Humic acids and nitrogen in lettuce seedlings production

The effects of humic acids on plants are variable, depending mainly on the source of production, the concentration adopted and the vegetal species used as bioindicator. Thus, the objective of this work was to evaluate humic acid and nitrogen concentrations in the production of lettuce seedlings. The experiment was conducted in a completely randomized design with four replicates. The treatments were obtained in the 3x5+2 factorial scheme, comprising three humic acid concentrations using the HA-Alternative source (7.3 mL L-1, 14.6 mL L-1 and 21.9 mL L-1), five concentrations of nitrogen (1, 2, 3, 4 and 5 dag kg(-1)), plus two controls (the first one represented by the commercial source of humic acids Fertiactyl GZ at the concentration of 7.3 ml L-1 and the second compound by the absence of the application of humic acids and nitrogen). The increase of nitrogen concentration in the different concentrations of HA-Alternative promoted a reduction in shoot dry mass, root dry mass and root length. The application of humic acids from both the HA-Alternative source and the commercial source Fertiactyl GZ promotes improvement in the quality of lettuce seedlings. The increase of nitrogen concentration reduces the quality of lettuce seedlings at concentrations higher than 1 dag kg(-1), due to the use of humic acids.