The effects of alumina-buffered phosphorus (Al-P) were evaluated on growth and drought tolerance of woody plants and on seedling establishment of several tree species grown in containers with soilless media. Al-P reduced phosphorus leaching in all species. Vegetative growth of rhododendron (Rhododendron catawbiense Michx. cv. ‘English Roseum’), forsythia (Forsythia intermedia Zab. cv. ‘Spring Glory’), Ohio buckeye (Aesculus glabra Willd.), and bur oak (Quercus macrocarpa Michx.), measured as plant height, stem caliper, or biomass, was as fast or faster with Al-P as with Osmocote (17–6–10) or monoammonium phosphate fertilizer. Imposition of summer drought during the first growth season slightly reduced growth of rhododendron, with a stronger effect in the second year, while forsythia was more affected in the first season. Rhododendron plants fertilized with Al-P wilted more slowly than controls fertilized with Osmocote. Al-P fertilized forsythia plants grew faster than controls whether drought was imposed or not. Rhododendron plants produced more flower buds in the first year when fertilized with Al-P than with conventional phosphorus fertilizers. At the lower desorbing concentration, drought caused no reduction in percent of plants producing flower buds. A recharging treatment was tested at the beginning of the second season to replace P lost from the Al-P. Recharged Al-P reduced branching and flowering of rhododendron at the end of the second season, possibly as a result of damage from the recharging treatment.
This project was funded by The Horticultural Research Institute, 1000 Vermont Avenue, NW, Suite 300, Washington, DC 20005. The authors wish to thank Ms. Tracey Harpster for her assistance in setting up this project.
2Former graduate student. Current address: Bioinformatics Group, Noble Foundation, Ardmore, OK 73461.
4Professor. To whom all correspondence should be addressed.