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With the reduction of both herbicide and mineral fertiliser use for environmental reasons, crop–weed competition for nitrogen might increase in arable fields. Adapting nitrogen fertilisation and selecting crop species/varieties according to their nitrogen-nutrition traits could provide options to influence competitive relationships among plants. A simulation study was conducted to identify which nitrogen-fertilisation options and crop traits related to nitrogen nutrition have the greatest influence on weed impacts in the agroecosystem. We examined indicators of both weed harmfulness (i.e., crop grain yield loss due to weeds, field infestation by weed biomass, and weed seed production) and weed benefits (i.e., weed species richness and weed-based food offer for bees). Sensitivity analyses were performed using a process-based model ( FlorSys) simulating crop and weed growth and dynamics over the years based on information on the cropping system, pedoclimate, and species traits. A maize monoculture from southwestern France was used as a case study. Different maize varieties (differing in their trait values related to nitrogen nutrition) were simulated under different scenarios of nitrogen fertilisation (application date and rate, crop residue management, and initial soil organic nitrogen) and weather. The analyses showed that nitrogen application rate and maize variety were the factors most influencing weed impacts on the agroecosystem. Decreasing nitrogen rates increased weed harmfulness and decreased maize yield potential (i.e., yield in the absence of weeds). The maize traits that both reduced weed harmfulness the most and increased maize productivity the most were low plant nitrogen demand, high root nitrogen uptake efficiency, and a specific leaf area (leaf area per unit leaf biomass) insensitive to plant nitrogen stress. These results are useful for better understanding the role of nitrogen in crop–weed competition and for identifying management strategies that promote biological weed regulation.
Perthame et al. (Fri,) studied this question.