6533b7d6fe1ef96bd12658b7

RESEARCH PRODUCT

Analysing and modelling the effect of nitrogen competition in weed regulation.

subject

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Reducing the use of herbicide and mineral fertilizers is crucial to develop sustainable cropping systems. Such changes might result in an increased weed flora as well as intensify competition for resources, particularly nitrogen, between crops and weeds. The aim of this thesis was to analyze and model (via the mechanistic crop model FLORSYS) the key processes underlying nitrogen competition, in order to determine if changes in nitrogen fertilization techniques and cultivar choice could promote biological weed regulation.At the beginning of the thesis, the FLORSYS model (which simulates the effects of cropping systems in interaction with pedoclimate on weed dynamics) only included light competition. A first step consisted in including nitrogen competition in the model. Experiments in controlled conditions were used to establish original formalisms and parameters characterizing the diversity of crop and weed traits related to nitrogen nutrition.Then, virtual experiments (simulations) with the new FLORSYS version identified nitrogen fertilization techniques and crop traits related to nitrogen nutrition that the most influenced weed impacts on production and biodiversity for a case study (maize monoculture in Aquitaine, France).Finally, for the case study, optimization algorithms were applied to nitrogen fertilization techniques and crop traits related to nitrogen nutrition to propose innovative cropping systems promoting biological weed regulation by competition and reconciling crop productivity and biodiversity.This thesis resulted in producing new knowledge on (1) how to model plant nitrogen nutrition in heterogeneous canopies and (2) the role of nitrogen in crop-weed competition. This work suggests that including nitrogen fertilization techniques and cultivar choice among levers would be helpful to promote weed biological regulation.