Nitrogen Rate, Irrigation Frequency and Volume Differentially Influence Growth, Flowering, and Nutrient Uptake of Container-Grown Rhododendron during the Following Growing Season

Abstract

Sustainable nutrient and water management are critical for optimizing the quality and subsequent landscape performance of nursery plants. In this 2-year study, we investigated the influence of different nitrogen (N) rates [N-free fertilizer (0 N) or N-free fertilizer plus 7 (0.5 N) or 14 (1.0 N) mg N per day from NH4NO3] and irrigation frequencies and volumes [once daily to 50% or 100% container capacity (CC) or twice daily with the same total amount of water as 100% CC] on plant growth, flowering, and nutrient uptake of three rhododendron cultivars, including one deciduous cultivar, Rhododendron ‘Gibraltar’ and two evergreen cultivar, Rhododendron ‘P.J.M.’ and Rhododendron ‘Catawbiense Album’. In each case, the plants were grown in soilless media in year 1 and transplanted to soil in year 2. Increasing the N rate in year 1 increased plant biomass and N content in both years and improved flowering performance the following year. Furthermore, in year 1, irrigation once daily to 50% CC or twice daily to 100% CC enhanced the uptake of several nutrients in each cultivar and the growth of the evergreen cultivars. Plants that were irrigated more frequently during year 1 performed better in the landscape the following year, while those irrigated to 50% CC only performed better in the deciduous cultivar. In the evergreen cultivars, lower irrigation volume altered nursery plant qualities, resulting in a trade-off between flower production and growth in year 2. Our results indicate that manipulating N rates and irrigation frequency and volume can be used to alter nursery stock qualities and improve subsequent performance in the landscape.