Predicting the impact of perennial phases on average leakage from farming systems in south-western Australia
P. R. WardCSIRO Centre for Environment and Life Sciences, Private Bag No. 5, Wembley, WA 6913; CRC for Plant-based Management of Dryland Salinity, 35 Stirling Hwy, Crawley, WA 6009, Australia. Email: phil.ward@csiro.au
Australian Journal of Agricultural Research 57(3) 269-280 https://doi.org/10.1071/AR04137
Submitted: 17 June 2004 Accepted: 15 March 2005 Published: 31 March 2006
Abstract
Rising watertables and dryland salinity in southern Australia are due to excess groundwater recharge after the replacement of native vegetation by annual crops and pastures. The inclusion of perennial plants into agricultural systems has been proposed as a possible method of recharge reduction, through the creation of a buffer (extra water storage capacity generated by the perennial in comparison with an annual crop or pasture). However, the role of perennial phases under conditions of highly episodic leakage is not well understood. In this paper, a simple Leakage/Buffer Model (LeBuM) was developed to determine the effect of perennial phases on long-term average annual leakage, incorporating episodic events. Mechanistic modelling studies on contrasting soil types were used to demonstrate that leakage for any given May–December period was directly related to soil water storage at 1 May. From this finding, it follows that leakage from a phase rotation can be calculated if the size of the buffer, and the leakage quantity in the absence of a buffer, are known for each stage of the rotation. LeBuM uses a long-term sequence of leakage values in the absence of a buffer as input, and the maximum buffer size, its rate of development, and the length of perennial and annual phases are specified as parameters. LeBuM was applied to leakage data modelled for 5 contrasting soil types over 100 years at 24 sites in the Western Australian wheatbelt. Phase rotations on duplex, waterlogging duplex, or loamy sand soils reduced leakage by >90% for regions with <380 mm annual rainfall, but were less effective in wetter regions and on deep sands or acid loamy sands. Nevertheless, phase rotations if adopted widely could delay the onset of salinity by as much as several decades.
Additional keywords: phase farming, lucerne, dryland salinity, LeBuM, episodic recharge.
Acknowledgments
Thanks to Dr Senthold Asseng for giving me access to his APSIM results for the 24 sites and 5 soil types in the Western Australian wheatbelt.
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