Doses de nitrogênio no acúmulo de nitrato e na produção da alface em hidroponia

Lettuce production in hydroponic system presents growing expansion in Brazil, but still there are problems of quality and risk of nitrate accumulation. This work was carried out to evaluate the lettuce production and nitrate accumulation in hydroponic system depending on the increasing levels of nitrogen in the nutrient solution. The experiment was conducted in greenhouse of the Universidade Federal da Paraiba, Brazil. The lettuce plants were grown in nutrient solution containing increasing levels of N (11, 13, 15, 17, 19 and 21 mmol L-1) during a 25-day period. An entirely randomized design with four replications was used. Plant total yield (PTT), plant commercial yield (PCM) and nitrate contents in the fresh matter of roots, stems and leaves of the lettuce were evaluated. There were no significant effects of increasing levels of N in nutrient solution on PTT and PCM, average values of 357.3 and 352.5 g/plant being observed, respectively. The increased levels of N in nutrient solution increased linearly nitrate content on all lettuce parts. The nitrate content reached 659, 623 and 615 mg/kg in the fresh matter of roots, stems and leaves, respectively, at the highest N level. Nevertheless, the maximum nitrate content observed in leaves was far below the risk level for human health.