Supplemental Light Improves Yield and Quality of Chives in a Commercial Hydroponic Production System

Grower interest in narrow-band light emitting diode (LED) lighting systems is increasing due to projected energy savings over conventional lighting systems and the potential to improve yield and quality by manipulating the light available to optimize growth while minimizing potential light stress. The percentages of blue and red in narrow-band wavelengths of light from LEDs have been shown to impact mineral uptake, pigment development, and the rate of growth and development of several plant species. Our objective was to determine the impact of supplemental light on the yield and quality of chives produced in a hydroponic system. In this experiment, chives (Allium schoenoprasum) were grown in a nutrient film hydroponic system with a complete nutrient solution under commercial greenhouse conditions. The following light treatments were utilized in this study: 1) natural sunlight; 2) high pressure sodium (HPS) lighting at 70 µmols m^-2 sec^-1intensity above natural sunlight intensity; 3) LED lighting at 70 µmols m^-2 sec^-1intensity above natural light with blue at 20% and red at 80%; and 4) LED lighting at 70 µmols m^-2 sec^-1intensity above natural light with blue at 21%, green at 23%, red at 50%, and far red at 6%. The daily light integral (DLI) during the growth period in the greenhouse averaged 8.5 mol m^-2 d^-1 (ranging from 4 to 18 mol m^-2 d^-1). The supplemental light treatments each provided 6.05 mol m^-2 d^-1. Total shoot fresh weight and dry weight were twice as high in all supplemental light treatments compared to the natural sunlight treatment.Shoot fresh weight was 37 % greater in the 20% blue/80% red LED treatment than in the HPS light treatment. Total carotenoid content was 20% higher in the 20% blue/80% red LED treatment than in the natural sunlight treatment. Carotenoid content was not significantly different between the natural sunlight and the HPS or the 20% blue/21% green/50% red/6% far red supplemental light treatments. The impact of supplemental light treatments on individual carotenoids, chlorophyll a and b, and mineral content of chives will be discussed. This experiment demonstrates that supplemental lighting with narrow band LEDs improves the growth and quality of chives grown under commercial greenhouse conditions. Further research is warranted to determine the precise quantity and quality of light needed to maximize yield and quality of chives and to evaluate whether this yield and quality increase will be economically beneficial to the grower relative to lighting cost.