250 tion and development. Twelve percent of national stormwater nutrient runoff is estimated to originate from urban residen- tial landscapes (USEPA 1994). Discharge of nutrients from urban stormwater sources within Florida are likely greater than national estimates due to high population density, rapid urban growth, and unique environmental conditions (Shober et al. 2010; U.S. Census Bureau 2011). Studies that quantify soil characteristics within a wide range of newly constructed urban residential landscape soils are needed to better understand the contribution of this source to water quality degradation. The objectives of this study were to: 1) quantify soil character- istics and examine variability at plot-level and community-level scales within newly constructed urban residential communities located in three central Florida counties (Orange, Lake, and Sem- inole), and 2) examine relationships between soil characteristics and infiltration rates near the soil surface that would have the greatest influence on runoff potential. Data collected from this investigation will provide a more accurate description of urban soil characteristics. In addition, this information can be used by land- scape planners to improve management practices and in selection of plant materials appropriate for anthropogenic environments. MATERIALS AND METHODS Site Description A total of nine urban residential communities were sampled from the adjacent counties of Orange, Lake, and Seminole in central Florida between January and May 2009. Communities were undergoing construction at time of sampling and were selected based upon access and visual representation of local environmen- tal variability. Communities contained a range of 11 soil series prior to development: Adamsville (Entisol), Apopka (Ultisol), Candler (Entisol), EauGallie (Spodosol), Millhopper (Ultisol), Myakka (Spodosol), Pomello (Spodosol), Smyrna (Spodosol), Sparr (Ultisol), Tavares (Entisol), and Zolfo (Spodosol). A total of 40 single-family unit lots within the nine communities were randomly identified and selected for sampling. An attempt to sample five lots within each of the nine communities was made; however, five lots were not available in each community. Thus, five lots were sampled in six of the communities, four lots were sampled in one community, and three lots were sampled in two communities. Average lot size was approximately 0.06 ha. All selected lots had been prepared for housing construction through land clearing, backfilling, and leveling prior to sampling. No residential structures or vegetation were present at sampled lots; however, underground site utilities had been installed. Sample Collection Five soil samples were collected at random locations within each lot using a soil core sampler (Model 200; SoilMoisture Equipment Corporation, Santa Barbara, California, U.S.). Soil cores sampled measured 5.7 cm in diameter and 3.0 cm in depth and were collected at a depth beginning 3.8 cm below soil surface to quantify soil characteristics near the soil surface. A Global Positioning System (GPS) unit (Model Nuvi 200; Garmin International, Inc., Olathe, Kansas, U.S.) was used to determine sampling location and position within Department of Agriculture-National Resource Conservation Service (NRCS) ©2013 International Society of Arboriculture Pearson et al.: Soil Characteristics That Influence Infiltration Rates soil maps. One additional soil sample was collected from each lot using a soil auger (Model S-110; Durham Geo-Enterprises, Inc., Stone Mountain, Georgia, U.S.) at a depth of 0–3 cm. . Cores were transferred to a laboratory oven (Model 18EM; Precision Scientific Group, Chicago, Illinois, U.S.) and dried for analysis using the standard method of Blake and Hartge (1986). Soil core sample mass was measured using a top-loading balance (Model PB5001; Mettler Toledo, Inc., Columbus, Ohio, U.S.). Two of the five soil core samples were used for determina- tion of soil moisture retention characteristics. Cores were satu- rated under vacuum then placed in a ceramic plate extractor (Model 1500F1; SoilMoisture Equipment Corp.) and analyzed in accordance with ASTM method D6836 (ASTM 2008). Mois- ture extraction was examined at 6.4, 9.8, 19.6, 39.2, 100, 500, and 1500 kPa to develop moisture retention characteristics. Sample mass at each pressure interval was recorded (Model PB5001; Mettler Toledo, Inc.). In addition to examining mois- ture retention characteristics, soil moisture data were used to quantify soil pore size distribution using the method of Klein and Libardi (2002). The soil sample collected with the auger was analyzed for particle size distribution for textural determi- nation using the standard method of Gee and Bauder (1986). One soil infiltration rate measurement was collected randomly within each lot using a falling head double-ring infiltrometer. The double-ring Sample Analyses Three of the five soil core samples were used for determination of soil Db infiltrometer was constructed of polyvinyl chloride pipe measuring 30.5 cm in length. This device had an outer ring diameter of 10.2 cm and an inner ring diameter of 5.1 cm. Both rings were installed to a depth of 10 cm below soil surface prior to measurement. Infiltration tests were con- ducted for a duration of 40 minutes (infiltration was observed to become constant within 15 minutes or less of test initiation). Statistical Analyses All data were analyzed by analysis of variance using the PROC GLM procedure in SAS with mean separation by Tukey-Kramer unless otherwise specified (SAS Institute 2008). Statistical analysis of Db was conducted comparing mean values among soil porosity, and soil moisture retention volume data using the PROC MEANS procedure in SAS (SAS Institute 2008). Regression analysis was conducted to examine relationships between soil infiltration rates, Db , soil moisture retention vol- umes, and percentage of soil sand, silt, and clay using the PROC REG procedure in SAS (SAS Institute 2008). All analytical tests were considered to be statistically significant if P < 0.05. lots and communities. Florida’s soil is dominated by sand par- ticle size fractions (0.05–2 mm), thus mean comparisons of per- centage sand among communities was conducted by Duncan’s multiple range test. Analysis of soil moisture characteristics compared mean soil moisture retention volumes between soil moisture potentials 6.4 and 100 kPa among lots and commu- nities. This matric potential range was selected because it best represents the range of soil moisture available for plant up- take in predominately sandy soils (Obreza et al. 1997). Mean comparisons of soil infiltration rates were analyzed among communities. Coefficient of variation was determined for Db ,
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