If long fallow cropping is leaky then shallow groundwaters on the Liverpool Plains should be of recent origin
R. R. Young A E , A. Broughton B C , J. M. Bradd D and J. F. Holland AA NSW Department of Primary Industries, RMB 944, Calala Lane, Tamworth, NSW 2340, Australia.
B NSW Department of Infrastructure, Planning and Natural Resources, Gunnedah Resource Centre, Curlewis Road, Gunnedah, NSW 2380, Australia.
C Present address: Groundwater Solutions, 115 Tasman Street, Mt Cook, Wellington, New Zealand.
D Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234, Australia.
E Corresponding author. Email: rick.young@agric.nsw.gov.au
Australian Journal of Experimental Agriculture 44(10) 1051-1056 https://doi.org/10.1071/EA03133
Submitted: 25 June 2003 Accepted: 19 January 2004 Published: 25 November 2004
Abstract
Previous groundwater studies have indicated that up to 195 000 ha of the Liverpool Plains catchment, south of Gunnedah, New South Wales, Australia, are at risk from shallow saline watertables. Replacement of hydraulically stable, native perennial grasslands with more ‘leaky’ annual cropping systems since the 1950s, particularly long fallow wheat–sorghum rotations, has been held responsible for an apparent increased frequency of shallow watertables and saline discharge. If so, then it follows that shallow groundwater in the alluvium will be recent (less than about 30 years old) and the solution to the problem is a straightforward reduction in deep drainage under farming systems via increased evapotranspiration. However, in this study, we have found levels of bomb pulse tritium in shallow groundwaters that indicate that about half of the shallow groundwaters in the Mooki subcatchment pre-date current agricultural practices. A hypothesis for this unexpected outcome suggests that the problem is complex and that solutions need to be site-specific.
Acknowledgments
We thank Robert Banks and Ian Acworth for helpful discussions regarding the origins of salt and the nature of salinity on the Liverpool Plains; Jane Coram for comments regarding predictive catchment models; Carol and Harry Rose for their determination to sample from even the lowest yielding piezometers; Bob Martin for comments on an earlier draft and Peter Freckleton for production of the map (Fig. 1). Jim McDonald, Des Schroder, John Kneipp and Bob Crouch were instrumental in highlighting and supporting research into resource management issues in the Liverpool Plains catchment in the 1990s. Funds for this study were provided by the Murray–Darling Basin Natural Resources Management Strategy.
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