12 Smith et al.: Above and Belowground Growth of Corymbia maculata in a Constructed Soil Experimental Profiles Three types of organic matter, coir fiber, composted green waste and composted biosolids were evaluated. Each was used as a soil amendment at the rates of 5, 10, and 20% by volume. Coir fiber is a product of the husk of the coconut, and is also known as coir fiber dust. It is used as a peat replacement in nursery media (Offord et al. 1998) and has been used in constructed landscape soils. The composted green waste was commercially composted to meet the criteria of Australian Standard 4434-2003 Mulches, composts and soil conditioners (Standards Australia 2003b). The composted biosolids met the Class A requirements of the United States Environment Protection Authority (1993) biosol- ids standards, and the AS 4454-2003 requirements for pasteuri- zation. Both the composted green waste and composted bio- solids were passed through a 5 mm (0.2 in) screen before use. The other factor was profile design where the three organic amendments were either restricted to the surface 150 mm (6 in) of the profile (layered profile) or mixed through the entire profile (uniform profile). In each design the organic amendment of the treated soil was at the three rates given above. The soil mixes were prepared in 50 L (13 gal) batches in a concrete mixer. Trace ele- ments (0.8 kg m-3 NSW) and ground dolomite (1 kg m-3) (0.5 and 0.6 lb ft-3 Micromax, Scott’s Australia, Baulkham Hills, respec- tively) were mixed in at this stage, prior to profile construction. Profile Construction A 25 mm layer of 4–5 mm angular gravel was placed in the bot- tom of each container as a filter and drainage layer. The sand or sand/organic mixes were placed in the containers in 150 mm layers, and each layer was lightly compressed manually. The to- tal depth of root zone was 600 mm (24 in), with a 25 mm deep irrigation volume left at the top of all planters to facilitate irri- gation by micro-sprays. After filling, the planters were irrigated several times to fully consolidate the constructed profile prior to planting. The bulk density of the constructed profiles ranged from 1.9 Mg m-3 m-3 (2530 lb yd-3 (3200 lb yd-3 ) for the unamended sand to 1.5 Mg ) for sands amended with 20% organic matter. Planting Stock, Planting and Maintenance Five-month old C. maculata seedling liners were purchased in square containers [50 mm wide x 130 mm (2 in x 5 in) deep]. They were selected for the experiment based on their uniformity of root system development, size, and leaf morphology. Relatively small plants were used because of the restricted volume of the experi- mental system. A single nutrition treatment was surface applied to all constructed profiles after planting. The slow release fertil- izer Once High Fine N (11:1:4) (Scott’s Australia) was used. This fertilizer was reapplied four months later at the same rate giving total N, P and K applications the equivalent of 1000, 90, and 340 kg ha-1 (890, 80, and 300 lb ac-1 ) respectively. These rates were based on growth responses observed in an initial experiment that evaluated nutrient responses in C. maculata growing in a sand profile with the surface 150 mm amended with coir fiber (Smith 2003). In greenhouse experiments to evaluate nutrient responses in forestry eucalypts, Olsen and Bell (1990) used an upper rate of 200 kg N kg ha-1 (180 lb N ac-1 et al. (1996) an upper rate of 400 kg N ha-1 (360 lb N ac-1 ) in a clay loam soil, and Bennett ) in a clay soil. The higher fertilizer used in this experiment was due to the low fertility of the sandy soil. Initial fertilizer recommen- ©2010 International Society of Arboriculture which had been calculated from the dimensions of the sampler. Root Density Measurements At the conclusion of the experiment, roots were harvested at three sample depths in each soil profile, to the east side of the transplanted root ball, using a metal core sampler [150 mm long x 25 mm (6 in x 1 in) diameter]. The first core was taken at the surface [0–150 mm (0–6 in)], the second from 180–330 mm (7–13 in), and the third from 350–500 mm (14–20 in). The core samples were washed through a series of sieves and the roots recovered. Root length was measured using a desktop scanner in conjunction with Rhizo V 4.1 software (Regent Instruments, Québec, Canada). The total root length in the samples at each depth was converted to root length density (LV cm cm-3 ) by dividing by the core volume, Statistical Analysis (Shoot and Root Growth) The unamended sand treatment could not be included in ANO- VAs because of incomplete replication, hence the analysis of the data was done in two stages. First, an ANOVA was performed us- ing all the fully replicated treatments. Means comparisons were made using Fisher’s least significant difference (P < 0.05). Then, to allow comparison of the unamended sand treatment with the or- ganic-amended treatments, Dunnett’s multiple comparisons with dations for plantation eucalypts planted in sandy soil in western Australia are as high as 18 g N (0.63 oz N) per tree (Cromer 1996) compared to the 3.9 g N (0.14 g N) per tree applied in this experiment. The experiment was conducted over the spring and early summer with the trees planted in the containers on August 2, 2000, and harvested on January 2, 2001. During the experiment the trees were irrigated with a microirrigation system controlled with a timer, as required to maintain soil moisture. All blocks and containers received the same irrigation treatment. The trees were grown outdoors in a nursery in Richmond, VIC, Australia. Aboveground Growth Measurements At the conclusion of the experiment, samples of youngest ful- ly expanded leaves were harvested for foliar nutrient analy- sis. The harvested leaves were dried at 80°C (176°F) to con- stant weight for subsequent tissue analysis. Each seedling was then cut off at ground level, or just above the lignotu- ber if one was present, and the entire seedling top dried at 80°C to constant weight. Reported total shoot dry weights in- clude the weights of leaves harvested for nutrient analysis. Chemical Methods for Analysis of Leaf Tissue and Organic Amendments Samples were oven-dried, ground to a fine powder and to- tal N was measured using a Carlo Erba NA 1500 analyser (Carlo Erba now Thermo Electric, Milano, Italy). Total P was measured by colorimetric analysis based on the reaction of soluble orthophosphate with molybdate-vanadate (Olsen and Dean 1965) in digests of finely ground samples prepared using Piper’s (1950) method, modified to omit perchloric acid, at high temperature [200–350°C (392–662°F)]. Total K was mea- sured in the same acid digests by diluting to an appropriate range and analyzing with a Varian SpectrAA 200 atomic ab- sorption spectrophotometer (Varian Australia, Mulgrave, VIC, Australia) in flame photometry mode (Knudsen et al. 1982).
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