Turf Fertilization Effects on Nitrogen Status of Kentucky Bluegrass and 'Autumn Blaze' Maple Growing in a Mixed Landscape

It is commonly assumed that trees growing in a lawn receive sufficient nitrogen (N) from lawn fertilization. However, few researchers have examined the effect of N lawn fertilization on N levels of trees growing in urban landscapes. In this study, we applied nitrogen at a rate of 48.8 (LN) or 195.2 (HN) kg N per hectare (1 or 4 pounds N per 1000 square feet) to separate tree medians containing Kentucky bluegrass (Poa pratensis L.) turf and 15 year-old Autumn Blaze maple (Acer xfreemanii ‘Jeffersred’). Nitrogen was applied in May 2013  using a 35N–0P–8.3K fertilizer (28.35% urea nitrogen from polymer-coated urea). Grass clippings and tree leaf samples are collected biweekly (June–September), dried, ground, weighed and analyzed for total N. Tree stem growth rate was measured by examining marked branch increments monthly. Dark green color index (DGCI) and calculated SPAD were measured  biweekly. As expected, the HN fertility rate stimulated consistently greater turf clipping yields thoughout the growing season than what was observed with the LN fertility rate. Tree growth rate was unaffected by fertlity treatment. Tree leaf N concentration and dark green color index (DGCI) was also unaffected by N fertility in the first year of this study.