S06 - Session P15 - Innovations in supplementary light in horticulture - Improvement of canopy photosynthesis and water use efficiency of hydroponics sweet peppers by supplemental inter-lighting

Authors: Dongpil Kim *, Sungmin Kwon, Inha Hwang, Jung Eek Son

In greenhouses, the higher plant density, the less sunlight in the canopy due to shading of adjacent plants. Recently, inter-lighting has been introduced to compensate for the lack of light in the middle and bottom part of the canopy, but most of research focused on growth and yield, not water use efficiency (WUE). The objective of this study was to quantify the improvement of photosynthesis and WUE of sweet peppers by supplemental inter-lighting using red and blue LEDs. The inter-lighting started at 34 days after transplanting (DAT). The ratio red and blue LEDs in PPFD was 8:2, and the total PPFD of inter-lighting sources was adjusted to 71 μmol·m -2 ·s -1 at a 20 cm distance. Two inter-lighting treatments were applied: Natural light (control) and red+blue (RB). To quantify the transpiration from the plants, the amount of daily transpiration was measured by subtracting the drainage from the supply using the change in hydroponic system weight. The photosynthetic rate was obtained with measuring light response curves. The photosynthesis and WUE at 40, 60, and 80 DAT were calculated based on the simulated light interception using 3D plant models The WUEs for biomass and fruit yield were higher in the RB that those in the control. These results were due to more significant increases in plant dry weight and fruit yield than the water consumption under the inter-lighting. The simulation results showed increases in photosynthesis and WUE at the canopy-level, which seems to be due to the improvement of canopy light distribution by inter-lighting. In this study, the improvement of photosynthesis and WUE by RB inter-lighting was quantified through analyzing the crop transpiration during the entire growth period. (This work was supported by IPET and KosFarm funded by MAFRA, MSIT, and RDA; 421001-03)