Interlighting in mini-cucumbers: interactions with overhead lighting and plant density.
Hao, X.M., Guo, X.-B., Chen, X., and Khosla, S. (2015). "Interlighting in mini-cucumbers: interactions with overhead lighting and plant density.", Acta Horticulturae (ISHS), 1107, pp. 291-296. doi : 10.17660/ActaHortic.2015.1107.40 Access to full text
Inter-lighting, applying supplemental light within crop canopy, has been shown to improve plant vertical light distribution and light use efficiency, with HPS (high pressure sodium) lamps in Scandinavia. However, it is not feasible on vegetables cultivated with the popular twin-row system (narrow row) used in major greenhouse vegetable production area in northern regions because of its high bulb temperature. Light emitting diodes (LEDs) have low operating temperature and thus are potentially a good fit for inter-lighting. Therefore, the effects of LED inter-lighting on plant growth, fruit yield, and light and energy use efficiency were investigated in this study. To optimize the production system with lighting, different levels of top HPS lighting, LED inter-lighting, and plant densities were also evaluated. Two experiments were conducted. Experiment one evaluated single row of LED inter-lighting module per twin-row (36.7 µmol m-2 s-1) without or with top HPS (165 µmol m-2 s-1) at 2.8 and 3.6 plants m-2, respectively. Experiment two evaluated double rows of LED inter-lighting modules per twin-row (73.4µmol m-2 s-1) without or with top HPS lamps (120 µmol m-2 s-1) at 2.8 plants m-2. LED inter-lighting improved fruit yield and quality. However, it had similar light use efficiency as the top HPS lighting based on the light reaching the crop canopy. Higher plant density at strong top HPS lighting (165 µmol m-2 s-1), improved the response to LED inter-lighting, and the response to LED inter-lighting was better at the lower top HPS lighting (120 µmol m-2 s-1). Therefore, the response of mini-cucumbers to LED inter-lighting can be optimized by using proper crop management and top/inter-light ratio. Because LED inter-lighting allowed more light to reach crop canopy and higher efficiency of electricity to light conversion, the plants grown with LED inter-lighting achieved higher energy use efficiency than that with the top HPS in both experiments.
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