Introduction
Deficiencies of plant nutrients in aquaponics are usually thought to be caused by nutritional imbalances of aquafeeds, being the main nutrient input into the system, even though studies aiming at optimising feed formulation had only limited success (Seawright et al., 1998). Meanwhile, chemical boundaries that limit the solubility of nutrients in water have not been closer investigated until today, even though known to be essential and assessed a long time ago for nutrient management in hydroponics (Sambo et al., 2019). This leaves aquaponics practitioners with hands tied as it remains unclear whether optimised feed formulation can actually contribute to an efficient management of plant nutrients in aquaponic systems.
The aim of this study was to test the hypothesis whether chemical boundaries determine nutrient concentrations in aquaponics and if results obtained in an aquaponic system are comparable with chemical equilibrium models.
Material and Methods
Three independent RAS (Vtotal = 4500L) were stocked with juvenile Nile tilapia (IBW = 140.7 g±32.0 g) at a stocking density of 15.4 kg m−3. Fish were divided to three tanks per RAS (Vtank = 650 L). Isonitrogenous and isocalorific experimental diets containing graded levels of potassium (K) and phosphorus (P) (see table 1) were administered to the fish stock at an average feeding rate of ≈ 2.5% d−1 kg−1BW. Water exchange took place at 5% d−1. Quantities of all inputs (feed, water, chemicals) and outputs (water, solids) were recorded. Water and solid samples for element analysis by ICP-OES were taken bi-weekly. The trial lasted for 84 d.
Chemical equilibrium modelling was done using Visual MINTEQ v3.1. In brief, water analysis data, including pH, temperature and obtained element concentrations, were examined for reaching solubility threshold concentrations of amorphous solids.
Results and Discussion
The evaluation of the results is not yet finished as not all sample analysis results were provided by collaborating laboratories until now. Final analysis of all relevant samples is expected to be finished by end of May.
References
Sambo, P., Nicoletto , C., Giro, A., Pii , Y., Valentinuzzi , F., Mimmo , T., Lugli , P., Orzes , G., Mazzetto , F., Astolfi , S., Terzano , R., & Cesco , S. (2019). Hydroponic solutions for soilless production systems: Issues and opportunities in a smart agriculture perspective. Frontiers in Plant Science , 10(923), 1–17.
Seawright, D. E., Stickney, R. R., & Walker, R. B. (1998). Nutrient dynamics in integrated aquaculture-hydroponics systems. Aquaculture , 160, 215–237.
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