The Impact of Daily Light Integral Supplements on Biomass Accumulation and Nutrient Uptake in Hydroponically Grown Genovese Pesto Basil
Hammock, H. A., D. A. Kopsell, and C. E. Sams.  2018.  HortScience, 53(9):S460. The Presentation was Third Place in the Oral Presentations Graduate Student Competition at the SRASHS Conference.

Light quantity, quality, and duration are three primary factors that impact plant growth and development. Light emitting diodes (LEDs) have the ability to manipulate each of these parameters and allow commercial growers to optimize biomass yield and plant quality. Many studies have evaluated the impact of spectral quality and minimum daily light integral (DLI) requirements for a variety of specialty crops, but an in-depth efficacy comparison of progressive DLIs using various supplemental lighting sources is needed in order to optimize quality and biomass yield of high-value specialty crops during unfavorable growing seasons. The objective of this study was to determine the impact of incremental DLI supplements on greenhouse hydroponic basil (Ocimum basilicum var. ‘Genovese’) production using broad spectrum HPS lamps and blue (B)/red (R) narrowband wavelengths from LED lighting systems. Overall edible biomass accumulation and nutrient uptake were evaluated. A total of nine lighting treatments were used: one non-supplemented natural light control, two HPS treatments with DLIs as 12 h and 24 h, and six 20B/80R LED treatments with progressive DLIs as 3 h, 6 h, 9 h, 12 h, 18 h, and 24 h. Each supplemental lighting treatment provided 100 µmols.m-2.sec-1. The DLI of the natural light control averaged 9.5 mol.m-2.d-1 during the growth period (ranging from 4 to 18 mol.m-2.d-1). Relative humidity averaged 50%, with day temperatures averaging 29.4 °C and night temperatures averaging 23.8 °C. All treatments were harvested 45 d after seeding. Edible biomass accumulation and nutrient uptake were significantly impacted by supplemental lighting treatments and growing season. The 12 h HPS treatment had the highest total biomass accumulation, both in fresh (FM) and dry biomass (DM); the 9 h LED treatment produced the lowest FM and DM averages across all seasons. The 18 h LED treatment produced the highest FM and DM of any other LED treatment, but was not statistically separate from the optimal HPS treatment. Mineral analysis revealed that both macro and micronutrient accumulation was impacted by various light treatments. This experiment shows that the spectral quality and DLI of supplemental lighting sources have varying levels of impact basil metabolism. LED and HPS lighting systems both have merits for improving biomass accumulation and nutrient uptake in hydroponically grown basil, but should be investigated further to determine optimal lighting types and practices for a variety of high-value specialty crops.