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RESEARCH PRODUCT

Are No-Till Herbicide-Free Systems Possible? A Simulation Study

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Conservation agriculture (CA) allows farmers to reduce costs and enhance soil health, buttends to increase either weed infestation and associated crop yield loss, and/or herbicide use.We aimed to investigate how much tillage contributes to reducing weed infestation and yieldloss, and which systems and weed species are the most affected if tillage is deleted. Wecollected farming practices on 395 arable cropping systems from Spain and France, andsimulated them over 30 years and with 10 weather repetitions, using FLORSYS. This processbased model (Colbach et al., 2021, Field Crops Res 261:108006) simulates daily multi-speciesweed floras and crop canopies from cropping systems and pedoclimate over the years. Threeseries were simulated, (1) using the recorded cropping systems, (2) eliminating tillage withoutotherwise changing management practices, (3) eliminating all herbicides without any otherchanges. Each series was run twice, once starting with a regional weed-flora pool to simulateweed dynamics and their impact on crop production and biodiversity, and once without weedsto predict potential crop yield. Among the recorded systems, herbicide treatment frequencyindex (HTFI) averaged over rotation increased when tillage frequency decreased. No recordedno-till system was herbicide-free. The untilled crops with the lowest HTFI (0.16) were unusualcrops, i.e., relay grass crops or multi-annual crops.Simulations of the recorded systems showed no correlation between tillage-frequency andweed biomass or yield loss. When tillage was deleted without any other change, yield lossalmost doubled. Tillage deletion similarly increased most of the other weed impacts, i.e.harvest pollution, harvesting difficulty or weed-based carabid-food offer. Weed offer for birdsand pollinators increased approximately twice as much whereas species richness, fieldinfestation and potential yield (in the absence of any weeds) varied little on average.We then identified (1) which weed species and traits (e.g., spring/summer annuals) increasedafter tillage suppression and in which cropping systems (e.g., species with persistent, thickcoated seeds in rotations with frequent winter crops), (2) which recorded systems were robustto tillage suppression in terms of weed-caused yield loss (e.g., with cover crops, summercrops), (3) which no-till systems (recorded or obtained after deleting tillage) limited yield loss(usually those with frequent and/or efficient herbicides), (4) which management techniqueswere associated with a reduction in tillage, in herbicides, and in yield loss (e.g., long anddiverse rotations, cover crops). No tested system achieved all three objectives simultaneously.The simulations indicated that two CA pillars (diverse crop rotations, cover cropping) wereessential to manage weeds in systems with reduced tillage and reduced herbicide use. Moreno-till cropping systems must be investigated to determine whether sustainable no-tillherbicide-free systems are possible.Funding: INRAE and the Ecophyto COPRAA project.