By choosing the right cultivars and adapting their irrigation regimes in young vineyards, winegrowers may mitigate the expected effect of climate change in coming years. This is according to Dr Hanlé Theron, who recently obtained her doctorate in viticulture from Stellenbosch University.
She studied under the supervision of Dr Kobus Hunter at the Agricultural Research Council (ARC) Infruitec-Nietvoorbij in Stellenbosch.
"Recent research indicates that the total area where wine grapes can be grown in South Africa in future may quite possibly shrink as a result of climate change. The wine industry is an important part of the South African economy, and therefore it is important to do research that can help the industry to alleviate the impact of climate change," explains Dr Theron, a lecturer at the Department of Agriculture at the Cape Peninsula University of Technology.
It is expected that wine grape production will in particular be affected by rising levels of atmospheric CO2, higher average temperatures and a decrease in rainfall.
"Most of our winegrowing areas already experience lower rainfall than in the past and this is already not enough to provide in the needs of the vineyards," she says.
"It is an expensive exercise to establish a vineyard and farmers want it to grow well and get into full production as soon as possible," continues Dr Theron. "The initial growth of a newly planted vineyard has a direct effect on the long-term vineyard performance and lifespan of the block. Young vine growth is extremely sensitive to environmental conditions and it is expected that future climatic conditions will influence vegetative growth in the first growing season."
She says that viticulturalists have already studied the effect of elevated CO2 levels and temperature on the growth of vines for many decades. Dr Theron contributed to existing knowledge by studying the overall effect of a combination of environmental factors (CO2, temperature and water provision) on the growth and functioning of young vines. In her research, Dr Theron focussed on the first few months after young Merlot and Shiraz vines are planted.
Shiraz was chosen because it has thus far done well in warm, drier wine production regions, while Merlot is considered more sensitive to extreme conditions, especially water stress and high temperatures.
To do this, she potted a total of 1296 Shiraz (SH 470) and 864 Merlot (MO 348) scions with 101-14 Mgt as rootstock (generally seen as sensitive to water stress) and let it grow in a glasshouse for twelve weeks in glasshouses situated at ARC-Nietvoorbij. Among other things, she closely studied the physiological activity of the young vines, their initial growth, the extent to which they take up and transport minerals and their production and internal translocation of metabolites.
Young vines exposed to higher CO2 levels and limited water were still able to photosynthesise well and used the available water and nitrogen efficiently - as long as the water deficit was not excessively severe.
"The detrimental effect of the water deficit on the physiological activity of the plants was countered to some extent by elevated CO2 levels," she explains.
This may be good news in terms of climate change, with its expected rising CO2 levels and declining amount of water available for irrigation.
Dr Theron also found that young Merlot vines were more sensitive to water deficit than young Shiraz vines. In contrast, Merlot responded better to elevated CO2 levels than Shiraz.
"Therefore, we cannot expect that all scion and rootstock cultivars will in all cases respond the same to climate change," she reasons.
According to Dr Theron, with smart choices in terms of scions and rootstock cultivars, winegrowers could reduce the effect of climate change on their farming activities and especially on newly planted vineyards.
She also offers the following advice:
- Vineyard soils must be prepared as deeply as possible. In this way, plant roots can penetrate as deeply into the subsoils in search of moisture. It will help to buffer vineyards in times of drought.
- Irrigation practices must be adapted to promote deeper and wider root growth and denser root distribution in young vines. This can be done by scheduling irrigation cycles further apart and then using greater volumes of water per irrigation.
- It is worthwhile to re-evaluate cultivation practices, especially in young vineyards. It would, for example, be better if cover crops did not unnecessarily compete with growing vines for water and nutrients.
- In future, farmers will have to reconsider the amount of nutrients they currently typically apply to especially young vines in newly planted vineyards. A vine will, for instance, only take up a certain amount of nitrogen from the soil while the remainder will then leach out, possibly to pollute water sources.
