Effect of LED supplementary light on the growth of horticultural crops

The regulation of light on plant growth and development includes seed germination, stem elongation, leaf and root development, phototropism, chlorophyll synthesis and decomposition, and flower induction. The lighting environment elements in the facility include light intensity, light cycle and spectral distribution. By using artificial supplementary light, the elements can be adjusted without being restricted by weather conditions.

Plants have the characteristic of selective absorption of light, and different photoreceptors perceive light signals. It has been found that there are at least three types of photoreceptors in plants, phytochrome (absorbing red light and far-red light), cryptochrome (absorbing blue light and near ultraviolet light) and ultraviolet light receptors (UV-A and UV-B). Using a specific wavelength light source to irradiate crops can improve the photosynthesis efficiency of plants, accelerate the formation of photomorphology, and thus promote the growth and development of plants. Plant photosynthesis mainly utilizes red-orange light (610-720 nm) and blue-violet light (400-510 nm). Using LED technology, it can radiate monochromatic light that conforms to the wavelength band of the strongest chlorophyll absorption (such as red light with a peak of 660nm, blue light with a peak of 450nm, etc.), and the spectral domain width is only ±20 nm. At present, it is believed that red-orange light can significantly accelerate the development of plants, promote the accumulation of dry matter, the formation of bulbs, tubers, leaf balls and other plant organs, cause plants to flower and fruit earlier, and play a leading role in plant color enhancement; Blue and purple light can control the phototropism of plant leaves, promote the opening of stomata and chloroplast movement, inhibit stem elongation, prevent plant growth, delay plant flowering, and promote the growth of vegetative organs; the combination of red and blue LEDs can make up for the two single colors, the lack of light forms a spectral absorption peak that is basically consistent with crop photosynthesis and morphogenesis, and the light energy utilization rate can reach 80% to 90%, and the energy saving effect is remarkable.

Equipped with LED supplementary lights in facility gardening can achieve a very significant effect of increasing production. Some studies have shown that the fruit number, total yield and single fruit weight of cherry tomatoes are significantly increased under 300 mol/(m2) LED light strip and LED light tube for 12 hours (8:00~20:00). The fill light of the light strip has increased by 42.67%, 66.89% and 16.97% respectively, and the fill light of the LED lamp has increased by 48.91%, 94.86% and 30.86% respectively. Supplementary light with LED lights during the whole growth period [the ratio of red and blue light to quality is 3:2, and the light intensity is 300 mol/(m2)] treatment can significantly increase the fruit quality and yield per unit area of zucchini and eggplant, and zucchini increased by 5.3 %, 15.6%, eggplant increased by 7.6%, 7.8%. Through the time-space adjustment of LED light quality and its intensity and duration during the whole growth period, the plant growth cycle can be shortened, the commercial yield, nutritional quality and morphological value of agricultural products can be improved, and the efficient, energy-saving and intelligent production of facility gardening crops can be realized.