In regions of intensive pig and dairy farming, nutrient losses to the environment at farm level are a source of concern for water and air quality. Dynamic models are useful tools to evaluate the effects of production strategies on nutrient flows and losses to the environment. This paper presents the development of a new whole-farm model upscaling dynamic models developed at the field or animal scale. The model, called MELODIE, is based on an original structure with interacting biotechnical and decisional modules. Indeed, it is supported by an ontology of production systems and the associated programming platform DIESE. The biotechnical module simulates the nutrient flows in the different animal, soil and crops and manure sub-models. The decision module relies on an annual optimization of cropping and spreading allocation plans, and on the flexible execution of activity plans for each simulated year. These plans are examined every day by an operational management sub-model and their application is context dependent. As a result, MELODIE dynamically simulates the flows of carbon, nitrogen, phosphorus, copper, zinc and water within the whole farm over the short and long-term considering both the farming system and its adaptation to climatic conditions. Therefore, it is possible to study both the spatial and temporal heterogeneity of the environmental risks, and to test changes of practices and innovative scenarios. This is illustrated with one example of simulation plan on dairy farms to interpret the Nitrogen farm-gate budget indicator. It shows that this indicator is able to reflect small differences in Nitrogen losses between different systems, but it can only be interpreted using a mobile average, not on a yearly basis. This example illustrates how MELODIE could be used to study the dynamic behaviour of the system and the dynamic of nutrient flows. Finally, MELODIE can also be used for comprehensive multi-criterion assessments, and it also constitutes a generic and evolving framework for virtual experimentation on animal farming systems.

Le contexte environnemental actuel, tant politique (objectifs de réduction des émissions de gaz à effet de serre) que sociétal (informationdu consommateur), nécessite de préciser les impacts de l'activité d'élevage bovin en matière de changement climatique. L'enjeuest de connaître précisément les niveaux d'émissions de gaz à effet de serre (GES) et de stockage de carbone, des différents modes deproduction. Pour cela, une évaluation basée sur la méthodologie de l'Analyse du Cycle de Vie (ACV) est mise au point à l'échelle dusystème d'élevage. Cette approche permet d'avoir une vision globale de l'activité d'élevage intégrant l'ensemble des processus interneset externes au fonctionnement de l'exploitation. Ainsi pour les systèmes laitiers français, l'empreinte carbone brute du lait est enmoyenne de 1,26 kg CO2/kg de lait. La prise en compte du stockage de carbone sous les prairies et les haies se traduit par une compensationcomprise entre 6 et 43% selon les systèmes, en fonction de la part de prairies. L'empreinte carbone nette du lait françaisest alors en moyenne de 1,0 kg CO2/kg de lait. Dans les systèmes bovins viande français, l'empreinte carbone brute est comprise entre14,8 et 16,5 kg CO2/kg viande vive en fonction du système de production (naisseur vs naisseur/engraisseur). Après prise en comptedu stockage de carbone qui permet une compensation comprise entre 24 et 53%, l'empreinte carbone nette est comprise entre 7,9 et11,3 kg CO2/kg viande vive. De nombreux leviers d'action sont identifiés dans les systèmes d'élevage de ruminants pour réduire l'empreintecarbone des produits au portail de la ferme. Certains concernent une optimisation des systèmes de production (ajustementdes apports alimentaires, gestion de la fertilisation…) et se traduisent par des économies en matière d'intrants. D'autres nécessitentla mise en place de nouvelles technologies et se traduiront donc par un investissement ou un coût de fonctionnement supérieur auxschémas actuels de production.

SUMMARYIn France, many dairy farms plan the allocation of animal wastes to the fields of the farm at the beginning of every year. This decision is complex, because many factors must be taken into account at the field and farm scales, including increasingly constraining environmental regulations. To evaluate the environmental impact of waste allocation strategies, these strategies have to be translated into consistent decisions. The objective of the current study was to reproduce the decisions made by farmers, in a wide range of contexts. For this purpose, a linear programming model that could help in generating yearly waste allocations was developed. The model, called Fumigene, takes into account the farmer's preferences and environmental, agronomic and feasibility constraints. It was applied on two case farms and the simulated waste allocations were compared to those chosen by the farmers over periods of 3 and 4 years, respectively. The evaluation showed that the waste allocations generated by the model were consistent with the strategies of the farmers. Fumigene was then used in investigating the impact of taking into account the phosphorus (P) fertilization constraints instead of only the nitrogen constraints. In the case studied, balancing P fertilization over 5 years led to small changes in waste allocation. Balancing P fertilization every year caused bigger changes and led to export of a part of the wastes. In a general way, Fumigene can be coupled with environmental evaluation tools to compare the impacts of different waste allocation strategies.

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