Impact of tree clearing on soil pH and nutrient availability in grazing systems of central Queensland, Australia
Kamaljit K. Sangha A C , Rajesh K. Jalota B and David J. Midmore AA Plant Sciences Group, Primary Industries Research Centre, Central Queensland University, Rockhampton, Qld 4702, Australia.
B Centre for Environment Management, Central Queensland University, Emerald Campus, Qld 4720, Australia.
C Corresponding author. Email: k.sangha@cqu.edu.au
Australian Journal of Soil Research 43(1) 51-60 https://doi.org/10.1071/SR03152
Submitted: 30 October 2003 Accepted: 22 October 2004 Published: 14 February 2005
Abstract
In Queensland, land is cleared at high rates to develop pastures for enhanced production and the associated monetary gains. However, pasture production declines over time in cleared pastures until a new equilibrium is reached. The present study focussed on elucidating the reasons for decline in pasture production and finding the key soil properties that are affected due to clearing. Paired sites for cleared and uncleared pastures were selected to represent 3 dominant tree communities of the semi-arid tropics in central Queensland, i.e. Eucalyptus populnea, E. melanophloia, and Acacia harpophylla. The cleared pastures were chosen to represent 3 different durations of time since clearing (5, 11–13, and 33 years) to evaluate the temporal impact of clearing on soil properties. Various soil parameters were studied: macronutrients—available N (NH4+and NO3–), total N, and available P; micronutrients—Cu, Fe, Zn, and Mn; exchangeable cations—Ca, Mg, Na, and K (also macronutrients); pHw; and electrical conductivity. Of these, pHw showed a significant response to time of clearing for all 3 tree communities. Soil pHw increased significantly at cleared sites relative to uncleared (native woodland) pastures, and the increase was highly correlated with concentrations of exchangeable Ca, Mg, and Na. The change in soil pHw and exchangeable cations was more evident at >0.30 m soil depth. The increase in soil pHw in cleared pastures decreased the availability of soil nutrients for plant growth and, hence, pasture productivity. The interactions of different soil properties down the profile as a result of changes caused by clearing are important when interpreting the effects of clearing on soil properties.
Additional keywords: tree clearing, pasture systems, soil nutrients, soil pHw, uncleared pasture systems.
Acknowledgments
We thank the landholders Mrs and Mr Spooner for permission to carry out this research on their property. The laboratory space and equipment provided by the Department of Natural Resources and Mines and the Department of Primary Industries at Emerald is gratefully acknowledged. The funds were provided by Central Queensland University, Queensland. Our thanks to Mr Robert Lowery for the technical help in sampling and processing of soil samples. Thanks to Dr Ram Dalal (Department of Natural Resources, Mines and Energy, Indooroopilly) and anonymous referees for suggested improvements to the original manuscript.
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