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International audience; Agriculture is increasingly relying on groundwater irrigation. In the context of climate change, it is crucial to develop reliable methods for sustainability assessment of current and alternative agricultural systems. Among agricultural-borne non-point source pollutants, nitrogen has been the focus of many studies due to its ubiquitous impact on ecosystems, sometimes referred as the "Nitrogen cascade". Modelling such impacts is of primary importance for understanding current agrosystems and to be able to assess their evolution. In the Berambadi catchment (84km2, Karnataka, Southern India), which is part of BVET/ Kabini Critical Zone Observatory, we monitored the effect of application of fertilizers and over-exploitation of water resources by intensive tube well irrigation on groundwater resource. The monitoring highlighted a huge spatial variability of groundwater composition with Cl and NO3 contents spanning 3 orders of magnitude with the highest concentrations found in the most severely groundwater depleted areas. The high nitrate contents in groundwater (on average 100 mgNO3/L, up to 360 mgNO3/L) induces a "hidden" supply by irrigation of 50 kg/ha/yr on average with extremes up to 200 kg/ha/yr (Buvaneshwari et al., 2017). Irrigation with this highly concentrated groundwater induces an important feedback in the soil-plant system. However, groundwater recycling is rarely taken into account in groundwater resource integrated assessment and modelling. Monitoring of the soil pore-water composition was done for a common cash crop, Turmeric, in order to perform a nitrate balance at soil-plant scale and evaluate the influence of soil (Ferralsol vs Vertisol) properties on the flux of nitrate leached towards groundwater. A clear contrasted behaviour was found between the studied soils: the high permeability of Ferralsol induces a flush down of almost all the nitrogen input but limits the intensity of evapotranspiration and hence the risk of salinization. On the contrary, the low permeability and high holding capacity of Vertisols make water and nitrate consumption by the plants more efficient. Moreover, denitrification in the deep soil horizons may limit even more the nitrate output from Vertisol. However, chlorine (and other major elements such as Na, Ca, Mg) concentrations increased dramatically with soil depth, making Vertisol prone to salinization. The water and nitrogen balances at the soil-plant scale were assessed by combining field data and STICS crop model for the two soils. To account for the significant feedback induced by the nitrate rich groundwater recycling, we further introduced the new nitrogen module in the developed integrated coupled crop and groundwater model (AICHA under the RECORD platform) which is designed to assess agricultural systems and their adaptation to climate change. The model results revealed that the solute recycling by pumping can lead to severe groundwater degradation both in terms of quality and quantity. Different scenarios were furthermore tested to optimize the fertilizer application to reduce nitrate leaching and to mitigate the high nitrate concentrations in groundwater. Keywords: Groundwater quality; soil degradation; agriculture; integrated model

National audience

National audience

National audience; With the increasing scarcity of natural resources, the unsustainability of the conventional and intensive agriculture and the need of food security, agronomy engineering is facing a serious challenge. In this context, different projects aim to design and evaluate innovative cropping systems in order to increase the productivity of agro-ecosystems while preserving the diverse ecosystem services they provide or support. Simulation can help agronomists to test the robustness of field experiments results by testing various soil and climate conditions. While there are already crop models that simulate correctly crop development, there are few models that simulate the way farmer conduct their cropping systems. Yet, it is a key challenge because innovative cropping systems are often based on new farming practices, which take more into account the state of the crop and of the environment than conventional cropping systems. In addition, the use of “fixed dates” in simulations for farming practices is not adapted because it is important to take into account weather variations, which have a strong effect on the dates of farming operations. Therefore, the evaluation of innovative cropping systems by simulation requires building decision model that mimic farmers’ decision-making, and help in analyzing impacts of farmers’ practices on the sustainability of the cropping system. The modelling and simulation platform dedicated to the study of agro-ecosystems RECORD (J-E. Bergez et al., 2013) has been developed at INRA (French national institute for agricultural research). One of the objectives of the RECORD project was to help modelers in developing decision models and in coupling them to crop models. A generic conceptual decision-modelling framework (Bergez et al., 2016) has been proposed. It allows to design flexible management plan of activities using the concepts of a directed multigraph without loops and of a knowledge base. In the context of cropping system modelling, the graph of activities represents the farmer’s work plan and relies on the knowledge base to activate or disable technical operations. The knowledge base evolves all along the simulation collecting information provided by the biophysical model, as the farmer does when monitoring and observing the environment. Based on this conceptual decision-modelling framework an original graphical plugin “Decision” (Bergez et al., 2016) has been developed. It helps agronomist modelers in sketching and implementing their decision models and in linking them with biophysical models. The plugin allows defining activities (tasks), relation between activities and decision rules to trigger the different tasks. As the RECORD platform is based on DEVS (Discrete Event System Specification) formalism (Zeigler et al., 2000), the software implementation of the plugin is expressed in this formalism. We have applied this decision-modelling framework to the context of an ongoing project whose issue is bio economic evaluation of innovative cropping systems compared to conventional ones. To produce simulation results required by this project, a coupled model has been designed following the conceptual approach that an agricultural system can be divided into three sub-systems: Agent, Operating, and Biophysical (Le Gal et al. 2009; Martin-Clouaire and Rellier 2009). The model couples the crop model STICS (Brisson et al., 1998, J-E. Bergez et al., 2014), to a decision model using the Decision plugin and to a climate series reader. The model is generic because STICS can simulate the behavior of soil–crop systems for a large range of crops, and because the decision model is parametrable. It is used for different species commonly cultivated in south west of France (maize, sunflower, wheat, sorghum …), for different years (1982-2012), for two ways of farming practices: conventional (what do farmers commonly use) and innovative which are currently tested in experimental fields.

L’ambition de l’étude Inra "EFESE-EA" est de décrire les mécanismes et déterminants de la fourniture des services écosystémiques par les écosystèmes agricoles sur la base d'une revue des connaissances existantes, et de procéder à leur évaluation à l’échelle nationale sur la base d’indicateurs définis dans le cadre de l’étude. L’organisation du travail, telle que prévue en début d’étude, se voulait séquentielle : (1) identification et spécification biophysiques d’une liste de biens agricoles et services écosystémiques ; (2) évaluation biophysique : quantification du niveau de fourniture des biens et services identifiés à l’étape (1) (3) évaluation économique : quantification de la valeur économique des services (le plus souvent dans une unité monétaire) Dans le temps imparti à l’étude, le collectif d’experts a donné la priorité aux volets biophysiques (1) et (2) afin : - d’instruire de façon robuste la conceptualisation des biens et services (volet 1) : ce travail constitue un front de recherche actuel, associé à une littérature académique abondante mais parfois non stabilisée, que le collectif d’experts s’est attaché à analyser de façon à proposer des choix de conceptualisation argumentés ; - de pousser au maximum l’exercice d’évaluation biophysique (volet 2) dans le cadre de la demande initiale formulée par le MEEM : cartographier la production d’un large panel de biens agricoles et les SE rendus par les écosystèmes agricoles à la résolution spatiale la plus fine possible, et à l’échelle France entière. A noter que le présent exercice ne constituant pas un projet de recherche mais bien une étude institutionnelle Inra (au sens des procédures DEPE), l’ensemble des évaluations développées dans le présent rapport est réalisée à partir de données existantes, aucun travail d’expérimentation visant à acquérir de nouvelles données de terrain n’ayant été conduit. Il résulte de ce choix de priorisation que : - le volet d’évaluation économique (3) est initié pour quelques SE mais peu développé en comparaison des volets (1) et (2) ; - tout en veillant à élaborer des méthodologies d’évaluation biophysiques traçables et robustes, les experts ont pris le parti de proposer des méthodologies plus exploratoires pour quelques SE pour lesquels les données actuelles ne permettent pas d’évaluer directement le niveau de fourniture à l’échelle France entière : dans ces cas particuliers (signalés explicitement dans les sections du rapport dont ils font l’objet), les méthodologies ont été mises en œuvre jusqu’à la réalisation des cartographies dans le but de donner à voir le potentiel qu’offrent ces méthodologies et la nature des résultats qu’elles peuvent produire sous condition de leur validation France entière, plutôt que dans le but d’interpréter pour eux-mêmes les résultats obtenus. Les experts se sont alors particulièrement attachés à relativiser les résultats quantitatifs ainsi produits, et à accompagner les cartographies d’un descriptif détaillé des protocoles de validation qu’il faudrait mettre en œuvre dans les suites de l’étude pour stabiliser et valider ces méthodologies exploratoires. Ce parti pris du groupe de travail EFESE-écosystèmes agricoles est compatible avec l’objectif poursuivi dans le programme EFESE, qui se donne pour objectif de produire un guide méthodologique pour l’évaluation des biens et SE en en pointant les limites, difficultés, précautions et améliorations possibles associées à chacune des pistes avancées.