Partial Rootzone Drying right? (if not ima look like a retard)
not sure if you've looked at this site or dont need info anymore but it may help.
Description
This project investigated the physiological responses of grapevine to deficit irrigation strategies including partial rootzone drying (PRD) and regulated deficit irrigation (RDI). The principle objectives of the project were to (1) establish if the response to partial rootzone drying (PRD) is as a consequence of irrigation amount or a unique vine physiological response to PRD; (2) to investigate the effect of limiting environmental conditions on vine responses to PRD and deficit irrigation; (3) to investigate the effect of PRD and deficit irrigation on berry metabolism and maturation; and (4) effect of PRD and deficit irrigation on vine water-use. The experiment used field-grown Shiraz grapevines in a commercial vineyard in the Strathbogie Ranges in north-eastern Victoria. The experiment ran from season 2001/2002 through to 2003/2004 in a medium vigour, warm climate vineyard, with soils of low water holding capacity. In the first two years of the experiment drip (DI) and PRD irrigation were applied at a single deficit rate (0.67 and 0.53 crop evapotranspiration; ETc), while in the third year both DI and PRD irrigation were applied at two rates, 0.9 ETc and 0.45 ETc. Season 2003/2004 was the main focus of the detailed investigation into the physiological response of the vines to PRD and deficit irrigation. This study has found the rate of irrigation, rather than the application of PRD, had a more significant effect on vine response in terms of viticultural parameters such as berry yield and vegetative growth. Measurements of stomatal conductance post-flowering illustrate that for most of the experiment all vines in the experiment were experiencing severe water stress. Application of PRD to vines resulted in a unique physiological response distinct from deficit irrigation; however the overall physiological responses of the vines were defined by the environmental conditions of the vineyard where the experiment occurred. Reduced
water availability, low to medium vigour vines, restricted root development and high evaporative demand were all factors in the vines response to PRD. Under these stressful conditions, while PRD did not maintain yield at deficit irrigation rates, it was responsible for significant physiological changes in the vine that could have long-term implications for yield stability. The application of PRD resulted in an improvement in plant water status and maintenance of leaf function as measured by photosynthesis (A), stomatal conductance (gs) and stem water potential (ΨS) throughout the season. When soil moisture was low, the greater resilience of these physiological parameters in the PRD treatments appeared to retard stress-induced senescence in severely stressed treatments. This may have implications for vine carbohydrate reserves in the long-term. PRD and deficit (0.45 ETc) irrigation treatments applied to these vines caused significant water stress, particularly post-veraison when fruit became a strong sink for photosynthate. Water stress created a source limiting condition within the vines that after veraison resulted in gas-exchange increasing in all leaves. Decline in photosynthesis associated with leaf position and leaf aging were only observed pre-veraison. This clearly illustrates that ripening berries, importing sugars and anthocyanin pre-cursors, become a significant sink post-veraison and are capable of increasing leaf photosynthesis at all leaf positions under source limiting conditions. It also highlights the stress these vines were under and why the physiological responses to PRD in this experiment were different from those in the initial PRD research. In this experiment, PRD at both irrigation rates improved plant water status and regulation of vine water loss. PRD did not lead to maintenance of yield, significant reductions in vegetative growth or improvements in water-use efficiency as was found in the
initial PRD experiments in grapevines. Application of both drip and PRD irrigation at deficit levels lead to significant decreases in yield and severe water stress in these vines. PRD increased vine stomatal sensitivity to water loss, which in turn leads to vines being able to maintain photosynthesis even when soil moisture was low. PRD encouraged extraction of soil water at deeper levels, which combined with increased stomatal sensitivity to water loss meant that the vines coped better with water deficits. The improvements in berry quality and composition found in other PRD experiments did not occur in this experiment. PRD did not affect yield compared to DI vines irrigated at the same level, however reducing irrigation amount significantly decreased yield, primarily through reduced bunch and berry number. Irrigation amount directly affected berry weight for most of the season, with deficit (0.45 ETc) irrigation vines reducing berry size until two weeks before harvest. PRD and deficit irrigation did not cause any difference in berry composition throughout ripening and at harvest. Deficit irrigation treatments (0.45 ETc) did not delay berry maturation compared to 0.9 ETc irrigated vines. The development of anthocyanins and phenolics was the same for all treatments and berry metabolism (sugar, acids, and anthocyanins) did not differ in response to irrigation treatments. Deficit irrigation reduced yield, but both PRD and deficit irrigation did not change berry metabolism and ripening. PRD improved plant water status and regulated total vine sap flow, which has important implications for vines in terms of maintaining photosynthetic capacity under water deficits. Ensuring that the vines cope better with stress directly affects leaf photosynthetic parameters and supply of sugars for ripening, carbohydrate reserves of vines and maintenance of yield and berry quality. Therefore, application of PRD in high stress environments may
have positive benefits on vine health and water-use, though the rate of irrigation application needs to be carefully monitored to ensure that vines are not too stressed and yield reductions occur.
