Abstract
Sustainability is the most critical point in micro-scale indoor crop systems. It can be improved through the optimization of all of the production factors, such as water, nutrients, and energy. The use of light-emitting diodes (LED) allows the fine regulation of the light intensity and light spectrum to be obtained, with a significant reduction in energy consumption. The objective of this study was the optimization of a LED-based protocol of light management for Romaine lettuce cultivation in a micro-growing environment specifically designed for home cultivation. Four different growing cycles were tested. In each one, the light spectrum was modified by increasing the percentage of red light and decreasing the blue light. This resulted in a change in the light intensity which ranged from 63.2 to 194.54 µmol m−2 s−1. Moreover, the photoperiod was shortened to reduce the energy consumption and, in the last cycle, the effect of the daily alternation of dark and light was tested. The fresh and dry biomass produced were measured and the energy consumed in each cycle was monitored. The quality of lettuce was evaluated by measuring several physiological indexes, including chlorophyll a fluorescence, chlorophyll, sugars, nitrate, lipid peroxidation, carotenoids, and phenolic index. The results obtained showed that the productivity and the quality of lettuce can be positively affected by modulating the light quality and intensity, as well as other cultural practices. At the same time, the estimation of the electrical energy consumption indicated that little changes in the lighting recipe can significantly affect the energetic, environmental, and economic impact of home productions.
Highlights
In the last few years, the use of solid-state lighting (SSL) technology has largely grown in several industrial sectors, including agriculture
When red light is used as the only light source, it usually leads to a reduction in the Fv/Fm [31], but in the present study, the decrease in the chlorophyll a fluorescence-related parameters was observed in the case of the lowest percentage of red light (69.9% in Cycle 1), indicating that there was a combined effect involving blue, green, and yellow light
It is possible to hypothesize that the nitrogen supplied in Cycle 1 was not sufficient to sustain the photosynthesis in plants subjected to 194.54 μmol m−2 s−1 for 16 h and that, possibly, plants grown under high light intensity would have benefited from an increment in the nitrogen availability in the nutrient solution
Summary
In the last few years, the use of solid-state lighting (SSL) technology has largely grown in several industrial sectors, including agriculture. Light-emitting diodes (LED) technology is based on the use of electronic devices built with semiconductor materials which efficiently convert the electricity into light. The use of LED-based equipment allows the modulation of the intensity and the composition of the light spectrum [1], enabling the optimal lighting condition for a specific crop at each developmental stage to be set, optimizing plant growth in the most energy-efficient way [2]. LED lamps facilitate the consumption of less energy (up to 70%) compared to traditional light sources [3,4], as LED lights operate at a lower temperature, have a reduced impact on the growing environment, and generally have a longer lifetime
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