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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #202253

Title: Seasonal Variation in Growth, Nitrogen Uptake and Allocation by Container-Grown Evergreen and Deciduos Rhododendron Cultivars

Author
item Scagel, Carolyn
item BI, GUIHONG
item FUCHIGAMI, LESLIE
item REGAN, RICHARD

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2007
Publication Date: 10/1/2007
Citation: Scagel, C.F., Bi, G., Fuchigami, L.H., Regan, R.P. 2007. Seasonal variation in growth, nitrogen uptake and allocation by container-grown evergreen and deciduos Rhododendron cultivars. HortScience. 45(6):1440-1449.

Interpretive Summary: In nursery production, container-grown plants use fertilizers inefficiently, resulting in the potential for nitrogen (N) runoff. Fertilization strategies that synchronize plant demand with N availability will decrease the potential for environmental contamination. Using deciduous and evergreen cultivars of container-grown Rhododendron, we determined the times of active N uptake and the locations of N storage in plants for ten months. Growth of Rhododendron was not dependant on N from fertilizer until mid-summer and plants continued to grow even after stem elongation and leaf production ceased. Although N uptake differed between cultivars, all cultivars were capable of N uptake in the autumn and early winter. Our results suggest that fertilizer application strategies for transplanted liners of these cultivars should include low N availability after transplanting followed by high N availability in mid to late summer. This type of strategy will not only improve N uptake efficiency from fertilizer, but also minimize N loss from the containers. The results also demonstrated that N uptake in the autumn may play an important role in supplementing plant N reserves required for growth during the next season as well as for balancing N losses caused by leaf abscission, root turnover, and maintenance functions that occur over winter.

Technical Abstract: Growth, nitrogen (N) uptake, and storage were assessed in deciduous and evergreen cultivars of 1-year-old Rhododendron (Rhododendron ‘P. J. Mezitt Compact’ (PJM), ‘English Roseum’ (ER), and ‘Gibraltar’ (AZ)). Increased N availability increased growth after July (ER, PJM) or August (AZ), and resulted in three to five times more total biomass. Biomass continued to increase after stem elongation and leaf production ceased. Nitrogen uptake was correlated with growth of all plant structures on AZ, while N uptake was only correlated with stem and leaf growth on PJM and ER. The rate of N uptake was highest before July for AZ and in August and September for the evergreen cultivars. Thirteen to 16% of total N uptake that occurred between May and February happened after N fertilization ceased at the beginning of September. Biomass loss after November accounted for a loss of 14-48% of the maximum total plant N content. Differences in N storage between the evergreen cultivars occurred primarily in their roots and leaves. Over winter, PJM stored more N in its roots, while ER stored more N in its leaves. Our results suggest that fertilizer application strategies for transplanted liners of these cultivars should include low N availability after transplanting followed by high N availability in mid to late summer. This type of strategy will not only improve N uptake efficiency from fertilizer, but also minimize N loss from the containers. The results also demonstrated that N uptake in the autumn may play an important role in supplementing plant N reserves required for growth during the next season as well as for balancing N losses caused by leaf abscission, root turnover, and maintenance functions that occur over winter.