Optimizing Growth of Crystal Lettuce Using Controlled Environments in a Thai Plant Factory

Abstract

The agricultural sector in Thailand faces significant challenges due to high summer temperatures reaching 40–43°C, which adversely affect plant growth and increase susceptibility to diseases. This study investigates the efficacy of using a Plant Factory with Artificial Lighting (PFAL) to optimize the growth conditions for Crystal Lettuce, aiming to enhance plant development and yield under controlled environments. The research focuses on determining the ideal environmental parameters within a PFAL to maximize the growth of Crystal Lettuce. Crystal Lettuce seeds were initially grown in cups filled with a perlite-vermiculite mix (3:1) and a nutrient solution with an electrical conductivity (EC) of 1400– 1600µS/cm and pH of 5.5–6.2. These seedlings were exposed to white LED lights with an intensity of 17750Lux for 10 hours daily. After initial growth, the seedlings were transplanted into a nutrient solution with an EC of 1750–1830µS/cm and subjected to yellow-white LED lights. The grow room, covering 160m2, maintained a controlled temperature of 30°C, humidity at 71%, and CO2 levels between 876–942ppm. Light intensity across different planting layers ranged from 7474 to 25722Lux. Results demonstrated that Crystal Lettuce plants in the middle of the planting layer, receiving approximately 23691Lux, exhibited the most significant growth, with a plant height of 18.75cm, fresh weight of 91.50g, and canopy width of 22.00cm. In contrast, plants on the edges with lower light intensities showed reduced growth. The study concludes that controlled environmental conditions in a PFAL, particularly optimized light intensity, substantially improve the growth of Crystal Lettuce. This research supports the potential of PFAL systems to enhance agricultural productivity in regions with challenging climates.