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Adoption de l’agriculture de conservation : adaptations agronomiques et réponses des communautés adventices

Abstract : Conservation agriculture is a farming system based on the continuous and simultaneous application of three principles: minimal soil disturbance, continuous residue cover on the soil surface and diverse crop rotations. Adoption of this form of sustainable agriculture in France since the 2000s has been hampered by a number of constraints, including the development and management of weed populations. From an agronomic point of view, the adoption of conservation agriculture and associated abandonment of tillage results in a significant loss of weed management practices for farmers. From an ecological point of view, its application can modify all the assembly processes that act on weed communities.To address the lack of existing knowledge on the subject, we were interested in 1) how farmers using conservation agriculture adapt their cropping practices and their weed management and 2) how weed communities respond to a continued application of conservation agriculture principles. To meet our objectives, two survey designs were used: a national online survey of application of conservation agriculture practices and a regional survey of a network of farm plots applying conservation agriculture in Bourgogne-Franche-Comté.Although adaptations of weed management practices may vary between farmers, the results showed that farmers using conservation agriculture compensate for the abandonment of tillage by employing different management practices related to chemical weeding (especially during the intercropping period) and plant competition (cover crop, combined/companion crops, sowing rate optimization). The mastered use of weed management practices following the principles of conservation agriculture, particularly the optimization of crop rotation, tends to be achieved only after several years (average 5 years) for a majority of farmers.For weed communities, the adoption of conservation agriculture results in a modification of the environmental and biological constraints that act on community assembly processes, thus gradually allowing new species to become established. The long-term application of conservation agriculture tends to result in the convergence of the taxonomic (species) and functional (traits) composition of the weed communities. This convergence is nevertheless modulated by local conditions: the weed flora occurring on a plot depends on the duration of the application of conservation agriculture and the identity of the crop established. The greatest taxonomic and functional shift in the weed community occurred following 10 years of conservation agriculture.In an overall context of policies aimed at decreasing pesticide use, and given the current importance of synthetic herbicides in weed management, the efficacy of conservation agriculture in controlling weeds may be questioned despite the very significant investment made by farmers in this system that aims to contribute to a sustainable agriculture.
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Damien Derrouch. Adoption de l’agriculture de conservation : adaptations agronomiques et réponses des communautés adventices. Sciences agricoles. Université Bourgogne Franche-Comté, 2020. Français. ⟨NNT : 2020UBFCK052⟩. ⟨tel-03133176⟩

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