Termografia por infravermelho para determinação da temperatura de bandejas na produção de alface

Abstract

This study was conducted in Recife – PE, under greenhouse conditions, with the aim to evaluate the variation of seedling trays’ temperature throughout the production of lettuce seedlings and its influence on the seedlings quality and on the final product. Two lettuce cultivars were used: Solaris and Vanda. The trays are made of expanded polystyrene, conventional polypropylene (black), polypropylene painted white and polypropylene painted gray. In order to perform a micrometeorological monitoring of the internal and external environment to the greenhouse, it was used two dataloggers equipped with sensors which allowed records of air temperature (Tar, ºC), relative air humidity (UR, %) and global solar radiation (Rg, MJ m-2 day-1). Trays’ and substrate surface’s temperature were measured by thermal images, using an infrared thermal imager. Substrate temperature monitoring was performed by a mini datalogger, with thermistor sensors inserted into the tray cells. Biometric evaluation and plant quality was performed in two steps. The first one at 24 days after seeding, measuring seedling height, plant collar, number of leaves, root length, aerial part dry matter, root dry matter, total dry matter and Dickson’s quality index. On the second step, from transplanting to final product phase (22 days), it was considered the following variables: number of leaves, plant diameter, commercial fresh matter, stalk diameter and commercial classification. It was used a completely randomized design under a factorial scheme of 4 x 2, with three replications. The black-painted polypropylene tray was the one who showed the highest surface temperature (31.1 oC), followed by the gray (30.4 oC), white (30.0 oC) and polystyrene (29.3 oC). The temperature of the substrate in the polystyrene tray (27.2 ºC) was higher than the other trays, followed by the black (26.8 ºC), gray (26.6 ºC) and white ones (26.5 ºC), respectively. Seedlings quality and the most important agronomical characters for lettuce commercialization were derived from the white tray, being its use the best alternative for lettuce cultivation. The cultivar Vanda showed the best production responses under the experiment conditions.