Innovations in irrigation – such as the partial root zone drying technique – are helping rural Australia create efficiencies and generate remarkable results.
One of the most important and encouraging innovations in irrigation has been the development of the partial root zone drying technique. Dr Peter Dry, working with Dr Brian Loveys from CSIRO, started working on what is now known as partial root zone drying as part of his PhD at the University of Adelaide in 1991. Fifteen years later it is a fully-fledged irrigation method and has been tested on numerous crops both in Australia and in Europe with remarkable results.
What is partial root zone drying?
It is called partial root zone drying (PRD) because, at any one time, only half the root zone is in a drying state. Using two rows of drip-line irrigation, instead of the usual one, one part of the root system side of the plant is kept wet whilst the other side is dried. The grower irrigates through one line at a time, two or three times a week for a couple of weeks (whatever local conditions dictate), then the same on the other line. That pattern continues throughout the season. The switching of the wetting/drying from one side to the other might be as short as three days in midsummer in some situations.
The drying roots send a hormonal message to the rest of the plant that it is deprived of water, so the leaf stomata close, preventing excess moisture loss and reducing excessive shoot growth. In other words the plant is “tricked” into believing it’s stressed and the end result is a plant which uses the water it has far more efficiently than it otherwise would. This allows up to 50% reductions in the total amount of water needed to irrigate many crops.
Peter Dry describes how this research began.“We were conducting experiments of plant growth under different conditions and with different amounts of hydration,” says Dry. “One weekend we left by mistake some plants that had only been watered from one side. When we got back the plants had continued to grow normally even though one side of the plant was completely dry. So we devised a series of experiments to find out what was occurring.
"In experiments with potted vines with roots split into two separated systems we alternately wetted or dried out each side with about two weekly intervals. Initially experimenting on vines, we learned that by alternating the withholding water from half of the root system, photosynthesis and growth were reduced. But the key insight these experiments confirmed was that the effect was transient only and, for this reason, the drying had to be alternated from one part of the root system to the other in order to maintain the signals.
“Despite the fact that part of the root system remained dry, photosynthesis and growth returned to pre-treatment levels within a few weeks. But importantly, excessive shoot growth rates and stomata conductance was reduced permanently, thus reducing water losses from the plant. This was the key insight. What seemed to be happening is that the dry side of the plant was sending signals to the rest of the plant that it was water stressed leading to the stomata partly closing”.
With these novel insights, Dry, Loveys and their colleagues were able to devise novel irrigation schedules that use half as much water as needed previously.
Trials and tribulations
The first field trials were conducted in 1994 and the results were published in 1996 at the Australian Wine Industry Technology Conference. Since then many PhD students have studied this effect on numerous plants and crops at the University of Adelaide working with CSIRO. Dr Mike McCarthy of South Australian Research and Development Institute (SARDI), who has been involved with the PRD research since 1997, is working on ways to make this method as effective as possible when applied at commercial scale. In Australia and overseas there has been interest in this innovation. This Australian group of researchers and practitioners works with Lancaster University’s Professor Bill Davies, a plant scientist from the biology department, whose breakthrough work on root signals provided much of the impetus for the PRD research.
This partnership has helped to fast track further research and commercial uptake of the idea globally. The results from Australia and the partnership with researchers here have helped Bill Davies to build the consortium IRRISPLIT, funded by the European Commission. The consortium, made up of scientists from Cyprus, Turkey, Portugal and the UK, is now testing the irrigation system on olives, citrus fruits, tomatoes, aubergines, raspberries and cotton. On all crops tried to date similar results have been achieved using this method.
www.pi.csiro.au
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