Top light spectral compositions affect response of greenhouse mini cucumber to intra-canopy lighting
Citation
Hao, X., Zhang, Y., Yelton, M. and Kholsa, S. 2019. Top light spectral compositions affect the response of greenhouse mini cucumber to long photoperiod of intra-canopy lighting. Oral Presention (Abstract).
Plain language summary
Supplemental lighting is essential for year-round greenhouse crop production in regions with low natural light conditions. The supplemental lighting for increasing daily light integral (DLI) can be added via lengthening photoperiods or increasing light intensity or both. Light addition via long photoperiods is more economical because less light fixtures are required and the waste heat from the light fixtures can be more efficiently used to meet heating requirement over a long period of time during a day, assuming the long photoperiods don’t negatively affect the response of plants to lighting. However, photoperiods longer than 17 or 18 hours cause photo-injury such as leaf chlorosis in greenhouse tomatoes, cucumbers and sweet peppers, limiting the yield increase at long photoperiods of lighting. Light spectra could affect the response of plants to long photoperiods of lighting. Therefore, this study was conducted to investigate the influence of light spectra on the response of greenhouse mini-cucumber to long photoperiods of intra-canopy LED lighting. The study was conducted in a large greenhouse (200 m2) during the winter 2017-18. The greenhouse was divided into 4 sections (50m2/section) and 2 top LED light spectral compositions (100% red or mixed - red:blue:white =76:16:8, at 18 h photoperiod and 140µmol m-2 s-1) were applied with 2 replications. Four intra-canopy light photoperiods (18, 20, 22, and 24 h at 40µmol m-2 s-1 of LED lighting, 87% red and 13% blue) were applied to the 4 plots inside each section. Plants grown under 100% red top light had larger top leaves and lower leaf chlorophyll than plants grown under mixed top light. The long photoperiods of intra-canopy lighting (even if at 24 hours) did not cause any significant difference in leaf chlorosis. Therefore, leaf chlorosis might not be photoperiodic in nature or might be more related to the physiological age of the leaf at the time of light exposure. The long photoperiods of intra-canopy light did result in misshaping (cupping) in the middle leaves. There was significant interaction between top LED spectra and intra-canopy LED photoperiods - the highest fruit yield and number of cupped leaves occurred at 20h photoperiod under 100% red top light while it was at 22h photoperiod under mixed top LED. The 100% red top light achieved the same fruit yield as mixed top light. Therefore, 100% red top supplemental light can be used in mini cucumber production.
Abstract
Supplemental lighting is essential for year-round greenhouse crop production in regions with low natural light conditions. The supplemental lighting for increasing daily light integral (DLI) can be added via lengthening photoperiods or increasing light intensity or both. Light addition via long photoperiods is more economical because less light fixtures are required and the waste heat from the light fixtures can be more efficiently used to meet heating requirement over a long period of time during a day, assuming the long photoperiods don’t negatively affect the response of plants to lighting. However, photoperiods longer than 17 or 18 hours cause photo-injury such as leaf chlorosis in greenhouse tomatoes, cucumbers and sweet peppers, limiting the yield increase at long photoperiods of lighting. Light spectra could affect the response of plants to long photoperiods of lighting. Therefore, this study was conducted to investigate the influence of light spectra on the response of greenhouse mini-cucumber to long photoperiods of intra-canopy LED lighting. The study was conducted in a large greenhouse (200 m2) during the winter 2017-18. The greenhouse was divided into 4 sections (50m2/section) and 2 top LED light spectral compositions (100% red or mixed - red:blue:white =76:16:8, at 18 h photoperiod and 140µmol m-2 s-1) were applied with 2 replications. Four intra-canopy light photoperiods (18, 20, 22, and 24 h at 40µmol m-2 s-1 of LED lighting, 87% red and 13% blue) were applied to the 4 plots inside each section. Plants grown under 100% red top light had larger top leaves and lower leaf chlorophyll than plants grown under mixed top light. The long photoperiods of intra-canopy lighting (even if at 24 hours) did not cause any significant difference in leaf chlorosis. Therefore, leaf chlorosis might not be photoperiodic in nature or might be more related to the physiological age of the leaf at the time of light exposure. The long photoperiods of intra-canopy light did result in misshaping (cupping) in the middle leaves. There was significant interaction between top LED spectra and intra-canopy LED photoperiods - the highest fruit yield and number of cupped leaves occurred at 20h photoperiod under 100% red top light while it was at 22h photoperiod under mixed top LED. The 100% red top light achieved the same fruit yield as mixed top light. Therefore, 100% red top supplemental light can be used in mini cucumber production.