Nutrient Use in Vertical Farming: Optimal Electrical Conductivity of Nutrient Solution for Growth of Lettuce and Basil in Hydroponic Cultivation

During the past few decades, vertical farming has attracted a lot of interest as an alternative food production method. Vertical farms use engineered growth environments and hydroponic cultivation techniques for growing plants indoors. One of the important factors in vertical farming for the cultivation of different plants is the amount of nutrients, which can be measured as electrical conductivity (EC). Studying the optimal EC is important for avoiding nutrient loss and deficiency in vertical farms. In this study, we investigated the effect of five EC levels (2, 1.2, 0.9, 0.7, and 0.5 dS m(-1)) of Hoagland nutrient solution on the growth and development of basil cultivar 'Emily' and lettuce cultivar 'Batavia-Caipira'. During the study, the environmental parameters were kept fixed using an automatic dosing machine. The experiment was done in automatic vertical farms using the hydroponic ebb-flow cultivation technique with a temperature of 20 +/- 1 degrees C, relative humidity of 50-60%, CO2 concentration of 450 ppm, pH = 6, the PPFD (photosynthetic photon flux density) of 215 +/- 5.5 mu mol m(-2) s(-1), and the photoperiod of 16:8 h (day/night). Each treatment was replicated four times. We studied the effects on several growth parameters (including the dry and fresh weight of leaves and roots, number of leaves, and leaf area) as well as the chlorophyll and nitrogen concentration of the leaves. According to the results, the basil and lettuce growth parameters among the five treatments have been significantly higher in the treatment with EC of 1.2 and 0.9 dS m(-1). These EC values are lower than the recommended EC value given as the optimum in the previous studies. However, the concentration of chlorophyll and nitrogen show different trends and were higher in full strength of nutrient solution with EC = 2 dS m(-1).

Automated summary

Vertical farming, utilizing engineered growth environments and hydroponic techniques, has become a popular alternative food production method. This study investigated the impact of different levels of electrical conductivity (EC) in Hoagland nutrient solution on the growth of basil and lettuce cultivars. Results showed that the growth parameters of basil and lettuce were significantly higher with EC levels of 1.2 and 0.9 dS m(-1), despite previous studies recommending higher EC values for optimal growth. However, the concentration of chlorophyll and nitrogen was higher in the full strength nutrient solution with an EC of 2 dS m(-1).