Evaluating Species-Specific Replenishment Solution Effects on Plant Growth and Root Zone Nutrients with Hydroponic Arugula (Eruca sativa L.) and Basil (Ocimum basilicum L.)

Managing nutrients in recirculating solutions can be challenging in hydroponic production, and poor management practices can rapidly result in root zone nutrient imbalances in reduced yield. Using mass balance principles to formulate hydroponic replenishment solutions is a proposed strategy to reduce nutrient imbalances and the need to periodically replace the hydroponic solution. Objectives were to (1) formulate species-specific nutrient replenishment solutions for arugula (Eruca sativa L.) and basil (Ocimum basilicum L.) using mass balance principles and (2) evaluate the effects of using these replenishment solutions on plant growth and root zone nutrients over time. In the first experiment, arugula and basil tissues were analyzed over 42 d for macronutrient concentrations which were used to custom formulate species-specific replenishment solutions for both species. In the second experiment, nutrients were resupplied for hydroponic arugula and basil over time using either the species-specific or a standard commercial hydroponic replenishment solution. Species-specific replenishment solutions resulted in decreased solution EC and concentrations of most macronutrients over time for both species. In contrast, replenishment with the standard hydroponic solution resulted in increased solution EC and concentrations of calcium, magnesium, and sulfate and decreased nitrogen, phosphorus, and potassium. Replenishment treatment had no effect on yield for arugula and basil; however, results suggested root zone imbalances may have still occurred eventually for both treatments and species. Species-specific replenishment solutions would be most effective in scenarios where solutions could be formulated for a specific crop, mixed using high-quality irrigation water, and where environmental conditions are controlled and stable, such as indoor farming systems. This study highlighted several practical challenges and considerations regarding the formulation of hydroponic solutions using mass balance.