©2023 International Society of Arboriculture Arboriculture & Urban Forestry 49(2): March 2023 93 microbial biomass (MBC and MBN), microbial activ- ity (PMC and SOLV), or the microbial substrate (SOM, POM, or POXC). Statistical Analyses Statistical tests were conducted using SAS JMP 13.2.1 software (SAS Institute Inc., Cary, NC, USA) with significance determined at a 95% confidence level. To answer the first research question, Pearson product-moment correlation analyses were con- ducted with the RUSI model and the tree metrics. The R-correlation and P-value statistics were used to eval- uate the strength and significance of the correlations. To answer the second research question, parameter weighting was applied (Table 3). For each model, all weights summed to one. Weights were developed using the data collected during the second sampling period and were tested on data collected during the a cooler until being transported to the laboratory where they were then stored at 5 °C until analyses were performed. Immediately after the first soil sampling, a top dress- ing of organic biosolids (Milorganite, Milwaukee, WI, USA) was applied by hand at 3 rates. Biosolids are high in carbon, nutrients, microbes, and microbial activity, and thus have been found to stimulate the biological communities and increase decomposition and nutri- ent mineralization (Sullivan et al. 2006). Application rates based on nitrogen (N) content were chosen in accordance with industry standards on urban tree fer- tilization (American National Standards Institute 2018). Ten sites per city received the maximum rate of 2.92 kg N 100 m-2, ten sites received the standard rate of 1.46 kg N 100 m-2, and the remaining ten sites received no soil amendment and served as the control. In the laboratory, each soil sample was sieved through a 6-mm screen for homogenization and removal of coarse material. Soil particle-size analysis was performed using the hydrometer method (Gee and Or 2002) to verify the field assessment of soil texture. The total soil organic matter (SOM) was deter- mined using the loss on ignition method at 360 °C for 6 hours (Nelson and Sommers 1996). The particulate organic matter (POM) was determined following par- ticle size fractionation (Gregorich et al. 2006). Potas- sium permanganate oxidizable carbon (POXC) was determined colorimetrically (Weil et al. 2003). Poten- tially mineralizable carbon (PMC) was measured as the amount of CO2 in 0.25-M NaOH traps following a 7-day soil incubation, which was then titrated to a phenolphthalein endpoint using 0.25 N HCl (Parkin et al. 1997). Soil respiration was determined using the Solvita® gel system (Solvita, Woodsend Laboratories, Augusta, ME, USA) which incubates a color gel pad- dle in a container with a field moist soil sample for 24 hours, after which the paddle color indicates the quan- tity of CO2 present (Haney et al. 2008). Microbial bio- mass carbon and nitrogen were determined using a chloroform fumigation and extraction (Vance et al. 1987), using efficiency factors of kN = 0.54 (Joergensen and Mueller 1996) and kC = 0.45 (Beck et al. 1997). After fumigation, samples were extracted using 0.5 M K2SO4 and analyzed for microbial biomass nitrogen and carbon on a PerkinElmer C:N analyzer (PerkinElmer Inc., Waltham, MA, USA). The labile organic matter parameters tested in this study attempt to assess soil biological condition by measuring the Table 3. Property weights for RUSI, weighted RUSI (RUSIw), and organic weighted RUSI (RUSIow) models. Precipitation (PPT), growing degree days (GDD), expo- sure (EXP), traffic (TRA), infrastructure (INF), surface (SUR), estimated rooting area (ERA), penetration (PEN), A-horizon (HOR), texture (TEX), structure (STR), wet aggregate stability (WAS), soil organic matter (SOM), electrical conductivity (EC), pH, and Solvita® (Solvita, Woodsend Laboratories, Augusta, ME, USA) soil respiration (SOLV). Property RUSI RUSIw RUSIow PPT 0.066 0.000 0.000 GDD 0.066 0.000 0.000 EXP 0.066 0.043 0.038 TRA 0.066 0.043 0.038 INF 0.066 0.043 0.038 SUR 0.066 0.087 0.077 ERA 0.066 0.087 0.077 PEN 0.066 0.087 0.077 HOR 0.066 0.130 0.115 TEX 0.066 0.130 0.115 STR 0.066 0.130 0.115 WAS 0.066 0.087 0.077 SOM 0.066 0.043 0.038 EC 0.066 0.043 0.038 pH 0.066 0.043 0.038 SOLV n/a n/a 0.115 Total 1.00 1.00 1.00
March 2023
| 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
