Simultaneous pH and EC control in hydroponics through real-time manipulation of the ammonium-to-nitrate ratio in the nutrient solution

Abstract

A control algorithm was developed and tested on a hydroponic ebb-and-flow system to assess the efficacy of the proposed control scheme. Three experimental runs were conducted with the purpose of testing the proposed control system on Brassica oleracea var. acephala. The first was an ideal case under sterile conditions, the second was under non-sterile conditions where bacteria were allowed to colonise the plant roots, and the last was a baseline run where nitrate was applied as the only nitrogen source. The system was able to control pH to within 0.5 of the set point (in this case 6.1) while EC control was sufficient to ensure that a steady stream of nutrients were available to the plants at all times. Relative growth rates were fast at maximum average values of between 0.20 per day and 0.21 per day for all of the runs and the yield of organic leaf matter was essentially the same across all the runs at 83 % to 86 % of total plant mass. Finally, the plants grown under the proposed control system were observed to exhibit some improvement in protein and chlorophyll content while the other nutritional characteristics considered were essentially unchanged between treatments. This was all accomplished without having to add any additional toxic ions like Cl- and Na+ as is the case in conventionally controlled systems.