YIELDS AND NUTRIENT UPTAKE FROM THREE AQUAPONIC SUB-SYSTEMS (FLOATING, NFT AND SUBSTRATE) UNDER TWO DIFFERENT PROTEIN DIETS
Aquaponics integrates recirculating aquaculture with soilless plant production. Research has proven that aquaponics is as productive as chemically-fertilized hydroponics. Although studies have been mainly carried out on floating systems, the potential of aquaponics under different designs still has to be fully understood. The present study assessed plant response and nutrient uptake of three different aquaponic subsystems against standard hydroponics (floating system).
Three 30-day crops of romaine lettuce (Lactuca sativa cv bionda degli ortolani) were tested in a heated greenhouse from 2 December 2010 to 3 March 2011 under a planting density of 20 plants m-2. Nile tilapia (Oreochromis niloticus) were stocked on 21 November 2010 in six independent 750 L aquaponic systems at 4 kg m-3 and fed two different diets: 31% protein (LP) (Skretting classic K P3) and 40% protein (HP) (Skretting classic K P2). Feeding regime was 1.7% BW (1st crop), 1.2% BW (2nd crop) and 1.1% BW (3rd crop). Each diet treatment was replicated three times. Water temperature in all tanks was 23 2 in all trials. A small quantity of potassium, phosphorus, magnesium and iron was added to tanks to raise nutrient levels to those of mature aquaponic systems. Each aquaponic system was supplied with a floating raft (Floating), a 63 mm trough under a water flow of 0.7 L min-1 (NFT) and 1L perlite vases positioned in a 1 cm shallow trough under constant sub-irrigation of 0.7 min-1 (Substrate). Aquaponic treatments were compared against standard hydroponic controls with 1.9 dS m-1 conductivity, N-NO3 196 mg L-1, N-NH4 21 mg L-1.
Fish performances were not different (P<0.05) in each crop. FCR was 2.2 (LP) and 2.0 (HP) for the first crop, 2.1 (LP) and 1.9 (HP) for the second crop, and 1.8 (LP, HP) in the third crop. SGR was 0.7% (LP) and 0.9% (HP) in the first crop and 0.6% (LP, HP) in both second and third crop. Plants best growth was in floating and NFT, while substrate systems were constantly underperforming. Nitrogen content in plant tissues showed same values (P>0.05) in all treatments in both second and third crop, when aquaponic N-NO3 concentrations were above 70 mg L-1.
Three 30-day crops of romaine lettuce (Lactuca sativa cv bionda degli ortolani) were tested in a heated greenhouse from 2 December 2010 to 3 March 2011 under a planting density of 20 plants m-2. Nile tilapia (Oreochromis niloticus) were stocked on 21 November 2010 in six independent 750 L aquaponic systems at 4 kg m-3 and fed two different diets: 31% protein (LP) (Skretting classic K P3) and 40% protein (HP) (Skretting classic K P2). Feeding regime was 1.7% BW (1st crop), 1.2% BW (2nd crop) and 1.1% BW (3rd crop). Each diet treatment was replicated three times. Water temperature in all tanks was 23 2 in all trials. A small quantity of potassium, phosphorus, magnesium and iron was added to tanks to raise nutrient levels to those of mature aquaponic systems. Each aquaponic system was supplied with a floating raft (Floating), a 63 mm trough under a water flow of 0.7 L min-1 (NFT) and 1L perlite vases positioned in a 1 cm shallow trough under constant sub-irrigation of 0.7 min-1 (Substrate). Aquaponic treatments were compared against standard hydroponic controls with 1.9 dS m-1 conductivity, N-NO3 196 mg L-1, N-NH4 21 mg L-1.
Fish performances were not different (P<0.05) in each crop. FCR was 2.2 (LP) and 2.0 (HP) for the first crop, 2.1 (LP) and 1.9 (HP) for the second crop, and 1.8 (LP, HP) in the third crop. SGR was 0.7% (LP) and 0.9% (HP) in the first crop and 0.6% (LP, HP) in both second and third crop. Plants best growth was in floating and NFT, while substrate systems were constantly underperforming. Nitrogen content in plant tissues showed same values (P>0.05) in all treatments in both second and third crop, when aquaponic N-NO3 concentrations were above 70 mg L-1.