Nitrogen Fertigation Rate and Foliar Urea Spray Affect Plant Growth, Nitrogen, and Carbohydrate Compositions of Encore Azalea ‘Chiffon’ Grown in Alternative Containers

The objective of this study was to investigate the plant vegetative growth, flower production, nitrogen (N) concentration, and carbohydrate compositions of Encore® azalea ‘Chiffon’ when fertigated with five N rates—0, 5, 10, 15, and 20 mM N—and grown in two types of containers, a black plastic and a biodegradable container, during one growing season. Foliar urea of 3% was applied to half of the plants in late fall to investigate its effect on plant N and carbohydrate concentrations. The paper biocontainers resulted in superior plant growth, increased plant size, dry weights, root length and surface area compared with the plastic containers with N rates of 10, 15, and 20 mM. The paper biocontainers also increased N uptake and carbohydrate concentrations mainly by increasing plant biomass. High N rates of 10 to 20 mM combined with urea spray and biocontainers generally resulted in the highest plant N concentrations. Foliar urea application in late fall tended to increase plant N concentration but decreased carbohydrates, including starch, glucose, fructose, and sucrose, to varying degrees, likely due to increased N assimilation. Fall foliar urea spray can be effective in improving the N status of azalea plants without affecting plant biomass.