J Soils Sediments (2011) 11:423–431 DOI 10.1007/s11368-010-0312-5
SOILS, SEC 2 • GLOBAL CHANGE, ENVIRON RISK ASSESS, SUSTAINALE LAND USE • RESEARCH ARTICLE
Structural and hydrological alterations of soil due to addition of coal fly ash Isa A. M. Yunusa & V. Manoharan & Inakwu O. A. Odeh & Surendra Shrestha & C. Greg Skilbeck & Derek Eamus
Received: 6 April 2010 / Accepted: 17 October 2010 / Published online: 17 November 2010 # Her Majesty the Queen in Right of Australia as represented by the University of New England, Australia 2010
Abstract Purpose We tested the potential of using coal fly ash for improving the physical and hydrological characteristics of coarse and medium-textured agricultural soils. Materials and methods Acidic (FWA) and alkaline (FNSW) fly ashes were used to amend a range of representative agricultural soils. In the first experiment, fly ash was applied to the top 10 cm of 1-m long intact cores of a sandy loam soil at rates of 0, 12, 36 or 108 Mg/ha and sown with canola; after harvest, bulk density (BD), aggregate stability and mean weight diameter (MWD) were measured on the soil. In the second experiment, we
Responsible editor: Hailong Wang I. A. M. Yunusa (*) School of Environmental and Rural Sciences, University of New England, Armidale NSW 2351, Australia e-mail:
[email protected] V. Manoharan : C. G. Skilbeck : D. Eamus Department of Environmental Science, University of Technology, Sydney, Broadway, SydneyP.O. Box 123NSW 2007, Australia I. O. A. Odeh Faculty of Agriculture, Food and Natural Resources, The University of Sydney, Sydney, NSW 2006, Australia S. Shrestha School of Engineering, College of Health and Science, University of Western Sydney, Locked Bag 1797, Kingswood Campus, Penrith South DC, NSW 1797, Australia
assessed water retention at field capacity (−300 kPa) and permanent wilting point (−1,500 kPa) for sandy and loamy soils amended with FNSW at 0.0–16% (w/w). The third experiment used rainfall simulation to assess erodibility of sandy and loamy soils mixed with FNSW at rates of 0, 5 or 20 Mg/ha. Results and discussion In the first experiment, fly ash had no significant effect on MWD of the soil. The BD in the 0– 10 cm layer (topsoil) was increased with addition of FWA, while FNSW applied at 108 Mg/ha reduced BD, relative to the control treatment. This was because FNSW had lower particle and bulk densities than FWA and the test soils. Ash addition increased macro-aggregation, significantly so in the 10–20 cm layer (subsurface layer), by reducing the percentages of micro-aggregates and silt + clay particles. Thus, macro-aggregation was positively correlated (p< 0.01) with MWD, but both were inversely correlated (p< 0.01) with micro-aggregates. In the second experiment, addition of fly ash enhanced plant water availability by increasing water retention at field capacity by threefold in the sandy soil and 1.5-fold in the loamy sand, but water retention at permanent wilting point was not affected. In Experiment 3, the addition of ash at 20 Mg/ha, but not at 5 Mg/ha, increased turbidity of runoff water from the amended soil due to the dispersal of fine particles by the impact of the simulated raindrops. Conclusions Moderate rates of fly ash (10% w/w), as a result of increased clay-size particles (Kalra et al. 2000; Pathan et al. 2003a). However, large proportions of fine particles in the
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soil may also increase the amount of water held at very low negative potential that could reduce the plant-available water as found when coarse sands were amended with coal fly ash (Campbell et al. 1983; Aitken et al. 1984) or with clay (Buchanan et al. 2010). The risk of fly ash added to the top soil layers being removed and eroded offsite during rainfall is a major environmental concern. This risk would be minimal since the ash is pozzolanic and would cement surface particles together (El-Mogazi et al. 1988) to minimise erosion. Cementing of the particles may, however, seal the surface of the receiving soil and thereby exacerbate runoff and erosion as reported by Gorman et al. (2000). Erosion from ash-amended soil is likely to be enhanced in the event of heavy rainfall or wind soon after addition of the ash and before its particles integrates into the soil matrix. During this period the fine particles in the treated soils become highly susceptible to detachment and transportation, as often found with loose fine particles in natural soils (Lehrsch and Baker 1989; Gorman et al. 2000). There have been few studies on assessing the use of fly ash to ameliorate soil physical problems that constrain plant growth, such as poor aggregation and water-holding capacity, and erosion, especially in medium- and heavytextured soils. The aim of this study was to test the hypothesis that addition of fly ash at moderate rates provides measurable improvements in the bulk density, aggregation and availability of soil water in light- and medium-textured soils.
2 Materials and methods Two contrasting types of fly ashes were collected from power stations located in New South Wales (FNSW) and Western Australia (FWA) in Australia. These power station burn black coals and produce Class F fly ash. Although the ashes vary in size, they predominantly contain particles ranging in size from 1.0 to 200 μm, and amount to about 60–95% of the total mass (Table 1). These fly ash types listed above were used in a series of experiments to quantify structural and hydrologic benefits of adding fly ash at moderate rates to a range of light- and medium-textured soils. 2.1 Experiment 1: assessment of soil structural parameters 2.1.1 Bulk density In this experiment, we used intact soil cores extracted in 1-m tubes (internal diameter of 150 mm) from Belanglo forest reserve (34.6° S, 150.4° E) in the Southern Tablelands of New South Wales, Australia. This soil has a mostly sandy loam profile and organic carbon content of about 3.1% in the surface
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Table 1 Selected physical and chemical properties of the fly ashes sourced from Western Australia (FWA) and New South Wales (FNSW) and used in the study Property
FWA
Physical Very fine sand/silt/clay (
