Sensor-Based Nutrient Recirculation for Aeroponic Lettuce Cultivation

Purpose The objective of this study was to investigate the effects of used-nutrient solution recirculation on nutrient efficiency improvement and reduction of environmental pollution of an ion-selective electrodes (ISEs)-based recycle-type aeroponic crop cultivation system. Methods A recycle-type aeroponic crop cultivation test bench was fabricated, which consisted of K + , NO 3 - , and Ca 2+ ISEs, pH, and EC sensor, and lettuce were cultivated for inspecting the nutrient solution recirculation process. The specific growth rate of lettuce was evaluated. Different percentages of the used-solution (20%, 40%, 60%, 80%, and 100% of the target volume) were recirculated to find a proper recirculation volume for maintaining the target nutrient level with the minimum supply of stock solutions. The nutrient saving percentage was determined by comparing the nutrient solution requirement with the open-type aeroponic system and open-field cultivation practices. Reduction of environmental pollution was assessed based on the possible environmental pollutions (i.e., surface water pollution, groundwater contamination, and contaminant deposition in the human body), which could be occurred by the direct discharge of the hydroponic nutrient solution. Results The minimum amount of stock solutions were required during the 60% used-solution recirculation. The nutrient solution requirement of the recycle-type aeroponic system was almost 3 to 5 times less than the open-type aeroponic system, and 3 to 6 times less than open-field cultivation based on nutrient consumption rates at different growth stages. An open-type aeroponic system might require more nutrient solution than the open-field cultivation practices based on the frequency of nutrient solution supply in the crop root zone. Although, the discharged nutrient solution increased the K + , NO 3 - , and Ca 2+ ion levels a little in the considered surface water reservoir, groundwater, and human body, long-term discharge of the high concentrated hydroponic nutrient solution would be hazardous. Conclusion The findings of this study showed that the nutrient saving efficiency of a recycle-type crop cultivation system is higher compared to the open-type and conventional cultivation practices, which can minimize the cultivation cost notably, and the environmental pollutions can be reduced significantly through the sensor-based nutrient management.