Boron contents and solubility in Australian fly ashes and its uptake by canola (Brassica napus L.) from the ash-amended soils
V. Manoharan A , I. A. M. Yunusa A D E , P. Loganathan B , R. Lawrie C , B. R. Murray A , C. G. Skilbeck A and D. Eamus AA Department of Environmental Sciences, University of Technology, Sydney, P.O. Box 123, Broadway, NSW 2007, Australia.
B Soil and Earth Sciences, Institute of Natural Resources, Massey University, Private Bag 11222, Palmerston North, New Zealand.
C NSW Agriculture, Department of Primary Industries, Locked Bag, Richmond, NSW 2753, Australia.
D Current address: School of Environmental and Rural Sciences, University of New England, Armidale, NSW 2351, Australia.
E Corresponding author. Email: isa.yunusa@une.edu.au
Australian Journal of Soil Research 48(5) 480-487 https://doi.org/10.1071/SR10073
Submitted: 21 September 2009 Accepted: 16 April 2010 Published: 6 August 2010
Abstract
Phytotoxicity due to excessive boron (B) uptake by plants impedes routine agronomic utilisation of coal fly ash. We assessed 11 fly ashes (pH 3.14–10.77) having total B content (Bt) of 12–136 mg/kg, of which 20–30% was hot water soluble (Bs) in the acidic ashes (pH <5) and 5–10% in the alkaline ashes, for their potential to supply B to plants and their risk associated with phytotoxicity. We found the Bs/Bt to be negatively correlated (R2 = 0.63**, N = 11) with ash pH.
We conducted two pot trials in which canola was grown in soils amended with fly ash. In the first trial, an alkaline fly ash (Bt 66 mg/kg) was incorporated at 5 rates of up to 625 Mg/ha into the top 50 mm of 2 acidic soils in 0.30-m-long intact cores, and sown with canola. Boron concentration in leaves at flowering reached the phytotoxic threshold, and both plant growth and seed yield were reduced, only at 625 Mg/ha. In the second trial, 4 fly ashes (pH 3.29–10.77, Bt 12–127 mg/kg) were incorporated at 4 rates of up to 108 Mg/ha into the top 0.10 m of 2 acidic soils in 1.0-m-long intact cores and then sown with canola. Ashes with highest Bt, when applied at 108 Mg/ha, increased B concentration in the topsoil only. Of the 2 ashes with the highest Bt, only that which produced low soil pH and applied at 108 Mg/ha increased B concentration in the shoot, but was still below phytotoxic threshold. The results suggest that B derived from these ashes may not cause phytotoxicity and excessive soil B accumulation if the ashes are applied at modest rates (<36 Mg/ha) to the topsoil layers.
Additional keywords: trace elements, boron toxicity, soil boron, soil pH.
Acknowledgments
We acknowledge with appreciation the assistance with laboratory procedures and facilities from Ms Narelle Richardson and Ms Gemma Armstrong, and thank Messers Nawash Haddad, Aining Mao, and Ibby Yunusa for their help with the intact soil core collection and with soil and plant processing. We express our gratitude to Assoc. Prof. Damian Gore and Mr Russell Field at Macquarie University for assisting with microwave digestion of the samples. We also thank Mr Jim Keegan at the Department of Chemistry, University of Technology Sydney, for his help with the ICP-MS analysis. We appreciate the valuable comments made by the two anonymous referees on the manuscript. This study was funded by the Ash Development Association of Australia and the Australian Research Council (LP045511).
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