Estimating extractable soil moisture content for Australian soils from field measurements
A. R. Ladson A D , J. R. Lander B , A. W. Western B , R. B. Grayson B and Lu Zhang CA Department of Civil Engineering, Institute for Sustainable Water Resources and CRC for Catchment Hydrology, Monash University, Vic. 3800, Australia.
B Department of Civil and Environmental Engineering, Centre for Environmental Applied Hydrology and CRC for Catchment Hydrology, University of Melbourne, Vic. 3010, Australia.
C CSIRO Land and Water and CRC for Catchment Hydrology, GPO Box 1666, Canberra, ACT 2601, Australia.
D Corresponding author. Email: tony.ladson@eng.monash.edu.au
Australian Journal of Soil Research 44(5) 531-541 https://doi.org/10.1071/SR04180
Submitted: 21 December 2004 Accepted: 20 February 2006 Published: 4 August 2006
Abstract
The amount of water that can be stored in soil and evaporated or actively used by plants is a key parameter in hydrologic models and is important for crop and pasture production. Often, the active soil moisture store is estimated from laboratory measurements of soil properties. An alternative approach, described in this paper, is to estimate the extractable soil moisture capacity from direct measurements of soil moisture content in the field. A time series of soil moisture values, over the depth of the soil, shows the actual changes in water content. The difference between the wettest and driest profiles is an estimate of the extractable soil moisture storage. We have gathered data on extractable soil water capacity for 180 locations over Australia and have compared our values with published results from the Atlas of Australian Soils (AAS), derived from profile descriptions and pedo-transfer functions. Our results show that data from the AAS provide a useful lower bound for measured extractable soil moisture storage, but of the sites examined, 42% had values >2 times those in the AAS. In part, this was because total soil depths were underestimated in the AAS results compared with the active depths from the measured data. Active depths are strongly related to vegetation type.
Additional keywords: Atlas of Australian Soils, plant-available water, dynamic soil store, extractable soil moisture.
Acknowledgments
We acknowledge the great assistance from the 90 soil scientists we contacted when seeking data for this project. We are also grateful for the rainfall data supplied by the Bureau of Meteorology. During this project, all the authors where supported with funding from the Cooperative Research Centre for Catchment Hydrology.
Part of this work was published in the proceedings of the Hydrology and Water Resources Symposium, 2002 (Ladson et al. 2002). The Institution of Engineers, Australia, is acknowledged as the publishers of that proceedings.
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