Biological control of weeds using cover crops : identification of the drivers and quantification of the effects at different temporal scales ; Régulation biologique des adventices par les couverts d’interculture : identification des déterminants et quantification des effets à différentes échelles temporelles

Searching for multiple sustainable levers to control weeds in arable fields and reduce the use of herbicides, cover crops (i.e. the plants sown after the harvest of a previous cash crop and terminated before the sowing of a following one) are a lever to explore. Particularly through the competition they generate, cover crops can biologically control weeds during the cover- and subsequent cropping periods, but their effects depend on numerous factors that may interact (e.g. pedoclimate, flora, farming practices). The objectives of this thesis were to identify the drivers of cover crop weed control during the cover- and subsequent cropping periods at different temporal scales, and to quantify their effects. A first series of field experiments identified cover crop composition and termination method as major drivers of weed control during the cover- and subsequent cropping periods. Although experimentations did not include any practices known to override cover crop effects on weeds in the cover- and subsequent cropping periods (e.g. tillage, weeding, fertilisation), the effects observed beyond the cover cropping period were very weak. Complementary field and greenhouse experiments showed that cover crop nitrogen supply can mediate the subsequent crop-weed competiton intensity. Looking foward, further research are needed in various production contexts by combining experimental and simulation studies, in order to increase the genericity of the results otained in this thesis. ; Dans la recherche de multiples leviers de gestion durable des adventices pour réduire l’utilisation d’herbicides en grandes cultures, les couverts d’interculture (i.e. plantes semées après la récolte d’une culture de rente et détruites avant le semis de la suivante) sont un levier à explorer. Notamment par la compétition qu’ils génèrent, les couverts d’interculture peuvent en effet réguler biologiquement les adventices en interculture et dans les cultures suivantes mais leurs effets dépendent de nombreux facteurs pouvant interagir entre eux ...