Department of Horticulture and Landscape Architecture, Oklahoma State University, 358. Ag Hall, Stillwater, Oklahoma, USA. 74078-6027. Department of Statistics, Oklahoma State University, 301F MSCS Bldg., Stillwater, Oklahoma, USA. 74078-6027. Department
Journal of Applied Horticulture, 2015, volume 17, issue 3, pages 181-185.
Abstract: Greenhouse production of Gaillardia is becoming increasingly popular for potted production due to growing interests in drought tolerant plant material. The objective of this study was to see if nondestructive handheld sensors could be used to monitor nitrogen (N) status in Gaillardia aristata ĎArizona Apricotí. Topdressed fertilizer treatments of 0, 4, 8, 10, or 12 g of controlled release fertilizer (CRF) 16N-3.9P-10K were added to greenhouse grown plants. Individual plants were scanned from 10 pots per treatment for Normalized Difference Vegetative Index (NDVI) and Soil-Plant Analyses Development (SPAD) over eight different sampling dates starting 7 days after fertilizer treatment application (DAT). Height, width, leaf N concentration, and number of panicles were also recorded. Linear, cubic, and quadratic trends were seen for NDVI and SPAD. Plant height was greatest in the 10 g treatment, but was not different than any other treatment. Plant width was greatest in the 12 g treatment, but was not different from the 4 g and 10 g treatments. Number of panicles was highest in the 12 g treatment, but was not different from the 10 g fertilizer treatment. Neither sensor showed correlations with leaf N concentration 7 DAT; however, the NDVI sensor showed the earliest correlation with leaf N concentration starting 14 DAT. Both sensors were correlated with each other at 35, 42, and 56 DAT. Results from this study indicate that 10 g CRF was sufficient for plant growth and flowering. Both sensors can be used to predict N status in potted Gaillardia; however, consistency in sample collection and sampling time may be necessary to correlate values with N status.