Aquaponics, which is the combination of hydroponics and aquaculture, is a rapidly developing technology that has potential to increase food production in urban and urbanizing areas. An experiment was conducted at Auburn University to determine the effects of hydroponic system type on mature size and micronutrient uptake in lettuce (Lactuca sativa L. 'Rex' ) irrigated with aquaculture effluent. The experiment consisted of three treatments and three replicates. Each replicate contained 48 individual plants. Treatments were: 1) substrate trough culture with a perlite substrate; 2) nutrient film technique; and 3) deep water culture. Aquaculture efflu ent was supplied from a biofloc- type recirculating aquaculture system producing Nile tilapia ( Oreochromis niloticus L.). Nitrate concentrations in aquaculture effluent ranged from 270 to 350 mg L-1 during the experiment while pH and electrical conductivity remained relatively constant from 6.0 - 6.4 and from 1.2 to 1.45 mS cm-1 , respectively. There were no significant differences in head fresh weight after 28 days. Chlorophyll content (SPAD index) was highest for the substrate troughs and lowest in nutrient film technique . There were slight differences in foliar nitrogen concentrations between hydroponic system type. Micronutrient concentration was significantly increased in substrate culture and deep water culture compared to nutrient film technique. The pH between repetitions varied slightly due to fluctuations in the tilapia aquaculture environment. Aquaculture effluent from the biofloc filter was not screened when filling the reservoir tanks. Micronutrient supplementation may not be necessary in aquaponics as long as particulate matter is allowed to interact with plant root systems. Further research should focus on identifying and quantifying plant growth promoting bacteria in aquaponic systems to further analyze nutrient acquisition relationships.
Keywords: aquaponics, hydroponics, lettuce, nutrient use efficiency, substrate