Abstract: This paper examines the effects of N03-N and NH4+ -N at concentration ranging from 1 to lOmmol/L on growth and development of Cymbidium sinense (Andr.) Willd. grown in soilless medium. N03-N and NH4+ -N at 1 mmol / L enhanced leaf growth at similar rate, but 50 mmol / L NH4+ -N sharply reduced the leaf growth rate. Flower buds and flowers could be formed normally by plant treated with NO3- -N at 1 and 10 mmol / L except 50 mmol / L. However, there was without folwer bud in all NH4+ -N treatments. We suggested that N03-N or NH4+ -N at low concentration should be applied in vegetative stage, and only N03-N at 1-lOmmol/L is favorable for the differentiation of flower bud during reproductive stage. It is considered that the slow growth of C. sinense may be caused by its lower photosynthetic rate and nitrate reductase ac-tivity, and the flowering of this plant is perhaps determined by C / N ratio.

Key words: Cymbidium sinense