Nutrients Use Efficiency in Coupled and Decoupled Aquaponic Systems

Abstract

Aquaponics is currently undergoing a transformation into an intensive food production system. The initially applied systems focused on small-scale, fish-centric coupled (CAP, the aquaculture, and the hydroponic units are arranged in a single loop, and the water flows continuously from the fish tanks to the plant unit and back) aquaponics. More recently, the primary area of research interest has shifted toward larger-scale, plant-centric decoupled (aquaculture and hydroponics units are arranged in a multi-loop setup as separate functional units that can be controlled independently) systems, aiming to achieve greater economic benefits and employ more environmentally friendly practices. The objective of this study was to address gaps in the expansion of decoupled larger-scale aquaponics and to provide a comprehensive understanding of the water and nutrient flow in the system. For this purpose, experiments were performed in a greenhouse on CAP and DCAP systems, while this study also included measurements in a pure hydroponic system (HP). This study presents an assessment of the water and nutrient flow in four different crops: basil; cucumber; parsley; and tomato, all co-cultivated with a tilapia aquaculture system. Significant nutrient deficiencies and imbalances were identified in the CAP solution, leading to pronounced impacts on nutrient assimilation, particularly for fruiting vegetables. However, the average nutrient use efficiency (NUE) for nitrogen, phosphorous, potassium, and calcium was found to be 42% higher in the CAP treatment compared to HP and DCAP treatments. The nutrient solution in the DCAP treatment did not exhibit differences in water quality parameters and nutrient efficiency when compared to HP, resulting in similar effects on nutrient assimilation. Nonetheless, it was observed that DCAP plants exhibited superior NUE compared to HP plants.

Exploring the Potential of Biostimulants to Optimize Lettuce Cultivation in Coupled and Decoupled Aquaponics Systems: Growth Performance, Functional Characteristics and Metabolomic Analysis

“…The limitations of CAP became evident from the initial harvest on D26, and by the final harvest on D54, there was an 80% reduction in aerial part fresh weight and a 28.7% decrease in leaf number. Previous studies have also reported lower yields in coupled systems compared to hydroponics [8,9,11,23]. Lettuce is a frequently studied species in the aquaponics literature [24].…”

“…The largest area is covered by the hydroponics unit (360 m 2 ) where the crops are cultivated, while the RAS is installed in a closed chamber (80 m 2 ) under controlled environmental conditions. A full description of both the hydroponics and the RAS sub-systems, as well as the environmental control within the RAS chamber and the whole greenhouse, can be found in our previous articles [8,9]. Briefly, the RAS sub-system comprises three fish tanks, each with a volume of 1.3 m 3 , connected with the mechanical filter (0.5 m 3 , Combi Bio 15, ProfiDrum, Retford, UK) and the bio-filter.…”

“…The mean pH value of the irrigation solution in all the treatments was set at 5.6, according to Aslanidou et al (2022) [8]. The electrical conductivity (EC) of the solution was measured weekly with a portable instrument (Combo pH-EC-TDS-Temp, 98130 Hanna Instruments, Woonsocket, RI, USA) and varied among the treatments.…”

“…were reared in the RAS system, with a total biomass of 32.7 kg, thus a stocking of 8.4 kg m −3 . The fish were fed ad libitum three times a day with Prodac Pond Sticks Color (crude protein 29.0%, crude ash 5.7%, crude fibers 3.3%, crude fat 2.9%, moisture 4.8%, omega 6 42.2%, omega 3 5.7%) [8].…”

“…The closed-loop, coupled aquaponics system described above has certain limitations that prevent it from being equally or more productive compared to conventional cultivation systems such as hydroponics [8][9][10]. The limitations concern the sub-optimal levels of some nutrients in the fish-derived water, resulting mainly in K and Fe deficiencies in crops [11,12].…”