Abstract

The growth and nitrogen (N) uptake of Rosa ‘Mariandel®’ were evaluated at four fertilization rates: 0, 0.4, 0.8 and 1.2 g N/liter (0, 0.016, 0.032 and 0.048 oz/qt). Plants were harvested at 6-week intervals. New shoots in all treatments retained the highest relative dry weight percentage, apparently at the expense of root. The total N concentration, content, and uptake at 12 and 18 weeks, but not at 6 weeks, after potting were significantly (r² > 0.59; P = 0.0005) affected by rates of fertilization. Although DM in the old shoots of all treatments slightly increased over the first 6 weeks, the corresponding N content decreased due to translocation. Except in old shoots, a significant linear trend occurred between DM accumulation and N content but not with N concentration (at least up to 12 weeks). However, N concentration in most plant parts was significantly (P < 0.05) correlated with the respective N content. Excluding N released from the substrate, plants in 0.4, 0.8 and 1.2 g N/liter treated pots received 80, 126 and 182 mg (0.003, 0.004 and 0.006 oz) N per week, respectively, as used Osmocote (15N–4P–7.5K–1.8Mg) showed a linear (r² > 0.99) N-releasing rate. The corresponding total mineralized N in each control pot was 96 mg (0.003 oz) and 140 mg (0.005 oz) over the first and the second 6-week interval. Overall, ‘Mariandel®’ grown in 0.8 and 1.2 g N/liter treated pots had the highest mean N concentration and content respectively.