Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2006
Publication Date: 3/1/2007
Citation: Bi, G., Scagel, C.F., Fuchigami, L.H., Regan, R.P. 2007. Differences in Growth, and Nitrogen Uptake and Storage between Two Container-Grown Cultivars of Rhododendron. Journal of Environmental Horticulture. 25(1):13-20.
Interpretive Summary: Increasing environmental concerns associated with nitrogen-runoff from agricultural sources have increased the need for efficient fertilizer management. Fertilizer inputs based on optimal plant needs (performance) and optimal time of application (uptake) will reduce overall fertilizer use, minimize point source pollution to groundwater, and enhance nursery stock quality. We determined nitrogen (N) uptake, remobilization, and storage from May to September in one-year-old liners of rhododendron and azalea after transplanting into larger pots. N uptake and uptake efficiency was low until July, which indicates that additional fertilizer application prior to this time may not be effectively taken up. N fertilizer management, in production of these cultivars from liner stock, should ensure N-availability is high during the period of rapid growth in July and August. Data obtained from this study provides growers with information on the times of active N uptake and use in deciduous and evergreen cultivars grown in containers. This information will aid in the development of fertilizer management strategies for nursery container production to decrease fertilizer use and production costs, improve plant quality, while minimizing N losses to the environment.
Technical Abstract: One year-old liners of rhododendron (Rhododendron ‘H-1 P.J.M’) and azalea (Rhododendron ‘Cannon’s Double’) were used to determine nitrogen (N) uptake, remobilization, and storage in relation to plant growth from May to September. Plants were grown with liquid fertilizer with or without N in a substrate of vermiculite, pumice, and sandy loam soil. The rate of N uptake was correlated with the rate of plant growth and maximum uptake occurred during July (azalea, >4 mg/d) and August (rhododendron, >2 mg/d). Compared to rhododendron, azalea grew faster and had a greater rate of N uptake and uptake efficiency (azalea, 12-33%; rhododendron, 8-16%). Old leaves of rhododendron remobilized N for new growth. New azalea leaves exported ~40% of their N by September when stems and roots were still actively accumulating biomass. All structures on rhododendron (except old leaves) were still accumulating biomass by September. Our results suggest that transplanted one-year-old liners of Rhododendron contain enough N reserves in the plant and in the substrate to support initial plant growth and that increasing availability of N in the substrate, during the period of rapid growth, can significantly increase N uptake, and improve vegetative growth and the N status of rhododendron and azalea.