Validation testing of an ion-specific sensing and control system for precision hydroponic macronutrient management

Validation testing of an ion-specific sensing and control system for precision hydroponic macronutrient management
박수현정대현Hak-Jin KimWoo-Jae ChoSeung-Hwan Yang
Issue Date
Computers and electronics in agriculture
VOL 156-668
Ion-specific nutrient management systems would replace conventional electrical conductivity-based management systems for more efficient maintenance of the concentration of each ion in nutrient solutions for closed hydroponic systems. This study reports on the validation testing of a previously developed ion-specific sensing and control system. Specific objectives were to (1) evaluate the ability of the system to maintain the target concentrations of five macronutrients, i.e., NO3− , PO43− , K+, Ca2+, and Mg2+ ions, required for crop growth in closed hydroponic systems based on both real-time measurement of NO3− , K+, and Ca2+ and the use of a concentration ratio method to replenish Mg2+ and PO43− , and (2) investigate the applicability of a cobalt rod-based electrode for hydroponic phosphate sensing. In a lettuce cultivation test conducted with the ebb-and-flow method over 21  days, most of the macronutrient concentrations were successfully maintained at the target levels with RMSE values of 25.2  ±  9.4, 19.1  8.1, and 11.5  6.1  mg∙ L− 1 for NO3− , K+, and Ca2+, respectively. In the case of Mg2+ and PO43− ions replenished in a proportional ratio to the supply of Ca2+ and NO3− ions, respectively, the Mg2+ concentrations were maintained between 18 and 25  1 at an almost constant level, whereas the PO43− concentrations increased steadily over time with no clear evidence of plant uptake, implying that the use of a concentration ratio method would not be effective in controlling the concentrations of PO43− in hydroponic solutions. As a phosphate sensor, the cobalt electrodes yielded an RMSE result of 10.9  7.1% from a comparison of the electrode method and standard analysis when tested in hydroponic lettuce samples taken once a day during the period of lettuce growing, thereby o
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