6533b851fe1ef96bd12a9fc9

RESEARCH PRODUCT

Mise en évidence du rôle de la diversité dans la dynamique des communautés d'adventices et des interactions adventices/cultures

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The main challenge of 21st century agriculture is to provide sufficient food for a growing to identify cropping systems which maintain crop productivity, minimize reliance on synthetic herbicides and nitrogen fertilizers, and promote weed diversity. We hypothesized that cropping system diversification, either at the annual scale through the introduction of cover crops, or at the plurennial scale through a diversification of the crop sequence and associated weed management tools, could be a viable means to reach these objectives. More specifically, we hypothesized that cropping system diversification could (i) contain weed abundance and thereby, allow a reduction of herbicide use and an increase in weed diversity, and (ii) alleviate weed:crop competition through a modification of weed communities or available resources. Three experiments were mobilized or implemented to test these hypotheses: (i) a long-term integrated weed management cropping system experiment focusing on contrasted agronomic pathways to reduce herbicide reliance (2001 2017, Dijon, France), (ii) a longterm factorial experiment focusing on the interaction between cover crops, nitrogen fertilization, and tillage systems (1993 onwards, Pisa, Italy), and (iii) a three year experiment focusing on the effect of contrasted weed communities on winter cereal productivity (2016 2018, Dijon, France). Firstly, results highlighted that low herbicide use, long-term weed management, and high crop productivity can be reconciled in grain-based cropping systems provided that a diversified crop rotation integrating a diverse suite of tactics (herbicides included) is implemented. Strict no-till was not able to achieve significant reductions in herbicide use, mainly due to the use of glyphosate for burndown weed control. All alternative cropping systems tested were able to increase weed diversity at both the annual and plurennial scale but each pathway selected distinct weed community characteristics. Tillage, crop type and weeding strategy appeared as the main factors structuring weed communities. Secondly, we identified that the weed suppressive potential of cover crops could not simply be summarized to biomass production: the slopes between cover crop and weed biomass depended on cover crop species. However, modifications in weed community abundance or structure during the fallow period did not carry over to the subsequent crops, possibly due to the combined effect of tillage and herbicides. Nevertheless, the introduction of cover crops, such as Vicia villosa Roth, allowed to reach maximum maize productivity while significantly reducing nitrogen fertilization. Finally, analysis of weed:crop competitive relationships showed that (i) not all weed communities were capable of generating yield losses, (ii) weed communities can generate yield losses through contrasted processes in time or space, and that (iii) weed diversity was highly correlated to low weed biomass and therefore, a reduced effect on winter cereal productivity. All results point out that ecological intensification in agriculture can maintain crop productivity while limiting chemical herbicides and nitrogen fertilizers, and that this generally favors higher weed diversity. Benefits associated to cropping system diversification were mainly visible when management intensity was reduced. The transition towards more environmentally sound cropping systems will require deep changes for farmers and the farming sector, and in the way farmers are rewarded for the agroecosystem services they provide.