Reprint of "Properties of soil materials derived from fly ash 11 years after revegetation of post-mining excavation"

Abstract

We investigated properties of soil materials derived from reclamation and revegetation on fly ash used to fill-in an area excavated during earlier mining. Changes in the soil environment that take place after this practice have to be well recognized, since knowledge of all aspects of fly ash revegetation is essential to sustainable reclamation. Fly ash was a by-product of lignite-burning in an electric power plant, and it was mixed with biosolids (3000tonnes of sewage sludge per ha) or boulder clay (4000tonnes per ha). Eight non-native tree and shrub species were planted in a random pattern on several areas reclaimed in different ways. Raw fly ash and fly ash mixed with biosolids or clay were amended with a mineral fertilizer (yearly doses of 300kgha−1N, 100kgha−1 P2O5, 100kgha−1 K2O) in years 2000–2003 and in 2006. Eleven years after revegetation, main physical and chemical properties of newly formed soil substrate were determined. Raw fly ash, due to its alkaline character, high salinity, and ability to cement, constituted unfavorable environment for plant growth. However, fly ash with the addition of biosolids or boulder clay exhibited granular soil structure in the surface layers, which facilitated plant root penetration and created favorable conditions for plant growth. In contrast, raw fly ash had lamellar structure, typical for materials of sedimentary origin. The soil substrates investigated on the reclaimed and revegetated materials did not reveal any features of genetic soil horizons, and we concluded that 11years was insufficient to develop regosols or technosol. However, introduced vegetation resulted in an improvement of the structure of the soil substrate. Mixing of the surface fly ash with biosolids and boulder clay clearly improved several substrate properties, including neutralization of the reaction, a decrease of salinity level, and improvement in physical properties; these effects contributed to an increase in efficiently useful water retention and the amount of water available for plants.