Drying temperature effects on bulk density and carbon density determination in soils of northern New South Wales
Brian Wilson A B C , Subhadip Ghosh B , Phoebe Barnes B and Paul Kristiansen BA NSW Department of Environment, Climate Change and Water, PO Box U221, University of New England, Armidale, NSW 2351, Australia.
B School of Environmental and Rural Sciences, University of New England, Armidale, NSW 2351, Australia.
C Corresponding author. Email: Brian.Wilson@environment.nsw.gov.au
Australian Journal of Soil Research 47(8) 781-787 https://doi.org/10.1071/SR09022
Submitted: 28 January 2009 Accepted: 31 July 2009 Published: 11 December 2009
Abstract
There is a widespread and growing need for information relating to soil condition and changes in response to land management pressures. To provide the information needed to quantify land management effects on soil condition, monitoring systems are now being put in place and these programs will generate large numbers of samples. Streamlined procedures for the analysis of large sample numbers are therefore required. Bulk density (BD) is considered to be one of several key indicators for measuring soil physical condition, and is also required to estimate soil carbon density. The standard analytical technique for BD requires drying the soil at 105°C but this procedure creates several logistical and analytical problems. Our initial objective was to derive correction factors between drying temperatures to allow for rapid, low-temperature estimation of BD on large sample numbers. Soil samples were collected from 3 contrasting soil types (basalt, granite, and meta-sediments) in 4 land uses (cultivation, sown pasture, native pasture, woodland) in northern New South Wales to test the effect of soil drying temperature on BD determination. Cores were divided into 4 depths (0–0.05, 0.050–0.10, 0.10–0.20, 0.20–0.30 m), and oven-dried at 40, 70, and 105°C. Drying temperature had no significant effect on BD but the effects of soil type, depth, and land use were significant, varying according to expectations based on previous studies, i.e. higher BD in granite-derived soils and lower in basalt-derived soils, increased BD with depth, and increasing BD with increasing management intensity. These results indicate that lower drying temperatures (40°C) were adequate for the efficient determination of BD especially where analysis of other soil properties from the same sample is required. However, before this approach is applied more widely, further calibration of BD and drying temperature should be undertaken across a wider range of soils, especially on clay-rich soils.
Acknowledgments
The authors grateful acknowledge the assistance of the various landholders on the Northern Tablelands of NSW for permitting access to their properties for soil sampling. Thanks also to Sandy Grant of the NSW Department of Environment and Climate Change for providing the location map. We are also grateful for the constructive comments provided by 3 anonymous reviewers. This work was supported by the NSW Department of Environment and Climate Change.
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