Arboriculture & Urban Forestry 32(3): May 2006 93 Response to Fertilization of Different Tree Species in the Urban Environment F. Ferrini and M. Baietto Abstract. The influence of fertilization on shoot growth, leaf gas exchange, leaf chlorophyll content, and mineral content was monitored on sweetgum (Liquidambar stryraciflua L.), Japanese pagoda tree (Styphnolobium japonicum Schott), and European ash (Fraxinus excelsior L.) over a 3-year period after planting in the urban environment. The research was carried out on newly planted trees that were placed in different urban sites and fertilized after planting. Fertilization was repeated for 2 years after planting at the beginning of the spring. There were contrasting results according to the species and the year of measurements. Fertilization was to a limited extent effective in the first year after planting but failed to provide better results in the following years. Thus, the results of this research do not support the utility of fertilizer application as a method to improve plant establishment, growth, or physiology after transplanting in the urban environment. Key Words. Fraxinus excelsior; leaf gas exchanges; leaf mineral content; Liquidambar styraciflua; plant nutrients; plant physiology; Styphnolobium japonicum. The supply of nutrients to trees planted in the urban environ- ment in the form of artificial fertilizers is a subject on which there are different opinions (Miller, 1998, 2003; Marion 2003). Experimental evidence and practical experience show that the different results can be related to the mechanical and physical condition of the soil, the climate, and the quality of plant material and its age (Gilman et al. 2000; Smiley et al. 2002; Sharenbroch and Lloyd 2004). In addition, the fertilizer type and the placement of the fertilizer may affect plant re- sponse (van de Werken 1984; Gilman 1987). Hence, a wide variation in the practical results of fertilizing trees in the urban landscape is to be expected, especially in the relative length of time that is necessary to produce comparable re- sults. In fact, particularly young trees may not, or often do not, promptly respond to applications of nitrogen or other elements (Gilman et al. 2000). As recently reported by Sharenbroch and Lloyd (2004), because of the limited re- search on urban plants, fertilization recommendations from nonurban systems have been adapted for use in urban areas. As regards the influence on plant growth, Whitcomb (1979) found that application of fertilizers did not enhance the posttransplant growth of several landscape trees. Current tree-care recommendations suggest limiting fertilization dur- ing the establishment period (Marion 2003; Siewert et al. 2003). Growth in the first year can also be affected by inter- nal reserves of nutrients and photosynthates. As a result, a plant that has been well fertilized in the nursery and has a large root system is likely to better tolerate poor growing conditions in the first year after planting. However, such plants may show less response to nutrient addition than plants with a low nutrient content, particularly in the early part of their first growing season (Bradshaw et al. 1995). On the other hand, some studies in the literature indicate that the application of inorganic fertilizers aids plant estab- lishment and that it is an acceptable method of improving tree health and vigor (Rao et al. 2003; Smith 2003). Schulte and Whitcomb (1975) found that nitrogen fertilization at planting positively affected growth in the first year after planting. More recently, results obtained by Ferrini et al. (2005) on English oak (Quercus robur L.) indicate that shoot growth, leaf area, chlorophyll content, and leaf gas exchange were higher in fertilized plants, especially during the second and third years after planting. As to the time of fertilization, research shows that in gen- eral the time of maximum nutrient uptake is from budbreak in spring to leaf color change in fall (Smiley et al. 2002), and the differences can be due to the different climate conditions. However, some authors state that early spring and late fall are not the best time to fertilize trees (Struve 2002); others rec- ommend fertilizing in early spring or late fall, despite low nitrogen uptake potential during those seasons (Rose 1999). Late nitrogen fertilization may decrease winter hardiness, sometimes exhibited by trees fertilized in the fall, although on this topic some contrasting results can be found in the litera- ture (Smiley and Shirazi 2003). All of this means that in case of doubt, the only definite answer can be obtained by local tests, because a precise knowledge of how trees respond to changes in tree fertility is critical to the effective use of fertilizers in the landscape (Hagen 2000). Thus, there is a need to perform experiments ©2006 International Society of Arboriculture
May 2006
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