Effect of wastewater from a pikeperch (Sander lucioperca L.) recirculated aquaculture system on hydroponic tomato production and quality

Abstract

Decoupled aquaponic systems (DAPS) use the wastewater of recirculated aquaculture systems (RAS) as water source for plant production in recirculated hydroponic systems. RAS wastewater is complemented with macro- and micronutrients to obtain equivalent concentrations and pH as in standard hydroponic nutrient solutions (NS). Unlike in single recirculating aquaponic systems, optimal growth conditions can be established in each production part of a DAPS (i.e. fish and plant parts) avoiding compromises. DAPS design seems more adapted for commercial farming operations but feasibility studies on large-scale systems are lacking. Therefore, the production of tomatoes (Solanum lycopersicum L., cv. Foundation) grown in a NS based on complemented pikeperch RAS wastewater (i.e. AP treatment) has been compared to that of tomatoes grown in conventional hydroponic NS (i.e. HP treatment), in semi-practice conditions. During 3 consecutive years, tomatoes were grown on rockwool slabs, in a large-scale Venlo-type climate-controlled greenhouse, using a recirculated drip irrigation system identical to the ones used by the professionals of the hydroponic tomato sector.While the electroconductivity was significantly higher in the AP treatment due to the presence of NaCl in the RAS wastewater, no significant differences for the total and marketable fruit yields, fruit number, and size were found between the AP and HP treatments. However, while the level of blossom-end rot (BER) varied substantially (0.9–18.6 %) in the HP treatment, it was remarkably constant and low (0.2-0.4%) over the years in the AP treatment, suggesting a beneficial effect of RAS wastewater. Our results clearly indicate the suitability of complemented pikeperch RAS wastewater as feeding water for professional HP tomato production using drip irrigation for DAPS. As RAS water contains a diversity of microorganisms and dissolved organic matter, it is assumed that some of these acted as plant biostimulants and mitigated the salinity stress and the BER symptoms.