Effects of Hydraulic Retention Time of Aquaculture Effluent on Nutrient Film Technique Lettuce Productivity

Abstract

Nutrient film technique (NFT) is a popular, ergonomic, hydroponic system, but is not often used in commercial aquaponic systems due to lower efficiency in overall nutrient removal. Experiments were conducted to assess if NFT lettuce production could be improved by exchanging aquaculture effluent more frequently, and if so, determine the optimal water exchange rate. The AE was taken from a biofloc-based nile tiapia production system. Treatments consisted of increasing hydraulic retention time (HRT (d)) viz: four-, eight-, twelve-, or sixteen-day water exchanges arranged in a randomized complete block design with five blocks. In one trial (trial 1) where iron (Fe) was not supplemented, there was one replication. There were three replications for the second trial with iron supplementation. The analysis of lettuce plant size index and chlorophyll index (SPAD units) in trial 1 was statistically different among the HRTs beginning 14 days after planting, exhibiting negative linear trends with increasing HRT. However, most foliar micronutrients were borderline sufficient, and all treatments showed foliar Fe deficiency. After iron supplementation (trial 2), lettuce plant chlorophyll and size index exhibited quadratic trends with increasing HRT on 14 and 21 DAP, respectively. In trial 2, plant fresh mass decreased linearly from 162.1 g/head to 147.1 g/head, with increasing HRT. Furthermore, iron supplementation eliminated Fe deficiencies in the plants albeit only up to 14 DAP. Our findings suggest that shorter hydraulic retention times provide a solution to using the NFT system in aquaponics especially with iron supplementation.

Aquaponics as a climate‐smart technology for sustainable food production: A comparison with conventional production system in United Arab Emirates

“…A short period of 0.34 h was the calculated HRT of the aquaponic system. According to Wallace‐Springer et al (Wallace‐Springer et al, 2022) and Shete et al (Shete et al, 2016), short HRT in aquaponics boosts water use efficiency by improving nutrient uptake by plants, reducing water loss, ensuring adequate oxygen supply, and preventing nutrient buildup, leading to a more efficient and productive system.…”

Pilot-Scale Evaluation of Poultryponics: Insights into Nitrogen Utilization and Food Pathogen Dynamics

“…Water was pumped from each treatment system to 37.9 L reservoirs (Botanicare, Vancouver, USA) via black polyethylene tubing connected with a drip emitter and placed under a 750 W LED fixture (640 μmol photons m –2 s –1 , Volt Lighting, VGL2–750-L, USA). The required water flow rate was set to 9.5 L day –1 to reach a 4-day HRT in the 37.9 L reservoirs . Each reservoir had a drain and a floating polystyrene board with precut holes for 6 plant grow spaces (18 plants per treatment).…”

“…The required water flow rate was set to 9.5 L day −1 to reach a 4-day HRT in the 37.9 L reservoirs. 34 Each reservoir had a drain and a floating polystyrene board with precut holes for 6 plant grow spaces (18 plants per treatment). Aeration of the reservoirs was provided by air pumps (Hailea, ACO-9730, Guandong, China) through diffuser stones submerged at the center of the reservoir.…”

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“…Ammonium, nitrite, nitrate, phosphate, sulfate, sodium, potassium, calcium, magnesium, and chloride analyses of water from outlets of all units were performed once a week using ion chromatography (Dionex 3000, Sunnyvale, CA). Chelated iron for plants was maintained at about 2 ppm in all tanks by adding Fe-EDDHA (Doctor Tarsa, Antalya, Türkiye) when needed (Yeşiltaş et al 2021;Wallace-Springer et al, 2022). pH values were followed by a benchtop instrument in the laboratory (Orion 4 Star, Thermo Scientific, USA).…”