To achieve clean and high-quality spinach production, the effects of daily light integral (DLI) and light spectrum on growth, nutritional quality, and energy yield of hydroponic spinach (Spinacia oleracea L.) were investigated in a closed plant factory under light-emitting diode (LED) lighting. The hydroponic spinach plants were grown under 16 combinations of four levels of DLI (11.5, 14.4, 17.3, and 20.2 mol m⁻² day⁻¹) with four light spectra: LED lamps with ratio of red light to blue light (R:B ratio) of 0.9, 1.2, and 2.2 and fluorescent lamps with R:B ratio of 1.8 as control. The results show that total fresh and dry weights, energy yield, and light energy use efficiency (LUE) of harvested spinach were higher under D17.3-L1.2 treatment compared to other treatments. The higher net photosynthetic rates were shown at DLI of 17.3 mol m⁻² day⁻¹ regardless of light quality. Higher vitamin C contents of spinach in all LED treatments were obtained compared with the control. L1.2 treatments with higher fraction of blue light led to more vitamin C content, lower nitrate content, and higher LUE independent of DLI. L2.2 treatment with more fraction of red light was beneficial to reduce oxalate accumulation. Power consumption based on increased total fresh weight under LED lamps with R:B ratio of 1.2 in different DLIs was over 38% lower than that under the fluorescent lamps and 1.73 kWh per 100 g FW at DLI of 17.3 mol m⁻² day⁻¹. In conclusion, lighting environment in DLI of 17.3 mol m⁻² day⁻¹ using LED lamps with R:B ratio of 1.2 is suggested for the design of a LED plant factory for hydroponic spinach production.

To rapidly produce strawberry (Fragaria × ananassa Duch. cv. Benihoppe) transplants from cuttings, suitable light intensities for unrooted runner plants at the rooting stage and rooted runner plants at the seedling stage were determined in a plant factory under LED lighting. At the rooting stage, unrooted runner plants at the 3-leaf stage were hydroponically rooted for 6 days under light intensity of 30, 90, 150, and 210 μmol m⁻² s⁻¹, respectively. At the seedling stage, rooted runner plants were hydroponically grown for 18 days under light intensity of 90, 180, 270, and 360 μmol m⁻² s⁻¹, respectively. The tube LED lights consisting of white and red LED chips were used as sole light source, and photoperiod was controlled as 16 h d⁻¹. The results showed that the maximum root number (7.7) and longest root length (14.8 cm) of the runner plants were found under 90 μmol m⁻² s⁻¹ at the rooting stage. Photosynthetic activity in runner plant leaves under 90 μmol m⁻² s⁻¹ were higher than that under 30, 150, and 210 μmol m⁻² s⁻¹. Higher light intensity at the range of 90–270 μmol m⁻² s⁻¹ increased the stomatal conductance of newly formed leaves of rooted runner plants, thus improving the net photosynthetic rate and growth of rooted runner plants at the seedling stage. The crown diameter, shoot and root dry weights, and root to shoot ratio of rooted runner plants increased by 9.7%, 38.8%, 106.1%, and 48.7%, respectively, when the light intensity increased from 90 to 270 μmol m⁻² s⁻¹. However, there was no further improvement of runner plant growth under 360 μmol m⁻² s⁻¹. Furthermore, no significant difference of increased dry biomass per mole of photons delivered was found between 180 and 270 μmol m⁻² s⁻¹. In consideration of transplant quality and economic balance, light intensity of 90 μmol m⁻² s⁻¹ at the rooting stage and 270 μmol m⁻² s⁻¹ at the seedling stage were suggested for rapidly producing hydroponic strawberry transplants based on unrooted runner plants in the LED plant factory.

Effects of LED light quality on the growth of pepper seedling in plant factory

Growth of cucumber seedlings in different varieties as affected by light environment

This study was conducted to compare the effects of broad spectrum during the whole seedling period and photon flux density (PFD) in the healing stage on the growth and energy use efficiency of grafted tomato (Lycopersicon esculentum Mill.) transplants in a plant factory. Fluorescent lights, white LED lights, and white plus red LED lights were applied at the growth processes of grafted tomato transplants from germination of rootstock and scion to post-grafting. Three levels of PFD (50, 100, 150 μmol m⁻² s⁻¹) were set in the healing stage under each kind of light quality. The results indicated that the growth and quality of grafted tomato transplants under different broad spectrums were influenced by the ratio of red to blue light (R/B ratio) and the ratio of red to far-red light (R/FR ratio). A higher R/B ratio was beneficial to total dry matter accumulation, but excessive red light had a negative effect on the root to shoot ratio and the seedling quality index. The higher blue light and R/FR ratio suppressed stem extension synergistically. The LED lights had good abilities to promote plant compactness and leaf thickness in comparison with fluorescent lights. The plant compactness and leaf thickness increased with the increase in daily light integral in the healing stage within a range from 2.5 to 7.5 mol m⁻² d⁻¹ (PFD, 50 to 150 μmol m⁻² s⁻¹). Compared to fluorescent lights, the LED lights showed more than 110% electrical energy saving for lighting during the whole seedling period. Higher PFD in the healing stage did not significantly increase the consumption of electric power for lighting. White plus red LED lights with an R/B ratio of 1.2 and R/FR ratio of 16 were suggested to replace fluorescent lights for grafted tomato transplants production considering the high quality of transplants and electrical energy saving, and PFD in the healing stage was recommended to be set to 150 μmol m⁻² s⁻¹.

To optimize the nutrient supply of strawberry, fertilization was reduced as much as possible on the premise of satisfying the elements needed for strawberry growth. This study put forward a modified nutrient solution formula (NM) by adjusting the ratios of N/K, K/Ca, NO3--N/NH4+-N in vegetative growth, flowering and fruiting, and fruit expanding stages based on Yamasaki strawberry nutrient solution formula (NY). Taking the NY as the control group, the NM was verified with elevated-grown 'Ssanta' strawberry using three different substrates (Vulcanics-added substrate, Horticultural substrate, Commercial substrate) in greenhouse. The results indicated that under the NM treatment, strawberry plants had better photosynthesis in the vegetative growth stage and flowering and fruiting stage, and the first crop yield and total crops yield per plant also increased by 20%. Although the vegetative growth stage was longer, it entered the full fruiting stage earlier so that the maturity stage was advanced one week. Compared to strawberries grown in horticultural substrate irrigated with NY, the fruit yield per plant of ‘Ssanta’ strawberry grown in horticultural substrate irrigated with NM increased by 26%, and the sugar-acid ratio and vitamin C content of primary fruits reached 10.6 and 74.1 mg/100g, improving by 41% and 34% respectively. Therefore, the NM based on the growth stage can optimize the element needs of strawberry in all growth and development stages and maintain the substrate's pH stability, improving the yield and quality of 'Ssanta' strawberry under substrate cultivation. Therefore, it is recommended to use the horticultural substrate irrigated with the modified nutrient solution for the ‘Ssanta’ strawberries cultivation elevated in greenhouse to improve the economic benefit of strawberry cultivation. Keywords: elevated-grown strawberry, nutrient solution formula, substrate cultivation, phenological stage, fruit yield, fruit quality DOI: 10.25165/j.ijabe.20231602.7797 Citation: Yu W Z, Zheng J F, Wang Y L, Ji F, Zhu B Y. Adjusting the nutrient solution formula based on growth stages to promote the yield and quality of strawberry in greenhouse. Int J Agric & Biol Eng, 2023; 16(2): 57-64.