2017 ASHS Annual Conference

Supplemental lighting is an expensive but a required input in greenhouse production. Currently, there are no simple and affordable techniques to measure how effectively plants use supplemental light in greenhouses. The efficacy of normalized difference vegetation index (NDVI) and quantum sensors to measure supplemental light use of petunia plants was tested in this study. The logic was that stress exposure would reduce supplemental light use and result in increased reflectance from the plants, which can be detected by the sensors. Incident photosynthetic photon flux (PPF), reflected PPF, leaf photosynthesis rate, and NDVI values were measured continuously after withholding irrigation. Our results indicate that both sensors can be used to measure supplemental light use of plants, but quantum sensors appear to be less sensitive than NDVI sensors to detect small changes in supplemental light use. The NDVI values showed reasonable correlation with leaf photosynthesis rate but were significantly influenced by solar angle which may limit their use to fixed lighting conditions.