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Enabling better global research outcomes in soil, plant & environmental monitoring.

Have you prepared your vines for next season yet?

By Alec Downey
Head of Plant Science Applications & Research
ICT International

 

Much is said about the need for watering vines after harvest, but until this point no physiological data has been measured to support either of the two presiding practices: a) turn the water off after harvest or b) continue to water after harvest.

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Figure 1. SFM1 Sap Flow Meter installed on a grape vine stem. (Photo: A. Downey)

Whilst it makes intuitive sense to water vines after harvest to assist them to setup carbohydrate reserves for the following season, how much water and for how long to water after harvest are questions that need answers.

Based upon the empirical sap flow water use data collected for Shiraz at Wemen, Victoria, in the 2015/16 season it would seem that the vines continued to use water for approximately two months post-harvest. A simple analysis of both the rate of reduction in water use and the responsiveness of the vine to irrigation over these two months is shown below. The use of Sap Flow Meters provides a substantial basis for viticulturalists or growers to build a protocol for establishing post-harvest irrigation guidelines for their own vineyards and ensure that they prepare their vines for next season before the current season is finished.

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Figure 2. increased sap flow or vine water use following post-harvest irrigation showing physiological activity for 2 months after harvest that occurred on March 22nd.

Week Preceding Harvest

The average water use per day is approx. 25 L per plant (0.54 ML for the 2.6 ha block), for the 7 days between February 9th to February 15th. An interpretation of the integrated Daily Water Use graph shows that vines were using a similar amount of water each day with little to no variation between days. Further evaluation of the Hourly Water Use graph confirms this interpretation, with each day’s midday maximum hourly water use rate being at or slightly above 1.4 L/hr.

Each day the timing and distribution of the water use is similar spanning a full 24 hours between 7:00am and 7:00am, and never reaching a zero-sap flow rate at night. This would indicate that the vines were continually under a degree of water stress as they are unable to fully rehydrate quickly each night, rather needing to continue to replenish water reserves overnight.

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Figure 3. Effect of berries or crop load on vine sap flow or water use

Week proceeding harvest

The average water use per day is approx. 20 L per plant (0.45 ML for the 2.6 ha block), for the 7-day period between
March 1st to March 7th. This equates to an approximate 20% drop in water use from the week preceding harvest.

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Figure 4. Effect of harvest on vine sap flow or water use

The subsequent week (Figure 2.) shows a further 20% drop to approx. 15 L 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 is halved from 15 L per day to 7.5 L per day. In early May water use is halved again dropping down to 3.5 L per day, and then reduces 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.

Discussion

Sap flow data immediately provides growers with valuable information about the continued use of water by the vine post-harvest and leading up to senescence. Whilst Sap Flow Meters can record the effect of irrigation on the vines post-harvest, further research is required to demonstrate the impact of this water stress has on the subsequent season or season’s yield. Such research would benchmark post-harvest irrigation practices. This would provide recommendations for growers in terms of the optimum level of irrigation during this phase and the length of irrigation required between harvest and senescence.

An SFM1 Sap Flow Meter can be installed by any grower, even without having ever used the equipment before. A Sap Flow Meter will provide 10-minute temporal resolution vine water use data all day, and all night throughout the entirety of the season.

They have proven to be extremely robust and reliable in the field with continuous operation for the full season without issue. Installation of a Sap Flow Meter requires significantly less time, effort, physical disturbance within the vineyard, and technical training than installing a capacitance soil moisture probe.

The SFM1 Sap Flow Meters are manufactured and stocked in Australia and can be purchased by growers either directly from ICT or authorised distributors.

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