Hydroponic Lettuce Production: Supplemental Lighting and Nitrogen Management

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ag Science and Natural Resources

Date of Award

Spring 5-1-2026

Abstract

Maintaining optimal daily light integrals (DLI) and nutrient solution concentrations is essential for enhancing growth, physiological, and phytochemical traits of leafy greens such as lettuce (Lactuca sativa L.) in greenhouse production systems. However, more information is needed to better understand the synergistic effect of supplemental lighting and nitrogen (N) concentrations on hydroponic lettuce production during seasons of low natural light. The objectives of this study were to determine the interaction between supplemental lighting and nitrogen concentration on physiological, growth, and yield traits of greenhouse hydroponic lettuce and evaluate cultivar-specific phytochemical contents of lettuce in response to the supplemental lighting in a greenhouse hydroponic system. Three lettuce cultivars (Nancy, Salvius, and Thurinus) were grown in fall and the winter under three light treatments: supplemental 80% red and 20% blue light (80R/20B) with a PPFD of 193.9 µmol·m-2·s-1 and a photoperiod of 9 hours; 80R, 10B, and 10% far red (FR) light (80R/10B/10FR) with a PPFD of 168.3 µmol·m-2·s-1 and a photoperiod of 10 hours; non-supplemental natural light control (NSL). Plants were also grown under two nitrogen concentrations (100 and 200 ppm N). Supplemental lighting treatments had limited effects on the weekly net assimilation rate, averaging 11.1 and 10.1 µmol·m-2·s-1 versus 12.0 and 10.6 µmol·m-2·s-1 in the control treatments in fall and winter cycles, respectively. In fall, with 200 ppm N, the 80R/20B and 80R/10B/10FR light treatments increased the fresh yield by 90% and 45%, respectively over the natural light control. In winter with 200 ppm N, there were no increases for these light treatments suggesting a limited benefit of supplemental lighting during this season. At 100 ppm N, there were no differences in yield response between light treatments in either season. Leaf area index (LAI) response to nitrogen concentration was higher in 200 ppm N in all light treatment in both seasons. Overall, the beneficial effect of supplemental lighting on the growth and yield was greater in fall fertilized at 200 ppm N than the same combination in winter. The 80R/20B was more effective at reducing nitrate content and increasing photosynthetic pigments whereas, the 80R/10B/10FR treatment was more effective at increasing Brix and antioxidant capacity.

Advisor

Desire Djidonou

Subject Categories

Agriculture | Life Sciences

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