Nitrogen balance for two container-grown woody ornamental plants

The woody ornamentals flex opaca 'Hedgeholly' and Lagerstroemia x 'Tonto' plants were grown in containers for 9 months, and fertilized with complete nutrient solutions differing in applied nitrogen ([N](A)) concentration: 15, 30, 60, 120, 210, and 300 mg l(-1). Shoot dry biomass and leaf area increased significantly with applied N concentrations up to 60 mg l(-1), but higher levels caused significant reductions in these parameters. Root dry weights decreased with increases in applied N. Tissue N concentrations and leaf chlorophyll levels increased in a typical saturation response with N supply, and maximum dry weight yields for flex and Lagerstroemia plants were observed at leaf N concentrations of 2.53 and 2.65%, respectively. Plants of both species fertilized with 15-60 mg l(-1) produced leachate N concentrations that were on average below the actual [N](A), whereas plants fertilized with 120-300 mg l(-1) resulted in leachate N concentrations that were higher than [N](A). Across the two species, N leaching losses (as a fraction of total N applied) increased from an average of 17.4% in plants receiving 15 mg l(-1) of N to an average of 52.0% for those fertigated with 2 10 and 300 mg l(-1). The fraction of applied N that was taken up by plants in both species decreased significantly with increases in [N](A), averaging 46.8 and 7.2% for the 15 and 300 mg l(-1) treatments, respectively. The N fraction retained by the growing medium at the end of the experiment was not significantly affected by [N](A), averaging 6.4 and 3.7% of the applied N in flex and Lagerstroemia, respectively. Interestingly, and regardless of [N](A), an average of 31% (range 22.8-40.6%) of the total applied N could not be accounted for at the end of the experiment in both species, and this fraction was attributed to gaseous N losses by denitrification. (C) 2002 Elsevier Science B.V. All rights reserved.