DECLIVIDADE DE SISTEMAS HIDROPÔNICO E AQUAPÔNICO NO CULTIVO DE ALFACE

Abstract

The aquaponic system consists in cultivating plants in residual water resulted from aquatic organism creation, mainly fish, case in which plants absorb essential nutrients, returning water of better quality to the fish. The nutrient concentration in the water depends on the diet provided to the fish, while the plant development depends on the bench inclination and the flow rate and drainage time. This research aimed to evaluate the lettuce yield (Lactuca sativa L.) americana, cv. Lucy Brown, in hydroponic and aquaponic systems along with producing Nile tilapia (Oreochromis niloticus) in southern Goiás State (GO), Brazil. The experiment was carried out in a fishpond with a shading screen, in Itumbiara municipality (GO), from November 2019 to April 2020. The experimental design was in randomized block, three replicates, 3 x 5 scheme, split plots, three types of water (hydroponics, conventional, and two residual water of tilapia with 18 and 15% crude protein diet) in the plots and five slopes (2, 4, 6, 8, and 10%) of PVC tubes in the subplots. The amount of feed was calculated according to the fish weight. The waters of the fishponds were decanted from solids, filtered by biological filter, and pumped into the nutrient film technique (NFT) channels. The flow rate (L h-1) in the tubes at the 25th day after lettuce transplantation, water physical-chemical parameters, plant yield, and foliar chemical analysis were evaluated The slope of 8% provided greater lettuce aerial part fresh mass, 466.8 g plant-1 on average. The water from the 18% crude protein diet provided greater yield and greater accumulation of macronutrients (N and P) in the lettuce aerial part. Higher slopes provided greater flows rates and shorter contact time of the nutrient solution with the roots, resulting in greater root and aerial part mass.