2017 ASHS Annual Conference

As an integrated food production system that links aquaculture with hydroponic crop production in a recirculating ecosystem, aquaponics holds great promise for helping to ameliorate agricultural challenges through efficient use of resources for crop production. It recycles more than 90% of its water, and dramatically reduces discharge of nitrogen (N)- and phosphorus (P)-rich wastewater to the environment. Improving N and P use efficiency through proper management practices is particularly important for better performance of an aquaponics system. The objectives of this study were to investigate nutrient use efficiency of aquaponics in comparison to hydroponics and examine the effects of vegetable species on the efficiency of each system. Three model crops, lettuce, basil, and tomato, were chosen in this study for their differences in edible parts as well as morphological and physiological functions. The crops were separately grown in tilapia-based aquaponics and compared with the ones in hydroponics controls. Water quality parameters (pH, dissolved oxygen (DO), temperature, and electrical conductivity (EC)) including N and P concentrations were monitored on a regular basis, and plant growth parameters (plant fresh weight, height, leaf number and length, and fresh weight) were recorded weekly. At harvest, the growth parameters were measured again, and plant tissues were separately harvested and processed for nutrient analysis. Water was sampled throughout production period for nutrient analysis. The EC of aquaponics increased gradually in all the aquaponics systems, with the highest increase in lettuce, followed by basil and tomato. Nitrate was one of the major contributors for such increase in the EC and increased by 3-fold during a three month production period; however, the concentrations remained low, ranging from 15 to 40% of those in hydroponics. Meanwhile, P concentrations maintained at the average of 30 ppm without significant differences among vegetable crops. Low nitrate levels in aquaponics changed biomass partitioning patterns of all the vegetables, particularly in tomato promoting earlier fruiting. In general, tomato preferentially accumulated nutrient elements in the leaves and stems, but basil and lettuce either in the leaves or roots, depending on the type of nutrients. N and P use efficiency was affected by the type of vegetables and was 3- to 5-fold higher in aquaponics compared to hydroponics. It is suggested that nutrient use efficiency of an aquaponics system can be further improved by selecting vegetable crops that can produce higher biomass with limited nutrient resources.