264 spacing between trees). Planting rows had been uniformly pre- pared by killing the turfgrass with glyphosate (Roundup®, Monsanto Co., St. Louis, Missouri, U.S.) and tilling the top- soil to 15 cm depth at the end of the previous growing sea- son. Average height of red maple, chestnut oak, and pin oak trees at planting were 2.9 m, 3.5 m, and 3.6 m, respectively. Trees were placed in holes dug 45 cm deep with a 61 cm diameter mechanized auger, backfilled to grade with the as- signed soil treatment, and thoroughly irrigated. Trees were then secured to a wire trellis spanning each planting row and mulched with a 5 cm deep × 2 m wide layer of uniform, shredded hardwood bark that was replenished seasonally for the duration of the study. The pre-emergent herbicide pendi- methalin (Pendulum® Aquacap, BASF Corp., Florham Park, New Jersey, U.S.) was applied to planting rows every March, and weeds were spot-treated during the growing season with the post-emergent herbicide glyphosate. Trees were drip-irri- gated once per week during the first growing season and then only during protracted drought in subsequent growing seasons. tosynthesis System (LI-COR Biosciences, Lincoln, Nebraska, U.S.). The flux chamber was affixed to the PVC ring, and the thermocouple was inserted 6 cm into the soil adjacent to the PVC ring. Volumetric soil moisture content was simultane- ously measured adjacent to the PVC ring with a 6-cm dielectric probe (TH2 0 Soil Moisture Meter, Dynamax, Houston, Texas, U.S.). Equipment malfunction prevented measurements dur- ing April 2006; therefore, the experiment was extended through November 2006 to achieve twelve monthly sampling sessions. Immediately following the second monthly sampling of res- piration, temperature, and moisture at a measurement sub-plot, a 5 cm diameter soil core was extracted from the sub-plot center at 0–10 cm soil depth. Soil samples were first passed through a 6 mm sieve to collect coarse mineral fragments, coarse woody debris, and coarse tree roots. The coarsely-sieved soil was then passed through a 2 mm sieve to prepare soil sub-samples for carbon–nitrogen analysis. In addition, thin tree roots (2–6 mm diameter) were manually collected from the sieve and fine tree roots (<2 mm diameter) were manually collected from the sieved soil using methods described by Oliveira et al. (2000). Root frac- tions were then compiled for each core sample, washed, digitized using a flatbed computer scanner, and analyzed for physical di- mensions using WinRHIZO Pro software (Regent Instruments, Quebec, Canada). Roots, mineral fragments, and woody debris were then oven dried at 65°C and weighed. Sub-samples of the finely-sieved soil were also oven dried at 65°C and then analyzed ©2012 International Society of Arboriculture Sampling and Measurements In November 2005 (20 months after planting), researchers be- gan a yearlong series of monthly soil and root measurements. Six measurement sub-plots were established equidistant around the perimeter of the amended root zone of each tree about 22 cm from its trunk. Each sub-plot was used for measurements dur- ing two consecutive months and then abandoned. Two weeks prior to each monthly measurement session, a PVC ring (10.1 cm inside diameter × 16 cm height) was placed at the cen- ter of the selected sub-plot and pressed through the mulch and into the soil to a 3 cm depth. Subsequently, soil respiration and temperature were concurrently measured using a LI-6400-09 Soil CO2 Flux Chamber coupled with a LI-6400 Portable Pho- Wiseman et al.: Organic Amendment Effects in the Root Zone for total carbon and nitrogen content by dry combustion with an automated gas combustion analyzer (Vario MAX CNS elemental analyzer, Elementar Instrument, Mt. Laurel, New Jersey, U.S.). In October 2006, soil samples were collected from the amended root zone of each tree to assay microbial biomass carbon (MBC). Three sub-samples per tree were collected with a 2.5 cm diameter corer at 0–7 cm soil depth and homogenized. All samples were immediately covered with a wet paper towel and quickly passed through a 2 mm sieve. Two, 25 g sub-samples were then collected from each sieved sample and each kept in a constant field-moist condition by placing in a sealed desiccator chamber along with 250 ml of distilled water for 24 hours. One of each pair of samples was then processed for MBC assay according to the chloroform fumigation extraction method of Horwath and Paul (1994). Fumi- gation destroys membranes and cell walls, allowing subsequent extraction of cell constituents with 0.5 M K2 procedure was performed on both fumigated and non-fumigated samples and extracted constituents were shipped frozen to the Soil Analytical Service Laboratory at North Carolina State University (Raleigh, North Carolina, U.S.) for total organic carbon (TOC) analysis using a TOC-5050 analyzer fitted with an ASI-5000 au- tosampler (Shimadzu Corporation, Kyoto, Japan). Total MBC of the extractant was calculated as the difference between TOC in fumigated and non-fumigated samples using an extraction effi- ciency factor of 0.35 (Voroney et al. 1991). Soil MBC was then calculated by adjusting extractant volume for soil mass and cor- recting for gravimetric moisture content at the time of sampling. SO4 Statistical Analysis Measured values of response variables were first screened for normality and homogeneity of variance; violations of these as- sumptions were corrected through natural log transformation of the measured values prior to statistical analysis. Response variables were analyzed using repeated measures ANOVA with the PROC MIXED procedure of SAS ver. 9.1 (SAS Institute, Cary, North Carolina, U.S.). Where main effects of indepen- dent variables were significant, multiple comparisons of re- sponse means were conducted using the LSMEANS PDIFF option. Where there were significant interactions between independent variables, the LSMEANS SLICE and DIFF op- tions were used to test their simple effects on response vari- ables. Microbial biomass carbon was analyzed using a two- factor ANOVA with the PROC GLM procedure. Multiple comparisons of treatment factor levels were performed us- ing Tukey’s HSD test. Regression models were created in JMP ver. 9.0.2 (SAS Institute, Cary, North Carolina, U.S.). RESULTS Root Growth There was a marginally significant tree species × soil amend- ment interaction (P < 0.075) for both total and fine root length (Table 2). There was a significant species difference in root mass, but no interaction with soil amendment measured dur- ing the second year after treatment. Red maple had greater root mass than both chestnut oak and pin oak. Although the relationship varied among amendment × species for root length, both total and fine root length were always lower in . The extraction
November 2012
| Title Name |
Pages |
Delete |
Url |
| Empty |
Ai generated response may be inaccurate.
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success.
Downloading PDF
Generating your PDF, please wait...
This process might take longer please wait
