In recirculating aquaculture and hydroponics systems, the waste products from fish production are used to produce vegetables or other crops of economic value, and the water is recirculated to the fish tanks. We studied growth, productivity and nutrient uptake of four leaf vegetable species (Lactuca sativa, Ipomoea aquatica,Brassica rapa var. chinensis and Brassica rapa var. parachinensis) in a controlled growth experiment with three root flooding treatments (drained, half-flooded and flooded) to assess their preferred hydroponic growth requirements, biomass production and nutrient removal capacities. Growth of the two Brassica varieties was clearly best at drained root conditions, while L. sativa and I. aquatica grew best with half-flooded and flooded roots. I. aquatica took up 3 times more N, P and K per plant than L. sativa, and 4 to 6 times more than the two Brassica varieties. At a plant density of 30 plants/m2, I. aquatica produced 146 g DW/m2 aboveground biomass during a 30-day cultivation period containing 2.8, 0.9 and 6.8 g/m2 of N, P and K, respectively. L. sativa produced 115 g DW/m2 of aboveground DW during a 60-day cultivation period, containing 2.2, 0.6 and 4.6 g/m2 of N, P and K, respectively. The two Brassica varieties produced much less aerial biomass (50-54 g DW/m2 during a 60-day period). Both I. aquatica and L. sativa are promising species to be included in integrated hydroponic and aquaculture facilities, with I. aquatica showing the most promise because of its higher growth and nutrient uptake capacity.
Key words: Lactuca sativa, Ipomoea aquatic, Brassica rapa, phytoremediation, lettuce, choy sum, water spinach, pok choi.
F, Flooded; HF, half-flooded; D, drained; Eh, substrate redox potential; FW, fresh weight; DW, dry weight; IRGA, infrared gas analyzer; Pmax,light-saturated rate of photosynthesis; PPFD, photosynthetic photon flux density;Rd, dark respiration rates.
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