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Are no-till herbicide-free systems possible? A simulation study

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Nathalie Colbach
Stéphane Cordeau

Abstract

Conservation agriculture (CA) allows farmers to reduce costs and enhance soil health, but tends 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 yield loss, and which systems and weed species are the most affected if tillage is deleted. We collected farming practices on 395 arable cropping systems from Spain and France, and simulated 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-species weed floras and crop canopies from cropping systems and pedoclimate over the years. Three series were simulated, (1) using the recorded cropping systems, (2) eliminating tillage without otherwise changing management practices, (3) eliminating all herbicides without any other changes. Each series was run twice, once starting with a regional weed-flora pool to simulate weed dynamics and their impact on crop production and biodiversity, and once without weeds to predict potential crop yield. Among the recorded systems, herbicide treatment frequency index (HTFI) averaged over rotation increased when tillage frequency decreased. No recorded no-till system was herbicide-free. The untilled crops with the lowest HTFI (0.16) were unusual crops, i.e., relay grass crops or multi-annual crops. Simulations of the recorded systems showed no correlation between tillage-frequency and weed biomass or yield loss. When tillage was deleted without any other change, yield loss almost 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 birds and pollinators increased approximately twice as much whereas species richness, field infestation 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) increased after 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 robust to tillage suppression in terms of weed-caused yield loss (e.g., with cover crops, summer crops), (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 techniques were associated with a reduction in tillage, in herbicides, and in yield loss (e.g., long and diverse rotations, cover crops). No tested system achieved all three objectives simultaneously. The simulations indicated that two CA pillars (diverse crop rotations, cover cropping) were essential to manage weeds in systems with reduced tillage and reduced herbicide use. More no-till cropping systems must be investigated to determine whether sustainable no-till herbicide-free systems are possible. Funding: INRAE and the Ecophyto COPRAA project.
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Dates and versions

hal-03887831 , version 1 (07-12-2022)

Identifiers

  • HAL Id : hal-03887831 , version 1

Cite

Nathalie Colbach, Stéphane Cordeau. Are no-till herbicide-free systems possible? A simulation study. XVII. Congress of the European Society for Agronomy, Aug 2022, Potsdam, Germany. ⟨hal-03887831⟩
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