290 Roberts: Compost-Containing Substrates teristics by promoting better soil structure and lowering pen- etration resistance to root growth as reported by Ferrini et al. (2005). Composts, defined here as products resulting from the controlled biologic decomposition of organic wastes, are proving to be potentially beneficial to plant growth when used as soil amendments (Tyler 1996). Because the availa- bility of newly marketed, economic, organically amended waste products is constantly changing, and because com- posted waste products have been used successfully to grow a wide variety of horticultural crops, including fruit trees (Au- tio et al. 1991), woody shrubs (Beeson and Keller, 2001), bedding plants (Klock-Moore 1999), vegetables (Ozores- Hampton et al. 2005), wildflowers (Roberts et al. 2001a), and turf (Roberts et al. 2001b), the present investigation was un- dertaken to further study the effects of compost-containing substrates, especially those containing municipal solid waste (MSW), on the survival and establishment of woody seed- lings. These studies were conducted in a greenhouse to help eliminate some of the environmental variables associated with field trials, other than planting medium composition, that might confound the results. Seedling material was used as a first step before testing on a larger scale using trans- planted trees in the urban landscape. METHODS A series of compost-containing media were obtained from commercial sources in the spring of 2003. Media used in this investigation included: Com-Til (CT), an MSW product from the city of Columbus, Ohio, U.S., composted with wood chips and screened to 1 cm (0.4 in); Garden Plus Topsoil (GPT), a mixture of 40% pulverized soil, 30% CT, and 30% flume sand (Earthco, Inc., Columbus, Ohio); Soil Plus (SP), a mixture of 60% soil, 20% CT, and 20% concrete sand (Jones Topsoil & Mulch, Columbus, Ohio); Container Mix (CM), a combination of biosolid compost, organic forest compost, rice hulls, pine bark, and silica sand (Kurtz Bros., Cleveland, Ohio); and Metro-mix 560 (MM560), a mixture of composted pine bark, coconut coir pith, sphagnum peat moss, processed bark ash, and perlite (Sun Gro Horticulture, Van- couver, BC, Canada). Metro-mix 360 (MM360), a noncom- posted soilless substrate consisting of horticultural vermicu- lite, sphagnum peat moss, processed bark ash, and washed sand (Sun Gro Horticulture), was used as the control medium in these investigations. Chemical and physical properties were determined for each medium. Chemical properties (pH and electrical conductiv- ity) were measured using three replicated samples containing equal parts substrate and deionized water (1:1 [v/v]). To de- termine physical properties, the technique of Niedziela and Nelson (1992) was used to measure bulk density, particle ©2006 International Society of Arboriculture density, air-filled porosity, and container capacity of three replicated water:substrate samples (2:1 [v/v]) of each me- dium. Percent pore space was calculated from bulk density and particle density measurements using the relationship de- scribed by Brady and Weil (1999). In the first series of experiments (part 1), accelerated- growth Jiffy Plug seedlings (5 cm [2 in] diameter plug size) of red maple (Acer rubrum L.) and green ash (Fraxinus penn- sylvanica Marsh.) were obtained from a commercial nursery and transplanted into 3.8 L (1 gal) plastic pots containing various combinations of CT and MM360. Jiffy Plug seedlings (seedlings in which the root system is growing in a peat pellet encased in biodegradable mesh) were used in this part of the study to simulate the conditions that exist when planting balled-and-burlapped rather than bare-root plant material. En- vironmental conditions in the partially shaded greenhouse during the January through March experimental period ranged from 18°C to 26°C (64°F to 79°F), 60 ± 12% relative humidity, and 80 to 120 W/m2 photosynthetically active ra- diation (PAR) (natural day length plus supplemental illumi- nation from 175-W metal halide lamps ona2hr photoperiod [0600 to 0800 hr]). In the second set of experiments (part 2), 2-year-old bare- root seedlings of red and sugar maple (Acer saccharum Marsh.) were obtained from a commercial nursery and planted in 3.8 L (1 gal) plastic pots containing either com- post-amended soils (GPT; SP), soilless compost-containing media (CM; MM560), or noncomposted soilless substrate (MM360). Environmental conditions in the greenhouse for these investigations, which ran from June through August, ranged from 19°C to 30°C (66°F to 86°F), 65 ± 15% relative humidity, and 90 to 120 W/m2 PAR. No supplemental illu- mination was used in part 2. Seedlings in both studies were hand-watered as needed and fertilized biweekly with a water-soluble, all-purpose fertilizer containing 21N-2.2P-16.6K and supplemented with 10% che- lated iron, 0.02% boron, 0.01% copper, 0.05% manganese, 0.01% molybdenum, and 0.07% zinc. Weekly height mea- surements were recorded for each seedling and, approxi- mately 12 weeks later, measurements of leaf area, leaf, stem, and root biomass were determined after harvesting the seed- lings, washing off the root systems, and oven-drying the tis- sue from each sample at 90°C (194°F) for 48 hr. Height growth measurements were expressed as percent increase in height and, to standardize variance, were converted to arcsin transformations before statistical analyses. The experimental design used in both studies was a completely randomized block with either five (part 1) or six (part 2) single-plant replications per treatment. For each species, differences in seedling growth were analyzed using the least significant dif- ference (LSD) method for pairwise comparisons at a prob- ability level of 0.05% (Analytical Software 2003).
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