Arboriculture & Urban Forestry 37(6): November 2011 a 15–20 cm depth using an air tool (Air Spade® series 2000, Concept Engineering Group, Verona, Pennsylvania, U.S.). Control trees received no amendment or tillage treatment, but were maintained with a 1.5 m radius vegetation-free zone. The AFM treatment began with air tillage, as previously described. Soils were then amended with 0.28 m3 of com- posted cow manure and the prescription fertilizer materials from the F treatment. Amendments were applied to a 1.5 m radius and incorporated into the loosened soil profile with the air tool. Finally, amended soil received a mulch layer as de- scribed for the M treatment. It is important to note that com- post was added as part of the full AFM process only and was not present in any individual treatment. Specific compost prod- ucts differed among sites, depending on local availability. Immediately after treatment application, 30 L of ir- rigation was applied to the 1.5 m treatment radius of all trees in Boston and Myrtle Beach. Boston trees re- ceived identical irrigation applications at one and three weeks post-treatment due to dry weather conditions. Because of long-term seasonal drought at the Anderson site, water applications were required to prepare the soil for air tillage. Anderson trees received 106 L of water injected approximately 15 cm beneath the soil surface. Trees receiv- ing A and AFM treatments were given split applications, with half of the water injected prior to treatment and half as a drench following treatment. M-, F-, and C-treated trees re- ceived the full irrigation amount after treatment application. In Pittsburgh, five centimeters of snow fell on the day following treatment application, making post-treatment irrigation unnecessary. No further irrigation or fertilization was supplied at any site over the course of the experiment. Bulk density and soil strength measurements Pre-treatment soil bulk densities were measured by collect- ing a 5.8 cm diameter soil core from beneath each tree, ap- proximately 0.75 m from the trunk. Cores were trimmed to 7.6 cm in length, and leaf litter and organic matter were re- moved from the top. The cores were stored at 5°C in wax- lined paper bags for less than one week before process- ing. Cores were transferred to aluminum trays, dried for seven days to constant weight at 65°C, and weighed to cal- culate dry bulk density (g/cm3 ). These data are reported in Table 1 and represent initial soil bulk densities at the sites. Bulk density measurements were not made after treat- ment application. Loosened, mulched, and/or amended soils have a tendency to compress during coring, causing bulk den- sity measurements to overestimate true bulk density (Tan 1996). Instead, a Clegg impact hammer with a 2.5 kg weight (Lafayette Instruments Company, Lafayette, Indiana, U.S.) was used to estimate soil strength. Hammer measurements were made yearly at each site. Mulch, if present, was tempo- rarily removed from the soil surface prior to measurement. The Clegg hammer drops a weighted accelerometer from a standard height and measures its deceleration upon im- pact with the soil surface. This measurement is reported as a Clegg Impact Value (CIV). Soils with high CIVs have greater unconfined compressive strength, and therefore pres- ent greater mechanical impedance to root growth (Pabin et al. 1998; Janoo et al. 1999; Waltz et al. 2000). Bulk density and soil strength are positively correlated, although the spe- RESULTS Soil Strength The AFM treatment significantly reduced soil strength rela- tive to control at all sites in 2006 (Figure 1). There were sig- nificant treatment × location interactions in all years, with the higher bulk density sites (Anderson and Myrtle Beach) show- ing the greatest magnitude and duration of response. The A and M treatments also reduced soil strength in Anderson and Myrtle Beach, although their effects were less pronounced. Soil Organic Matter The effect of treatment on soil organic matter also differed across sites (Figure 2). Pittsburgh had the highest percentage of initial soil organic matter of any site (7.4%). None of the treatments increased soil organic matter above control levels at this site, but the A treatment significantly decreased levels. Anderson and Boston had initial soil organic matter percent- ages of 4.2% and 6.2%, respectively. At these sites, the AFM and M treatments significantly increased soil organic matter, while the A treatment had no effect. The sandy soil of Myrtle Beach had extremely low initial soil organic matter (1%). The AFM treatment was the only treatment to increase soil organic matter at this site; the effect lasted only through 2007. 295 cific relationship between them differs with soil water content and soil type (Mirreh and Ketcheson 1972; Sojka et al. 2001). Soil Nutrient and Organic Matter Measurements Composite soil samples from three locations within the treated radius of each tree were collected in spring 2006 and 2007 for soil nutrient analysis. Samples were mailed overnight to the Clemson University Agricultural Services Laboratory for soil pH, CEC, organic matter, and mineral nutrient analyses (Moore 2010). Soil Water Content Measurement In Anderson, a time domain reflectometry probe (20.5 cm length) was placed horizontally in the soil beneath one tree from each treatment (five probes total). Volumetric soil mois- ture content was measured weekly during the growing season using the TRASE time domain reflectometry system I (Soil moisture Equipment Corp., Santa Barbara, California, U.S.). Data from the mulched treatments (M and AFM) and the unmulched treatments (A, F, and control) were combined for analysis. Statistical Analyses The effects of treatment, location, and their interactions on soil parameters were analyzed using a general linear model. Mean separations were performed with Fisher’s least sig- nificant difference (SAS PROC GLIMMIX, SAS version 9.1; SAS Institute, Cary, North Carolina, U.S.). The effects of treatment and time on soil moisture content in Anderson were analyzed using a repeated measures model in GLIMMIX, and mean separations were performed as previously described. Data met normality and equality of variance assumptions. ©2011 International Society of Arboriculture
November 2011
| Title Name |
Pages |
Delete |
Url |
| Empty |
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. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
