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Precise estimation of vegetable nitrogen (N) status is critical in optimizing N fertilization management.However,nondestructive and accurate N diagnostic methods for vegetables are relatively scarce.In our two-year field experiment,we evaluated whether an active canopy sensor (GreenSeeker) could be used to nondestructively predict N status of bok choy (Brassica rapa subsp.chinensis) compared with a chlorophyll meter.Results showed that the normalized difference vegetation index (NDVI) and ratio vegetation index (RVI) generated by the active canopy sensor were well correlated with the aboveground biomass (AGB) (r =0.698-0.967),plant N uptake (PNU) (r =0.642-0.951),and root to shoot ratio (RTS) (r =-0.426 to-0.845).Compared with the chlorophyll meter,the active canopy sensor displayed much higher accuracy (5.0％-177.4％ higher) in predicting AGB and PNU and equal or slightly worse (0.54-1.82 times that of the chlorophyll meter) for RTS.The sensor-based NDVI model performed equally welt in estimating AGB (R2 =0.63) and PNU (R2 =0.61),but the meter-based model predicted RTS better (R2 =0.50).Inclusion of the days after transplanting (DAT) significantly improved the accuracy of sensor-based AGB (19.0％-56.7％ higher) and PNU (24.6％-84.6％ higher) estimation models.These findings suggest that the active canopy sensor has a great potential for nondestructively estimating N status of bok choy accurately and thus for better N recommendations,especially with inclusion of DAT,and could be applied to more vegetables with some verification.