Efficient nitrogen (N) management is essential for improving fertilizer use efficiency and minimizing nutrient losses in greenhouse ornamental production systems for plants such as poinsettias (Euphorbia pulcherrima ‘Bravo Bright Red’). We evaluated two handheld optical sensors, the SPAD-502 chlorophyll meter and the GreenSeeker™ active canopy sensor, for diagnosing plant N status and assessed whether a micronutrient supplement(BAM-FX)influenced sensor responses across N rates. Seventy plants were arranged in a completely randomized design with seven treatments consisting of three Nutricote 18-6-8 rates (2.8, 4.1, and 5.5 g/pot), applied alone or with BAM-FX soil drenches. The canopy normalized difference vegetation index (NDVI), soil plant analysis development (SPAD) values, leaf N concentration, and leachate properties [nitrate ðNO32Þ; phosphate ðPO32 4 Þ; pH, and electrical conductivity (EC)] were measured at 20, 35, 48, and 55 days after N top-dressing (DAT). Canopy development was tracked most strongly by the NDVI during the early phase (20–35 DAT) and showed the strongest relationship with leaf N at midseason (48 DAT), supporting its use as a canopy-scale indicator of N sufficiency. SPAD readings were more sensitive at early and late sampling dates, reflecting stage-dependent variation in leaf chlorophyll not consistently captured by the NDVI. Leachate NO32 increased with higher fertilizer inputs early in the growth cycle, indicating greater nutrient losses before peak plant uptake, whereas PO32 4 remained low. Moderate to moderately high N rates without BAM-FX maintained high optical indices while avoiding excessive NO32 leaching and EC accumulation. BAM-FX produced variable and inconsistent effects on sensor responses and canopy vigor. We concluded that integrating NDVI, SPAD, and leachate monitoring provides a practical framework for optimizing N management in poinsettia production.
