|Authors: ||J. Pineda-Pineda, I. Miranda-Velázquez, J.E. Rodríguez-Pérez, J.A. Ramírez-Arias, E.A. Pérez-Gómez, I.N. García-Antonio, J.J. Morales-Parada|
|Keywords: ||greenhouse, fish density, tilapia, nutrients, hydroponics|
This research was conducted in order to determine the best fish density for growing both fish and lettuce (Lactuca sativa L.) in aquaponics, under greenhouse conditions.
Densities of 10, 15, 20 and 25 kg m-3 of tilapia (Rocky Mountain strain.) with a plant density of 25 lettuce m-2 were established in an aquaponic system.
The variables measured were related to vegetative growth (fresh weight, plant height and stem diameter), nutrient content in plant tissue (N, P, K, Ca, Mg, Fe, Cu, Zn, Mn and B) and concentration of N-NO3-, P-H2PO42-, K+, Ca2+ and Mg2+ in the nutrient solution, during two aquaponic cycles of lettuce cultivation.
The highest fresh lettuce weight, plant height, stem diameter, nutrients in aquaponic solution and tissue nutrients content were obtained with a fish density of 25 kg m-3. The nutrient concentration in aquaponic nutrient solution increased according to fish density.
At the end of experiment (60 days after transplanting), N-NO3-, Ca2+ and Mg2+ concentration reached its highest values of 105, 38.5 and 38 mg L-1, respectively; meanwhile P-H2PO42- and K+ reached its highest concentration (15 and 14 mg L-1, respectively) between 21 and 35 days after starting the experiment.
These results indicate that the aquaponic system provide only 62% of N-NO3-, 48% of P, 5% of K, 21% of Ca and 79% of Mg in relation to the Steiner Universal Nutrient Solution for hydroponics.
However normal tissue nutrient content was observed, with exception of K, Ca and Cu, but no signs of nutrient deficiencies were observed in lettuce leaves.
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