraction. Residue decomposition first resulted in net immobilization of soil mineral N for all the residues. The intensity and duration of this immobilization depended on the tissues and the N content of the residues. Compared to the control, the residues with low N content, still induced net N immobilization after 168 days (−22 to −14 mg N g −1 of added C) whereas the high N residues induced little net immobilization or mineralization, at −3 to + 4 mg N g −1 of added C at the same date. The NCSOIL model was used as a tool to calculate, by fitting simulation against the data, the gross N mineralization and immobilization fluxes and also to determine the total N fluxes involved over the 168 days of decomposition. Depending on the tissues and their N content, gross cumulative immobilization ranged from 71 to 113 mg N g −1 of added C and gross mineralization varied from 66 to 123 mg N g −1 of added C. The differences in net mineralization, observed during decomposition of the tissues with low and high N contents, were well explained by the differences between gross mineralization fluxes which were themselves attributable to the different quantities of N mineralized from the residues. The use of modeling to calculate the total gross N fluxes demonstrates that the total amount of N involved in the decomposition of crop residues is much higher than the resulting net fluxes quantified either by N balance or by 15 N tracing.

International audience; Statistical relationships were established between the fate of C and N from 47 types of crop residues and their biochemical characteristics during a soil incubation at 15°C. The incubations were carried out under nonlimiting N in order to differentiate the effects of biochemical characteristics of residues from those of soil N availability. Depending on the residue, the apparent mineralization of residue C after 168 d varied from 330 to 670 g kg−1 of added C. Mineralization kinetics were described using a two-compartment decomposition model that decomposes according to first-order kinetics. Amounts of C mineralized after 7 d and the decomposition rate coefficient of the labile fraction were related mainly to the soluble C forms of the residue. No statistical relationship was established between the N concentration of residues and their decomposition in the soil. The incorporation of crop residues into soil led to various soil mineral N dynamics. Two residues caused net N mineralization from the time of their incorporation, whereas all the others induced net N immobilization (1–33 g N kg−1 of added C). After 168 d, only residues with a C/N ratio

International audience

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National audience

There is still disagreement about whether crop growth rate or soil nitrate concentration control nitrogen absorption by crops under field conditions. The influence of these factors on the control of N uptake rate was examined in the absence of water stress, using data on dry matter production, above-ground nitrogen accumulation and soil nitrate concentration from several N-fertilizer experiments on winter wheat, winter oilseed rape and maize. The results confirmed that crops can accumulate nitrogen far in excess of the ‘critical dilution curve’, which defines the minimum amount of nitrogen needed for maximal growth rate: the N concentration in plants could exceed the critical N concentration by 70 to 80% for the three species studied. The nitrate uptake rate index (NUI) was calculated as the ratio of actual and critical N uptake rates, at intervals of 1 week. NUI varied with nitrate concentration in the 0–30 cm soil layer according to a Michaelis–Menten equation (with one or two components). This response was compared with the kinetics of saturation of the nitrate uptake systems: the high affinity transport system (HATS) and the low affinity transport system (LATS). As a result, it is proposed that there is a critical N dilution curve delimiting two domains of N use by plants. This is linked to the two nitrate transport systems, with HATS working at low nitrate concentrations, below the critical dilution curve, and LATS at high nitrate concentrations, above the curve. NUI provides another method for calculating the actual nitrate uptake rate, which depends on the maximal crop growth rate (without N deficiency) and on the external nitrate concentration.

Après une rapide synthèse des processus contrôlant le ruissellement et l'érosion, l'influence des pratiques agricoles est présentée à deux échelles : la parcelle agricole et le bassin versant. Au niveau de la parcelle, les pratiques agricoles déterminent la nature et la densité du couvert végétal ou des résidus de récolte protégeant le sol de l'impact des gouttes de pluie et ralentissant la vitesse du ruissellement. Parallèlement, ces pratiques déterminent une succession d'actions mécaniques sur le sol conduisant soit à un ameublissement ou soit à un compactage du sol. L'ameublissement favorise l'infiltration, mais également l'érosion, tandis que le compactage favorise le ruissellement, mais limite l'érosion. Au niveau du bassin versant, les pratiques agricoles mises en oeuvre à l'échelle de la parcelle fixent la distribution spatiale de surfaces émettrices d'un ruissellement et de surfaces ayant un sol à faible cohésion. Leur position relative le long d'un réseau de collecteurs permet d'expliquer la localisation et l'intensité de l'érosion. Cette structure hydrographique du bassin versant évolue au cours du temps sous l'action du climat et des pratiques agricoles. L'étude des effets des pratiques agricoles à l'échelle du bassin versant impose le recours à la simulation numérique à l'aide de modèles d'érosion adaptés. / We first review the processes controlling runoff and erosion and then examine the influence of agricultural practices on these phenomena on the scale of the agricultural field and the cultivated catchment. Agricultural practices determine the kind and density of plant and mulch cover in a given field. The cover protects the topsoil from rainfall and reduces the runoff speed. At the same time, agricultural practices are associated with a succession of mechanical actions on the soil that can cause fragmentation and compaction. These actions have opposite effects. Fragmentation increases the infiltration rate, but also the risk of erosion, while compaction increases the runoff rate, but reduces the risk of erosion. The agricultural practices used on each field determine the spatial distribution of areas able to produce runoff in a catchment area, and the areas susceptible to erosion. The relative position of an area along the runoff collector network determines the location and risk of erosion. This catchment hydrographic structure changes under the combined effects of climate and agricultural practices. Understanding the effects of agricultural practices on the catchment require the use of digital simulations with appropriate erosion models.

International audience

International audience

International audience; The Châlons experiment started with the sowing of a rapeseed crop (Brassica napus L.) in September 1994, and stopped at its harvest in July 1995. It involved three fertilizer N treatments and a bare control. The soil was a rendzina overlying a subsoil of mixed compact and cryoturbed chalk. The variables monitored were: crop biomass, C and N content, soil matric potential, water and mineral N contents, actual evapotranspiration, nitrous oxide emissions, and ammonia volatilization, along with the usual meteorological data. Mass-balance estimates of water drainage and NO3 leaching below the root-zone, along with 15N balances accounting for the short-term dynamics of fertilizer N are also available. The data are accessible on the Internet through a World Wide Web server by means of a specific frontend, and may be used to test or calibrate soil-crop models. (© Inra/Elsevier, Paris.); La base de données CORD (Châlons Oilseed Rape Database) archive les résultats d’une expérience intensive conduite en région Champagne sur la dynamique des flux d’eau, de carbone et d’azote dans un système sol-plante, à l’échelle de la parcelle agricole. L’expérience a débuté au semis d’une culture de colza (Brassica napus L.) en septembre 1994, et a duré jusqu’à la récolte de celui-ci en juillet 1995. Trois traitements azotés, ainsi qu’un témoin en sol nu ont été suivis, et le sol était une rendzine sur craie à poches de ryoturbation. Les variables mesurées comprennent : biomasse et contenu en carbone et azote de la culture, profils de potentiel matriciel, d’humidité et d’azote minéral du sol, évapotranspiration réelle, émissions d’oxyde nitreux et volatilisation d’ammoniac, ainsi que les variables climatiques usuelles. De plus, le drainage et le lessivage de nitrate sous la zone racinaire ont été estimés par défaut de bilan. Enfin des bilans à l’azote marqué ont permis de rendre compte du devenir de l’engrais sur des pas de temps courts. Les données sont accessibles sur un serveur internet par l’intermédiaire d’une interface spécifique, et peuvent par exemple servir au test ou au calage de modèles de simulation des systèmes sol-culture. (© Inra/Elsevier, Paris.)

The Châlons experiment started with the sowing of a rapeseed crop (Brassica napus L.) in September 1994, and stopped at its harvest in July 1995. It involved three fertilizer N treatments and a bare control. The soil was a rendzina overlying a subsoil of mixed compact and cryoturbed chalk. The variables monitored were: crop biomass, C and N content, soil matric potential, water and mineral N contents, actual evapotranspiration, nitrous oxide emissions, and ammonia volatilization, along with the usual meteorological data. Mass-balance estimates of water drainage and NO3 leaching below the root-zone, along with 15N balances accounting for the short-term dynamics of fertilizer N are also available. The data are accessible on the Internet through a World Wide Web server by means of a specific frontend, and may be used to test or calibrate soil-crop models. (© Inra/Elsevier, Paris.), La base de données CORD (Châlons Oilseed Rape Database) archive les résultats d’une expérience intensive conduite en région Champagne sur la dynamique des flux d’eau, de carbone et d’azote dans un système sol-plante, à l’échelle de la parcelle agricole. L’expérience a débuté au semis d’une culture de colza (Brassica napus L.) en septembre 1994, et a duré jusqu’à la récolte de celui-ci en juillet 1995. Trois traitements azotés, ainsi qu’un témoin en sol nu ont été suivis, et le sol était une rendzine sur craie à poches de ryoturbation. Les variables mesurées comprennent : biomasse et contenu en carbone et azote de la culture, profils de potentiel matriciel, d’humidité et d’azote minéral du sol, évapotranspiration réelle, émissions d’oxyde nitreux et volatilisation d’ammoniac, ainsi que les variables climatiques usuelles. De plus, le drainage et le lessivage de nitrate sous la zone racinaire ont été estimés par défaut de bilan. Enfin des bilans à l’azote marqué ont permis de rendre compte du devenir de l’engrais sur des pas de temps courts. Les données sont accessibles sur un serveur internet par l’intermédiaire d’une interface spécifique, et peuvent par exemple servir au test ou au calage de modèles de simulation des systèmes sol-culture. (© Inra/Elsevier, Paris.)

International audience; The soil water and N dynamics have been studied during two long fallow periods (between wheat or oilseed rape and a spring crop) in a field experiment in Châlons-en-Champagne (eastern France, 48°50′ N, 2°15′ E). The experiment involved frequent measurements of soil water, soil mineral N, dry matter and N uptake by cover crops. Water and N budgets were established using Ritchie's model for calculating evapotranspiration in cropped soils and a model (LIXIM) for calculating water drainage, N leaching and N mineralisation in bare soils. During the first autumn and winter, a radish cover crop (grown from September 1994 to January 1995) was compared to a bare soil. During the second period (July 1995 to April 1996), a comparison was carried out between (i) oilseed rape volunteers, (ii) bare soil with two types of oilseed rape residues incorporated into the soil (R0 and R270 residues) and (iii) bare soil without residues incorporation. R0 and R270 residues came from two preceding oilseed rape crops which received two rates of N fertilizer (0 and 270 kg N ha-1).Soil mineral N content was markedly reduced by the presence of radish cover crop or oilseed rape volunteers during autumn. The calculated actual evapotranspiration (AET) did not differ much between treatments, meaning that the transpiration by the cover crop or volunteers was relatively low (100–150 L kg-1 of dry matter). Consequently, nitrate leaching was reduced during the rest of the winter and spring as well as nitrate concentration in the percolating water: 45 vs. 91 mg NO3- L-1 for radish cover crop and bare soil, respectively. The incorporation of oilseed rape residues to soil also exerted a beneficial but smaller action on reducing the nitrate content in the soil. This effect was due to extra N immobilisation which reached a maximum of about 20 kg N ha-1 in mid-autumn for both types of residues. Nine months after the incorporation of the oilseed rape residues, and comparing to the control soil without residues incorporation, N rich residues induced a significant positive N net effect (+ 9 kg N ha-1) corresponding to 10% of N added whereas for N poor residues no net effect was still obtained at the end of experiment (−3 kg N ha-1, not significantly different from 0).To reduce nitrate leaching during long fallow periods, it is necessary to promote techniques leading to decrease mineral-N contents in the soil during autumn before the drainage period, such as (i) residue incorporation after harvest (without fertiliser-N) and (ii) allowing volunteers to grow or sowing a cover crop just after the harvest of the last main crop.

National audience

International audience; STICS (Simulateur mulTIdiscplinaire pour les Cultures Standard) is a crop model constructed as a simulation tool capable of working under agricultural conditions. Outputs comprise the production (amount and quality) and the environment. Inputs take into account the climate, the soil and the cropping system. STICS is presented as a model exhibiting the following qualities: robustness, an easy access to inputs and an uncomplicated future evolution thanks to a modular (easy adaptation to various types of plant) nature and generic. However, STICS is not an entirely new model since most parts use classic formalisms or stem from existing models. The main simulated processes are the growth, the development of the crop and the water and nitrogenous balance of the soil-crop system. The seven modules of STICS - development, shoot growth, yield components, root growth, water balance, thermal environment and nitrogen balance - are presented in turn with a discussion about the theoretical choices in comparison to other models. These choices should render the model capable of exhibiting the announced qualities in classic environmental contexts. However, because some processes (e.g. ammoniac volatilization, drought resistance, etc.) are not taken into account, the use of STICS is presently limited to several cropping systems. (© Inra/Elsevier, Paris.); STICS est un modèle de culture conçu comme un outil de simulation opérationnel en conditions agricoles. Ses variables de sortie sont relatives à la production, à la fois en quantité et en qualité, et à l’environnement. Ses entrées sont relatives au climat, au sol et au système de culture. STICS est présenté comme un modèle montrant les qualités suivantes : robustesse, facilité d’accès aux données d’entrée, souplesse d’évolution par une présentation modulaire et généricité (facilité d’adaptation à divers types de plantes). Pourtant, il ne s’agit pas d’un modèle entièrement nouveau dans les formalismes utilisés. Ils sont, pour la plupart, issus de modèles existants. Les grands processus simulés sont la croissance et le développement de la culture ainsi que les bilans hydrique et azoté du système sol-culture. Les sept modules de STICS sont décrits successivement avec une discussion sur les choix théoriques comparés à ceux d’autres modèles : développement, croissance aérienne, composantes du rendement, croissance racinaire, bilan hydrique, environnement thermique de la culture, bilan azoté. Il ressort que ces choix confèrent à priori au modèle les qualités annoncées dans un contexte environnemental classique. Cependant, l’absence de prise en compte de certains processus (exemples : volatilisation de l’ammoniac, résistance à la sécheresse, ...) restreint pour l’instant son utilisation à certains systèmes de culture. (© Inra/Elsevier, Paris.)

STICS (Simulateur mulTIdiscplinaire pour les Cultures Standard) is a crop model constructed as a simulation tool capable of working under agricultural conditions. Outputs comprise the production (amount and quality) and the environment. Inputs take into account the climate, the soil and the cropping system. STICS is presented as a model exhibiting the following qualities: robustness, an easy access to inputs and an uncomplicated future evolution thanks to a modular (easy adaptation to various types of plant) nature and generic. However, STICS is not an entirely new model since most parts use classic formalisms or stem from existing models. The main simulated processes are the growth, the development of the crop and the water and nitrogenous balance of the soil-crop system. The seven modules of STICS - development, shoot growth, yield components, root growth, water balance, thermal environment and nitrogen balance - are presented in turn with a discussion about the theoretical choices in comparison to other models. These choices should render the model capable of exhibiting the announced qualities in classic environmental contexts. However, because some processes (e.g. ammoniac volatilization, drought resistance, etc.) are not taken into account, the use of STICS is presently limited to several cropping systems. (© Inra/Elsevier, Paris.), STICS est un modèle de culture conçu comme un outil de simulation opérationnel en conditions agricoles. Ses variables de sortie sont relatives à la production, à la fois en quantité et en qualité, et à l’environnement. Ses entrées sont relatives au climat, au sol et au système de culture. STICS est présenté comme un modèle montrant les qualités suivantes : robustesse, facilité d’accès aux données d’entrée, souplesse d’évolution par une présentation modulaire et généricité (facilité d’adaptation à divers types de plantes). Pourtant, il ne s’agit pas d’un modèle entièrement nouveau dans les formalismes utilisés. Ils sont, pour la plupart, issus de modèles existants. Les grands processus simulés sont la croissance et le développement de la culture ainsi que les bilans hydrique et azoté du système sol-culture. Les sept modules de STICS sont décrits successivement avec une discussion sur les choix théoriques comparés à ceux d’autres modèles : développement, croissance aérienne, composantes du rendement, croissance racinaire, bilan hydrique, environnement thermique de la culture, bilan azoté. Il ressort que ces choix confèrent à priori au modèle les qualités annoncées dans un contexte environnemental classique. Cependant, l’absence de prise en compte de certains processus (exemples : volatilisation de l’ammoniac, résistance à la sécheresse, ...) restreint pour l’instant son utilisation à certains systèmes de culture. (© Inra/Elsevier, Paris.)

International audience; he feasibility of studies on nitrate transformations during incubation in controlled conditions of air-filled porosity using a method of soil core preparation was investigated. Repacked cores were obtained by uniaxial confined compression in a cylindrical mould of a mass of calibrated and conveniently wet aggregates with a water content selected to saturate the textural porosity of the soil aggregates, imposing structural porosity and thereby producing controlled conditions of aeration. The principle and the descrip- tion of the incubation method are explained and some denitrification and respiration data obtained with low and increasing OZ partial pressures are presented. Reproducibility of the results was considered satisfactory and compared with published data; it was much better than the reproducibility of data obtained from the incubation of undisturbed soil samples and similar to those obtained with homogenized and unstructured samples.

International audience

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International audience

In the first part of this chapter, we propose to determine the curve of critical plant N% for cereals during the development of the crop ranging from tillering to anthesis, for different cultivars and growth conditions. The results are mainly derived from Justes et al. (1994) with winter wheat. The validity of the curve of critical plant N% will also be evaluated for spring barely and durum wheat.

chap. 12; National audience

*INRA Bioclimatologie Grignon Diffusion du document : INRA Bioclimatologie Grignon; National audience

International audience

International audience

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International audience

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A set of N-fertilization field experiments was used to determine the 'critical nitrogen concentration', i.e, the minimal concentration of total N in shoots that produced the maximum aerial dry matter, at a given time and field situation. A unique 'critical nitrogen dilution curve' was obtained by plotting these concentrations Nct (% DM) vs. accumulated shoot biomass DM (t ha-1). It could be described by the equation: Nct = 5·35DM-0·442 when shoot biomass was between 1·55 and 12 t ha-1. An excellent fit was obtained between model and data (r2 = 0·98, 15 d.f.). A very close relationship was found using reduced N instead of total N, because the nitrate concentrations in shoots corresponding to critical points were small. The critical curve was rather close to those reported by Greenwood et al. (1990) for C3 plants. However, this equation did not apply when shoot biomass was less than 1·55 t ha-1. In this case, the critical N concentration was independent of shoot biomass: the constant critical value Nct = 4·4% is suggested for reduced-N. The model was validated in all the experimental situations, in spite of large differences in growth rate, cultivar, soil and climatic conditions; shoot biomass varying from 0·2 to 14 t ha-1. Plant N concentration was found to vary by a factor of four at a given shoot biomass level. In the heavily fertilized treatments, shoot N concentration could be 60% higher than the critical concentration. Most (on average 80%) of the extra N accumulated was in the form of reduced N. The proportion of nitrate to total N in shoot mainly depended on the crop stage of development. It was independent of the nitrogen nutrition level.