Carry over effects of cover crop mixtures and management practices on subsequent crops and weeds in no-till systems
Résumé
Cover crop (CC) mixtures appear as a promising agroecological tool to suppress weeds and
maintain crop productivity while reducing chemical inputs such as herbicides and nitrogen
fertilizers. The weed suppressive effect of CC and CC nitrogen release have been related to CC
composition, soil resource availability and CC termination methods but the relative effect of
these factors and their interactions remain poorly documented, especially in the case of CC
mixtures. Most studies have focused on the subsequent spring crop, and hence, lacked to
investigate long-term carry over effects of CC. A two field: year experiment was conducted to
investigate the effect of CC mixture (2 or 8 species including or not legume species, compared
to a bare soil control), resource availability (water and nitrogen) at CC sowing and CC
termination method (rolling and glyphosate, compared to a winterkill control) on weed
biomass and productivity of two subsequent unweeded, unfertilized and direct seeded crops
(spring barley and winter linseed in year 1 and 2, respectively). In the context of reduction of
herbicide use, our experiments showed that the use of CC to reduce weed biomass in the
subsequent crop was not relevant when CC were terminated by winter or rolling since CC
probably protected weeds from winter instead of creating a physical barrier for weed
emergence, weed community composition in crop being mainly represented by weed
volunteers. Weed biomass was the main driver of the subsequent crop productivity but the
latter was enhanced after fertilised or legume-based CC, probably because of a higher
nitrogen release. No relevant long-term effect of CC on the subsequent crop was observed in
our experiment, probably because nitrogen was used by the previous crop and weed
community composition changed by year. Our results highlight the importance CC
composition and management for weed suppression and crop productivity in low-intensity
biodiversity-based cropping systems.