Daily Light Integral and Nutrient Solution Electrical Conductivity for Tomato and Bell Pepper Seedling Production in an Indoor Vertical Farm with Artificial Lighting

Indoor vertical farms (IVFs) provide the conditions for producing seedlings of good quality. However, their effectiveness depends on the daily light integral (DLI) and nutrient management. This study examined the effects of DLI and nutrient solution electrical conductivity (EC) on tomato and bell pepper seedlings produced in an IVF or a greenhouse. Seedlings in the greenhouse were harvested 45 (tomato) and 55 (bell pepper) days after sowing, while those in the IVF were harvested after 30 and 40 days, respectively. The optimal EC was 2.0 for tomato and 2.4 dS m−1 for bell pepper. Tomato seedlings showed a decreased shoot-to-root ratio in the IVF. Tomatoes in the IVF reached 241% higher total biomass than greenhouse seedlings at 31.7 mol m−2 d−1, while bell peppers had an increase of 333% at 39.6 mol m−2 d−1; however, a DLI of 23.7 mol m−2 d−1 was enough to cause an increase of 153% and 264%, respectively. Nutrient concentration decreased in IVF seedlings, which was attributed to a dilution effect; in contrast, the nutrient content of tomato and bell pepper were highest when grown in the IVF when irrigated with solutions at 2.0 dS m−1 and a DLI of 31.7 mol m−2 d−1.