Can ligneous residues be recycled for weed control?

The use of pesticides in agriculture causes problems for human health and the environment, so that alternative solutions for weed control are urgently requested. In this study we test the possibility to recycle composted wood and white fir bark as biopesticide at three different experimentation scales: (i) in Petri dish, hot water extracts of the ligneous residues were used for a germination test with rapeseed and winter wheat seeds; (ii) in greenhouse pots, two successive cycles of rapeseed sowings were carried out with an equivalent of 300 m³ ha - ¹ and 600 m³ ha - ¹ of ligneous residues so to assess the effect on crop seedling biomass; (iii) in a field experiment, 300 m 3 ha -1 of ligneous residues were spread as mulch or incorporated into the soil just before the sowing of rapeseed in 2022 without any herbicide application. We observed that fresh bark extract prevented winter wheat and rapeseed germination, while extracts of decomposed bark and composted wood did not affect crop seed germination. In the greenhouse experiment, the biomass of rapeseed seedlings was lower with ligneous residues compared to the control, particularly with bark. In the field, only the bark had a negative effect on the number of emerging weeds during the autumn 2022, while no difference in weed biomass was observed between treatments in the following spring 2023. Overall, the 3-cm thick mulch alone was not sufficient to control the weed biomass in the field but seems promising as part of an integrated weed management strategy.