Quantifying the nitrogen demand of individual plants in heterogeneous canopies: A case study with crop and weed species

Crop mixtures may decrease reliance on pesticides but reducing herbicide use might increase weeds. Individual-based crop models can provide management guidelines. In heterogeneous canopies, light availability of individual plants depends on their dominant or dominated position. Estimating nitrogen demand at the plant scale, independently of light environment, is a challenge for modelling. A relationship linking shoot nitrogen amount to leaf biomass (or leaf area) at optimal nitrogen nutrition was investigated to establish if it could allow estimating nitrogen demand at the plant scale independently of its light environment. Crop and weed species were grown in greenhouse under various nitrogen treatments and, for two species, under two light levels. M the plant scale, shoot nitrogen amount was proportional to leaf biomass (or leaf area) at optimal nitrogen nutrition at vegetative stage. M reproductive stage, the relationship was allometric. The effect of light on shoot nitrogen amount per leaf biomass was minor and greater when using leaf area. Using data from previous experiments showed that the relationship using leaf biomass was stable across diverse growing conditions. The relationship linking shoot nitrogen amount to leaf biomass at optimal nitrogen nutrition can be used to model nitrogen demand of individual plants in heterogeneous canopies.