Circularité de l'azote et besoins énergétiques de fermes en agriculture biologique situées en Bretagne : enseignements d'une analyse de terrain

Organic farming is gaining increasing interest for its potential to reduce the environmental impact of farming systems. However, few studies have been conducted on nitrogen management practices and farm energy use. This study analyzed nitrogen and energy flows on three organic farms - vegetable, mixed crop-livestock and cereal farms - in Brittany. The results show that the vegetable and cereal farms invest the most nitrogen and energy in their functioning and produce the most per unit area. On the other hand, mixed crop-livestock farms, due to their strong diversification, require less energy and recycle nitrogen better, but have a low nitrogen efficiency, mainly due to losses in the management of livestock effluents. Our results reflect the diversity of nitrogen management, highlighting local exchanges of matter for farm functioning. However, farmers' choices are influenced by the availability of resources, and by the competition from the development of methanization units.