Effects of Ultraviolet Light Exposure Duration onthe Leaf Development of Pak-choi (Brassica rapa L. subsp. chinensis) Grown in a Greenhouse Tower Hydroponic System

Abstract

The increasing demand for sustainable vegetable production has encouraged the adoption of greenhouse hydroponic systems integrated with supplemental lighting technologies. This study evaluated the effects of different ultraviolet (UV) light exposure durations on the leaf development of pak-choi (Brassica rapa L. subsp. chinensis) grown in a greenhouse tower hydroponic system. A completely randomized design (CRD) with five treatments and three replications was employed: T1–Control (natural light), T2–UV light at 30 cm for 4 hours, T3–UV light at 30 cm for 8 hours, T4–UV light at 50 cm for 4 hours, and T5–UV light at 50 cm for 8 hours. The leaf number and leaf area were measured at 10, 20, and 30 days after transplanting (DAT), and the data were analyzed using analysis of variance (ANOVA) followed by Tukey’s Honest Significant Difference (HSD) test. Results showed that T3 consistently produced the highest leaf number (5.63, 7.43, and 12.30) and the largest leaf area (31.40, 51.37, and 118.97 cm²) across all observation periods, while the control treatment recorded the lowest values. The findings indicate that an 8-hour UV exposure at a 30 cm distance significantly enhanced the vegetative growth of pak-choi under greenhouse hydroponic conditions. This study demonstrates that optimizing UV light exposure duration can improve crop productivity and supports sustainable protected agriculture by contributing to Sustainable Development Goals 2 (Zero Hunger), 12 (Responsible Consumption and Production), and 13 (Climate Action).