Nitrogen budget in recirculating aquaponic systems with different fish stocking density

Abstract

As in any agroecosystem, also in aquaponics the nitrogen (N) balance represents an important tool to evaluate sustainability, and to identify factors that can improve N use efficiency (NUE) and reduce N losses. In this respect, fish stocking density has been little investigated, hence this research aimed to evaluate the N balance of a low technology aquaponic (AP) system managed at two fish densities in comparison with a hydroponic system (HP). In the fish tanks common carp at two initial stocking densities were reared (2.5 and 4.6 kg m–3 in low and high AP, hereafter named APL and APH, respectively) and the vegetated sector was cultivated with a leafy vegetable crop succession (Catalogna chicory, lettuce, Swiss chard). The N balance considered N input as fish feed or fertiliser, and N content in the initial water and the N output as N in the incremented fish biomass, in the harvested vegetables, in the sediments, and in the remaining water. Total N loss was estimated by difference. The total N input and the N loss through gas emission in the atmosphere were much higher in AP than in HP, particularly at high stocking density. The opposite trend was observed for the N input recovered in vegetable aboveground biomass. The N input recovered as fish biomass was slightly higher in APL compared to APH. The better results of APL than APH suggest that in low-tech AP system lower initial fish density should be adopted at the system start up to maximise both production and N recovery.

Evaluation of the Water Quality and Farming Growth Benefits of an Intelligence Aquaponics System

“…The plants in an aquaponics system can absorb nutrients from the excrement of fish in the system and purify the water, as well as reduce the water waste and produce additional crops, but the addition of an element is needed, because fish mainly supply nitrogen [3]. In addition, the start-up period highly influences the N budget [4]. Aquaponics is a system that integrates recirculating aquaculture with fish-vegetable production and represents an innovative and sustainable practice [5].…”

Comparative life cycle assessment of rainbow trout (Oncorhynchus mykiss) farming at two stocking densities in a low-tech aquaponic system

“…In our system, the release of nitrogen and phosphorous contributed to 30% of the eutrophication potential, while the remaining part was derived from electricity and feed production. Previous studies have observed divergent results about the effect of the stocking density on EP category, exacerbating (Maucieri et al, 2020) or mitigating (Ghamkhar et al, 2021) the whole impact. This might imply the need for upgrading the system set-up, enhancing the removal of solids derived from fish faeces and uneaten feed.…”

Aquaponics as a Promising Strategy to Mitigate Impacts of Climate Change on Rainbow Trout Culture

“…According to several studies, different plants and fish will have different optimal ratios and largely depend on factors, such as fish stocking density, aquaponics type, plant species, planting density, hydroponic or soil crop production system type, water flow rate, and external factors [ 179 ]. Therefore, the density of plants that will be grown in a system of aquaponics depends on the species and the density of the fish [ 180 ].…”