Monitoring nitrogen variability in two Mediterranean ornamental shrubs through proximal fluorescence-based sensors at leaf and canopy level

•Fluorescence-based sensors can help to reduce N losses in ornamental shrubs•An optimal N rate of 450 mg L−1 was identified for P. lauroceraus and L. japonicum•Optical indices allow the estimation of chlorophyll and N at leaf and canopy level•Sufficiency thresholds of Nitrogen Balance Index (NBI) were provided•NBI mapping can identify plant N variability under homogeneous fertilization