2019 ASHS Annual Conference

Aquaponics is an emerging sustainable production system, which creates a closed-loop ecosystem for fish, microbes, and plants. As water is critical to recycle ionic nutrients and oxygen in the production loop, its movement and the rate of turnover require optimization to ensure good water quality and growth environment for both of fish and crops. Although FAO guideline for densely-stocked aquaponic systems is to cycle the water two times each hour, it is still doubtful whether this turnover rate is necessary in aquaponics at low stocking densities or planted with plants have high ability to uptake nutrients. Therefore, water flowrate and crop growth potential were evaluated as factors determining water quality and cash crop yields in aquaponic system. Six vegetable crops with different growth rates were cultured in tilapia-based aquaponics systems, which include two fast-growing crops, Chinese cabbage (Brassica rapa) and lettuce (Lactuca sativa); two medium-growing crops, mustard (Brassica juncea) and chia (Salvia hispanica); and two slow-growing crops, basil (Ocimum basilicum) and Swiss chard (Beta vulgaris). Flow rate treatments were low (1000 L/day, LFR), medium (2000 L/day, MFR), and high (3000 L/day, HFR) flow rate. Fish were fed once a day by 1% fish fresh weight. Water quality parameters were measured daily. The pH was adjusted at around 7. Water was sampled for total ammonium nitrogen (TAN), nitrite, nitrate, and phosphate measurements every three days. Photosynthetic rate (Pn) and leaf temperature were measured. At the beginning and harvest, crop and fish growth parameters were measured. This study was conducted for 4 weeks and repeated twice. Data showed that flow rate was negatively correlated with water temperature and electricity conductance. In addition, nitrate, phosphate and sulfate levels showed significant negatively correlation with flow rate, indicating a higher nutrient removal of crops at HFR. Lower EC (better water quality) at HFR also enhanced fish production. Crops grown at HFR showed higher SPAD value, photosynthetic rate, stomatal conductance, transpiration rate and total nitrogen content. Interestingly, HFR increased the fresh and dry mass of slow-growing crops, while no significant difference was found between HFR and MFR for fast-growing and medium-growing crops. It was concluded that flow rate at 3000 L/day is sufficient for the growth and yield of crops regardless of growth rate, and flow rate can be lowered to 2000 L/day for fast-growing crop species.