94 Ferrini and Baietto: Response to Fertilization of Tree Species in the Urban Environment rate = mmol m−2 Treatment Control Fertilization Table 1. Effect of fertilization on net photosynthesis (Pn), evaporation rate (E), on water use efficiency (WUE) and on chlorophyll content (mg * cm−2 ) of Styphnolobium japonicum Schott trees (Pn = µmol m−2 s−1 of H2 sampling dates in the first and in the second year and five in the third year. 2003 Pn 11.22 b* 14.03 a E 2.44 b 3.05 a WUE 4.60 a 4.60 a Chlor. 15.98 a 16.67 a *Values differ significantly when followed by different letters at P 0.05 (LSD test). under different soil and climate conditions. The following study was therefore undertaken to determine the influence of fertilization on three typical tree species in the urban envi- ronment. MATERIALS AND METHODS Two experiments were initiated in spring 2002 in two differ- ent urban sites, one in a new parking lot situated in the S-W part of Milan, Italy, and the other in a downtown street. The soil tests results of three samples per each location (obtained by mixing five subsamples per each sample) taken prior to treatment application and establishment of the planting showed silty-loamy soils with a subalkaline pH for both lo- cations, with a balanced composition in terms of nutrient content except for nitrogen, which was around 0.6 g/kg (0.2 oz/1.32 lb) in the parking lot and 0.45 g/kg (0.2 oz/1 lb) in the street. Experiment 1 In spring 2002, 14 common ash (Fraxinus excelsior L.) trees, 5 years old, 4 to 4.5 m (13.2 to 14.9 ft) tall, 14 to 18 cm (5.6 to 7.2 in) in circumference (measured at 1.3 m height [4.3 ft]) and 10 Japanese pagoda trees (Styphnolobium japonicum Schott, formerly known as Sophora japonica L.), 5 years old, 4 to 4.5 m (13.2 to 14.9 ft) tall, 14 to 18 cm (5.6 to 7.2 in) in circumference (measured at 1.3 m height [4.3 ft]) were planted in parking-lot islands in a new public parking lot. All trees were obtained from the same nursery and planted at the same time. Japanese pagoda tree is one of the few commer- cially important, temperate, woody members of the Papilion- oideae family that do not nodulate, though recent research has shown that this species also has putative early noduling (Foster et al. 2000). Planting holes were 1.5 times the width and the same depth of the root ball (size of the root ball was 40 to 45 cm [16 to 18 in] in diameter). Trees were placed in the holes and backfilled with excavated soil and were planted in a completely randomized block design. Trees were watered and some soil was added to compensate for settling. Trees of all treatments were regularly irrigated in the first year after transplanting, then only when needed during the spring– summer period. ©2006 International Society of Arboriculture Before budbreak, seven subjects of Fraxinus and five of Styphonolobium were fertilized with 1 kg (2.2 lb) of 15-9-15 (commercial product Nitrophoska® Gold®–BASF with 2.5% nitric nitrogen, 7.5% ammoniacal nitrogen, 5% slow-release nitrogen [ISODUR], 9% P2O5, 15% K2O) fertilizer granules were distributed over the soil surface (approx. 2.5m2 [27 ft2]) around the planting hole by superficial hand-tilling (<10 cm [4 in], with no real damage to roots) with a hoe and mixing with the soil. The amount chosen was higher than those gen- erally recommended for urban tree fertilization (10 to 40 g/m2 [0.35 to 1.4 oz/108 to 432 ft2] of nitrogen) (Bradshaw et al. 1995; Rose 1999; Struve 2002) because soil chemical analy- sis before the beginning of the experiment indicated low soil N values at both locations. Seven ashes and five Japanese pagoda trees were hand- tilled at the same time and used as control. The second and the third year after transplanting, all the treatments were re- peated: the same amount of fertilizer was applied immedi- ately before budbreak by superficial hand-tilling, and control plants were hand-tilled at the same time. Trees were grown in a lawn situation with no clipping removal and the turf was not allowed to grow close to the trunk. Experiment 2 In spring 2002, 30 sweetgum trees (Liquidambar styraciflua L.), 6 years old, 5 to 6m(16.5 to 19.8 ft) tall, 14 to 18 cm (5.6 to 7.2 in) in circumference (measured at 1.3 m height [4.3 ft]) were planted along a busy lane where trees are subjected to a rather high stress level (mainly from air pollution and soil compaction). All trees with identical size characteristics were obtained from the same nursery. Planting holes were 1.5 times the width and the same depth of the root ball (size of the root ball was around 50 cm [20 in] in diameter). Trees were placed in the holes and backfilled with excavated soil and were treated in a completely random- ized block design. Trees of all treatments were watered and some soil was added to compensate for settling. Trees of all treatments were irrigated twice a week during spring and summer. Before budbreak (early April), ten subjects were fertilized with the same product and using the same technique as de- scribed in experiment 1; ten trees received a second fertiliza- Pn 9.86 a 8.25 b E 3.13 a 2.55 b s−1 of CO2 2004 WUE 3.15 a 3.24 a Chlor. 14.33 a 15.20 a ; Evaporation O; WUE = Pn/Evaporation rate). Data on leaf gas exchange are the average of three
May 2006
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