This thesis tested the hypothesis that nitrogen use efficiency of subirrigated potted chrysanthemum (Chrysanthemum morifolium Ramat.) can be improved by managing the NO3- status of the plant. Replacement of NO3- with water one week prior to flower development was the most effective method of reducing tissue NO3- content and improving the nitrogen usage index, as compared to various combinations of NO3- and Cl-. Shoot or flower dry mass and N content were unaffected and the medium electrical conductivity was reduced. Supplying N in the NH4+ form in combination with NO3- did not affect nitrogen use indices. Reducing N supply improved various indices of nitrogen use efficiency, with a slight loss of quality. Elimination of NO3- prior to flower development and reduction in N supplied are effective strategies for improving nitrogen use efficiency in subirrigated potted chrysanthemums without sacrificing quality. / Cecil Delworth Foundation