Turning salt and water into wine

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Dr Peter Dry with South African PhD student, Keren Bindon, inspect the vines at Adelaide University's Waite Campus, where PRD experiments were first trialled.
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Monday, 13 November 2000

Dryland salinity and declining river systems. Together they paint a bleak picture for Australia's agriculture. The federal government's 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 don't 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 Adelaide's 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 grapevine's 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 the benefits are not limited to vines.

"With grape vines and other crops such as citrus, pears and peaches, we can produce the same commercial yield with half the district average of water applied," said Dr Peter Dry, Senior Lecturer in Viticultural Science. "In most situations we've been able to double the water use efficiency, so that has big implications. We are short of water, so if we can get twice as much fruit per megalitre of water, that's very important," said Dr Dry.

Much of South Australia's agriculture relies on the River Murray and its increasingly saline water, but salinity doesn't seem to be a problem with this technology.

"So far we haven't done much research on using PRD saline water," said Dr Dry, "except for experiments where the water is relatively saline, and we've had exactly the same results," he said.

"We've assumed so far that because we are putting on half the water, we're only putting on half the amount of salt on, but I guess the distribution of salt in the soil, and how the roots take up the salt, is one of the issues," said Dr Dry.

"We have 2 new PhD students working on comparisons of conventional irrigation versus PRD using 2 water qualities, River Murray water and bore water," said Dr Dry. "The bore water is extremely saline, and we've got 2 amounts of irrigation so we have 8 treatments in that experiment."

"One student is going to be looking at the movement of salt in the salt profile; the accumulation of salt, its effect on the soil structure and also the accumulation of salt within the vine itself, both in the leaves and the fruit." Said Dr Dry. "The other will be looking not so much at the salinity but at the fruit quality," he said.

Australia is not the only country to suffer from saline soils, and availability of fresh water is a growing problem worldwide. Hence the large number of PhD students who come to study at the Waite campus."

"We are now seeing that other countries have the same sorts of problems," said Dr Dry. "PRD is a whole new growth industry. We have all these PhD students in South Australia who are looking at aspects of PRD; I think there are 5 or 6 now who started this year."

Those students will eventually return home, to grow a greater diversity of crops in an increasing number of countries. PRD is being trialled on tomatoes in Europe, raspberries in Scotland, citrus and grapes in the Mediterranean Basin and grapes in Argentina and California.

It sounds like a case study in innovation and the commercialisation of pure research; also areas that the federal government is being urged to encourage. And a test case it may prove to be, but not necessarily to the benefit of the researchers. Brilliant ideas do not always translate to commercial rewards.

"We have looked at that," said Dr Dry. "You can't patent this idea."

"You are right, I think its a perfect example of innovation, and obviously it would be nice to get more funding to explore other aspects of this," said Dr Dry. "We are getting some funding for PhD students so we shouldn't be complaining too much, but I'm about to write another application, and I'm not quite sure, with these initiatives that you mention, how we're going to get money out of them. We're waiting for someone to tell us the cheque is in the mail."

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