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This is an article written about PRD mostly in grapes
Partial rootzone drying (PRD) is an irrigation technique which we have been developing here in Australia. All the initial work was done with grapevine, although we are also working on its implementation in a number of other crops. The work on developing PRD commenced in 1992 when experiments at the CSIRO and in overseas laboratories showed that, if only part of the root system dried and the remaining roots were kept well watered, chemical signals produced in the drying roots reduced stomatal aperture. The principal chemical signal appears to be the plant hormone abscisic acid (ABA). At the same time the fully hydrated roots maintained a favourable water status throughout the aerial parts of the plant. In other words, it was possible to separate the biochemical responses to water deficit from the physical effects of reduced water availability. In addition to reduced stomatal conductance it was noted that shoot extension was also inhibited. A surprising finding was that if one part of the root system remained dry for an extended period, the effect was temporary, and stomatal conductance, photosynthesis and growth returned to pre-treatment levels within a few weeks. Armed with knowledge about the transient nature of the effect and the likely role of ABA it was possible to devise irrigation schedules which keep one part of the root system, or the other, always in a state of drying so as to maximise the production of ABA and hence its inhibitory effects on transpiration and growth. In practice this means applying water to one side of the plant for about two weeks and then changing to the other side. During the two week irrigation cycle it is important that water is supplied with sufficient frequency to the wet side to prevent excessive soil drying and to meet the needs of the whole plant. If all of the plant's roots become dry, a water deficit will be induced and this may impact negatively on crop yield. Our experiments have also shown that the dry roots are maintained in a healthy condition by water supplied to them from the wet roots. In grapevines subjected to PRD there is a consistent reduction in vegetative growth as measured by pruning weight. Another measure of canopy density is the amount of light reaching the bunch zone and this figure is consistently higher in PRD than in control vines and it is likely that this can influence some fruit quality parameters, although some of our recent experiments suggest that PRD may be specifically influencing some of the volatile flavour compounds produced by grapes. Crop yield if not significantly affected by PRD, but because water requirement is reduced due to partial stomatal closure and reduced canopy area, water use efficiency is increased. Incidentally, we have never claimed that yields are increased by PRD. This might be asking a bit much. Here are a few recent references which may be of interest. Loveys, B.R., Dry, P.R., Stoll. M. and McCarthy, M.G. (2000). Using plant physiology to improve the water use efficiency of horticultural crops. Acta Horticulturae 537, 187-199 Stoll, M., Loveys, B. R. and Dry P.R. (2000) Hormonal changes induced by partial rootzone drying of irrigated grapevine Journal of Experimental Botany, 51, 1627 -1634 Dry, P.R., Loveys, B.R., Stoll, M., Stewart, D., and McCarthy, M.G. (2000) Partial rootzone drying - an update. Australian Grapegrower and Winemaker 438, 35-39 Loveys, B., Stoll, M, Dry, P. and McCarthy, M. (1998) Partial rootzone drying stimulates stress responses in grapevine to improve water use efficiency while maintaining crop yield and quality Australian Grapegrower and Winemaker, Technical issue. 414, 108-114 Dr Brian Loveys Phone (08)83038615 |
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