Arboriculture & Urban Forestry 42(3): May 2016 Table 1. Soil analysis. Data are the average of five different samples taken in the planting area. Gravel % Sand 2.0 16.6 Silt 53.3 Clay 30.1 Active lime 1.0 pH 8.0 Organic matter (%) 1.5 N (%) 0.1 K2 O (ppm) 132.94 P2 O5 12 195 ppm CEC (meq/100 g) 25 C/N 8.8 Table 2. Compost analysis. Data are the average of 10 different samples taken in the compost shipped to the planting area. Volatile solids are the fraction of compost that is lost after 24 hours in oven at 105°C. They include humic and fulvic acids, nonhumic organic matter, and nutrients in volatile forms. Data are expressed over dry matter (DM) of compost. Humidity Glass and plastic Total carbon Volatile solids Humic and fulvic Ashes (%) 35.74 (g/100 g DM) 1.03 64.28 11.59 34.69 ing the summer period; leaf gas exchange was measured using the CIRAS-2 portable infrared gas analyzer (PP-Systems, Hertfordshire, UK). The readings were taken between 9:00 am and 12:30 pm, which was presumed to be the diurnal period when photosynthetic rates would be maximal, on sunny days under fixed CO2 centration (Ca con- diance (1300 mmol m-2 = 380 ppm) and saturating irra- s-1 provided by a built-in red-light-emitting diode radiation source); mea- surements were conducted on 90 fully expanded leaves (three per treatment and block) selected from the outer part of the crown and at different heights (Fini et al. 2009); whole-canopy photo- synthesis was calculated from Pn and leaf area; the plant modelling system WIMOVAC (v. 0.0.9, University of Illinois) was used to eliminate inaccuracies due to self-shading of the canopy 8) leaf greenness index was determined on five leaves with a portable chlorophyll meter (SPAD-502 Minolta Corp., Ramsey, New Jer- sey, U.S.); previous calibration curves were established by measuring absorbance at 664, 647, and 625 nm with a spectrophotometer (U-2000, Hitachi High Technologies America, Inc., Schaumburg, Illinois, U.S.), after extrac- tion with dimethylformamide (DMF); tripli- cate readings were taken around a midpoint near the midrib of each leaf and then averaged 9) presence of weeds on the mulch was visually checked 3 months and 12 months after mulch was laid. Statistical Analyses All data were subjected to one-way analysis of variance (ANOVA) using SPSS 20.0 statistical package for Windows® (SPSS Inc., Chicago, Il- linois, U.S.), and means were separated using N 0.92 (g/100 g DM) (g/100 g DM) acids (g/100 g DM) (g/100 g DM) (g/100 g DM) (g/100 g DM) (g/100 g DM) 28.29 P2 O5 0.11 K2 1.70 O pH C:N 7.38 30.66 HSD test (P ≤ 0.05). Data on leaf gas exchange have been processed per single sampling date, merged together, and processed again to ob- tain the average value on an annual basis. RESULTS AND DISCUSSION Effects of Mulching on Growth and Leaf Area Mulching with compost positively affected shoot growth of elm trees over the entire period of measurements (Table 3). Mulched plants had greater shoot growth than the other treatments, regardless of layer thick- ness. It was only in the third year that trees with the 5 cm layer did not show statisti- cal difference with respect to the control. Plant height was greater in the 10 cm layer treatment, especially when compared to the control. Trunk diameter at planting was similar (P > 0.05) among treatments (data not shown). However, since the end of the first growing sea- son, trunk diameter was greater in 10 cm treat- ment compared to the 5 cm group, which, in turn, showed greater diameter than control in the first and third year after planting (Table 3). Pruning weight (measured two years after planting) was more than twice as much in the mulched trees compared to control. Greater plant growth in response to mulching has been observed by many authors (Chalker-Scott 2007; Ferrini et al. 2008b; Fini and Ferrini 2011), despite the temporary N-immobilization that can follow the application of mulches with high C:N or high (lignin + polyphenol):N ratio (Palm 1995; Ferrini et al. 2008a; TerAvest et al. 2011; Rhoades et al. 2012). Others authors, however, found no N-immobilization after the ©2016 International Society of Arboriculture
May 2016
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