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Sustainable Hydroponics Using Zero-discharge Nutrient Management and Automated pH Control

Authors: Noah James Langenfeld and Bruce Bugbee

Abstract

Here we review the 400-year history of hydroponic culture and describe a unique management approach that does not require leaching or discarding solution between harvests. Nutrients are maintained at a low and steady concentration by daily additions of a dilute solution that replaces the transpired water along with the nutrients that were removed in growth each day. A stable pH and a low steady-state concentration of ammonium are maintained through automated additions of a solution of nitric acid and ammonium nitrate. Ample solution volume (at least 20 cm deep) stabilizes nutrient concentrations, reduces root density, and improves uniformity. Gentle aeration at ≈100 mL·min−1·L−1 maintains dissolved oxygen near saturation and increases uniformity throughout the rhizosphere. These practices facilitate a uniform, closed, root zone with rigorous pH control that provides the micromolar nutrient concentrations of N and P that are representative of field soils.


Fig. The automated pH control system described in this paper. Each PVC tower holds the pH control solution that is automatically dispensed through a solenoid pinch valve when needed. The system pictured can independently control the pH in three hydroponic containers.


Selected Figure



Keywords: aeration; ammonium; manifold; nitrate; pH control; pinch valve

HortScience 2024, 59(8), 1202-1206

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