Babyleaf NFT production and water management in aquaponic system

Fish production in aquaculture is continuously increasing worldwide and the need for further increases is expected in the future. Aquaculture has several disadvantages considering environmental impact and water consumption, consequently aquaponic (AP) systems were proposed as one of the possible solutions for these issues. Although AP is an effective combination of vegetable and fish production, there is a mismatch between the nutrients provided by the fish compartment and the requirements of the plants. Once the system becomes limiting for the plant growth (usually P and/or K elements), the remaining N accumulates in the system water. Therefore it is necessary to replace periodically the system water. This work is focused on this specific phase: investigating the further utilization of the AP system water that is depleted of P and K, but still rich in N. This system water (FW) was used in a separate aquaponic mesocosm and compared with the same water supplemented with macro-nutrients (CFW) and with a hydroponic control (HC). Mizuna (M) and rocket salad (R) were used as short-cycle vegetables crops in a NFT system. Evapotranspiration in the system and water quality parameters were significantly influenced by the treatments. The starting N-NO3 concentration, similar in all systems, decreased by 31.2% in FW, 72.0% in HC and 82.7% in CFW. SPAD, plant height and total yield highlighted the inability of FW to meet the nutritional needs of both species. The highest production was recorded for CFW followed by HC (-7.5%) and FW (-74.7%) probably due to the presence of organic compounds with biostimulant activity. Mizuna was able to absorb more nutrients, because of the production of a developed root system. FW must be integrated with macro- and mesonutrients in order to ensure a suitable production; the use of CFW for short-cycle vegetable cultivation is an effective solution to manage the fish water at the end of an AP cycle, achieving significant production, reducing nitrogen load and further reducing the environmental impact of the system.