CSIRO Publishing, MelbourneД¬ondon AG and Richards RA (1993) Challenges ahead in using carbon isotope discrimination in plant-breeding programs. Oecologia 79: 1вЂ“5Д¬ommonwealth of Australia (1996) State of the Environment, Australia 1996. Oecologia 115: 306вЂ“311Д¬aldwell MM and Richards JH (1989) Hydraulic lift water efflux from upper roots improves effectiveness of water uptake by deep roots.

A.A Balkema Publishers, RotterdamД«urgess SSO, Adams MA, Turner NC and Ong CK (1998) The distribution of soil water by tree root systems. In: Dillon P and Simmers I (eds) International Contributions to Hydrogeology. Journal of Hydrology 119: 1вЂ“20Д«ond WJ, Smith CJ and Ross PJ (1998) Field validation of a water and solute transport model for the unsaturated zone. Journal of Hydrology 60: 157вЂ“173ДЄllison GB, Cook PG, Barnett SR, Walker GR, Jolly ID and Hughes MW (1990) Land clearance and river salinisation in the western Murray Basin, Australia. They suggest adoption over a range of arable land units could cause local retreat of water tables by 0.3 m y в€’1 initially, leading to a new equilibrium level which would still remain elevated with respect to that under natural vegetation.ДЄllison GB and Hughes MW (1983) The use of natural traces as indicators of soil-water movement in a temperature semi-arid region. Simulations of phase farming point to a halving in long term drainage. An effective buffer is thus provided to restrict drainage under an ensuing cropping phase in a manner that more closely emulates natural systems. Inclusion of a perennial lucerne phase in rotation with crops confers environmental benefit through summer uptake from a rooting depth double that of crops.

The associated limited scope for soil water uptake carries the penalty of increased frequency of drainage and the subsequent resource degradation currently associated with farmland. Low seasonal vapour pressure deficit explains the observed benefits of enhanced biomass production due to high water use efficiency. Characteristic patterns of water use by agricultural systems, comprised mainly of determinant annual species, are truncated in time but feature elevated peak rates coinciding with periods of maximum soil water availability during the cooler months. A strategy of tempered water use during periods of rainfall excess in winter/spring enables seasonal carryover of soil water to be withdrawn by deep roots for summer functioning. Contrasting patterns of water use indicate pronounced physiological activity in summer by natural ecosystems ensuring the persistence of the dominant perennial species. Water balance information at locations across southern Australia is analysed to identify mechanistic causes for higher water tables under agricultural systems compared to natural vegetation.

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