Lettuce has a predisposition to nitrate accumulation and has led many researchers to develop research to reduce this accumulation. The objective of this study was to evaluate the effect of nitrate concentration (NO3-) and nitrate/ammonium ratio (NO3-:NH4+) on growth, production and accumulation of these nitrogen compounds in lettuce grown in a hydroponic system in southern Amazon. There were performed two experiments with Iceberg lettuce type, in a floating-hydroponic system under protected cultivation. In the first experiment, five nitrate concentrations (2.5, 5.0, 7.5, 10.0 and 15.0 mmol L-1) were evaluated. In the second experiment, the best NO3- : NH4+ ratio was evaluated with five proportions 0:100, 25:75, 50:50, 75:25 and 100:0 in the nutrient solution. At 35 days after transplanting, the evaluations were performed. The nutrient solution containing nitrogen (N) as nitrate source in the concentration of 15.0 mmol L-1 contributed to higher lettuce productivity, being the concentration recommended for hydroponic grown system in southern Amazon. It is recommended to use about 23% of the N in nutrient solution in ammonium form, where higher N-ammonium concentrations are not indicated for Icebeg lettuce type because it reduces the productivity of this green leaf vegetable, causing toxicity symptoms.
Key words: Nitrogen, vegetable, nutrient solution, food security.
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