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Plant Sciences Building, Athens, GA 30602-7272
* Corresponding author (mjs38{at}psu.edu).
Received for publication March 20, 2003.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: BA, bottom ash • BS, biosolids • CCB, coal combustion by-products • CP, compost • DAP, days after planting • EC, electrical conductivity • FA, fly ash • QS, quartz sand
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Fly ashes have been classified by the American Society for Testing and Materials (ASTM, West Conshohocken, PA) into two categories: Class C and Class F (Mattigod et al., 1990). Class C ashes are derived from sub-bituminous coals (mined in the western USA) and are commonly low in S and high in base cations and contain >50% SiO2 + Al2O3 + Fe2O3. Class C fly ash is more highly pozzolanic and therefore more valuable as a cement additive than Class F fly ash. Class C fly ash can possess measurable calcium carbonate equivalencies and is sometimes used as a lime substitute. Class F ashes are derived from bituminous coals and are high in Fe and S, low in base cations, and contain >70% SiO2 + Al2O3 + Fe2O3. Class F fly ashes may possess regulated metal concentrations that limit their potential use. Class F fly ash is sometimes used in structural fill and other engineering applications, but the majority is impounded in lagoons or landfilled (Miller et al., 2000). Increasing costs of CCB disposal have stimulated development of innovative and practical CCB applications.
Coal combustion by-products are chemically diverse. Fly ash composition varies by the coal from which it was derived, conditions during combustion, efficacy of emission control devices, and post-production storage and handling (Adriano et al., 1980). Physical characteristics of CCB are also diverse. Sand-sized components of BA (0.05–2.0 mm in diameter) are relatively inert, possess low trace metal concentrations, and have a lesser particle density than sand. Fly ash is largely silt-sized (2–50 µm in diameter) with greater specific surface area and bulk density than its coarser BA counterpart.
Coal combustion by-products have practical agronomic value under specific conditions. However, mixtures of CCB and organic waste products more reliably provide primary nutrients needed to support agronomic crops. Sajwan et al. (1995) found biosolid and FA mixtures in ratios of 4:1, 2:1, 4:3, or 1:1, applied at rates of 124 to 248 Mg ha–1, to benefit growth and nutritional status of cereal crops compared with nonamended soil. A greenhouse study using corn indicated FA mixed with poultry manure produced more dry matter than FA and sewage sludge. Plant tissue analysis indicated higher levels of K and N in the poultry manure were largely responsible for the observed biomass increase (Schumann and Sumner, 1999).
Due to their low nutrient analysis, CCB–organic waste mixtures must be applied at relatively high rates to benefit agronomic production systems. Furthermore, the potential for these waste and by-product applications to degrade soil or ground or surface water quality, and possibly enter the food chain, obligates careful assessment. Section 503 of the Clean Water Act limits accumulation of regulated metals in soil by land application of organic wastes (USEPA, 1993). This regulation requires tracking of additions at application sites to prevent regulated metals from exceeding maximum soil concentrations. The risk of reaching these ceiling limits at a land application site is lessened when the resident process and application exports the treated soil and growth media concomitantly with the final product. This would include the "soil" growth media of either container-grown horticultural plants or turfgrass sod.
An extensive investigation of an acidic, Class F fly ash application to a sod production field has recently been conducted in the southeastern USA (Adriano and Weber, 2001). Fly ash was applied to a Congaree silt loam (fine-loamy, mixed, active, nonacid, thermic Oxyaquic Udifluvents) at rates equivalent to 0, 280, 560, and 1120 Mg ha–1. The FA material was tilled into the soil and seeded with centipedegrass [Eremochloa ophiuroides (Munro) Hack.]. In the establishment period, diminished growth and vigor were observed as long as 57 DAP in plots treated with the two highest FA rates. The foremost-observed physical benefit of FA application was increased water retention at a 10-kPa tension. Concentrations of B, Mo, As, Be, Se, and Ba were significantly increased in centipedegrass leaf tissue in the three years following FA application. Conversely, Mn, Zn, and Mg leaf tissue content was lowered in FA-amended plots. Soil chemical effects were principally soluble salt and soil pH increases. Electrical conductivity (EC) of soil extract increased directly with FA application rate, with the largest increases observed in the first year following application. Ground water, present at a depth of 2.7 m on the experimental site, was sampled from installed wells from 1994 through 1997, and did not indicate influence of FA on pH or trace element concentrations (Adriano et al., 2002).
Cisar and Snyder (1992) reported a method utilizing commercial compost spread over a plastic barrier and concluded the time required for sod production was significantly shortened compared with traditional production methods. Following installation of both the experimental and commercially grown sod, the sod grown on compost possessed greater root weight and length. Another study examined zoysiagrass [Zoysia matrella (L.) Merr. and Z. japonica Steud.] sod production on soil-less media (Ruemmele et al., 2001). In this greenhouse study, rice hulls, composted rice hulls, grass clippings, and a peat–vermiculite mixture were blanketed to a 1-cm depth and sprigged. Results showed all alternative-media sod was produced in less time than conventionally grown field sod. Other studies have examined municipal compost and lime-stabilized biosolids as production media and report soil chemical relations (nutrient and/or salt imbalances) play a decisive role in the rate of sod establishment and maturity (Breslin, 1995; O'Brien and Barker, 1998).
Morphology and growth habit of turfgrass makes it a well-suited candidate for stabilization and vegetation following CCB–organic waste land applications (Adriano et al., 2002). Turves rarely suffer phytotoxicity from accumulated non-essential elements because most amass apically, and leaf tips are frequently removed by mowing practices. A growth chamber study showed soil amendment with FA or flue gas desulfurization gypsum to be the only two CCB (of eight tested) to benefit the root length and dry matter yield of wheat (Triticum aestivum L.) and ryegrass (Lolium multiflorum Lam.), respectively (Wright et al., 1998). Hybrid bermudagrass is an aggressive turf adapted to a wide range of soil types, generally performing best on fine-textured soils with high fertility and available moisture. The salt tolerance of bermudagrass is considered good (Beard, 1973).
Studies have shown the combination of biosolids and CCB to result in a soil amendment with balanced nutrients and stable regulated metals (Wong, 1995; Jackson and Miller, 1999, 2000). Considering current levels of CCB production, local availability of biosolids and biosolid products, and favorable reports of growth media use accelerating sod production rate, our objective was to evaluate the environmental risks and production benefits of using fly ash, bottom ash, and organic waste mixtures as supplemental soil and growth media for commercial production of hybrid bermudagrass sod.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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To measure total elemental content of growth media, inorganic media components (CCB and sand) were ground and hydrofluoric acid–aqua regia digested in TFE-fluorocarbon-lined sample digestion bombs (Parr Instrument, Moline, IL) (Jones and Dreher, 1996). Biosolids and compost were digested by Method 3050B (USEPA, 1998). The toxicity characteristic leaching procedure (TCLP) (USEPA, 1998) was conducted on experimental BA and FA (Table 1). All component characterizations were conducted in duplicate and corrected for initial moisture content. Sample splits, blanks, and digests of standard reference materials (SRM 1633b, 1573a, and 2709; National Institute of Standards and Technology [NIST], Gaithersburg, MD) were systematically included to measure accuracy and precision of the laboratory analyses. Elemental concentrations were determined using inductively coupled plasma–mass spectroscopy (ICP–MS) (Elan-6000; PerkinElmer, Wellesley, MA). Growth media pH H2O (1:5) and EC (saturated paste) were measured on freshly prepared samples, whereas elemental composition of growth media mixtures was calculated from component analyses (Table 2) (Rhoades, 1982; Thomas, 1996).
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Year One (2000) Growing Procedures
Preliminary greenhouse tests of hybrid bermudagrass sprig establishment on CCB–biosolids (BS)–compost (CP) mixtures were run in spring of 2000. On the basis of those results, three mixes of CCB and biosolids or compost were selected for use in the Year 1 field study. These treatment growth media mixes (formulated on a volume basis) were: two parts BA to one part CP (2BA + 1CP); one part BA to one part CP (1BA + 1CP); and four parts BA to one part FA to one part BS (4BA + 1FA + 1BS). The control growth media consisted of two parts quartz sand (QS) mixed with one part CP (2QS + 1CP). Mix physicochemical properties are described in Tables 1 and 2. All experimental growth media were considered exceptional quality sludges under USEPA regulations and thus, unrestricted for land applications not exceeding agronomic requirements (USEPA, 1993).
The sod production field experiment was initiated in May 2000. Mixes were uniformly spread to depths of 2, 3, and 4 cm (200, 300, and 400 m3 ha–1) over a compacted subsoil of the Cecil series (fine, kaolinitic, thermic Typic Kanhapludults). The field site received full sun throughout the summer and was equipped with an automated, potable water, overhead irrigation system. The experimental growth media were not tilled into the soil. The sod production field was irrigated with 3 cm water on 2 and 6 June 2000 to purge any salts from the root zone. The sod field experimental setup was a two-way strip-plot design with four replications (Gomez and Gomez, 1984). This strip-plot layout allowed linear mowing passes over plots with equal growth media application height. This prevented mower "scalping" of the turfgrass sod late in the production cycle.
Mature ‘TifSport’ (formerly ‘Tift 94’ and ‘Tifway II’) bermudagrass (Hanna et al., 1997) sod was obtained from a foundation-stock field at the Georgia Crop Improvement Association, Athens. The bermudagrass sod was washed free of all soil and pulverized into vegetative sprigs. The 48-m2 experimental site was established with viable sprigs at an equivalent rate of 60 kg moist sprigs ha–1 on 8 June 2000. A broadcast application of commercial fertilizer provided 12, 49, and 10 kg ha–1 of actual N, P, and K, respectively, on 9 June, 1 DAP. A loose-weave, outdoor-type polymer tarp covered the plots to minimize evapotranspirational losses and protect the field from inclement weather until vegetative cover reached 50% of the field area. During this period, all plots were irrigated equally to maintain adequate moisture and rolled weekly with a water-ballast roller. Thirty-six days after planting the tarp was removed, and the field was mowed every 3 to 4 d with a motorized reel-mower at a height of 3 cm and the plots irrigated equally to prevent wilt for the remainder of the experiment.
Beginning 54 DAP, leaf clippings were harvested every second mowing, then rinsed, oven-dried at 95°C, cooled, and immediately analyzed for N content by dry combustion (Nelson and Sommers, 1996) using a CNS-2000 analyzer (LECO, St. Joseph, MI). When mean N concentration of clippings harvested from media-type plots fell below a predetermined threshold, all replications of that media-type were immediately fertilized with an NH4NO3 solution providing 24 kg N ha–1. At 60 and 80 DAP, leaf clippings were collected from each growth media type, triple-rinsed with deionized water, and digested (Jones, 1991). Elemental composition of plant tissue was analyzed using inductively coupled plasma–mass spectroscopy.
Following the 99-d maturation period, bermudagrass sod was harvested with a walk-behind sod harvesting device (Ryan Sod Cutter; Textron Golf, Augusta, GA). Sod grown on varying growth media volumes was harvested at corresponding depths; for example, sod grown on the 4-cm application media volume was cut to include approximately 3 cm of the growth media. Accordingly, the height of the cutting blade was adjusted three times. Three days following, sod was installed conventionally on a maintained turfgrass area at the Georgia Agricultural Experiment Station in Griffin. Remaining sod at the production site was treated with label rates of glyphosate (RoundUp Pro; Scotts, Columbus, OH) on 19 and 29 Sept. 2000.
Year Two (2001) Growing Procedures
A second sod production field study was conducted in 2001 to retest the 4BA + 1FA + 1BS growth media mixture and newly formulated variations of Year 1 growth media mixtures. Year 2 growth media mixes were again formulated on a volume basis (Table 2). These experimental mixtures were formulated as follows: one part BA to two parts CP (1BA + 2CP); two parts BA to one part FA to one part BS to one part CP (2BA + 1FA + 1BS + 1CP); four parts BA to one part FA to one part BS (4BA + 1FA + 1BS [a repeat treatment from Year 1]); and three parts BA to one part FA to one part BS (3BA + 1FA + 1BS). The control growth media consisted of one part QS mixed with two parts CP (1QS + 2CP). Mix physicochemical properties are described in Table 2. As in Year 1, all experimental growth media were considered exceptional quality sludge under USEPA regulations (USEPA, 1993).
The Year 2 field experiment was initiated in May. The site of the Year 1 experiment was stripped to a 2-cm depth and compacted with a vibrating-platform compactor. Mixes were uniformly spread to heights of 4 cm (400 m3 ha–1) in a randomized complete block design with five media types replicated in four blocks. Experimental growth media were not tilled into the soil, but blanketed and left undisturbed. The sod field was irrigated on 10 and 16 May to purge any excessive salts. Mature ‘TifSport’ bermudagrass sod was obtained from the same foundation-stock field as in Year 1 and sprigs were applied at the 60 kg ha–1 rate on 20 May 2001. A broadcast application of granular fertilizer provided 49, 49, and 41 kg ha–1 of actual N, P, and K, respectively, on 4 June, 14 DAP. The loose-weave tarp was used as described previously and plots were rolled with a water-ballast roller weekly. Once >50% of the field was covered with bermudagrass vegetation, it was mowed and irrigated as described in Year 1.
Due to the inclusion of Class B biosolids in three of the five treatment mixes, growth media were analyzed to quantify pathogenic organisms. Two cores of sod and growth media were harvested with 73-mm-i.d. steel rings from each replicated plot at 47 and 84 DAP. The same day, growth media were separated from the bermudagrass and collected in a paper bag. Each paper bag was then inverted gently five times, sampled (10 g), and diluted with 90 mL sterile, deionized H2O. This dilution was then gently mixed on a stirring table for 20 ± 1 min. A 10-mL aliquot of the above mentioned mix dilution was removed by sterile pipette and added to 90 mL of sterile deionized H2O. This 100:1 soil dilution was analyzed by Method 9223B, the enumeration procedure for quantitative analysis of E. coli (American Public Health Association, 1998) (Colilert-18; Idexx Laboratories, Westbrook, ME). These procedures were conducted to quantify E. coli pathogens included within the handleable sod product.
After the second mowing, leaf clippings were collected and subjected to N analysis and N-fertilized as described in Year 1 methods. Portions of clippings harvested at the second mowing (68 DAP), the seventh mowing (85 DAP), and 3 d before harvest (111 DAP) were triple-rinsed with deionized water and nitric acid digested to determine trace element concentrations. Following the 114-d maturation period, bermudagrass sod was harvested as in Year 1; however, all sod was cut to a depth of 4 cm (including 3 cm of growth media). Following harvest, requisite square areas for installation of each treatment sod were stored for subsequent transport.
The following day, additional TifSport bermudagrass sod was purchased from a retail outlet (Ward's Super Sod, Bogart, GA) and both retail and experimental sod were transported to the Georgia Agricultural Experiment Station and installed conventionally on a maintained turfgrass area.
2000 and 2001 Post-Production Analysis
Remaining sod (representative of each experimental unit) was randomly subsampled in triplicate using a ring sampler (73-mm i.d.). The sampled sod, comprised of biomass and growth media, was then carefully extruded from each ring, and the biomass (shoots, stolons, rhizomes, and roots) manually separated from the growth media. Traditional elution methods of soil removal were avoided to prevent any dispersion of the silt-sized fly ash or inadvertent water extraction of regulated metals from the growth media. The loamy sand textural class of the growth media, combined with its limited volume (3-cm depth of the harvested sod product), facilitated this normally difficult separation procedure. The collected growth media were then dried to a constant mass. Growth media bulk density, pH, EC, organic matter content, and extractable metals were measured by standard laboratory procedures (Spurway and Lawton, 1949; Lindsay and Norvell, 1978; Ben-Dor and Banin, 1989; Nelson and Sommers, 1996). In Year 2, sod biomass was earlier subsampled to a depth of 3 cm (in duplicate) on 12 Aug. 2001 (84 DAP). Following all collections, separated sod biomass was placed in a 150-µm sieve, rinsed in deionized H2O, and oven-dried (95°C) before weighing.
On 10 April 2001, the installed Year 1 sod was rated for visual quality and rooting strength (King and Beard, 1969). These same ratings were measured on the installed Year 2 sod in April 2002.
Experimental Design
In Year 1, the study was configured in a two-way strip-plot design. Sod biomass data (at harvest) were analyzed for growth media, application volume, and interactive effects. Bermudagrass leaf tissue collection was made by a mower pass across all application volumes of a growth media treatment "row" in each block. Once prepared, the dry mass of leaf tissue harvested from the treatment "rows" of each block was predicted to be insufficient for trace metal characterization. Therefore, blocks of harvested leaf tissue were pooled (by mix) for digestion in Year 1 and resultant data were not subjected to statistical analysis. Biological and physicochemical characteristics of growth media in Year 1 were determined from core samples removed from only the 400 m3 ha–1 plots, and thus statistically analyzed as a randomized complete block design (RCBD). In Year 2, experimental design for the sod production field study was a RCBD. Sod biomass or leaf tissue elemental composition measurements taken on multiple dates in Year 2 were analyzed as split-plots in time.
The GLM procedure of SAS (Version 8.2; SAS Institute, 2001) facilitated analysis of variance (ANOVA) of all data. The homogeneity of variance (HOV) assumption for all main effects was validated using Levene's test (Levene, 1960). Predetermined multiple comparisons of treatments within significant (P 
0.050) main or interactive effects were conducted using Tukey's Studentized range procedure.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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37 g N kg–1 tissue for bermudagrass grown on all mixes (data not shown). These concentrations, sufficient for bermudagrass growth, were maintained throughout both experimental periods (Carrow et al., 2001). In both years, growth media type affected concentrations of micronutrients and regulated metals in bermudagrass leaf tissue. At 60 DAP in Year 1, sod growing on 4BA + 1FA + 1BS media had accumulated As and Se levels near 1 mg kg–1 dry leaf tissue (Table 3). Leaf tissue of sod growing on the control, 1BA + 1CP, and 2BA + 1CP growth media, collected 60 DAP, possessed As and Se concentrations below 0.2 and 0.7 mg kg–1 dry leaf tissue, respectively. At 80 DAP, no bermudagrass leaf tissue possessed >0.7 mg Se kg–1 dry leaf tissue, and only the leaf tissue collected from the 4BA + 1FA + 1BS plots contained measurable As levels (0.3 mg As kg–1). Considering that FA possessed the greatest concentration of As and Se of all the media components, it is not surprising that the 4BA + 1FA + 1BS mix fostered growth with comparatively elevated concentrations of those elements. Concentrations of metals in bermudagrass clippings were well below maximum acceptable levels for most animal feed use (National Resource Council, 1980). In Year 2, concentrations of Cd measured 68 DAP (0.4 mg kg–1) were higher than levels normally observed in grasses but did not significantly differ by mix-type (data not shown). Levels of Cd in the bermudagrass clippings at all harvest dates were less than levels recorded in leaves of cabbage (Brassica oleracea var. capitata L.) and lettuce (Lactuca sativa var. capitata L.) grown on the native soils of Imperial Valley, CA (Shacklette, 1980). Throughout Year 2, mean tissue concentrations of As, Cd, Cu, Pb, Se, and Zn never exceeded maximum acceptable levels in animal feed (data not shown) (National Resource Council, 1980). Levels of Mo in bermudagrass leaf tissue grown on media containing FA significantly decreased from 68 to 111 DAP (Fig. 1) . Manganese concentrations of grass leaf tissue were sufficient among all mix types, although significant differences by mix type were observed (Fig. 1). Tissue levels of Ni did not reach phytotoxic levels during the propagation period (Fig. 1) (Carrow et al., 2001). TifSport hybrid bermudagrass does not appear to hyperaccumulate metals in leaf tissue, and hence no measurable risk to workers handling leaf clippings exists.
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Year 2 results were similar to those observed in Year 1, as mixture composition significantly affected sod biomass production, but only 84 DAP. At that time, sod grown on the 3BA + 1FA + 1BS and 4BA + 1FA + 1BS mixtures possessed significantly greater biomass than the 1BA + 2CP mixture after 12 wk (Table 5). At 114 DAP, there were no significant differences in biomass by mix types. Although a mix type by harvest date interaction was observed, sod biomass of the 3BA + 1FA + 1BS, 4BA + 1FA + 1BS, and 2BA + 1FA + 1BS + 1CP mixtures did not significantly improve or decline between the two collection dates. Arguably, these mixes containing FA and BS could have been harvested as early as 84 DAP. Sod produced on these growth media fostered production of biomass similar to the retail sod (Table 5).
Post-Harvest Characteristics
Following sod harvest, significantly different values of bulk density by media type were observed (Table 6). Due to the high rate of organic matter inclusion and its inherent low mass, bulk densities of experimental sod growth mixes were low. Growth media EC of all mixes declined over the production periods. In both years, media pH of the mixes containing compost increased from planting to harvest, whereas the pH of the 4BA + 1FA + 1BS mix decreased slightly. This effect was probably due to the high pH of the FA component (Table 2). Exchangeable acidity in all mixes was low.
Extractable metals remaining in the media and sod product varied by extractant used (Table 7). Regulated metals were measured at higher concentrations in the diethylene-triaminepentaacetic acid (DTPA) than the acetic acid extract, with the exception of As. Extractable metals by DTPA or acetic acid methods did indicate plant availability following the production cycle (Table 7). These levels of regulated metals and micronutrients were measured to determine their availability once finished sod was purchased and installed by end-users. In this described experimentation, the elements of greatest environmental risk are As and Se. Both elements occur as oxyanions, are potentially toxic trace elements, and possess oxidation states of varying toxicity and mobility (Jackson and Miller, 1999). In Year 1, leaf mass digested, dilution method, and instrument detection limits prohibited characterization of As and Se concentration in bermudagrass leaf tissue below 0.2 and 0.7 mg kg–1, respectively. Despite this, plant uptake of As and Se diminished over the propagation period in both years. Of three repeated measures over 20 experimental units, measurable As was detected only once in Year 2 (0.2 mg As kg–1 leaf tissue, 68 DAP, 4BA + 1FA + 1BS), and Se was not detected at all. Biosolids utilized in this experimentation possessed elevated levels of Al and Fe (data not shown), and these oxyhydroxide forms are known to have high affinities for both arsenate and selenate in solution.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Management practices required for land application of Class B biosolids include preliminary baseline metal concentration determination of soils at the site, use of riparian buffers for protection of surface waters, and assessment of nutrient sequestration capacity of the soils on-site so that nutrient loading of ground water is prevented (USEPA, 1993). In the case of turfgrass, some states require an additional specific management practice that restricts harvest of sod for 1 yr, if sod is intended for a site with a "high potential" for public exposure (USEPA, 1993). Required practices are likely to vary by state, and local solid waste permitting authorities should be contacted by potential applicators.
Turfgrass sod products are associated with sizable retail markets. Implementing CCB and organic waste products as growth media in production of these items appears to be an agronomically, environmentally, and economically sound method of societal waste utilization. All soil and plant materials associated with our experimental productions possessed trace element concentrations below regulated levels. Experimental mixes containing fly ash and sewage sludge fostered significantly greater bermudagrass biomass following the experimental period than the control mix, indicating an agronomic advantage in CCB–biosolid use.
It is critical to note that all societal waste products may not have a beneficial use. Eligibility of by-products for land application may not be based on expense reduction compared with original disposal costs. Furthermore, combinations of by-products for land application should be made for the sole purpose of adding value, not diluting regulated components originally exceeding thresholds. Beneficial use policy should mandate elemental characterization of materials, a true applicability of the material to its target system, site specifications that protect against environmental risk, and long-term soil and water quality monitoring protocol.
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ACKNOWLEDGMENTS |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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= 0.05). Growth media mix types were comprised of quartz sand (QS), bottom ash (BA), fly ash (FA), municipal compost (CP), or anaerobic digested biosolids (BS) in the volumetric ratios indicated.