Dryland salinity and declining river systems. Together they paint a bleak picture for Australias agriculture. The federal governments recent initiative will look for ways to tackle both, but some players are already well ahead of the game.

Plants can process a vast amount of water. In a process called transpiration, they suck water up through their roots and expel it from their leaves through stomates, small cells that open or close to increase or reduce water loss. A rainforest can release enough water in this way to form a cloud above it.

Vineyards dont change the climate much, but they do transpire a good deal of water; a problem as they grow in size and number and take their water from declining and increasingly saline river systems.

In this setting, anything that reduces river water irrigation without compounding the problems of saline soils has got to be a winner. Partial Rootzone Drying, or PRD, has emerged as just such a technology.

It has been developed at the University of Adelaides Waite campus by a team of scientists led by Dr Peter Dry, Senior Lecturer in Viticulture science, and Dr Brian Loveys of CSIRO Plant Industry.

If part of the grapevines root system is slowly dried, but the remaining roots kept well watered, the vine is fooled in thinking that most of its roots are drying out. It produces chemical signals that close the stomates and cause reduced shoot growth and leaf area, thus conserving water. The wet roots, however, keep the plant healthy and productive.

The plant adapts and the stomates re-open, but by reversing the treatment and wetting the dry roots while drying those that had been wet, the reduced shoot growth and partial closure of stomates can be prompted again, and maintained over a long period.

By continually altering irrigation, half the roots can be kept moist while the other half are kept dry. This maintains fruit production, but uses far less water, and
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Contact: Dr Peter Dry
pdry@adelaide.edu.au
618-8303-7374
Adelaide University
2-Nov-2000