Influence of coal fly ash application on trace element mobility and distribution in soil, plant and leachate

A greenhouse study was conducted to assess growth and elemental uptake by canola ('Brassica napus') on acidic soils amended with four chemically different unweathered fly ashes. The ashes were incorporated into the top 10 cm of 1 m long intact soil cores at the rate of 0, 12, 36 and 108 Mg ha⁻¹. The objective of this study was to characterise growth responses and the distribution of B, Mo and Se in leachate, soil and plant. We observed increases in the soil pH and that of the leachate within 5 months of fly ash addition. Concentrations of Mo and Se increased significantly in the stem, while that of B was slightly increased, with 108 Mg ha⁻¹ fly ash application. Compared with the untreated control, acidic fly ashes increased above ground biomass produced by canola by up to 25%, but biomass was unchanged or reduced by alkaline ashes. In general, concentration of B, Mo and Se in canola seed increased with higher rates of fly ash. While concentrations of Mo and Se in the soil were only slightly increased, that of B was elevated significantly in the top 0-10 cm of the soil with the application of alkaline fly ashes. The concentrations of the trace elements in the leachate were generally below detection limit. Accumulation of the three metals in soil and plant were all below phytotoxic levels. The results of this study suggest that fly ash has the potential to increase plant growth without any detrimental effects on soil or groundwater. This is a limited study and there is a need for continuous monitoring of trace elements in the soil-plant and water system under field conditions.