2018 ASHS Annual Conference

Aquaponics is a rapidly emerging agricultural production system, which recycles effluent from aquaculture to feed crops with nutrients, creating a symbiotic ecosystem for fish, microbes, and plants production in a closed system. Water and nutrients added into aquaponics system are recycled for fish and crop production, and therefore, water flow rate in an aquaponics system may be associated with water environment such as water quality and nutrient availability, consequently affecting the performance and growth of crops grown in the system. In addition, since different crop species have different production periods and nutrient requirement, their performance and yield may be also varied by water environment in an aquaponics system. This study was conducted to investigate the performance and growth of crop species in an aquaponics system with different water flow rates. Six vegetable crops varying in their production period were cultured in tilapia-based aquaponics systems, which include basil (Ocimum basilicum), chia (Salvia hispanica), Tokyo Bekana (Brassica rapa), lettuce (Lactuca sativa), mustard (Brassica juncea) and Swiss chard (Beta vulgaris). Water flow rates were set at low (1000 L/day, LFR), medium (2000 L/day, MFR), and high (3000 L/day, HFR). Fish were fed once a day with fish feed by 1% fish fresh weight. Water quality parameters (dissolved oxygen (DO), mg·L^-1; temperature, °C; pH; electrical conductivity (EC), µS·cm^-1) were measured daily. The pH was adjusted by using a mixture of potassium hydroxide and calcium hydroxide (v:v=1:1) at around 7.0. 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 third week when crops showed highest growth rate. At harvest, crop growth parameters were measured, including plant height, leaf length, leaf number, chlorophyll content (SPAD value), and leaf area. Initial and final fresh and dry weights of fish and vegetable crops were measured. Data showed that HFR significantly lowered the pH, EC, water temperature, TAN, nitrate and phosphorus. During the second and third week, the pH in HFR was significantly lower than LFR. EC in HFR was significantly lower than that of LFR from the second week. Particularly, TAN and nitrate concentration was significantly lower in HFR in the first week compared to LFR. Such water environment in HFR improved crop growth in aquaponics. The SPAD and Pn values of crops in HFR/MFR were significantly higher than LFR. Crops in HFR showed significantly higher total dry weight from increased shoot and root dry weights. HFR improved crop performance and yield in aquaponics possibly through enhancing environment for microbial nitrification activities, which might have led to better environment for crops to uptake nitrate and phosphate demonstrated by lower EC and nitrate and phosphate in the effluent. Interestingly, crops in different production periods also showed different growth performance during the study. Fast-growing crops showed significant higher total fresh weight, shoot fresh weight, leaf area, Pn than slow-growing crops. In summary, we concluded that high water flow rate at 3000 L/day improved performance and yield of fast-growing crops in an aquaponics system.