Individual-based 3D modelling of root systems in heterogeneous plant canopies at the multiannual scale. Case study with a weed dynamics model

Reducing pesticide use in agriculture is essential but involves shifting towards more complex agroecosystems. Plant canopies are expected to be more heterogeneous because a more abundant weed flora is likely to remain in low-herbicide fields, and because intercropping (i.e. mixing various crops species or varieties) is a promising option to reduce chemical inputs. Simulation models are useful to understand and design complex agroecological cropping systems, but they rarely represent the root systems of plants. However, belowground processes, such as competition for soil resources or infection by root-parasitic plants, are key determinants of the structure of plant communities. The aim of our study was to develop a model that simulates heterogeneous 3D individual-based crop-weed canopies from cropping system and pedoclimate and that will ultimately be used to design agroecological cropping systems. Therefore, we (1) connected a root system model (RSCone) to a weed dynamics model (FlorSys) in order to include both above and belowground parts of plants, (2) evaluated the prediction quality of our model, and (3) analysed the influence of species parameters on potential soil-resource uptake and root infection by parasitic plants. We used the well-known allometric relationship between root and total plant biomass to connect RSCone and FlorSys, and we created new formalisms to model the effect of soil compaction on root growth. Our model was shown to correctly predict long-term weed dynamics in various cropping systems. From step 3), we characterized crops and weed communities that are potentially competitive for soil resources and most likely to be infected by parasitic plants, and we deduced agronomic recommendations. For example, species emerging and occupying the soil quickly were the most likely to relay broomrape infestation and control of such species should take precedence. Although we focussed on crop-weed competition, our approach can be applied to other heterogeneous canopies, for designing crop mixtures for example.