Organic carbon partitioning in soil and litter in subtropical woodlands and open forests: a case study from the Brigalow Belt, Queensland
S. H. Roxburgh A B F , B. G. Mackey A C , C. Dean A B D , L. Randall A E , A. Lee A C and J. Austin A EA Co-operative Research Centre for Greenhouse Accounting, GPO Box 475, Canberra, ACT 2601, Australia.
B Ecosystem Dynamics Group, Research School of Biological Sciences, The Australian National University, Canberra, ACT 0200, Australia.
C School of Resources, Environment and Society, The Australian National University, Canberra, ACT 0200, Australia.
D Current address: Department of Infrastructure, Planning and Environment, PO Box 2130, Alice Springs, NT 0870, Australia.
E Bureau of Rural Sciences, PO Box 858, Canberra, ACT 2601, Australia.
F Corresponding author. Current address: Bushfire Co-operative Research Centre & School of Biological, Earth and Environmental Sciences, The University of New South Wales, NSW 2052, Australia. Email: Stephen.Roxburgh@ensisjv.com
The Rangeland Journal 28(2) 115-125 https://doi.org/10.1071/RJ05015
Submitted: 12 February 2005 Accepted: 16 November 2005 Published: 9 November 2006
Abstract
A woodland–open forest landscape within the Brigalow Belt South bioregion of Queensland, Australia, was surveyed for soil organic carbon, soil bulk density and soil-surface fine-litter carbon. Soil carbon stocks to 30 cm depth across 14 sites, spanning a range of soil and vegetation complexes, ranged from 10.7 to 61.8 t C/ha, with an overall mean of 36.2 t C/ha. Soil carbon stocks to 100 cm depth ranged from 19.4 to 150.5 t C/ha, with an overall mean of 72.9 t C/ha. The standing stock of fine litter ranged from 1.0 to 7.0 t C/ha, with a mean of 2.6 t C/ha, and soil bulk density averaged 1.4 g/cm3 at the soil surface, and 1.6 g/cm3 at 1 m depth. These results contribute to the currently sparse database of soil organic carbon and bulk density measurements in uncultivated soils within Australian open forests and woodlands.
The estimates of total soil organic carbon stock calculated to 30 cm depth were further partitioned into resistant plant material (RPM), humus (HUM), and inert organic matter (IOM) pools using diffuse mid-infrared (MIR) analysis. Prediction of the HUM and RPM pools using the RothC soil carbon model agreed well with the MIR measurements, confirming the suitability of RothC for modelling soil organic carbon in these soils. Methods for quantifying soil organic carbon at landscape scales were also explored, and a new regression-based technique for estimating soil carbon stocks from simple field-measured soil attributes has been proposed.
The results of this study are discussed with particular reference to the difficulties encountered in the collection of the data, their limitations, and opportunities for the further development of methods for quantifying soil organic carbon at landscape scales.
Additional keywords: bulk density, flux, organic matter, RothC, surface.
Acknowledgments
We thank Drs Neil McKenzie and Jan Skjemstad for technical advice. We further thank Drs Skjemstad and RDB Whalley and 3 anonymous reviewers for comments on an earlier draft of the manuscript.
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