The specialization of agriculture has led to a disruption of nutrient cycles. Many studies ask for interactions between farms at the territorial level. But the implementation of collective solutions at this level requires the involvement of a diversity of stakeholders who are not all in direct interaction. This is why we have carried out a companion modelling approach to support a municipality to think about the collective management of nitrogen, particularly from effluents. The support approach involved elected officials, advisory and support organizations, associations, cooperatives and agri-food industries and a variety of farmers. From individual interviews and a collective restitution we produced a representation of the actors, resources, dynamics and interactions necessary to talk about nitrogen management in the territory. On this topic, the stakeholders individually identify 38 types of people involved and 53 resources mobilized. Two dynamics stand out: the presence of imported nitrogenous elements in the territory and the decrease in the number of livestock in favour of cultivated surfaces on increasingly large farms. These dynamics make the stakeholders of the territory put forward the solution of the biogas production facility which can convert these inputs into digestate usable on the cultures, even if several fears around the composition of these digestates exist. Nevertheless, with the decrease in the number of animals, farms that do not use all their effluents are rare, limiting the possibilities of direct interactions between farmers and cereal growers on the territory. This work therefore highlights the importance of off-farm actors for nitrogen management at the territorial level, but it also questions the role of farmers in collective management and the resilience of these tools in the event of a decrease in livestock production. These aspects will be the objectives of the role-playing game currently being prepared, which will allow farmers and elected officials to reflect on possible options for better nitrogen management on the territory.