Effects of fire retardant on heathland soils in south-eastern Australia
P. Hopmans A , N. Collett A C and R. Bickford BA School of Forest and Ecosystem Science, The University of Melbourne, 123 Brown Street, Heidelberg, Vic. 3084, Australia.
B formerly of Department of Sustainability and Environment, Forest Science Centre, 123 Brown Street, Heidelberg, Vic. 3084, Australia.
C Corresponding author. Email: ncollett@unimelb.edu.au
Australian Journal of Soil Research 45(8) 607-617 https://doi.org/10.1071/SR07040
Submitted: 23 March 2007 Accepted: 29 October 2007 Published: 7 December 2007
Abstract
A study was undertaken to assess the effects of fire retardant application, unmodified by heat of fire, on soil properties in 2 fire-prone heathland communities at Marlo and the Grampians in south-eastern Australia. Fire retardant (Phos-Chek D75-R at 0.144 g/L) was applied at rates of 0.5, 1.0, and 1.5 L/m2 and compared with control treatments of nil and 1.0 L/m2 of water. Monitoring of surface soils showed that pH at both sites decreased while soil salinity increased immediately after application followed by a rapid decline to pre-treatment values within 12 months. The impact of retardant on total carbon and nitrogen was minor and within the range of natural variation of C and N in surface soils at both sites. Levels of readily available or labile forms of N increased at both sites but declined rapidly to background values after 12 months. Applications of retardant progressively increased extractable P in the surface soil at Marlo, in contrast to the Grampians where a rapid increase was observed after two months followed by a decline after 12 months. These results showed a significant increase in labile P in the surface soil after 12 months and also indicated that a large proportion of the phosphate applied had leached into the subsoil. Likewise, fire retardant applied at the highest rate caused increases in labile sulfate after 2 months at both sites, followed by a rapid decline to background levels. It is expected that the elevated levels of soil phosphate in particular could have a long-term impacts on growth and composition of heathland vegetation known to be sensitive to elevated levels of phosphate in soil.
Acknowledgments
The authors wish to thank Mike Wouters, Greg McCarthy, Paul Clements, John Collopy, David Smith, and Carolien Schoenborn for their assistance with the establishment of the trials and the collection of soil samples. We also like to thank Tina Bell for the detailed descriptions of vegetation at each site. We gratefully acknowledge the assistance from Sharon Edwards, Debbie Renfree, and Matthew Lee with the chemical analysis of the many soil samples collected for this project.
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