Nutrients in lettuce production in aquaponics with tilapia fish compared to that with hydroponics

ABSTRACT In aquaponic systems, the residual water from the cultivation of fish is not enough to meet the nutritional demands of plants. The main objective of this study was to investigate how to adjust a nutritive solution for the cultivation of lettuce (Lactuca sativa L.) in aquaponics, based on hydroponics. The treatments included six separate crops of lettuce in an aquaponic system, while the hydroponic system served as the control. In each treatment, three blocks were used to quantify the parameters of ‘head’ diameter, number and dry weight of leaves, shoot dry weight, root dry weight, total dry weight, and the concentration and accumulation of nutrients in the total dry weight of the lettuce plants. The lower nutrient supply led to the occurrence of the lowest total dry weight in the C2 leaf crops when compared to that of the other crops of aquaponics, which had adequate time for system maturation. The system maturation and the use of a balanced solution in the C5 and C6 crops allowed the head diameter of the aquaponics plants to be equal to those of the hydroponics plants. In the aquaponic system, N and Fe were the most limiting macronutrient and micronutrient, respectively. To produce lettuce in an aquaponic system, it is necessary to ‘ripen’ the crop water for at least 30 days, and supplement micronutrients in the form of mineral fertiliser.摘要 在鱼菜共生系统中，鱼类养殖产生的尾水无法满足植物的营养需求。本研究旨在以水培法为参照，探究如何适配鱼菜共生系统中生菜（Lactuca sativa L.）栽培所需的营养液。实验设置共包含鱼菜共生系统下的6组独立生菜栽培处理组，并以水培系统作为对照组。每组处理均设置3个重复区块，用于测定生菜的叶球直径、叶片数量与干重、地上部干重、根部干重、总干重，以及生菜植株总干重中养分的浓度与累积量。与其余拥有充足系统成熟时间的鱼菜共生栽培组相比，C2组养分供给不足，导致其总干重最低。C5与C6组通过系统成熟化处理与平衡营养液的施用，使鱼菜共生栽培生菜的叶球直径达到了与水培组相当的水平。在该鱼菜共生系统中，氮（N）与铁（Fe）分别为最主要的限制性大量营养素与微量营养素。若要在鱼菜共生系统中栽培生菜，需将养殖水体熟化至少30天，并以矿物肥料的形式补充微量营养素。