LEACHING LOSSES OF N FROM CONTAINER-GROWN ROSES

'Royalty' roses were grown under different leaching rates and applied N concentrations for 1 year in 20-1 microlysimeters in a greenhouse. During this period, there were eight synchronized flowering flushes at approximately 6-week intervals. Analysis of leachates collected from the microlysimeters indicated leaching losses of 21, 40 and 49% of the applied N from plants irrigated at a leaching fraction of 25% with nutrient solutions containing 77, 154 and 231 ppm N, respectively. Average leachate N concentrations were 79, 257 and 441 ppm. There were no significant differences among treatments in number of flowers or harvested dry matter per plant, and, except for the 77 ppm N treatment, only minor differences in leaf N content (3.2-3.4%). The concentration of the 77 ppm N treatment was increased to 105 ppm in April because of the appearance of N deficiency symptoms. The N present in the harvested flowers accounted for 49, 24 and 21% of the N applied to the 77 (105), 154 and 231 ppm N treatments. Plants irrigated with 154 ppm N at leaching fractions of 10, 25 and 50% had corresponding N leaching losses of 22, 38 and 56%. The average leachate N concentrations were 296, 240 and 181 ppm, respectively. The 50% leaching fraction produced yields that were significantly higher than those of the other treatments. The leaf N content was similar among the treatments (3.3-3.4%), but the N recovered in the harvested flowers accounted for 34, 30 and 22% of that applied to the 10, 25 and 50% leaching fraction treatments. The plant N demand estimated from these studies would be met by the addition of N fertilizer at levels substantially lower than those currently recommended.