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Title: Bud Necrosis of Green Ash Nursery Trees is Influenced by Nitrogen Availability and Fertilizer Type

Author
item Scagel, Carolyn
item REGAN, RICHARD - Oregon State University
item BI, GUIHONG - Mississippi State University

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2009
Publication Date: 2/1/2010
Citation: Scagel, C.F., Regan, R., Bi, G. 2010. Bud necrosis of green ash nursery trees is influenced by nitrogen availability and fertilizer type. HortTechnology. 20(1):206-212.

Interpretive Summary: A study was conducted to determine whether nitrogen (N) status of nursery-grown green ash (Fraxinus pennsylvanica ‘Summit’) trees in the autumn is related to tip die back during the following spring. In 2005, different rates of N from either urea formaldehyde (UF) or a controlled release fertilizer containing ammonium nitrate (CRF) were applied during the growing season to green ash trees, and leaves were sprayed or not with urea in the autumn. Trees with low N content in the autumn grew less in the spring of 2006, but stem and bud necrosis was more prevalent on trees grown at the highest N rate. Providing N as ammonium nitrate in CRF appears to increase bud failure and shoot dieback symptoms of green ash trees compared to trees fertilized with N from UF. Higher bud failure is associated with higher N concentrations, lower C/N ratios, and differences in N partitioning between trees fertilized with N as CRF and UF. Significant relationships between bud failure and N status and C to N ratios in different tissues suggest a combination of tree N status and the balance between N and C in certain tissues plays a role in the occurrence of bud failure of green ash trees in the spring. Our results suggest tree N status may play a role in tip dieback of green ash trees; however, the type of fertilizer used in production may have a larger effect on dieback. This may have to do with differences in how trees metabolize the different N types, where and when the N is stored, and how it is remobilized in the spring, especially in relation to C metabolism.

Technical Abstract: A study was conducted to determine whether nitrogen (N) status of nursery-grown green ash (Fraxinus pennsylvanica ‘Summit’) trees in the autumn is related to tip die back during the following spring. In 2005, different rates of N from either urea formaldehyde (UF) or a controlled release fertilizer containing NH4NO3 (CRF) were applied during the growing season to green ash trees, and leaves were sprayed or not with urea in the autumn. Growth and N content were determined in the autumn of 2005 and spring of 2006, and stems and buds were evaluated for necrosis in the spring of 2006. Trees with low N content in the autumn grew less in the spring of 2006, but stem and bud necrosis was more prevalent on trees grown at the highest N rate. Compared to trees grown with a similar amount of N from UF, growing trees with CRF altered N allocation in 2005 and carbon (C) and N metabolism and fluxes in stems in 2006. Additionally, trees grown with CRF had less total shoot growth in the spring of 2006 and more bud failure than trees grown with a similar N rate from UF. Significant relationships between bud failure and N status and C to N ratios in different tissues suggest a combination of tree N status and the balance between N and C in certain tissues plays a role in the occurrence of bud failure of green ash trees in the spring.