Effect of plant species on nitrogen and phosphorus removal in aquaponic system  

Aquaponics is a hybrid production system that integrates aquaculture with hydroponics to grow various crops with fish wastewater in a recirculating system. A well-managed aquaponics can improve nutrient retention efficiency, reduce water usage and waste discharges to the environment, and enhance profitability by simultaneously producing two cash crops. By practicing aquaponics systems in non-traditional locations for agriculture or on marginal lands, aquaponics can function as a sustainable model for food production. Although different types of crops have been tested in aquaponics, the selection of plant species has relied mainly on experience. Nitrogen (N) and phosphorus (P) are major nutrients available in aquaculture effluents causing environmental issues. Thus, improving nutrient use efficiency through proper crop choice is a critical task for better performance of aquaponics system. Since different plants have different growth characteristics, different cultural strategies need to be developed to achieve the best production efficiency. However, limited studies have been conducted to systematically investigate the effect of plant species on the performance of an aquaponics system. The objective of our research was to evaluate the effect of plant species on N and P removal in aquaponics system in order to improve nutrient recovery by utilizing aquaculture effluents as sustainable mineral nutrient sources for vegetable production.

Three vegetable crops (lettuce, basil, and tomato) were separately grown in aquaponic systems. Water quality parameters were monitored daily and N and P concentrations were measured every other day. The results showed that plants effectively removed N and P during their production cycle with increasing removal rate as their biomass increased. Although there were no significant (p>0.05) differences in daily removal efficiency among plant species when the plants were young, tomato showed significantly (p<0.05) higher N removal rate compared to other plant species as they grew mature. However, N accumulated over time in aquaponics systems while P level was maintained throughout production period. Our results indicate that N and P removal and recovery efficiencies are varied by plant species and production stage. It is concluded that, in combination with proper crop choice, reducing N and P inputs in the system is critical to effectively manage aquaponic system.