Submitted to: Journal of Horticultural Science and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2007
Publication Date: 9/1/2007
Citation: Bi, G., Scagel, C.F., Fuchigami, L.H. and Regan, R.P. 2007. Rate of nitrogen application during the growing season alters response of container-grown rhododendron and azalea to foliar urea in the autumn. Journal of Horticultural Science & Biotechnology. 82(5):753-763.
Interpretive Summary: Environmental concerns about nitrogen (N) runoff from container nursery production have increased the need for improved fertilization practices that increase the efficiency of fertilizer use and decrease the potential for environmental contamination without impacting crop productivity or quality. Using deciduous and evergreen cultivars of container-grown Rhododendron, we determined the influence of (1) N fertilization rate on N uptake efficiency and plant performance during the following growing season; and (2) foliar urea application in the autumn on N storage and reliance on fertilizers for growth in the following growing season. Our results show that foliar urea applications in the autumn to container-grown Rhododendron can improve N storage during winter and plant performance the following spring. Foliar urea applications can also decrease plant dependency on N fertilizers in the spring. We also found that increased N availability in the growing medium decreases N uptake efficiency and the relationships between N fertilizer rate, N uptake efficiency, and growth need to be considered when selecting optimum rates for N fertilization. A combination of optimum fertilization practices during the growing season with foliar urea applications in the autumn may be a useful management strategy to decrease fertilizer inputs, improve N uptake efficiency, and optimize growth of container-grown Rhododendron. Foliar fertilization in the autumn to container grown Rhododendron has potential to decrease N leaching and problems with hardiness sometimes associated with high N availability, and improve plant performance the following spring
Technical Abstract: One-year-old liners of rhododendron (Rhododendron ‘H-1 P.J.M’) and azalea (Rhododendron ‘Cannon’s Double’) grown at different N fertilization rates were used to assess the influence of foliar urea application in the autumn and soil nitrogen (N) applications during the growing season on N storage, N uptake and use for new growth. N uptake efficiency during the first growing season declined with increasing rate of N fertilization. For both cultivars, foliar urea application in the autumn significantly increased N storage without affecting plant size, regardless of plant N status. Leaves of rhododendron served as a primary storage site for N. Plants sprayed with foliar urea in the autumn had more new growth the following spring than plants receiving no urea regardless of whether plants received fertilizer in the spring. For azalea, N uptake in the spring was, in general, not affected by urea applications during the previous year. For rhododendron, urea application in the autumn decreased N uptake in the spring. For both cultivars, increasing N availability during the growing season increased the shoot to root ratio of plants. Our results suggest that combining optimum fertilization practices during the first growing season with foliar urea application in the autumn may be used as a management strategy to improve N uptake efficiency, increase N storage and optimize growth of Rhododendron.