This study was conducted with the objective of evaluating the nitrogen fertilization in orchid seedling formation. The experiment was conducted in a greenhouse environment with a coated polypropylene mesh with retention capacity of 60% of the solar radiation flux at the greenhouse of the Department of Agronomy of State University of Londrina – PR, Brazil. One year old seedlings of the orchid species Oncidium baueri has been used (Lindl.) from in vitro propagation, with an average height of 8.0 ± 1.0 cm. The experimental design was completely randomized with four replications and the treatments resulted from a 2×7 factorial design in which the factors were two sources (urea and ammonium sulfate) and seven doses of nitrogen applied fortnightly (0.00, 0.75, 1.50, 2.25, 3.00, 3.75, and 4.50 mg/pot). The experiment was conducted for a period of one year and the following variables were evaluated: largest pseudobulb length, plant height, highest root length, leaf area, root number, dry matter, number of leaves, and Dickson quality index. The use of ammonium sulphate resulted in the highest average values to the length of the longest pseudobulb, plant height, leaf area, length of the longest root, and plant dry matter, except for the number of leaves and Dickson quality index. The application of nitrogen between 3.20 and 4.33 mg/pot resulted in the highest values for the length of the longest pseudobulb, number of roots, length of the longest root, number of leaves, plant height and Dickson quality index for O. baueri (Lindl.) orchid. The plant height and leaf area variables increased significantly with increasing doses of N regardless of the source used, but the length of the longest pseudobulb, number of roots and dry matter production of plant only increased when urea was used as a nitrogen source.
Key words: Orchidaceae, nitrogen, fertilization, vegetative development.
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