Journal of Arboriculture 31(4): July 2005 183 2. excavated soil plus leonardite, along with 2 kg [4.4 lb] of a commercial product known as Humisol™; or 3. excavated soil plus NPK (12-12-17) with magnesium (2), sulfur (5), and some microelements (boron [0.02] and zinc, [0.01]), along with 1 kg of commercial product known as Nitrophoska blu Spezial-BASF, with 5.5% nitric nitrogen and 6.5% ammoniacal nitrogen. Holes backfilled with excavated soil were used as a control. The second and the third year after transplanting, all the treatments were repeated. The same amount of leonardite and fertilizer was applied immediately before budbreak, and 10 kg (22 lb) of compost was added 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; all the other plants were hand-tilled at the same time. Trees were grown in a lawn situation with no removal of clippings, and the turf was not allowed to grow right up to the trunk. Twelve single-plant replicates of four backfilling materi- als were planted in a completely randomized block design. Trees were watered, and some soil was added to compensate for settling. Trees in all treatments were irrigated once a week during spring and summer, with 40 to 50 L per plant (11 to 13 gal). Data Collection At the end of June, when no further shoot elongation was detected, shoot length was determined on 20 shoots per plant. Leaf area was calculated by measuring the area of 50 leaves per plant with a CID CI-203 leaf area meter (CID Inc., Vancouver, WA). Trunk diameter was measured at 30 and 120 cm (12 and 48 in.) above grade for 3 years on all plants just before budbreak. Instantaneous net photosynthesis (Pn), transpiration rate (E), and water use efficiency (WUE, calculated by dividing Pn by E) were measured 75, 100, 123, and 150 days after budbreak (DABB) in the first year using the ADC-LCA-2 portable infrared gas analyzer; 75, 100, 130, and 160 DABB in the second year; and 60, 75, 90, 120, 135, and 150 DABB in third year using the CIRAS-1 portable infrared gas analyzer (PP Systems, Hertfordshire, UK). The readings were taken between 800 and 1800 hours on five fully expanded leaves per plant; the leaves were chosen from the outer part of the crown and at different heights, under conditions of natural light saturation (PAR > 1000 µmol m–2 s–1 ). Chlorophyll content was determined in the second and third year after transplanting at 90 and 130 DABB on the same leaves with a portable chlorophyll meter (SPAD-502 Minolta Corp., Ramsey, NJ). Previous calibration curves were established by measuring absorbance at 664, 647, and 625 nm with an Hitachi U-2000 spectrophotometer, after extraction with dimethylformamide (DMF) (Moran 1982) (R2 = 93.3%, regr. eq. –9.84 + 0.713x). Triplicate readings were taken around a midpoint near the midrib of each leaf sample and averaged. At the end of the third year following transplanting, soil samples were taken to evaluate the influence of the various treatments on soil characteristics. All the data regarding plants were analyzed using the one-way analysis of variance (ANOVA) using SPSS (Release 11.5 for Windows). Treatment means were separated by protected LSD, with P < 0.05 level of significance. Soil physical characteristics were evaluated through bulk density, penetration (cone) resistance, and macroporosity measurements. Bulk density determination was performed using the core method (Blake and Hartge 1986) at 10 to 20 and 30 to 40 cm (4 to 8 and 12 to 16 in.) depths. In-field penetration resistance was measured by a handheld electronic cone penetrometer (RIMIK model CP20), following ASAE standard procedures (1982). A 12 mm (0.5 in.) diameter cone with a 30-degree included angle and a 60 cm (24 in.) driving shaft was used, and data were recorded at 15 mm (0.6 in.) intervals. Nine replications (three measurements in three different locations) were carried out for each treatment; significance levels of the 0 to 15, 15 to 30, 30 to 45, and 45 to 60 cm (0 to 6, 6 to 12, 12 to 18, and 18 to 24 in.) depth cone resistance mean values were assessed by ANOVA (LSD test) at P < 0.05. To evaluate the pore system of the soils, undisturbed soil samples from different depths (10 to 20 and 30 to 40 cm [4 to 8 and 12 to 16 in.]) were taken in triplicate. Samples were dried by acetone replacement (Miedema et al. 1974), impregnated with a polyester resin, and made into 6 × 7 cm (2.4 × 2.8 in.) vertically oriented thin sections (Murphy 1986). Images were captured with a video camera from each section. These images covered 4.5 × 5.5 cm (1.8 × 2.4 in.) of the thin section, avoiding the edges where disruption could have occurred. The images were analyzed by image analysis techniques using Image-Pro Plus software produced by Media Cybernetics (Silver Spring, MD). The instrument was set up to measure pores larger than 50 µm. Pore shape factor was expressed as perimeter2 shape factor, pores were divided into regular pores (shape factor 1–2), irregular pores (shape factor 2–5), and elon- gated pores (shape factor >5). Pores of each shape group were further subdivided into size classes according to either the equivalent pore diameter for regular and irregular pores, or to the width for elongated pores (Pagliai et al. 1984). Thin sections were also checked for microstructures using a Zeiss “R POL” microscope at 25× magnification. /(4π * area). Using the ©2005 International Society of Arboriculture
July 2005
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