Background:Global food production systems generate impacts such as eutrophication, caused by nutrient run-offfrom agricultural exploitations and exacerbated by climate change. Hydroponic cultivation methods arecommon in Mediterranean areas, although there is a gap in the literature with regard to their study. This studyaims tofill that gap, by assessing nutrientflows in hydroponic crops.Results:The results showed that most of the nutrients were drained with the leachates (51% on average), afigurewhich could be lower, if the nutrient supply were adjusted to the needs of the plants or if (closed hydroponic)nutrient recirculation were implemented, without compromising the nutrient uptake of the plant. Moreover, thestudy revealed that a significant quantity of nutrients was retained in the substrate (perlite) during the crop,reaching average values of 5% of incoming calcium, 6% of nitrogen, and 7% of phosphorus. In the case ofphosphorus and calcium, a regression model is presented for the estimation of their retention in hydroponiccrops.Conclusions:Although further studies will be needed to confirm the above trends, the study makes a significantcontribution to understanding the metabolism of nutrients in hydroponic crops and tofiner adjustments of thenutrient balance.

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