Aquaponics vs. hydroponics: production and quality of lettuce crop

Aquaponics is an environmental-friendly production system due to its full reuse of waste and nutrients. The research, carried out at the Experimental Farm of the University of Tuscia, compared summer yields of two romaine lettuce crops (Lactuca sativa L. ‘Integral’) grown on aquaponic and hydroponic floating systems. For the hydroponic treatment a nutritive solution of 1.7 dS m-1 and pH 5.5 supported plant growth. For the aquaponic system two treatments under different fish densities supplied nutrients at different concentrations. Every aquaponic treatment consisted of 3 independent 250-L tanks stocked with Nile tilapia (Oreochromis niloticus L.). Each fish tank fed a 1.5 m2 floating system under a 20 plant m-2 density. For the first crop 110 g and 24 g tilapia were stocked at system setup respectively under a low (5 kg m-3) and high (8 kg m-3) density and supplied nutrients with an electrical conductivity (EC) of 0.4 and 0.6 dS m-1. For the second crop 168 g and 90 g tilapia respectively stocked under a low (6 kg m-3) and high (20 kg m-3) stocking density raised EC levels to 0.5 and 1.0 dS m-1. Production of 2.8 kg m-2 from the first hydroponic crop was similar to the 2.7 kg m-2 assessed in the high density aquaponic treatment. Conversely the 2.3 kg m-2 measured in the low density treatment was smaller. For the second trial no differences were noticed between the 6.0 kg m-2 measured in the hydroponic system and the 5.7 and 5.6 kg m-2 assessed in the high and low-density aquaponic treatments, respectively. Nevertheless different nutrient concentrations in water affected plant mineral composition. Aquaponic leaves were poorer in phosphorus but richer in calcium, potassium magnesium and sodium.