Role of the spectral characteristics of radiating sources in the formation of lettuce yield in hydroponics cultivation

Growing plants indoors in the controlled environment involves the use of LED systems with an adjustable spectrum and intensity with manual or remote control. The aim of the study was to determine the role of different LED emission spectra in growth, development, and yield of lettuce cultivated hydroponically to develop requirements for the LED irradiator design. Studies were carried out in a growth chamber with periodic flooding hydroponics when irradiating lettuce plants of Kuk, Afitsion, and Khrizolit varieties under multispectral irradiators. The first irradiator has a radiation spectrum coinciding with the spectral distribution function of relative photosynthetic activity of solar radiation (control). The radiation of the second one coincides with the function of the spectral sensitivity of plants according to K.J. McCree. The third irradiator has an adjustable spectrum by three control channels for three parts of the spectrum coinciding with chlorophyll synthesis functions. It was found that the response of different lettuce varieties to the spectral composition of irradiation is specific. The maximum yield of the Kuk variety (4.45 kg/m2) was obtained under the first irradiator, that of lettuce Afitsion (4.7 kg/m2) and Khrizolit (6.55 kg/m2) – under the second one. Based on the results obtained the authors made requirements and designed an LED irradiator, which combines all the advantages of LED and digital technologies and provides for the implementation of the required radiation functions for laboratory research and in-vitro plant cultivation. It is noted that the LED module of the irradiator should include LEDs of violet, blue, red, dark red, and far red radiation, as well as LEDs of warm and cool white light colours.

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