The aim of this study was to determine the effects of different compositions of environmental substrates on hydroponic tomato cultivation. Three different substrates were used in coir chip:dust (v/v=50:50; CP1), coir chip:dust (v/v=80:20; CP2), and rock wool cube with CP2 (CPR). The amount of irrigation during the cultivation period was 190 mL/(plant·time) in all substrates. The pH and EC were 5.8-6.2 and 2.6-2.9 dS/m, respectively. The drainage rate in CP1 was 31%, in CP2 was 36%, and in CPR was 29%. The growth of tomato plants in terms of height was higher in CP1 and CPR. The leaf area was greater in CP2. The fresh and dry weights were greater in CP2 and CPR treatments. The net photosynthesis in CP2 (19.31 μmol CO2/m2s) and root activity in CP2 were higher among all three treatments. The soluble solid content of fruit was not significantly different among treatments. The yield per plant in CP2 and CPR treatments was 17% greater than the yield per plant in CP1. Therefore, the most suitable substrate for hydroponic tomato cultivation is the substrate mixed with coir chip:dust (v:v=80:20; CP2), i.e., CPR.

In this study, a solar light collector that collects and transmits solar light required for crop production in a closed plant production system was developed. The solar light collector consisted of a Fresnel lens for collecting solar light, and a tracking actuator for tracking solar light from sunrise to sunset to increase the light collection efficiency. The optical fiber that transmitted solar light was made of Glass Optical Fiber (GOF), and it had an excellent optical transmission rate. After collecting the solar light, the amount of light was measured at 5, 10, 15, 20, 25, and 30 cm distances from the GOF through the darkroom by using a light sensor logger connected to a quantum and pyranometer sensor. Compared with solar light, the light intensity of pyranometer sensor measured at 5 cm was 114% higher than solar light, and 61% at 10 cm. In addition, it was observed that it is possible to transmit the necessary amount of light for growing crops up to about 15 cm (as over 22%) through GOF. Therefore, adding diffusers to the solar light collector should be expected to replace artificial light in plant factories or plug seedlings nurseries for leafy vegetables. More studies on the solar light collection devices and the light transmission devices that have high light collection efficiency should be conducted.