Yield and Quality of Leafy Vegetables Grown in Soilless Culture: A Comparison of Hydroponics and Aquaponics Culture Systems

Leafy vegetables are good/inexpensive sources of essential plant-based minerals and secondary metabolites that promote human health and wellbeing; high-value vegetables can also be a source of income supplementation among low-income, small-holder farmers, however, the seasonality of these crops severely limit their utility in combating mineral malnutrition and alleviating poverty. Soilless culture production systems such as hydroponics are well-suited for year-round production of such nutrient-rich foods. Combining hydroponic culture with fish production (aquaponic systems) further enhances input resource use efficiency, making it an ideal system for addressing many health problems associated with malnutrition and poverty. Aquaponics is a biologically-integrated system that combines fish production (aquaculture) with hydroponic vegetable production in a recirculating setup. Waste products from the aquaculture component serve as inputs for the hydroponic component, which in turn serves a biofiltration function. The interaction of fish and vegetables in aquaponics results in a production system that is more productive than either component alone. The goal of this study was to evaluate the productivity and quality of vegetables grown under two soilless culture systems: hydroponics versus aquaponics. Two greenhouse-based recirculating systems served as a source of fertigation solution for vegetable crops grown on floating rafts. One system was stocked with Koi fish (Cyprinus carpio) while the other was operated as a hydroponics system. In each system, two cultivars of mustard green (Brassica juncea; ‘Florida Broadleaf’ and ‘Red Giant’) and Amaranth (Amaranthus spp. ‘Red Garnet’ and ‘Green Leaf’) were grown. Leaf yield, leaf area, leaf chlorophyll (CHLL), and mineral contents were measured during, or at the end of the crop growth cycle. Fresh mass yields of both mustard varieties were 60% to 65% higher in aquaponic culture compared to hydroponics. Total leaf area and CHLL were also significantly higher (60%  to 56% and 47% to 69%, respectively) in mustards grown in aquaponic culture. Yields differed between the two varieties of amaranth evaluated. Fresh weight, leaf area and CHLL of ‘Red Garnet’ were significantly higher (14%, 8%, and 7%, respectively) in aquaponic culture. Measured parameters were similar in both production systems for the ‘Green Leaf’ amaranthus cultivar. In addition to high resource use efficiency (space, water, nutrients), aquaponic systems are ideal for off-season production of nutrient-rich indigenous vegetables to promote food security. Careful selection of suitable cultivars would further maximize the benefits of production under this system.