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The science of matching crop irrigation to actual water usage

RD&A News | August 2021
13 Aug 2021
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How much irrigation is enough? It’s an age-old question for growers, and one a recently-completed Wine Australia Incubator Initiative project hopes to provide the answer to.

“In today’s increasingly water-scarce environment, optimising irrigation scheduling is critical to conserving fresh water, controlling vine size and achieving yield targets,” said principal investigator, Dr Vinay Pagay, senior lecturer in viticulture and vineyard engineering at the University of Adelaide.

“A mismatch between irrigation applications and actual crop water use is one of key reasons for low water use efficiency in many vineyards.”

Dr Pagay and his team undertook a project to investigate and quantify the seasonal water requirements of productive Chardonnay and Shiraz grapevines in the South Australian Riverland region over the 2019–20 and 2020–21 growing seasons.

The team used three approaches to quantify water requirements: whole canopy gas exchange in which canopy transpiration, dry matter production and water use efficiency were quantified; crop evapotranspiration (ET); and sap flow sensors. The measurements were taken at flowering, bunch closure, véraison, harvest, and post-harvest on a 24-hour basis.

The team found canopy daily water use for well-irrigated vines ranged from 26–39 L per vine in Chardonnay and 24–33 L in Shiraz in 2020–21. Interestingly, higher values were observed in Chardonnay early in the season and Shiraz late in the season.

Post-harvest water use dropped by 42 per cent compared to harvest in Shiraz and by 28 per cent in Chardonnay. Daily dry matter production exceeded 200 g per vine at véraison with correspondingly highest seasonal canopy water use efficiencies observed during this time. Both ET and sap flow estimates of canopy transpiration were lower than whole-canopy estimates.

Not surprisingly, canopy water use increased by up to 14 per cent during heatwaves. However, Dr Pagay noted the additional irrigation applied during the heatwave period was adequate to support this increased transpiration rate.

Dr Pagay said the project was important because, for the first time, it provided quantitative estimates of grapevine water use based on both direct and indirect measurements.

“These estimates are critically important for growers seeking to optimise their irrigation practices,” Dr Pagay said.

He said such optimisation increased water use efficiencies – and thereby water savings – without yield and grape quality penalties.

The end result? Greater economic return for the grower.

“Quantitative information of grapevine water use throughout the season allows growers to optimise irrigation applications while achieving specific targets of yield or grape composition,” Dr Pagay said.

He said timing of irrigation was a key element in achieving water efficiencies.

“Water uptake rates are the highest early in the day, so irrigation should be applied overnight if possible to ensure maximum soil moisture availability to the vine and to avoid transient vine water stress.”

Growers seeking to increase water retention in the rootzone could also consider vineyard floor practices including the use of undervine cover crops, mulches and biochar.

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This content is restricted to wine exporters and levy-payers. Some reports are available for purchase to non-levy payers/exporters.