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Journal of Environmental Quality 32:687-693 (2003)
© 2003 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America

TECHNICAL REPORTS
Waste Management

Properties of Several Fly Ash Materials in Relation to Use as Soil Amendments

S. M. Pathana, L. A. G. Aylmoreb and T. D. Colmer*,a

a School of Plant Biology, Univ. of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia, Australia
b School of Earth and Geographical Sciences, Faculty of Natural and Agricultural Sciences, Univ. of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia, Australia

* Corresponding author (tdcolmer{at}cyllene.uwa.edu.au)

Received for publication January 28, 2002.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Fly ash samples from five power stations in Western Australia and Queensland, and two soils used for horticulture in Western Australia, were evaluated for a series of physical and chemical properties. Soils were comprised primarily of coarse sand-sized particles, whereas most of the fly ashes were primarily fine sand- and silt-sized particles. Hydraulic conductivities in the fly ashes were 105- to 248-fold slower than in the soils. The water-holding capacities of fly ashes at "field capacity" were three times higher than those of the soils. Extractable P in the fly ashes (except Tarong and Callide) were 20- to 88-fold higher than in the soils. The pH showed considerable variation among the different sources of fly ash, with samples from Muja being the most acidic (pH = 3.8; 1:5 in CaCl2 extract) and from Gladstone the most alkaline (pH = 9.9). The toxicity characteristic leaching procedure (TCLP) values indicate that the potential for release of trace elements from the fly ashes was well below regulatory levels. When applied at sufficient rates (e.g., to achieve 10% w/w in surface layers) to sandy soils, fly ash altered texture and increased water-holding capacity. Depending on the source of fly ash used, such amendments could also provide P and aid nutrient retention by increasing the phosphorus retention index (PRI) and/or cation exchange capacity (CEC). The considerable variability in physical and chemical properties among the fly ash samples evaluated in the present study supports the notion that field trials are essential to the future development of soil amendment strategies making use of any particular source of fly ash.

Abbreviations: CEC, cation exchange capacity • PRI, phosphorus retention index • TCLP, toxicity characteristic leaching procedure


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
FLY ASH is the fine residue captured from flue exhausts when coal is burnt in power stations. The physical and chemical properties of a particular fly ash are dependent on the composition of the parent coal, conditions during coal combustion, efficiency of emission control devices, and practices used during storage and handling (Adriano et al., 1980). Fly ashes from anthracite, bituminous, sub-bituminous, and lignite coals are likely to differ in chemical composition. In Australia, power is generated from bituminous, sub-bituminous, and lignite coals, but little information is available on the potential use of fly ashes derived from these coals as soil amendments. Interest in the use of fly ash as a soil amendment results from (i) the need to develop sustainable uses of this by-product (Adriano et al., 1980; Bilski et al., 1995) and (ii) reports showing improved growth of some crop (El-Mogazi et al., 1988; Rees and Sidrak, 1956), pasture (Hill and Lamp, 1980; Summers et al., 1998), and turf (Adriano and Weber, 2001; Pathan et al., 2001) species, following addition of fly ash to some soils.

Fly ash is comprised primarily of fine sand- and silt-sized particles, therefore if applied at sufficient rates it can be used to change soil texture to increase soil water-holding capacity (Adriano et al., 1980; Aitken et al., 1984; Gangloff et al., 2000). The physical structure of fly ash often consists of "hollow spheres" and these particles show an increased surface area, capillary action, and nutrient-holding capacity compared with sands (Fisher et al., 1976). Fly ash has also been reported to improve the nutritional status of soils via increases in cation exchange capacity (CEC) and by provision of some essential nutrients (Carlson and Adriano, 1993; Roberts, 1966; Summers et al., 1998). However, since almost all naturally existing elements are present in fly ash (Adriano et al., 1980; El-Mogazi et al., 1988; Summers et al., 1998), the potential release of trace elements may also be an issue determining the suitability of some sources for use as a soil amendment (Adriano et al., 1980; Bilski et al., 1995; Page et al., 1979).

Knowledge on the physical and chemical properties of fly ashes is essential for understanding, and in the future predicting, the behavior of fly ashes in agricultural and horticultural ecosystems. The present study evaluated selected physical and chemical properties, of relevance to plant production systems, for fly ashes from five power stations in Western Australia and Queensland, as well as two soils from Western Australia. The influences of these properties on the potential use of the various sources of fly ash for soil amendment are discussed.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Sample Collection
Fly ash samples were collected from five power stations: Kwinana and Muja (Western Australia), and Tarong, Callide, and Gladstone (Queensland). Fly ashes obtained from Western Australia were derived from sub-bituminous black coals, while Queensland fly ashes were derived from bituminous black coals. A representative bulk sample of freshly precipitated (unweathered) fly ash was taken from the hopper of each power station. In addition, for Kwinana Power Station, three ash types were collected: 3 yr old (weathered) from stockpile, 3 mo old (weathered) from stockpile, and freshly precipitated (unweathered) from hopper. The weathered fly ash from Kwinana had been collected from the electrostatic precipitators and pumped as a slurry to an old limestone quarry where the water drains or evaporates, leaving the solid particles. The three different samples from Kwinana were taken to evaluate the effects of the slurry process and weathering in the stockpile on the basic properties. All samples were taken during March and April 1999. After collection, the dry ash was thoroughly mixed and stored in plastic-lined containers at room temperature before use.

Two soils (top 200 mm) were collected from the Spearwood and Bassendean dune systems of the Swan Coastal Plain in Western Australia (McArthur and Bettenay, 1960). The particular soil collected from the Spearwood dune system is known locally as Karrakatta sand (Xeropsamments; USDA, 1992). Virgin Karrakatta sand was collected from a site (31°56' S, 115°47' E) cleared of natural vegetation in 1996 in Shenton Park, approximately 8 km west of Perth CBD. The soil taken from the Bassendean dune system is known locally as Joel sand (Arenic Haplohumods; USDA, 1992). The Joel sand was collected from a site (32°23' S, 115°52' E) under rain-fed annual pasture for the previous 12 yr, approximately 50 km south of Perth CBD, and 8 km west of the town of Serpentine. Soils were collected during March 1999. After collection, samples were air-dried for 5 d, passed through a 2.0-mm sieve, and stored at room temperature before use.

Physical Characterization
Particle size distributions were determined for fly ash and soil samples pretreated with dispersing agent before using the pipette method (Day, 1965; Green, 1981). Bulk densities of soil were measured with a soil sampler of known volume to collect intact cores, which were oven-dried and weighed (Blake and Hartge, 1986a). In the case of fly ash samples, these were firmly packed in a cylinder and then bulk densities were measured. While the procedure will not necessarily achieve the real status under field conditions, it should be indicative of the relative differences among fly ash samples. Particle density for soils and fly ashes was determined with the pycnometer method (Blake and Hartge, 1986b). Specific surface area (surface area per unit mass) was determined by Brunauer–Emmett–Teller (BET) nitrogen adsorption (Feller et al., 1992) with a surface area analyzer (Gemini 2375; Micrometrics, Norcross, GA).

Air-dry samples of soil, fly ash (Kwinana 3 yr old, weathered), and mixtures of fly ash with both soils (5, 10, 20, and 50% by weight) were firmly packed into permeameters (Buchner funnels) and hydraulic conductivities were measured with a constant head method (Klute and Dirksen, 1986). Fly ash was mixed with soil with a tumbler to provide a homogeneous mixture. "Water release characteristics" were measured with pressure plates (Klute, 1986) for samples of soil, fly ash, and mixtures of fly ash from Kwinana (3 yr old, weathered) with both soils at several rates (5, 10, 20, and 50% by weight). In brief, air-dry samples were firmly packed into a core of radius 26.8 mm and height 10 mm and then saturated with water at atmospheric pressure. The cores were then placed on a porous ceramic plate in a pressure chamber and equilibrated at matric potential values of -5, -25, -100, -250, and -1500 KPa. The gravimetric water content of each soil, fly ash, and the mixtures of fly ash with both soils were measured after equilibration at each matric potential. Volumetric water contents were calculated after correcting for the bulk density measured for each sample.

Chemical Characterization
The pH of 0.01 M CaCl2 after being mixed with soil or fly ash (1:5 w/v) (White, 1969) and electrical conductivity (EC) of extracts in deionized water (1:5 w/v) were measured with a pH and EC meter, respectively. Exchangeable cations (Na+, K+, Mg2+, and Ca2+) and cation exchange capacity (CEC) were measured for samples prewashed with an aqueous solution of glycol (Rayment and Higginson, 1992) followed by the 0.01 M silver thiourea extraction method (Pleysier and Juo, 1980), and using atomic absorption spectroscopy (AAnalyst 3000; PerkinElmer, Wellesley, MA). Samples were also saturated with Ag+ to displace into solution all cations from exchange sites, so that total CEC could be determined (Hendershot et al., 1993). Total C and N were determined according to standard procedures with a C and N analyzer (CHN 1000; LECO, St. Joseph, MI).

Extractable P, in 1.0-g samples of soil or fly ash shaken in 100 mL of 0.5 M NaHCO3 at room temperature for 16 h (Olsen et al., 1954 as modified by Colwell, 1965; Rayment and Higginson, 1992), was quantified by the colorimetric method (Murphy and Riley, 1962) using a spectrophotometer (UV 1601; Shimadzu, Kyoto, Japan). The phosphorus retention index (PRI), a measure of the ability of a substrate to adsorb P (Allen and Jeffery, 1990), was determined by measuring the P remaining in a solution that originally contained 10 mg kg-1 P and 0.02 M KCl, after shaking with soil or fly ash samples (1:20 w/v) for 16 h at room temperature.

Chemical Composition
The chemical compositions of soil and fly ash samples prepared as fused beads (i.e., glass disks) were analyzed using X-ray fluorescence spectrometry (XRFS) (PW 1400; Philips, Eindhoven, the Netherlands). The fusion was accomplished by mixing of 7.0 g of Norrish flux (mixture of LiBO2 and Li2B4O7, 12:22) and 0.7 g of soil or fly ash. Each mixture was poured into a Pt crucible and heated at 1050°C in a muffle furnace for 40 min (Karathanasis and Hajek, 1996). Certified reference materials of known composition were used as standards. Blank glass disks were also prepared in the same manner to correct for impurities in the Norrish flux. The losses on ignition (LOI) of samples were determined separately by heating known weights of previously dried samples to 1050°C for 40 min and measuring the weights remaining.

Potential for Release of Trace Elements
The toxicity characteristic leaching procedure (TCLP) is the test most generally accepted by the USEPA for determining the potential toxicity of materials under the Resource Conservation and Recovery Act (RCRA) (Testa, 1997). The TCLP was used to determine the amounts of "trace elements" that could potentially leach from the soil and fly ash samples. The samples were mixed with 0.57% glacial acetic acid (1:20 w/v; pH approximately 2.88) and extracted according to standard procedures (USEPA, 1992). The elements in the extraction solution were measured with inductively coupled plasma–mass spectrometry (ICP–MS) (Elan 6000; PerkinElmer, Wellesley, MA). Recoveries of spikes of the various elements (except Ba and B, which were not tested) when added to the extracts ranged from 93 to 112%.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Physical Characterization
The two soils were comprised primarily of coarse sand (Table 1). By contrast, fly ashes (with the exception of Tarong) were primarily fine sand- and silt-sized particles. Considerable variation in particle size distribution was evident among the fly ashes, with the samples from Tarong being coarser than the others (Table 1). In a study of four fly ash samples from the UK, the proportion of silt-sized particles ranged from 45 to 70% (Townsend and Hodgson, 1973); together with the present results supporting the view that fly ash is usually dominated by silt-sized particles (Adriano et al., 1980; Aitken et al., 1984; Ghodrati et al., 1995). Thus, fly ash incorporated at a sufficient rate could exert a beneficial effect on soil water-holding capacity in sandy soils, since fine-textured substrates can hold more water than coarse-textured substrates (Aitken et al., 1984; Brady and Weil, 1996; Chang et al., 1977).


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  		Table 1. Particle size distributions in selected soil and fly ash samples taken from locations in Western Australia and Queensland.{dagger}

 
The bulk densities of fly ashes were 1.4- to 1.9-fold lower than the sandy soils (Table 2). Townsend and Hodgson (1973) reported that fly ashes from the UK have bulk densities from 0.99 to 1.73 g cm-3. Fly ash amendments to a variety of agricultural soils tended to decrease the bulk density (Campbell et al., 1983; Page et al., 1979). The large proportion of silt-sized particles in fly ash presumably results in this effect on soil bulk density. The particle densities of fly ashes were not much different from the two sandy soils (Table 2), or from values of 2.6 to 2.75 g cm-3 common for most mineral soils (Brady and Weil, 1996).


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  		Table 2. Bulk density, particle density, and specific surface area of selected soil and fly ash samples taken from locations in Western Australia and Queensland.{dagger}

 
Specific surface areas of the fly ash samples were higher than in the two sandy soils; however, there were large differences among the samples (Table 2). Specific surface areas of fly ashes from Western Australia were 8- to 25-fold higher than those of the samples from Queensland. The differences in specific surface areas among the samples tested were also investigated with adsorption of water vapor (Orchiston, 1953), giving results similar to those from the N adsorption method. An earlier study also showed specific surface areas were quite variable among different sources of Australian fly ash (Aitken et al., 1984). Surface area is an important property since this influences the degree of interaction of nutrient ions in a soil solution with the solid matrix. For example, CEC and nutrient adsorption are both closely related to the specific surface area of a substrate (Fisher et al., 1976).

The hydraulic conductivity in Kwinana fly ash (3 yr old, weathered) was 105- to 248-fold slower than in the two sandy soils (Table 3). The hydraulic conductivities in the other fly ashes were similar to that in Kwinana fly ash (1.28–1.62 mm h-1), with the exception of Tarong (4.33 mm h-1), reflecting the similarities and differences in particle size distributions (Table 1). In addition, incorporation of fly ash from Kwinana (3 yr old, weathered) into the two sandy soils significantly reduced the hydraulic conductivity, even at only the 5% (w/w) fly ash rate (Table 3). Earlier studies also showed that hydraulic conductivity of sandy soils decreased markedly after fly ash incorporation (Aitken et al., 1984; Campbell et al., 1983; Chang et al., 1977). Under field conditions, however, declines in hydraulic conductivity or infiltration following fly ash amendment may be less than in the present study, since mixing in the field would not be as homogenous, presumably leaving preferential flow pathways. Nevertheless, since higher applications of fly ash progressively reduced hydraulic conductivity, this characteristic might therefore define the maximum desirable incorporation rate. Thus, moderate rates (5–10% w/w) of fly ash may be the most appropriate for use in fields.


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  		Table 3. Hydraulic conductivity in soil, fly ash (Kwinana 3 yr old, weathered), and mixtures of fly ash with two sandy soils.{dagger}

 
Water retention characteristics show that the water-holding capacities in fly ashes at -5 KPa (field capacity) were three times higher than those in the two sandy soils (Fig. 1) . The water-holding capacities in the two sands were markedly improved by the incorporation of Kwinana (3 yr old, weathered) fly ash (Fig. 2) . For example, additions of 10% (w/w) fly ash to the soil almost doubled volumetric water content at field capacity. In addition, plant-available water, defined as that released between matric potentials of -5 KPa (field capacity) and -1500 KPa (wilting point), also increased (P < 0.001) progressively with each larger addition of Kwinana (3 yr old, weathered) fly ash (Fig. 3) . For example, addition of 10% fly ash to the two soils increased plant available water 1.5- to 1.9-fold. The fly ash–soil mixture at 10% (w/w) is similar to the rate of fly ash incorporated into the surface layers on a commercial turf farm in Western Australia, for which similar improvements in soil water-holding capacity have been measured in the field (data not shown).



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  		Fig. 1. Water retention characteristics of selected soil and fly ash samples from locations in Western Australia and Queensland at different (-5, -25, -100, -250, and -1500 KPa) matric potentials. Data given are means of three replicates ± standard errors. Standard errors are not visible when smaller than the size of the symbols.

 


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  		Fig. 2. Water retention characteristics of (A) Karrakatta sand and (B) Joel sand with Kwinana fly ash (3 yr old, weathered) incorporated at different rates (% w/w) and at different (-5, -25, -100, -250, and -1500 KPa) matric potentials. Data given are means of three replicates ± standard errors. Standard errors are not visible when smaller than the size of the symbols.

 


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  		Fig. 3. Effect of Kwinana fly ash (3 yr old, weathered) incorporated at different rates (% w/w) with Karrakatta sand and Joel sand on plant-available water (-5 to -1500 KPa matric potentials). Data given are means of three replicates ± standard errors.

 
The substantial increases in plant-available water in fly ash–amended soils, relative to the native nonamended sandy soils, undoubtedly resulted from incorporation of the fine-sized particles leading to increased total porosity (Aitken et al., 1984) and perhaps more importantly a shift in pore size distribution from primarily large "macropores" to more "micropores" (Adriano and Weber, 2001; Ghodrati et al., 1995). The addition of fly ash to sandy soils has been shown to increase the water-holding capacity and plant-available water at field capacity and down to the wilting point as the soil dries (Aitken et al., 1984; Campbell et al., 1983; Chang et al., 1977; Gangloff et al., 2000). Therefore, fly ash–amended soils, in combination with appropriate irrigation scheduling, should aid water management for crops grown in sandy soils.

Chemical Characterization
The results of the chemical characterization showed considerable variation in several properties among the fly ashes (Table 4). For example, the pH in 1:5 CaCl2 extracts ranged from 3.8 to 9.9, with fly ash from Muja being the most acidic and from Gladstone the most alkaline. The electrical conductivity in 1:5 H2O extracts also varied, ranging from 0.09 to 1.44 dS m-1, with samples from Gladstone being the most saline (Table 4). For Kwinana fly ash, the pH and electrical conductivity of the weathered samples were significantly lower than of the unweathered fly ash (Table 4).


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  		Table 4. The pH, electrical conductivity (EC), cation exchange capacity (CEC), extractable P, and phosphorus retention index (PRI) of selected soil and fly ash samples taken from locations in Western Australia and Queensland.{dagger}

 
Chemical properties related to the presence of nutrients, or capacity to retain nutrients, are also important in determining the value of using fly ash as a soil amendment. The exchangeable Ca2+ was relatively high in fly ash from Kwinana (1.9–12.2 cmol kg-1) and Gladstone (17.8 cmol kg-1), as compared with the other sources (0.4–1.2 cmol kg-1) and two sandy soils (1.5–1.8 cmol kg-1). The total CEC of the sandy soils was very low compared with most of the fly ashes, except Muja and Tarong (Table 4). Higher CEC in fly ash than in the two sandy soils could be expected to aid the retention and availability of cationic plant nutrients, such as K+, in these soils when amended with fly ash (Roberts, 1966; Summers et al., 1998).

The two sandy soils contained low levels of total C (1.6%) and N (0.08%). Total C in fly ash from Queensland (0.4-1.1%) was 3- to 20-fold lower than in the samples from Western Australia (3.0–8.2%). Therefore, C to N ratios in the Western Australian fly ashes were 60 to 68, being three- to fivefold higher when compared with the fly ashes from Queensland (14–23), as well as the two sandy soils (20–22).

The extractable P in the fly ashes (except Tarong and Callide) was 20- to 88-fold higher than in the two sandy soils (Table 4). For the samples from Kwinana, extractable P values in the weathered fly ashes were 3.3- to 4.4-fold lower (P < 0.001) than in the unweathered fly ash. The relatively high levels of extractable P in some ash samples supports the notion that fly ash may provide plant-available P, this being one mechanism by which growth of clover on a sandy soil may have been enhanced by amendment with fly ash (Summers et al., 1998). The PRI values of fly ashes were 2- to 658-fold higher than in the two sandy soils (Table 4). The PRI values in the weathered fly ashes from Kwinana were 20- to 30-fold lower (P < 0.001) than in the unweathered fly ash. The high PRI in unweathered fly ashes from Kwinana and Gladstone may have been due, at least in part, to the higher pH and Ca2+ levels in these samples. A high capacity to "retain" P in substrates can reduce P availability to plants, although the reversibility (i.e., desorption and/or solubilization) will also influence P availability with time. Sandy soils amended with weathered fly ash that has a moderate capacity to "retain" P (Table 4) may show a decrease in P leaching without compromising P availability to plants, resulting in environmental benefits.

Chemical Composition
The chemical compositions of the sandy soils and fly ash samples are given in Table 5. The soils are composed mainly of SiO2, whereas the major matrix elements in fly ashes were oxides of Si, Al, and Fe, together with significant percentages of Ca, K, Na, P, and Ti. In addition, there was considerable variation in the ratios of these and other elements among the different sources of fly ash. For example, the amount of Fe2O3 in the fly ash from Kwinana (unweathered) was 2- to 28-fold higher than in any of the other samples (Table 5); a property that presumably contributes to the relatively high PRI in this fly ash (Table 4). The levels of P2O5 in fly ashes from Western Australia were 2- to 68-fold higher than in those from Queensland. In addition, a higher C content in fly ash from Western Australia resulted in the losses on ignition being 5- to 14-fold higher, compared with samples from Queensland.


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  		Table 5. Chemical composition of selected soil and fly ash samples taken from locations in Western Australia and Queensland.{dagger}

 
Potential Release of Trace Elements
The concentrations of trace elements in TCLP extracts from the fly ash samples (Table 6) were lower than the soluble threshold limit concentrations (STLC) as set by the USEPA (Testa, 1997). For example, the amount of Cd extracted from the Kwinana fly ash, even the unweathered sample, was small (0.024 mg L-1), when compared with the STLC of 1.0 mg L-1 for this element (Table 6). The TCLP is a measure of the potential for leaching; however, in the field leaching from fly ash–amended soils may be a slow process (Ghodrati et al., 1995), so concentrations of these elements released at any one time would be much lower than the values determined in the TCLP. For Kwinana fly ash, data on total trace elements are available (Summers et al., 1998), and the low concentrations of trace elements in the TCLP extracts are consistent with the low total concentrations (with the exception of Ba) in this material. Even though total Ba in Kwinana fly ash is present at levels higher than the other trace elements, the concentrations of Ba in the TCLP extracts were still below the STLC (Table 6). Therefore, the five sources of Australian fly ash evaluated in the present study do not contain problematic levels of "leachable" trace elements.


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  		Table 6. Trace element concentrations in toxicity characteristic leaching procedure (TCLP) extracts from selected soil and fly ash samples taken from locations in Western Australia and Queensland.{dagger}

 
The present results support earlier work on fly ash–amended soils, showing that trace element leaching was very low and unlikely to affect ground water quality (Ghodrati et al., 1995). In another study of fly ash from the USA, extractable levels of some micronutrients (Mn, Cu, Zn) were greater than normally found in many coastal plain soils, but the nonessential elements Cd and Pb increased only slightly in fly ash–amended soils (Sims et al., 1995).


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
This laboratory study showed that addition of fine-textured fly ash to coarse-textured sandy soils can lead to a substantial increase in soil water-holding capacity, but also reduced soil hydraulic conductivity. In addition, fly ash may provide a source of extractable P and increase CEC. Possible release of trace elements was evaluated with the TCLP; values obtained for all trace elements tested, for the fly ashes tested from Western Australia and Queensland, were well below the regulatory guidelines set by the USEPA. Thus, amendment of sandy soils with fly ash, in combination with appropriate management regimes, potentially may increase crop production by reducing episodes of water deficit and aid in the retention of nutrients in the root zone. Since fly ash from various sources can differ widely in several properties, physical and chemical characterization in the laboratory can be helpful to evaluate the potential to use a particular fly ash source for soil amendment. Field trials would provide additional information about potential beneficial reuse of fly ash. In particular, the effects on soil properties when the fly ash–soil mixture is more heterogeneous than the near-homogeneous mixes accomplished in this laboratory study, and the responses of crops, should be evaluated.


   ACKNOWLEDGMENTS
 
We thank Western Power Corporation and the Ash Development Association of Australia for financial support of this research. Michael Smirk is thanked for instruction on the use of analytical equipment. We also thank the members of the UWA Turf Industries Research Steering Committee for their valuable advice and enthusiastic support during this project.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 


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JEQ 2003 32: 377-382. [Full Text]  




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