Irrigation can be reduced by 50% of the current irrigation application, with little effect on overall sap flow, or plant water use during the cropping season for Grapes. However, vines exhibit to use water, for two months after harvest and this calls for further research in understanding the physiological benefits of watering the vines after harvest for the next season cropping.
Experimental testing of full and half irrigation treatment between bud burst and harvest evidently showed that the sap flow from the fully irrigated treatment was higher by 15%, for the time of the day, between 10am and 2pm. However, during the other time of the day, the sap flow values for both treatments were nearly similar. In addition, the total sap flow accumulated over the day showed that the difference between the two irrigation treatments became less apparent and the sap flow from full irrigation ranged between 2 and 8% that of the half irrigation treatment. To summarize, these preliminary results suggest the irrigation can be halved, with little effect on overall sap flow, or plant water use.
Further study to examine the impact of the same treatments on the yield and other physiological parameters of the Grape vine would give more information and better understanding, in relation to water application, growth, yield and management of Grape vines.
In order to answer the questions whether watering after harvest vines would have physiological significances and how long should we supply water, ICT international conducted an experiment to investigate the soil water use extent of the vines after harvest. Based on the data collected for Shiraz vines in 2015/16, the plant continued to use water for nearly for two months after harvest. The sap flow data showed that the average water use of the vines a week before harvest was 25L per plant per day (0.54ML for the 2.6ha block), for the period between 9th Feburary-16th February. The vines used nearly equal amount of water for the 7 days, with slight variations. Further, the hourly maximum rate was also the same, during this period, 1.4Lhr–1. Each day, the timing and distribution of the water use was similar and remained the same on 24 hrs, between 7am and 7am. Evidently, zero sap flow rate was not observed during this time. And this indicates vines were continually under stress to the extent that they were not able to fully rehydrate, they rather required to replenish more water reserves overnight.
The average water use per day is approx. 20L per plant (0.45 ML for the 2.6 ha block), for the 7-day period between March 1st to March 7th after harvest. This equates to an approximate 20% drop in water use from the week preceding harvest. In subsequent week, a further 20% drop to approx. 15L per day and this level is maintained for the following 3 weeks with a gradual, but steady decline when small variations in water use for rainfall is considered. At the end of April, as senescence sets in, water use declined by 50%, from 15L per day to 7.5 L per day. In early May, water use is again further dropped by 50%, to 3.5L per day, and then reduced to essentially zero in the second week of May. Finally reducing to approx. 0.4L per day last week of May to facilitate basic respiration of the vine during dormancy.
Sap flow measurements were taken using SFM1.