Nutrient solution concentration and flow rate affect sweet basil growth, yield, and water productivity in a recirculating gravel film hydroponic system

This study investigated the interactive effects of three electrical conductivity (EC) levels (1.0 – 1.5, 2.0 – 2.5 and 3.0 – 3.5 mS/cm) and two water flow rates (24 and 48 L/h) on sweet basil growth, yield and water productivity. The trial was conducted over two consecutive growing seasons (2020 – 2021 and 2021 – 2022) in a gravel film recirculating hydroponic system, operating under a shade net. Sweet basil growth and yield generally increased with increasing EC levels. However, the EC levels 2.0 – 2.5 and 3.0 – 3.5 mS/cm were comparable in their performance, resulting in significantly higher leaf chlorophyll content (43.9 – 51.2 SPAD readings) and fresh marketable yield (1.0 – 1.4 kg/plant) over the two experimental seasons. The results further revealed that 24 L/h was the optimal water flow rate, as it resulted in reduced seasonal crop water consumption of 0.011 m3/plant and increased water productivity of 106.4 kg/m3 (on fresh mass basis). The significant interactive effects endorsed the combination of 24 L/h flow rate and 2.0 – 2.5 mS/cm EC as the optimal and most efficient management practice for sweet basil grown in a recirculating gravel film hydroponic system. Identifying optimum EC level and water flow rate of the nutrient solution will contribute to increased fresh marketable yield and quality, leading to potential increases in income generation and profitability of farmers due to reduced use of production inputs such as water and fertilizer. A novel linear fertilizer application model was successfully developed and validated to assist farmers with nutrient solution management in recirculating hydroponic systems.