Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: 2/13/2008
Publication Date: 7/1/2008
Citation: Scagel, C.F., Regan, R.P., Bi, G., Hummel, R. 2008. Cold hardiness of green ash nursery trees is influenced by nitrogen fertilizer type and rate. HortScience. 43:1264.
Technical Abstract: Tip dieback and bud death in the spring can decrease salability and growth of nursery trees of green ash (Fraxinus pennsylvanica ‘Summit’). For some species, tip dieback in the spring is correlated with low nitrogen (N) reserves in trees; however, application of nitrogen (N) fertilizers late in the growing season can decrease cold hardiness of buds and stems. To determine whether N status of green ash in the autumn influences tip dieback during the following spring, one-year-old whips of green ash were grown in 2005 with different rates of N from urea formaldehyde (UF) or with a controlled release fertilizer (CRF) during the growing season and leaves sprayed or not with urea in the autumn. Trees with low N content grew less in the spring of 2006 but stem and bud necrosis was more prevalent on trees grown at the highest N rate. Additionally, plants grown with CRF had more bud failure in the spring compared to plants grown with a similar N rate from UF. To determine whether the form of N fertilizer influences tip die back, trees of green ash were grown during 2006 with different rates of N from either UF or CRF. The influence of N rate and type on cold tolerance of shoots and buds was evaluated in the autumn and winter. Both fertilizer type and rate influenced the level of cold tolerance. This was especially evident in mid-winter hardiness levels of both the shoots and buds and during the de-acclimation period in February. There was a strong positive relationship between the N concentration of all plant tissues (shoots and roots) and the lowest survival temperatures of both stems and buds; however, stems and buds of plants fertilized with UF were generally more cold tolerant than stems and buds on plants fertilized with ammonium nitrate. Our results indicate that trees at a similar N status can withstand different levels of cold depending on the type or form of fertilizer used during production.