Résumé du projet CoSAC (en anglais) : Conception de Stratégies durables de gestion des Adventices dans un contexte de Changement (climat, pratiques agricoles, biodiversité)
Reduced herbicide use required by French and European legislation will change weed management. Weeds are very harmful for crop production but contribute to biodiversity in agricultural landscapes. Consequently, reduced herbicide use, agricultural production and biodiversity conservation must be reconciled in arable crops. The project team consists of multidisciplinary partners (ecologists, agronomists, modellers,...) from research and development in order to: (1) understand and quantify with experiments the effects of novel agricultural practices on weed flora and on the functioning of the agroecosystem, (2) design tools predicting the effects of agricultural practices and pedoclimate on weed flora, (3) use these tools to design weed management strategies and to evaluate their performance in various contexts of changing agricultural practices, climate and biodiversity, (4) facilitate the adoption of the novel weed management strategies by farmers.
Task 1 will focus on crop diversification (cover crops, crop associations), localized technology (local herbicide spraying, fertilizer placement in crop rows, strip-till) and no till. These techniques will be monitored in field experiments, the underlying processes will be studied in controlled conditions (competition for light, nitrogen and water; root architecture; seed germination on soil surface...) and in fields (weed detection and identification by aerial image analysis; soil structure and hydrothermal conditions in no-till).
Task 2 will use these results to improve the existing FLORSYS model which quantifies the effects of cropping system and pedoclimate on weed dynamics and calculates indicators of weed harmfulness (e.g. crop yield loss) and benefits (e.g. species richness, food offer for bees). FLORSYS will be further improved by adding herbicide resistance and seed dispersal functions, by upscaling from the field to a multi-field mosaic, by improving the phenology prediction, and by completing the weed evaluation indicators. FLORSYS will be used to run sensitivity analyses to identify correlations between cultural techniques and weed species traits. These simulations will also be used to develop a decision-aid tool for evaluating cropping systems in terms of weed harmfulness and benefits, after questioning future users (scientists, advisors, farmers) to identify pertinent evaluation criteria and model uses. If possible, another tool for designing cropping systems as a function of the user's goals in terms of weed harmfulness and benefits will be developed.
Task 3 will use FLORSYS and its tool progeny to evaluate existing cropping systems identified in past farm surveys, existing farm networks (DEPHY) and cropping system trials (INRA, ARVALIS, SYPPRE project). New cropping systems reconciling reduced herbicide use, agricultural production and biodiversity conservation will be designed by experts (scientists, advisors), and evaluated with FLORSYS and its progeny. Existing and prospective cropping systems will then be improved in a second loop based on their simulated performance in a second loop of conception. Then, the sensitivity of the best strategies to different changes (regulations, socio-technical context, climate, weed flora) will be tested. The best systems will be evaluated by multicriteria analysis (DEXIiPM® and SYSTERRE®) for their economic, environmental and organisational performances. To take account of farmers' objectives and constraints during cropping system design, farmer interviews will be organized to identify obstacles that hinder the adoption of technical innovations.
Task 4 will organize the publication and dissemination of the project results, via meetings, website, training sessions on the newly developed tools and weed management strategies for advisors and farmers.