Effects of different LED lights and substrate media on growth of lettuce in an aquaponic system

Light emitting diodes (LED) are a good source of light energy because its light intensity can be adjusted, it has a low operating temperature as well as a long life and it uses less energy than other light sources. Current agriculture production places increasing emphasis on producing clean food, conserving the environment and effectively utilizing energy. Lettuce (Lactuca sativa L. 'Ziwei') production in an aquaponic system, exploiting waste excreted by fish as the plant fertilizer, was investigated. LEDs of various colour combinations were used as light sources for growing lettuce; included 1) fluorescent (a non-LED control), 2) white LED, 3) white and red LED (1:1), 4) white and red LED (1:2), 5) white and red LED (2:1) and 6) white, red and blue LED (1:1:1). Plants were grown on two substrates (laterite rock and expanded clay balls) in flood and drain aquaponic systems. Lettuce grown under white and red LEDs light (1:1, 1:2 and 2:1) on the laterite rock had the greatest plant height, leaf length, leaf width, leaf number, SPAD value, fresh and dry weight of stem and roots without iron deficiency symptoms. The combination of white and red LEDs lights (1:1, 1:2 and 2:1) and laterite rock has potential to improve growth of vegetables grown on aquaponic systems in greenhouse and plant factories.