Weed dynamic in Conservation Agriculture: experiences from the Isite-BFC regional network of farmers and cropping system experiments on agroecology in France.

ISBN: 978-84-09-37744-2International audienceConservation Agriculture (CA) relies on three fundamental pillars: diversified crop rotation, permanent soil coverand no soil disturbance. Weed control relies on few tools because pre-sowing tillage, pre-emergence herbicidespraying and in-crop mechanical weeding are not possible. This could lead to drastic changes in weed communitiesand quickly after the transition to CA, with fewer annual species (weed seeds remain on the soil surface, a conditiondeemed to be unfavourable to weed germination) and higher perennial species. However, the implementation ofCA principles could be transcribed into a wide array of cropping systems because the objectives of farmers differ,and/or because systems are implemented in different production situations (e.g., associated or not to livestock, soiltype, irrigation). Therefore, the Isite-BFC regional network gathers CA farmers and experimenters from cooperatives and research institute (INRAE) to share their experiences, detailed practices and weed surveys initiated since2007 in some sites. Weed diversity was high in all systems compared to what is known from tillage-based agriculture. Weed community changes over time depending on the diversity of crop rotation tested and initial weedingpressure. Since CA is challenged by potential glyphosate ban in Europe, the application of glyphosate was stoppedin 2018 in some sites and thus, cropping systems were redesigned accordingly to ensure weed management overthe long run, economic profitability and multiperformance