Water and Nutrient Reuse within Closed Hydroponic Systems

Currently, little research exists on the maintenance of individual nutrient balance within the nutrient solutions of closed hydroponic systems and how this maintenance may result in reductions in water and nutrient consumption. In this study, a nutrient solution management procedure was developed to maintain outputs while minimizing inputs. Lactuca sativa (lettuce) crops were grown in six closed hydroponic systems utilizing the nutrient film technique. Electrical conductivity was used as the primary indicator of nutrient solution quality and determined if the nutrient solution was discarded and replaced (control systems) or restored (test systems). Restorations in test systems were made individually to nitrogen, phosphorus, and potassium through the addition of KH2PO4, KNO3, and Ca(NO3)2 stock solutions. Test and control systems both showed similar fresh mass and foliar nutrient concentrations across two successive growth runs. Test systems consumed approximately 42% less water, 23% less KH2PO4, 57% less KNO3, and 58% less MgSO4 and trace elements than control systems across two runs. This study provides evidence that, for lettuce, similar crop yield with fewer inputs can be achieved under this nutrient solution management plan than under more traditional plans. This research suggests that in many current applications, nutrient solutions are being discarded prematurely and nutrient solution lifespan can be increased through simple procedural changes, decreasing environmental impacts and production costs