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Assessment of two alkaline flyash-fertilisers for use on acid soils

Kaye M. Spark and Roger S. Swift

Faculty of Natural Resources, Agriculture and Veterinary Science, University of Queensland, Gatton, QLD 4343, Australia. Email:


The amount of coal flyash reused is significantly less that the quantities produced, creating problems of storage of this waste product for the coal-based power generation industry. Previous research has indicated that flyash is useful for increasing the water holding capacity of soils and alkaline flyash has been used to ameliorate the problems associated with acid soils, but the uptake of this type of soil amendment has been generally low. The production of a flyash-fertiliser, a “blend” of flyash with inorganic compounds that can act as a source of plant nutrients (e.g. Ca, K), has the potential to increase the usefulness of the flyash and so enhance its reuse in agricultural applications.

In this study the impact of two alkaline flyash-fertilisers on the physical and chemical characteristics of two types of acids soils (ferrosols and podsols) has been assessed. Using laboratory based studies, analyses included soil acidity, total extractable, water soluble, leachable and plant available heavy metals, and plant available boron for application rates up to 10% flyash-fertiliser.

The results indicate that the alkaline flyash used at rates of between 5 and 10% would have an optimal usefulness as an amendment in acid soils, with the rate depending on the nature of the soil and the degree of the soil acidity.

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