Speaker
Description
Introduction. To reduce herbicide use, different avenues of biological weed regulation are currently investigated. Among these, weed seed predation by carabid beetles appears promising. Though observed in different cropping systems and conditions in fields, there has been to date no demonstration that this process actually influences weed dynamics over time and reduces weed harmfulness for crop production. Consequently, the objective of the present paper was to (1) model the impact of cropping system, field margin and pedoclimate on weed seed predation by carabids to complete the FLORSYS model, which simulates weed dynamics and crop production from cropping systems, soil and weather, (2) evaluate whether including seed predation is needed to correctly predict weed dynamics in different cropping systems, (3) determine which components of the seed predation submodel are the most influential.
Modelling weed seed predation. The new seed-predation submodel (Perthame et al., 2023) calculates the daily predation rate for each weed species from seed traits, weather data, canopy state variables and management operations. In FLORSYS, this predation rate is applied to the newly shed weed seeds on the soil surface. The equations and parameters were based on past publications from our team and other literature. Then, simulations were run with FLORSYS over 13 years, with and without the seed predation submodel, using weather data and management operations from 10 fields from the INRAE Dijon-Epoisses experimental station. The resulting output in terms of weed and crop state variables (plant density, biomass, seed bank, yield) were compared to measurements from the 10 fields, showing that including weed seed predation in the simulations improved the model's prediction quality, by reducing the overestimation in weed-variable predictions.
The factors influencing weed seed predation. A sensitivity analysis to the components of the predation submodel was run, by repeating the simulations after successively switching off individual components of the submodel. This showed that daily incident radiation, light interception by plant canopy, harvest, carabid reproduction and daily temperature had the most influence on seed predation rates.
In addition, the simulations showed that weed seed predation by carabids can contribute to managing weeds, by reducing field infestation and improving crop yields, but with large variations among crops (Figure 1). In average over all tested cropping systems, years and repetitions, seed predation slightly decreased species richness (from 59% of possible species to 57%). The effect took several years to become noticeable, even in the most affected cropping system, and the difference between years and crops was more important (Figure 1.A). Predation had no significant effect on species evenness in average but could improve evenness in some crops and years (Figure 1.B).. Both bird and bee food offer tended to be lower in the presence of seed predation (-6% and -23%, respectively) but the differences were very small compared to the variations due to crops and years (Figure 1.C and D).
The effect of predation on field infestation and crop yield was much more important, with roughly a 50%-decrease in field infestation and a 7%-increase in yield in average. These variations were even larger in the cropping systems with the largest impact (Figure 1.E and F), though the effect of crops and years remained more influential, even for field infestation.
Conclusion and perspectives. The present model-based approach is one of the rare studies to demonstrate the actual effect of weed seed predation on weed dynamics and crop production. The simulations with FLORSYS showed that weed seed predation can indeed contribute to managing weeds, by reducing field infestation, increasing weed-flora evenness and improving crop yields. To determine which cropping systems and field margins favour weed seed predation enough to noticeably contribute to biological weed regulation, more and more diverse cropping systems and weather series must be explored by simulation.
References
Perthame, L., Petit, S., Colbach, N., 2023. Modelling weed seed predation and its effects on crop production under contrasted farming systems. European Journal of Agronomy 151, 126953. https://doi.org/10.1016/j.eja.2023.126953
Funding
INRAE
ANR PPR BeCreative (ANR-20-PCPA-0001)
COPRAA funded by the Office Français de la Biodiversité (OFB)
| Keywords | Biological regulation; weeds; mechanistic model; model validation; weed seed predation |
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