Arboriculture & Urban Forestry 32(6): November 2006 293 Table 2. Growth of containerized Jiffy Plug red maple (Acer rubrum L.) and green ash (Fraxinus pennsylvanica Marsh.) seedlings in composted MSW media and in a noncomposted substratez . Species Mediay Red maple CT MM360 (MM) 3CT:1MM 1CT:1MM 1CT:3MM Green ash CT Height growth (%) 1.0 ab 4.9 ab 0.0 b 3.6 ab 7.4 a MM360 (MM) 27.9 a 3CT:1MM 1CT:1MM 1CT:3MM 2.6 bc 3.9 bc 13.1 b 0.0 c Biomass (g) Leaf 0.63 bc 3.23 a 0.0 c 0.54 bc 2.33 ab 1.83 c 6.06 a 3.02 bc 4.45 ab 2.57 bc Stem 4.24 b 5.63 a 4.28 ab 4.54 ab 5.14 ab 4.22 c 6.88 a 4.48 c 5.87 b 4.73 c Root 4.83ns 5.50 5.17 4.74 5.67 4.45 c 10.54 a 4.96 c 7.42 b 5.58 c same column differ significantly when followed by a different letter, LSD0.05; ns not significant. yRefer to text for description of media composition. Total 9.70 bc 14.36 a 9.41 c 9.82 bc 13.13 ab 10.50 c 23.42 a 12.46 c 17.48 b 12.86 c R/S 1.09 ab 0.65 c 1.21 a 1.01 ab 0.85 bc 0.80ns 0.82 0.73 0.76 0.82 Leaf area (cm2 ) 22.4 bc 113.6 ab 0.0 c 6.0 c 136.8 a 41.3 c 434.7 a 142.8 bc 288.1 ab 85.5 c zSeedlings grown for 12 weeks (January to March) in 1 gal plastic containers in the greenhouse (80 to 120 W/m2 photosynthetically active radiation [natural daylight + supplemental illumination from 175-W metal halide lamps ona2hr photoperiod 0600 to 0800 hr]). Each value represents the mean of six replications. To standardize the variance, height growth percentages were converted to arcsin transformations before statistical analyses. Within each species, values in the planting holes backfilled with a proprietary product contain- ing composted poultry litter. The current study, although in- volving plant material considerably smaller in size, also sug- gests that red maples planted in backfill amendments con- taining appreciable quantities of solid waste compost (CT in this instance) may not grow as well as similar maples planted in backfill soils amended with a noncomposted substrate such as MM360. For Jiffy Plug green ash seedlings, growth (percent height increase and total biomass) was significantly better when seedlings were planted in MM360, a noncompost-containing substrate (Table 2). Leaf, stem, and root biomass were also consistently greater for seedlings grown in the noncomposted substrate; however, no significant differences in root:shoot ratio were observed between any of the treatments. In mix- tures of CT and MM360, green ash grew best in a medium containing equal parts of both substrates (1CT:1MM). These results are different from those observed for red maple, in which seedlings grew best in a mixture containing more MM360 (1CT:3MM). One possible explanation may be the difference in physical properties between the two media. Bulk density, particle density, air-filled porosity, and con- tainer capacity of 1CT:1MM were all significantly higher than for 1CT:3MM (Table 1). Because the growth rate of green ash normally exceeds that of red maple (Nowak et al. 2002), one might expect a faster-growing species to outper- form a moderately growing one, especially in short-term studies such as those reported here. Watson et al. (1992) have reported that root density (after 1 year) and terminal growth and trunk diameter (after 2 years) of Fraxinus pennsylvanica ‘Summit’ trees (5 to 7 cm [2 to 2.8 in] in diameter) were not significantly different when planted in unamended backfill soil, in soil amended with sand and composted organic matter, or in friable topsoil. The authors concluded that although there is no reason not to use amended backfill soils when transplanting trees of this size, there may be no significant benefit in terms of increased growth. In the current study, the only appreciable growth advantage noted for transplanted green ash seedlings was when a noncom- posted substrate (MM360) was used exclusively as the grow- ing medium. Under these circumstances, height growth, total biomass, and leaf area were all significantly greater than for most of the remaining treatments (Table 2). Part 2: Growth of Bare-Root Seedlings in Biosolid Compost (GPT; SP; CM), in Compost Without Biosolids (MM560) and in Noncomposted Substrate (MM360) There seemed to be no particular advantage in growing bare- root red maple seedlings in any of the composted media, with or without biosolids, versus growing them in a noncomposted substrate (Table 3). Within the compost treatments used in this investigation, seedlings grown in media containing bio- solids (GPT, SP, CM) generally grew better than seedlings planted in a medium without biosolids (MM560), but only occasional significant differences were noted. The root:shoot ratio of compost-grown maples was generally higher than for maples planted in a noncomposted medium (Table 3), sug- gesting that root growth might be stimulated to a greater degree than shoot growth in these treatments; however, the variability between replicates was so great that no definite conclusions could be drawn from these data. In a study of posttransplant growth of 1-year-old, bare-root red maple seedlings, Kelting et al. (1998) reported that a ©2006 International Society of Arboriculture
November 2006
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