2014 ASHS Annual Conference

Determination of variable-rate nitrogen (N) fertilization using optical spectrometry sensors in flowers is becoming an interesting vista for commercial growers. Nitrogen (N) is an important component of proteins and chlorophyll (Chl), and has been correlated with nondestructive reflectance sensors as a means to determine N status during crop production. In this experiment, chrysanthemums ‘Amico Bronze’ and ‘Jacqueline Yellow’ had different fertilizer treatments (0, 5, 10, 15, or 20 g of 16-9-12 N-P-K) ranging from deficient to excess with 10 replications each. Continuous response variables of Normalized Difference Vegetation Index (NDVI), Soil Plant Analytical Development (SPAD) and atLEAF sensor readings were analyzed using generalized linear mixed models methods for six weekly (10, 17, 24, 31, 38 and 45 days after adding treatments; DAT) repeated measurements. The results indicated that leaf N (LN) was correlated with N treatment in all treatments except 17 DAT. Normalized Difference Vegetation Index was correlated with LN in the early stages of plant growth as well as the final stage before flowering. Normalized Difference Vegetation Index increased linearly up to 31 DAT for all treatments then plateaued 45 DAT. The SPAD readings were correlated with LN as early as 24 DAT, whereas, NDVI was correlated as early as 10 DAT. Finally, after 45 DAT all sensors were correlated with LN in ‘Jacqueline Yellow’. The Atleaf sensor was not correlated with LN at any sampling date. The results of this study indicate that both SPAD and NDVI meter can be used to indicate N status in chrysanthemums.