Optical sensors are a fast and nondestructive new technology used to estimate plant chlorophyll content by measuring leaf reflectance or absorbance of light. The objective of this study was to evaluate the reliability of normalized difference vegetative index (NDVI) values calculated by the GreenSeeker™ hand held sensor as an indirect indicator of dianthus (Dianthus chinensis L.) N status, and investigate nutrient supplementation on deficient ‘Telstar™ White’ and ‘Telstar™ Red Picotee’ plants. Pots were supplemented with 0, 5, 10, 15, and 20 g of 15N-3.9P-10K controlled release fertilizer (CRF). Soil and plant analysis development (SPAD) chlorophyll meter, GreenSeeker™ NDVI sensor, and atLEAF meter readings were recorded for four consecutive weeks. At 49 d after planting (DAP), the 0 and 5 g treatments were found deficient and half of the pots were supplemented with extra fertilizer for treatment correction (C 0 and C 5, respectively). The SPAD and atLEAF readings showed stronger correlation to actual leaf N concentration compared with the GreenSeeker™. The GreenSeeker™ readings were less correlated with leaf N concentration at early stages of establishment due to the plants’ small size and background noise, as well as at later stages of establishment due to anthesis. Dianthus quality responses generally increased as fertilizer rates increased. The additional correction treatment showed a significant improvement in C 5 and no significant improvement on C 0, indicating that the correction treatment was beneficial for dianthus when initial amount of fertilizer was applied.
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