Integrating plant-plant competition for nitrogen in a 3d individual-based model simulating the effects of cropping systems on weed dynamics

Archive ouverte : Communication dans un congrès

Moreau, Delphine | Pointurier, Olivia | Perthame, Laurène | Beaudoin, Nicolas | Villerd, Jean | Colbach, Nathalie

Edité par HAL CCSD

International audience. Promoting biological weed regulation by shifting resourceavailability and use from weed to crop may providean option for a more sustainable weed management.Light is generally the main resource for whichcrops and weeds compete in conventional croppingsystems. But, with the necessity to reduce mineral nitrogenfertilizer use, better managing crop-weed competitionfor nitrogen may become crucial. However, itrequires better understanding the functioning of heterogeneouscanopies in nitrogen-deficient situations. Simulationmodels are powerful tools to reach this goal.Our objective was to integrate plant-plant competitionfor nitrogen into the FlorSys model, already simulatingcompetition for light. The final aim was to provide thefirst mechanistic and 3D individual-based model simulatingthe effects of cropping system and pedoclimateon weed dynamics, integrating competition for nitrogen.The new formalisms were mostly inspired from pre-existingmodels and adapted to make them compatiblewith the individual-based representation of FlorSys.Soil-nitrogen concentration is predicted by the STICSsoil submodel linked to FlorSys. Plant nitrogen uptakewas simulated by confronting plant nitrogen demand(driven by shoot growth) to plant nitrogen supply (dependingon root characteristics, soil-nitrogen availabilityand the presence of neighboring plants with roots inthe same soil zone). Competition for nitrogen occurredwhen the amount of nitrogen available in a soil voxel(i.e. 3D soil pixel) was lower than the requirements ofall the plants with roots in this voxel. A nitrogen stressindex allowed to account for the impact of plant nitrogennutrition on plant photosynthesis, biomass allocationand morphology. To reflect the plant adaptation tothe spatial heterogeneity in soil-nitrogen availability,we introduced ‘compensation’. For a given plant, if nitrogenuptake in one soil voxel is insufficient to fulfilplant nitrogen requirements in this voxel, this local nitrogen-deficiency could be compensated by increasingnitrogen uptake in other nitrogen-richer voxels. Thenew formalisms needed only seven plant parameterswhich we measured for several crop and weed species.Simulations showed that, despite simplifying hypothesesin formalisms, predictions were consistentwith knowledge on canopy functioning and crop-weedinteractions.The nitrogen version of FlorSys will be useful to understandthe role of nitrogen in crop-weed interactionsand to identify sustainable management strategiespromoting weed regulation by competition (see Perthameet al., this congress). Due to its process-basedrepresentation and genericity (it can simulate diversecrop species), it will also be useful to better understandcrop-crop interactions in intercropping.

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