QUANTITIES AND FORMS OF NITROGEN UPTAKE THROUGHOUT DEVELOPMENT IN CHRYSANTHEMUM.

Abstract

Changes in quantity and form of nitrogen used were evaluated during development of Dendranthema × grandiflora `Iridon', `Sequoia' and `Sequest' grown in hydroponic solutions containing 28 ppm NO 3- (as Ca(NO3)2) and 28 ppm NH4+ (as(NH4)2SO4). Four plants of each cultivar were harvested every ten days over ninety days. Data were collected on plant height, leaf number, flower bud diameter, and root and shoot dry weights. Nutrient solutions were changed every ten days and sampled at days 1, 5, and 10 of each cycle. Concentrations of NO3- and NH 4+ of nutrient solutions and dried plant tissues were determined by micro-Kjeldahl. Total tissue nitrogen was determined for `Sequoia' by macro-Kjeldahl. Depletion of nitrogen from solutions approximated a 1:1 ratio for NH4+:NO3- throughout the crop cycle (r = 0.96). Although the sample date × cultivar interaction was significant for both forms of nitrogen, overall patterns of nitrogen uptake were similar among cultivars. Nitrogen uptake expressed per gram of tissue dry weight was greatest in the first month of development. However, total nitrogen uptake was greatest from days 40 to 60. Developmental stages corresponding to this period are a cessation of new leaf development and flower bud diameters of approximately 1.0 cm. Nitrogen uptake decreased rapidly as flowers expanded. Correlations between morphological changes and nitrogen demands could maximize the efficiency of nitrogen applications.