Arboriculture & Urban Forestry 38(6): November 2012 by soil C/N ratio in certain circumstances (Månsson et al. 2009). Besides the deliberate incorporation of organic matter, carbon enters soil from plant litter, carbon-rich rhizodeposition products (e.g., root exudates, dead cells, CO2 ), and dead roots (along with their associated mycorrhizae) (Grayston et al. 1997). As much as 40% of carbon assimilated through photosynthesis is returned to the environment through rhizodeposition (Lynch and Whipps 1990; van Veen et al. 1991), and nearly half of carbon allocat- ed to fine roots and mycorrhizae can be deposited into soils as roots turn over (Fogel and Hunt 1983). Not only does soil carbon increase activity of microorganisms, but the presence of micro- organisms can induce positive feedback responses that increase root exudation, further enhancing soil carbon content (Meharg and Killham 1991). Root carbon therefore exerts a significant influence on the soil microbial community (Brant et al. 2006). The purpose of this study was to examine the effects of or- ganic matter amendment on soil carbon dynamics and microbial activity within the root zone of trees planted into soil unoccu- pied by plants and to determine if these effects could be sustained over time. The soil surrounding the roots of newly transplanted trees was amended with organic matter and researchers measured the effects on soil carbon dynamics, microbial biomass, and tree growth up to 33 months after treatment. Researchers stud- ied three deciduous tree species of contrasting cultural require- ments, transplanted with three distinct types of organic matter incorporated into the backfill soil of their planting holes. The research objectives were to determine 1) if a single application of organic matter could alter carbon dynamics and increase soil microbial activity within the root zone; 2) whether the type of MATERIALS AND METHODS Study Site and Experimental Design The study was conducted at the Virginia Tech Urban Horticul- ture Center in Blacksburg, Virginia, U.S. (USDA Hardiness Zone 6b) from March 2004 to December 2006. Soil at the center is a Groseclose silt loam (fine, mixed, semiactive, mesic Typic Hapludults); typical bulk density and pH of the Ap horizon (0–18 cm) is 1.05–1.35 g cm-3 and 6.1–6.7, respectively (Harris et al. 2008). Average annual precipitation is about 109 cm, and the growing season typically lasts from early May to mid-October. The experiment consisted of three tree species and four back- fill soil treatments combined factorially and replicated four times each in a completely randomized design, totaling 48 experimen- tal units. The backfill soil treatments were unamended site soil (CON), and site soil amended with sphagnum peat moss (PM), leaf-based compost (LBC), or biosolids-based compost (BBC) as described in Table 1. See Bowden et al. (2007) for addition- al information concerning the preparation of LBC and BBC. In March 2004, bare-root, seedling-grown pin oak (Quercus palustris Münchh.), red maple (Acer rubrum L.), and chest- nut oak (Quercus montana Willd.) were randomly assigned to a backfill soil treatment and a planting location within five ad- jacent planting rows measuring 35 m long × 2 m wide (3.5 m Table 1. Soil amendments incorporated into backfill soil during transplanting of bare root, hardwood tree seedlings to a field site in Blacksburg, Virginia, U.S., in March 2004. Amendment Control Peat moss Descriptionz Unamended native silt loam Pro-Moss ‘Emerald’ 4.8 Canadian sphagnum peat moss Leaf-based compost Finely ground yard waste composted with poultry litter at 1:2 volumetric ratio for four months Biosolids- based compost Three-month-digested 6.7 biosolids from a wastewater treatment plant combined with wood chips at 1:2 volumetric ratio. Composted 30 days, cured 4 months, and sieved to remove wood chips. z See Bowden et al. (2007) for more details on properties and production process of these composts. y Total Kjeldahl Nitrogen EPA 351.3 (USEPA 1979) x Plant available nitrogen estimated by adding 100% of the measured N and the fraction of organic N estimated to be mineralizable during the first seasons. Mineralization coefficient of 0.1. w Total phosphorus EPA method SW846-6010B (USEPA 1996) ©2012 International Society of Arboriculture 15.9 2,181 9.0 17 265 76 Wolf Creek Waste- water Treatment Plant, Abingdon, Virginia, U.S. 6.6 n/a n/a n/a 125 n/a n/a Premier Horticulture, Hand-mixed 1:4 Quakertown, volumetric Pennsylvania, U.S. 17 2,623 4.1 18 311 159 Panorama Pay-Dirt, ratio peat moss to native soil Earlysville, Virginia, volumetric U.S. to native soil Hand-mixed 1:4 volumetric ratio compost to native soil Hand-mixed 1:4 ratio compost pH 6.1-6.7 TKNy (g/kg) n/a PANx (mg/kg) n/a Total Pw (g/kg) n/a C:N ratio TOC Gravimetric (g/kg) moisture n/a n/a content (%) n/a n/a Manufacturer Amendment method Soil only 263 organic matter and tree species would influence these outcomes; and 3) whether these changes might be attributable to enhanced root production and rhizodeposition in the amended backfill soil.
November 2012
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