Basil and Swiss chard: Edible crops for use in floating treatment wetlands improving agricultural runoff

Abstract

The plant species established within floating treatment wetlands (FTWs) influence nutrient removal efficiency. To enhance adoption of FTWs by agricultural producers, both economic and ecological benefits from FTWs are needed to increase their use within irrigation retention reservoirs. Thus, we ascertained the feasibility of growing food crops in FTWs by evaluating two edible plant species to determine survivability and nutrient accumulation when grown in FTWs. We quantified plant growth (at saleable/harvestable size), nutrient uptake in root and shoot tissues, and overall nutrient removal efficiency of sweet basil (Ocimum basilicum) and Swiss chard (Beta vulgaris) over a six- or eight-week period, respectively, with exposures to simulated irrigation return flow with moderate or high concentrations of nutrients present. Two cultivars of basil were mixed within each mesocosm to create a mixed planting design across the two fertilizer treatments and two types of Swiss chard (species and ‘Bright Lights’) were evaluated separately. Nitrogen (N) and phosphorus (P) removal efficiencies were calculated for a 7-day hydraulic retention time. Growth and nutrient removal efficiency were similar within each species. The average N removal rate was 0.077 and 0.19 g·m⁻² day⁻¹ for basil and 0.16 and 0.30 g·m⁻² day⁻¹ for the Swiss chard for moderate and high nutrient treatments, respectively. The average P removal rate was 0.015 and 0.036 g·m⁻² day⁻¹ for basil and 0.019 and 0.043 g·m⁻² day⁻¹ for Swiss chard for moderate and high nutrient treatments, respectively. Most nutrients were fixed within plant shoots. Multiple harvests throughout the growing season could potentially lead to increased profits and nutrient uptake. Additional research is needed to determine if higher nutrient reductions can be achieved through additional harvests, greater planting densities, or increased percent cover. Both basil and Swiss chard are promising plant selections for FTWs, pairing nutrient removal with marketable crop production.