Economic and environmental advantages of using fly ash as a soil amendment in agronomy

In this paper we highlight the findings of our ongoing studies on the agronomic use of Australian coal fly ashes in the light of pre-existing concerns that the ashes could cause phytotoxicity and, hence, reduced growth and yield of crops. We tested canola on soil treated with an alkaline fly ash added at up to 625 t/ha, and obtained increases in seed yields with fly-ash rates of not more than 36 t/ha, beyond which there was no further response in yields. Concentration of B was elevated in the leaves with ash addition of 625 t/ha, while that Mo elevated in the leaves and grains with addition of fly ash at all rates, but that of Zn was not affected by addition of fly ash. There was a correlation between plant dry weight and tissue concentration of P at flowering, suggesting that addition of fly ash might have enhanced P nutrition. We found in another experiment that both acidic and alkaline fly ashes applied at not more than 12 t/ha significantly increased the pH of acidic soil by up to a unit of 0.4 within 6 months of soil treatment. Much of the benefits of fly ash in terms of amelioration of acidity and other nutritional benefits could be achieved with fly ash applied at not more than 10 t/ha without any detrimental effects on the environment. Salinity (EC < 4.0 dS/m) and B concentration (< 60 mg/kg hot water soluble) are the main criteria for selecting Australian fly ashes for soil amelioration. Developing a sustainable application for fly ash in agriculture should reduce the need for its disposal in landfill, while saving farmers at least 30% the cost associated with treating the soil using lime.