Impact de la conduite des cultures intermédiaires sur la flore adventice : résultats de l’analyse de 31 essais

National audienceData of 31 field trials were analysed to quantify the impact of cover crops grown during summerfallow on weeds during this period. Results show that weed abundance at the date of cover-cropdestruction greatly varies between experimental locations which differed in terms of pedoclimate,previous crop etc. Cover-crop above-ground biomass did not impact weed plant density. However,weed above-ground biomass decreased with increasing cover-crop biomass. Cover-crop speciesgreatly differed in their ability to reduce weed biomass, according to their own biomass, their speedof soil coverage at early stages and their above-ground plant morphology. Cover crops with highlevels of biomass and rapid soil coverage strongly reduced weed biomass but without eliminatingweeds entirely. Weeds density monitored in crops following the cover crops were neithercorrelated to weeds abundance during the fallow period nor to cover crop biomassLes données de 31 essais ont été analysées afin de quantifier l’impact des cultures intermédiairessur les adventices pendant l’interculture. Les résultats montrent une très grande variabilité de ladensité d’adventices à la destruction du couvert, principalement selon l’effet site (pédoclimat,précédent cultural, parcelle, etc.). La biomasse aérienne du couvert n’a pas d’effet sur la densitéd’adventices (nombre d’adventices/m²). En revanche, la biomasse aérienne d’adventices (t/ha dematière sèche) décroit avec la biomasse aérienne du couvert. Il existe des différences notoiresentre espèces de couvert, selon leur production de biomasse, leur vitesse de couverture du sol etles caractéristiques de leurs parties aériennes. Les couverts à forte biomasse et forte vitesse decouverture du sol limitent nettement la biomasse des adventices sans pour autant les fairedisparaître. La densité d’adventices observée dans la culture suivante n’est ni corrélée à la densitéd’adventices pendant l’interculture, ni à la biomasse du couvertAbstractData of 31 field trials were analysed to quantify the impact of cover crops grown during summerfallow on weeds during this period. Results show that weed abundance at the date of cover-cropdestruction greatly varies between experimental locations which differed in terms of pedoclimate,previous crop etc. Cover-crop above-ground biomass did not impact weed plant density. However,weed above-ground biomass decreased with increasing cover-crop biomass. Cover-crop speciesgreatly differed in their ability to reduce weed biomass, according to their own biomass, their speedof soil coverage at early stages and their above-ground plant morphology. Cover crops with highlevels of biomass and rapid soil coverage strongly reduced weed biomass but without eliminatingweeds entirely. Weeds density monitored in crops following the cover crops were neithercorrelated to weeds abundance during the fallow period nor to cover crop biomas