Use of alkaline flyash-based products to amend acid soils: Extractability of selected elements and their uptake by plants

In addition to promoting plant growth, the incorporation of flyash material into soil also has the potential to affect the solubility and plant availability of some elements. This paper reports on the effect of 2 flyash products (FAP) on the extractability and plant uptake as a function of pH of selected elements of concern in the environment: As, B, Cd, Co, Cu, Cr, Mn, Pb, Ni, and Zn. The results for the growth response of maize plants (Zea mays L.) in the FAP-amended soils have been reported in a companion paper. The addition of the FAP to the soils used in this study at rates up to 5% w/w resulted in increased levels of Cu, Mn, Ni, As, and Co in an acetic acid extract. The levels of Cr, Mn, Ni, Pb, Zn, As, and Co in these extracts all showed a dependency on pH for some soils. Maize plants grown in the amended soils exhibited an increase in the plant uptake of Cu, Mn, and Ni in some soils. However, none of the elements studied increased the plant uptake to levels which would generally be considered toxic to plants or cause problems in the food chain. The presence of the FAP decreased the plant availability of Ni at low pH and levels of Mn and Cd in the acetic acid extract were decreased, most likely due to sorption of these elements by the FAP. There is no evidence that either the flyash alone, or the 2 FAP used in this study would pose a threat to plants or the environment when used at levels of up to 5% w/w. Possible beneficial effects for the environment were observed as the incorporation of FAP into soils has the capacity to reduce the uptake and potential toxicity of Cd, Ni, or Mn in some soils.