Interactive effects of electrical conductivity and light intensity on growth, yield, and nutrient dynamics of hydroponic lettuce

Abstract Precise management of nutrient solution properties, such as electrical conductivity (EC), and environmental factors, such as light intensity (LI), is essential for optimizing crop yield and quality in hydroponic production. This study evaluated the individual and combined effects of two EC ranges (EC1: 1. 5–2. 0 dS m-1; EC2: 4. 5–6. 0 dS m-1) and three LI levels (L1 = 145, L2 = 185, and L3 = 240 mol m-2 s-1) on the growth, yield, leaf mineral uptake, and nitrate accumulation of butterhead lettuce grown in hydroponic system under artificial lighting. The greatest leaf area (1338. 31 cm2) and yield (57. 97 g plant-1) were observed in EC1L3 treatment, corresponding to reductions of 75% and 77. 2%, respectively, compared to EC2L3 (330. 79 cm2 and 13. 98 g plant-1), indicating the adverse effects of salinity stress. Furthermore, within the same EC1 level, LI positively impacted yield, which increased by 47% under EC1L3 compared to EC1L1. Mineral composition analysis revealed that EC2 significantly reduced the uptake of essential macronutrients nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) and micronutrients boron (B), zinc (Zn), manganese (Mn), iron (Fe), and copper (Cu), whereas LI had no significant effect, except for a minor interaction in B uptake. An inverse correlation (R² = -0. 80) between solution and leaf nitrate levels was observed; however, leaf nitrate content was low and did not differ significantly across treatments. This closed-loop hydroponic study in a vertical cultivation setup offers practical insights for efficient controlled environment agriculture (CEA) systems. The results highlight that the interaction between EC and LI plays a significant role in influencing lettuce morphology and yield, but not mineral uptake. Maintaining EC between 1. 5 and 2. 0 dS m-1 and LI at 240 µmol m-2 s-1 resulted in the highest growth and yield under the tested conditions. The findings from this study will be critical for future research on investigating the interactive effect of different light and nutrient recipes for other hydroponic crops.