@article{Maucieri_Nicoletto_Zanin_Birolo_Xiccato_Sambo_Borin_2020, title={Nitrogen budget in recirculating aquaponic systems with different fish stocking density}, volume={15}, url={https://www.agronomy.it/agro/article/view/1639}, DOI={10.4081/ija.2020.1639}, abstractNote={<p>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<sup>–3</sup> 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.</p> <p> </p> <p><strong>Highlights</strong> <br>- The higher initial fish density had higher N input, but resulted in a lower N recovered in fish and vegetable biomass, and much higher N loss as gas emissions. <br>- The lower initial fish density combined a lower N input to a higher recovery in fish and vegetable biomass, and a lower N loss as gas emissions. <br>- The lower initial fish density allowed to maximise both production and environmental preservation.</p>}, number={3}, journal={Italian Journal of Agronomy}, author={Maucieri, Carmelo and Nicoletto, Carlo and Zanin, Giampaolo and Birolo, Marco and Xiccato, Gerolamo and Sambo, Paolo and Borin, Maurizio}, year={2020}, month={Sep.}, pages={239–245} }