Arboriculture & Urban Forestry 33(2): March 2007 141 sisted of 23.8% sand, 30.2% clay, and 46.0% silt; the sand was also well graded. Two types of organic amendment were used: sphagnum peat and food waste compost. The sphagnum peat was Ca- nadian stock, medium graded, and chosen because of its tra- ditional use in the horticultural industry. The food waste com- post—a 3 year composted stock of food waste, manure, wood chips, and sand—was donated by Ithaca College and was selected because of its potential usefulness to the industry. The amendments were analyzed for pH, exchange acidity, and nutrient, organic matter, and moisture content. Procedure Gravel 2.5 cm (1 in) in diameter or larger was removed from soil samples as were any obvious clumps of organic matter. The soil was then divided and the appropriate amounts of sphagnum peat or food waste compost were added. The amendments were added to the soils at 0%, 10%, 33%, 50%, and 75% on a volume-to-volume basis. Aquagro (Aquatrols Corp. of America, Paulsboro, NJ, U.S.) wetting agent was added to the peat samples at a rate of 0.06 g per sample. Each sample was contained within a 7.62 cm (3 in) × 10.16 cm (4 in) metal soil core ring. Half of the samples were recompacted by 25 blows with a standard 38 cm (15 in), 2.5 kg (5.5 lb) Proctor Hammer to yield ASTM 100% proctor density (Daddow and Warrington 1983). The compacted samples were wetted and brought to their plastic limit, the lowest moisture content at which a soil can no longer be deformed without cracking. To test for the plastic limit, samples were placed on a pressure cell apparatus and set to pressures of 1 kPa, 2.5 kPa, 5 kPa, 10 kPa, 20 kPa, and 40 kPa, reflecting a range from a very wet soil to a very dry soil. The samples were left at each pressure for 2 days, after which time they were tested for plasticity. Plasticity was achieved when soil ribbons the approximate consistency of putty were formed. To assess large pore (0.78 mm [0.03 in]) drainage, the samples were saturated in plastic vats over a period of 5 days. Water levels were raised slowly to prevent air entrapment. The samples then drained for 3 hr. Weights were taken before and after saturation and after drainage. The drained samples were then placed on a pressure cell apparatus and pressurized to 10 kPa. Once equilibrium was reached, the samples were removed from the pressure cell apparatus and weighed. Those not to be compacted were resaturated using the procedure described. Those to be com- pacted were placed on a steel tray on a concrete floor for stability. A wooden disk of one-inch thickness was used for even distribution of the compactive force. These samples were again resaturated. All resaturated samples were drained for 3 hr and weighed. They were then placed into a laboratory oven and dried at 105°C (221°F) for 48 hr after which the final dry weight was taken. Bulk den- sity, macroporosity, and total porosity were calculated as fol- lows: Bulk Density = mass of dry soilbulk volume Total porosity: Saturated weight − oven dry weight = weight of water Weight of water × Bulk Density = Total Porosity Weight of oven dry soil minus ring weight Macroporosity on a total soil volume basis: Saturated weight − 3 hr weight − weight of water lost aftera3hr drain 3 hr drained weight = macroporosity on total soil volume basis ring volume Statistical Analysis Statistical analysis and evaluation was conducted using Minitab 10X for Macintosh. Analysis included curve estima- tion, pairwise comparisons, Tukey’s and Dunnett’s T3 sig- nificance tests, and one-way analysis of variance. RESULTS The results showed that both sandy loam and clay loam soils, when amended with peat or food waste compost, had lower bulk density and higher macroporosity than those not amended even after recompaction (Table 1). With one excep- tion, the higher the rate of added amendment, the greater the change (Figures 1 through 8). Differences between amend- ments were not significant. Bulk Density Sandy Loam The sandy loam samples with 0% amendment had a bulk density of 1.5 mg/m3 uncompacted, 1.8 mg/m3 compacted. The addition of 10% food waste compost did not significantly reduce the bulk density in either case; the addition of 10% peat did but only in uncompacted samples. The addition of 33% food waste compost lowered the bulk density to 1.2 mg/m3 (20% change) for uncompacted samples and 1.5 mg/m3 (17% change) for compacted samples. When amended with 33% peat, the bulk density of the sandy loam decreased to 1.2 mg/m3 in uncompacted samples and 1.4 mg/m3 in compacted samples, a 20% decrease in both cases. The decrease in bulk density brought the 33% amended samples below the threshold for potential root restriction. With the addition of 50% food waste compost, the bulk density decreased to 1.2 mg/m3 in uncompacted samples and to 1.4 mg/m3 in compacted samples. Peat amendment by 50% yielded the same decrease. ©2007 International Society of Arboriculture
March 2007
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