Variability Of Soil Physical And Chemical Properties In An Established .

“Urban soils are those strongly influenced by human activities such as construction,transportation, manufacturing processes, industry, mining, rural housing and similaractivities”.Natural or undisturbed soil genesis is expressed using the traditional framework todescribe the five state factors associated with soil formation and ecological development asdescribed by Jenny (1941). These factors include: climate, organisms, parent material, reliefand time (Jenny, 1941). According to Jenny (1941), natural soils exhibit intact soil profiles thatcan be keyed based on diagnostic horizon development. However, it was later found thatdirect and indirect anthropogenic interactions imparts changes and alterations that introducenew pedogenic situations (Effland and Pouyat, 1997) and that urban soils become uniquematerials made up of a new or novel composite of once naturally stratified horizon layers(Pavao-Zuckerman, 2008). Effland and Pouyat (1997) used this new knowledge to modifyJenny’s model to account for anthropogenic factors in the states of soil formation framework.Now within the natural soil genesis framework, urban soils are considered to be pedologicallyreset, starting over from a new parent material within the confines of the framework previouslydocumented by Jenny (1941) and Effland and Pouyat (1997).Study ObjectivesGiven that human populations will continue to move from rural areas to urbanizedcities, a critical look at how anthropogenic activity influences urban soil behavior is necessary.Previous research contended that more study was required to differentiate (e.g. pH, bulkdensity, structure, texture) urban soils based on in-situ characteristics (Pouyat et al., 2007). Ourstudy attempts to answer how anthropogenic activity affects soil properties at the residential7

community scale. Residential development often involves the construction of housing in phases(i.e., groups of homes); a process that can take several months to years to complete. Studieshave found that soils within urban areas vary significantly due to differences such as, exposureto heavy mechanical equipment, multiple sources of fill soil, and burial of native soils and debris(Effland and Pouyat, 1997). Similarly, our study will identify soil physical and chemicalcomposition and the extent of variability within soil horizons and soil properties within a singleresidential community, which can be compared with results of other urban soil studiesconducted at the metropolitan and regional scales (Effland and Pouyat, 1997; Pouyat et al.,2010; Shuster, 2011; Hagan et al., 2012). To our knowledge, few studies have intensivelycompared native soils to similarly mapped soils in a nearby residential neighborhoodcommunity to evaluate differences in chemical and physical soil properties at the residential lotscale. Therefore, the objective of this study was to determine the variability of chemicalproperties in collected from established ( 10 years) residential yards by examining theproperties of surface soils and soil profiles. We also investigated the influence of vegetation(ornamental plants vs. turfgrass) and phase of development on soil chemical properties. Thelong-term goal of this study is to integrate this knowledge into a systems managementapproach to remediating urban soils based on pre- and post-management decisions usingspecific analysis of the building phase or housing unit.Materials and MethodsStudy LocationThe study was conducted in Rivendell, a master-planned residential community locatedin Osprey, Sarasota County, FL (Fig. 1). Rivendell was developed in five primary development8

phases and associated sub-phases (Fig. 1) The development phases (listed as units on thecommunity map; Fig. 1) were built out between the years of 1998 and 2004. The median homeprice in Rivendell at the time of construction was 365,000. Residential lots in phases 2 (homebuilt in 1998-2003), 3A (1999-2002), 3B (2001-2002), 3C (2001-2002), 3D (2002-2003), 3E(2001-2002), 4A (2002-2004), 4B (2002-2003), and 5 (2002-2004) were sampled. Wehypothesized that soil fill materials and constructions practices that would impact soilproperties would be similar within a single building phase. Homes were selected for intensivesoil sampling from a list of Rivendell residents who responded to a landscape preferencessurvey conducted by the University of Central Florida Stormwater Academy; all soil sampleswere collected with homeowner consent. Soil samples were also collected from Oscar SchererState Park, which bordered Rivendell on the south and east sides.Soil Sampling and AnalysisComposite soil samples were collected at a depth of 0 to 15 cm at two locations perresidence (i.e., turfgrass areas and ornamental plant beds) for a total of 98 residentiallandscape composite soil samples. Four additional composite samples were collected fromOscar Scherer State Park to provide a baseline (natural soil) with which to compare physical andchemical properties of soils collected from Rivendell residential areas. Approximately 10 to 15soil cores (75 to 100 g of soil) per composite sample were randomly sampled using a soil probeat each residence and in the park areas. Composite soil samples were air-dried and sieved topass a 2-mm screen. Soil texture was determined using the USDA Soil Texture by Feel Methodguide introduced by Thien (1979). Soil bulk density (Db) was determined in the top 10-cm ofsoil within the ornamental landscape bed area of each residential lot using the standard9

method presented by Blake and Hartge (1986). Bulk density was not determined in the turfareas due to the presence of excessive thatch in most St. Augustinegrass lawns and theresulting risk of severe damage to the turf. Bulk density measurements were not completed onthe Oscar Scherer park samples.Organic matter (OM; loss on ignition), pH (1:2 soil to deionized water ratio), andelectrical conductivity (EC; 1:2 soil to deionized water ratio) were determined using thestandard methods of the University of Florida Institute of Food and Agricultural Sciences (UFIFAS) extension soil testing laboratory (Mylavarapu and Kennelley, 2002b). Soils were extractedwith 2M KCl (1:25 soil to solution ratio) (Mulvaney, 1996) and analyzed for soil ammonium-N(NH4-N) (U.S. Environmental Protection Agency, 1993a) and nitrate nitrite-N (NOx-N) (U.S.Environmental Protection Agency, 1993c) using a discrete analyzer (AQ2, Seal Analytical, WestSussex, UK). Soils were also digested using and analyzed for total Kjeldahl N (TKN) (U.S.Environmental Protection Agency, 1993b) using a discrete analyzer (AQ2, Seal Analytical, WestSussex, UK). Soils were also extracted using the Mehlich 3 (M3) extraction (Kovar andPierzynski, 2009) and analyzed for P, K, Ca, and Mg using inductively coupled plasma – atomicemission spectroscopy (ICP-AES). Current UF-IFAS soil test interpretations are based on theMehlich 1 (M1) soil test (Kidder et al., 2003); however, since M3 provides better results whensoil pH tends to be slightly alkaline (as was the case with residential soils in Rivendell) we optedto use M3. Therefore, soil test interpretations for P and K were converted to M3 equivalentsbased on the relationship between M1 and M3 as reported by Sikora (2002).Deep core samples were also collected from ornamental landscape beds at 16 selectedresidences within the Rivendell community and from two locations in Oscar Scherer Park10

(representing more natural soil conditions). Deep core samples were collected with a 10-cmdiameter bucket auger from the soil surface to the water table or 122 cm below grade,whichever was deeper. Samples collected with the auger were deposited onto a section of 10cm 122 cm PVC tube that was cut in half for viewing. Deep core samples were describedbased on methods outlined in the USDA Field Book for Describing and Sampling Soils(Schoeneberger et al., 2002) to characterize soil profiles. The following characteristics weredescribed for each soil core sample:1. Depth – Depth was recorded as the “bottom depth” of each specific horizon or layer.2. Color – Munsell soil color charts were used to determine the hue, value, and chromaand the associated color name on moist samples from each horizon. For example, 10YR4/4 would be noted as “reddish brown”.3. Texture – The soil texture by feel method (Thien, 1979) was used to estimate textureclass based on the soil textural triangle (e.g., sand, sandy loam, loamy sand, etc.)4. Water Laid or Transported Deposits – This term refers to the identification of parentmaterials. Multiple parent materials were identified as “marine deposits” based on thepresence of fine to medium shell fragments within the samples.5. Redoximorphic features (RMF) – Color patterns in the soil, surfaces of peds, pores orbeneath the surfaces of peds were identified. Redoximorphic features descriptionsincluded redox concentrations, redox depletions, or reduced matrix.6. Horizon boundary – The horizon boundary is also known as the distinctness of boundaryand describes the point at which a different horizon becomes more dominant. It is the11

transition of another horizon (top depth) based on abrupt or diffuse morphologicaldifferences.Data AnalysisDescriptive statistics (e.g., mean, median, range, etc.) were determined for allcomposite samples using the PROC MEANS procedure in SAS (Sas Institute, 2003). The effect ofvegetative cover (turfgrass vs. ornamental) and building phase were assessed using the a mixedmodel ANOVA using PROC MIXED procedure in SAS (Sas Institute, 2003) with vegetation orbuilding phase as a fixed effect. The normality assumption was checked by examining histogramand residual plots. Mean separations were determined using Tukey’s honestly significantdifference test (HSD) at α 0.05. Deep core samples were described to provide a qualitativeview of differences between samples collected at the park and residential sites (i.e., differencesin horizonation and general properties between natural and residential soils and between soilscollected from individual lots). Statistical analysis was not completed on the deep core samplecharacteristics due to the descriptive nature of the data.RESULTS AND DISCUSSIONResidential Topsoil Composite SamplesSoil texture for all composite samples was sand or loamy sand with no trend fordifferences in soil texture based on vegetative cover. Texture was identified by feel (qualitativemeasure); qualitative data regarding percent of sand, silt, and clay was unavailable due to timeand funding constraints. Sandy soils have high bulk densities (due to the heavier weight ofsand-sized particles) and are well suited for construction of roads and buildings (Brown, 2003).12

Soils in both of these textural classes are dominated by sand-sized particles and tend to havehigh permeability, low organic matter content, and low natural fertility (i.e. low cationexchange capacity). Due to the low production capacity of sandy soils, we suggest thatestablishment and maintenance of plants will depend on frequent, but judicious applicationrates of water and nutrients to urban residential soils (Erickson et al., 2001).Soil organic matter (OM) content ranged from 12.8 to 81.9 g kg-1 with a mean OM g kg-1equal to 32.6 for all composite samples collected from the Rivendell residential landscapes(Table 1). Organic matter content in soils collected from Rivendell homes constructed inbuilding phase 3A, 3B, 3C, 3E, and 4A was significantly higher than for samples collected fromhomes in building phase 2, 3D, 4B, and 5 (Table 3). Variability of OM content in urban soilsacross building phases may be due to differences in fill material quality, which was possiblyassociated with nearby remnant soils applied at final grade (Pouyat et al., 2007). Soil samplesfrom Oscar Scherer Park (Table 2) had similar levels of OM (mean OM 27.6 g kg-1) as samplescollected from the residential lots (Table 3). However, variability of soils within the residentiallots were found to have significant higher levels, for example, mean value for one residentialset was 81.9 g Kg-1. Similar to our study, Scharenbroch et al. (2005) found that the OM contentof urban soils was highly variable, as was soil biological activity, and nutrient content. Therewas a significant vegetative cover effect on OM content in our study, where soils collected fromornamental areas had higher OM than soils in turf areas (Table 4). Higher OM values inornamental beds may be due to the regular use of mulches or other organic materials duringbed preparation, such as enriched top soil, compost, leaf litter and other organic materials(Craul, 1999). Alternatively, soils with low organic matter content may be affected by13

inappropriate cultural practices, such as the removal of turf clippings that from lawns aftermowing, which limits the recycling of OM back into soils in turf areas (Craul, 1999).Overall, bulk density (Db) values of soils collected within the ornamental beds in 48Rivendell residential units varied widely (Table 1). Bulk density was not determined in lawn orpark areas due to difficulties obtaining a reliable sample. The Db of ornamental bed soils inRivendell ranged from 0.48 to 2.37 g cm-3, with a mean soil Db in ornamental beds of 1.44 g cm-3(Table 4). It is clear that the Db of some soils was approaching or exceeding the 1.7 g cm-3threshold for Db in sandy soils, indicating severely compacted conditions. Severe compactionmay impact soil functions like nutrient adsorption, gas exchange, root penetration, drainageand other natural biological processes (Hanks and Lewandowski, 2003). Soil Db values reportedin our study were significantly higher than soil Db values reported by Hagan et al. (2012). Hagenet al. (2012) reported a mean bulk density of 1.01 g/cm3for soils in older residential landscapesin Florida ( 20 yr). In contrast, Scharenbroch et al. (2005) reported that soil Db valuesdecreased with age of landscape. In our study, building phase had an influence on soil Dbvalues, where soils collected from residential landscape beds within building units 3A and 4Bhad significantly higher soil Db than soils collected from units 2, 3B, 3C, 3D, 3E, 4A, 5 (Table 3).Higher Db values recorded for building units 3A and 4B could be related to the sources of thesoil fill material, the use of heavy equipment during construction, the excessive foot traffic, orother human activity on wet soils (Craul, 1994).Overall, the pH of composite soils collected in residential landscapes ranged fromslightly acidic to alkaline, ranging from 6.50 to 8.10 with a mean pH of 7.54 (Table 1). Overall,soil pH in residential landscapes did not fall within target pH levels (6.0 to 6.5) for establishment14

and growth of turf and ornamental plant species (Kidder et al., 1998). In contrast, undisturbedcomposite soil samples from nearby Oscar Scherer State Park were very acidic, with soil pHranging from 4.05 to 4.30 with a mean pH of 4.20 (Table 2). This is typical of sandy Flatwoodssoils due to soil formation under pine vegetation and facultative organism activity. Pouyat et al.(2007) reported a significant relationship between land use and/or land cover and soil pHassociated with turfgrass management. Vegetative cover did not affect soil pH (Table 4); wesuggest that the use of acidifying fertilizers or other management practices were similar in turfand ornamental areas and therefore did not affect soil pH (Jim, 1998a; Pouyat et al., 2007). Inour study, building phase influenced soil pH levels, where samples collected from homesconstructed in phase 4B exhibited significantly lower (neutral) than samples collected fromhomes built in phase 3B, 3C, 3D, and 5 (Table 3). Higher soil pH values in phase3B, 3C, 3D, 3E,4A and 5 could be related to origin of the soil fill materials. For example, fill materials may havesignificant alkaline buffering capacities (Marcotullio et al., 2008) and/or were of limestoneorigin (USDA-NRCS, 2004), which is typical of Florida soils. We did identify fill materialscontaining high concentrations of calcium carbonate from marine deposits (as evidenced by thepresences of visible shell fragments) and/or construction debris containing concrete materialsin some landscapes, which could result in semi-alkaline to alkaline soil pH (Pouyat et al., 2007).All residential landscape soils appeared to have elevated levels of NH4-N, NO3-N andTKN, with concentrations ranging 308 to 1965 mg kg-1 (mean 988 mg kg-1) (Table 1) comparedto samples collected from the nearby Oscar Scherer Park (TKN range 502 to 804 mg kg-1;mean 635 mg kg-1) (Table 2). Law et al. (2004) and Hagan et al. (2012) observed similardifferences in TKN elevated levels and related them to socioeconomic factors. For example,15

high income was associated with more intensive landscape practices (e.g. fertilization andIrrigation) that could increase soil TKN. Elevated levels of soil N could be a result ofanthropogenic factors, landscape irrigation, or fertilizer amendments (Pouyat et al., 2010).Vegetative cover also influenced concentrations of NH4-N, NOx-N, and TKN in soils, where soilscollected from turf areas had significantly higher concentrations of inorganic N than soils fromthe ornamental area (Table 4). It is possible that mineralization of N in turf clippings increasedthe amount of extractable soil N, or that inputs of N from turf fertilization could explain thehigher extractable N in turf areas (Kopp and Guillard, 2004). Building phase also had an effecton soil TKN, but not on soil NOx-N or NH4-N (Table 3). Soil TKN values were significantly higherfrom homes built in phase 3E than for homes built in phase 2, 3D, 4A, or 5 (Table 3).Runoff and leaching of P is a concern for a majority of Florida’s sandy soils, becausepollutants in runoff and leachate can alter freshwater aquatic life and impact overall waterquality (Sharpley et al., 1996). Based on the soil test interpretations for Florida presented in(Table 5), overall soil test M3-P concentrations ranged from “low” to “high” (Table 1). Forreference, no plant response is expected from additions of P when crops are grown in soilswhere the soil test levels falls within the “high” (41-65 mg kg-1) or “very high” ( 65 mg kg-1) soiltest M3-P categories (based on the mathematical relationship between M1 and M3 for Floridasoils presented by Mylavarapu et al. (2002), In fact, based on soil test P concentrations, cropresponse was expected for only 8 of the 96 soils sampled. In contrast, the mean concentrationof M3-P in the Oscar Scherer samples was 10.4 mg kg-1, which would be categorized as “low”and “very low” based on the Florida soil test M1 and M3-P interpretations (Table 3).16

In addition, there was a significant vegetative cover effect on M3-P, where soilscollected from turf areas had lower M3-P concentrations than soils collected from ornamentalbeds (Table 4). It is possible that higher M3-P in ornamental areas is related to the use of higherfertilization rates and frequent application of high P ornamental fertilizers when compared toturf areas; ornamental fertilizer tend to have higher P contents (usually to promote flowering)than turf fertilizers, which were recently mandated by state law to contain no more than 2%P2O5 (Hochmuth et al., 2011). There was a significant building unit phase effect on M3-P, wheresoils collected from phases 4B and 5 (Table 6.) Fill material may be associated with a higherM3-P value.Overall soil test M3-K concentrations ranged from “very low” (0-50 mg kg-1) to “veryhigh” ( 351 mg kg-1) (Table 1) based on M3 soil test interpretations (Table 5) (base

marked a significant change in human population trends worldwide, where rural habitation shifted to developing suburban and urban areas (Marcotullio et al., 2008; United Nations . physical properties, as well as significant difference in state factors compared with natural, undisturbed soils (Lehmann and Stahr, 2007; Pickett and