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RESEARCH PRODUCT

Which nitrogen fertilization techniques and crop traits promote weed biological regulation by competition?

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International audience; Environmental concerns compel us to reduce agriculturalchemical inputs such as herbicides and mineralfertilizers, particularly nitrogen. Reduced herbicide usemay increase weeds and reduced mineral fertilizationmay limit nitrogen resources. Thus, crop-weed competitionfor nitrogen may increase.Weeds with high nitrogen nutrition requirements areoften hard to manage. They could be disadvantagedby driving crop-weed competition through an adequatechoice of crop species/varieties (according to their nitrogennutrition traits) and/or adaptation of nitrogen fertilization(rate, date, straw burial or export). This studyaimed to identify which crop traits and nitrogen fertilization options can reduce weed harmfulness while maintainingcrop production over the years.A maize monoculture from Aquitaine (France) was simulatedover 10 years and 5 weather repetitions usingFlorSys1. This process-based model simulates cropgrowth and weed dynamics over the years with a dailytime step from inputs describing cropping system andpedoclimate and from species traits. We simulatedmany combinations of nitrogen fertilization (dates andrates, straw burial vs export) and initial soil organic nitrogencontent with three maize varieties (one actualV1 and two virtual named V2 and V3) differing by theirtrait values related to nitrogen nutrition. The effectsof fertilization, initial soil organic nitrogen supply andmaize variety on potential yield and weed (dis)serviceindicators were studied.A sensitivity analysis revealed that maize variety, nitrogenrate and initial soil organic nitrogen content affectedthe indicators the most. Nitrogen date and strawburial vs export affected them the least. Compared tothe V1 maize variety, in average, V2 improved potentialyield, weed services (weed species richness, beefood offer) and decreased disservices (yield loss dueto weeds, weed seed production). Variety V3 had theopposite effect. Depending on their traits related to nitrogennutrition, maize varieties reacted differently tofertilization techniques. For V1 and V2 to a lesser extent,increasing nitrogen rate increased potential yield,species richness, decreased weed seed productionand bee food offer. It was the opposite for V3. Increasingnitrogen rate decreased yield loss for each variety,it was stronger for V1 and V2 than for V3. Interestingly,an increase of initial soil organic nitrogen of 50 kg/hadecreased potential yield by 0.5 to 1 q/ha dependingon the variety.Further simulations applying optimization algorithmswill be carried out to identify nitrogen dates and ratesthat maximize yield, bee food offer and minimize yieldloss.1Colbach N, et al. (2014), Weed Research, 54: 541-555. https://doi.org/10.1111/wre.12112