Indian runner ducks are used for snail and other pest control in the vineyard. (Photo: Supplied) 
To what extent does soil health contribute towards what’s in the glass? That’s the question a new study on the effect of soil health on viticulture has answered by proving that it is critical to plant and animal life, as well as the quality of wine.
The method — once condemned at agricultural schools because of the belief that grazing animals spread weeds, and cause compaction in the soil and other damage — defies old thinking by introducing ruminants in a controlled manner to the vineyard. Cattle, sheep and other ruminants not only keep the weeds under control, but they add organic matter, thereby helping sequestrate carbon in the soil.
Regenerative viticulture aims to restore soil health by mimicking natural processes. As soil life improves, so does its ability to absorb carbon dioxide from the atmosphere, making it a valuable tool in combating global warming. Accumulating organic carbon in vineyard soils improves their health, resilience to erosion, and drought resistance due to enhanced water retention.
Irish Dexter cattle in the Hartenberg vineyard. (Photo: Supplied)
Conducted by Stellenbosch University and Hartenberg Family Vineyards, the study has revealed that a single parcel of vineyard and vintage can produce two different wines, which are poles apart in terms of the aroma, chemistry and flavour, proven by differing levels of alcohol, residual sugar, tannin, pH, total acidity, anthocyanins (pigment) and extract.
Hartenberg, founded in 1692, was acquired in 1986 by the Mackenzie family, who introduced cattle to the property in 2017 to graze fallow lands and areas that required manual maintenance. They discovered that the ruminants significantly impact soil health. Through further research, their viticulturist, Wilhelm Joubert, discovered that grazing animals could also have a positive impact on plant and soil health within the vineyards if they were managed effectively.
In 2010, Joubert — deemed to be the regenerative viticulture pioneer in South Africa — first introduced cover crops to capture nitrogen from the air and improve soil structure and biomass.
Joubert, who had an epiphany after reading Allan Savory’s book Holistic Management, says once they introduced high-density grazing, they started to see nature responding in a way that was hard to believe. They realised that if it works in the fallow lands and pastures, it must work in the vineyards if they apply the same principles of regenerative viticulture.
Early tests conducted after introducing animals to the vineyards demonstrated positive results already within the first season, as the combined effects of the cattle’s treading hooves, grazing habits, saliva, manure, and urine improved soil health.
That discovery set the farm on a course to regenerative agriculture, which has proven to improve the general health and well-being of the property.
Ankole keep the weeds trimmed at Hartenberg. (Photo: Georgina Crouth)
Regenerative agriculture is a farming system that focuses on improving soil health, biodiversity, and ecosystem function. It aims to restore and maintain the health of the land, rather than simply extracting resources. Its key principles include building and maintaining healthy soil, promoting biodiversity, managing water resources sustainably, mitigating climate change, and creating resilient farming systems.
By adopting regenerative practices, farmers can improve their yields, reduce their reliance on synthetic inputs, and contribute to a more sustainable food system.
Ruminants are an essential component of regenerative agriculture.
The core principle of regenerative viticulture, which collaborates with nature, rather than fights against it, is to enhance land productivity and biodiversity on wine farms. A crucial aspect of this approach is restoring soil health and fertility by increasing organic matter and closing the carbon cycle through harmonious farming practices. Cover crops, which are hardy plants, play a vital role in this. By annually rotating and sowing various cover crop species, farmers can add specific nutrients to the soil.
Hartenberg has been pesticide-free since the early 2000s, relying on biological control methods, one of which is the use of ladybirds to combat leafroll virus, which is transmitted by female mealybugs. It has also introduced indigenous wasps to control mealybugs, with the result that all vineyards under the age of 18 remain virus-free, which is a significant achievement compared to industry standards.
A duiker in the Hartenberg vineyard. (Photo: Supplied)
The farm has also discontinued the use of rodent bait stations, instead installing 15 nesting boxes for barn owls for natural control.
Another more recent introduction is Indian runner ducks (inspired by Vergenoegd Löw Wine Estate) to control snails and other bugs in the vineyard.
The farm is renowned for its sheep and temperamental long-horned Ankole (brought to the property after the Mackenzies travelled to Uganda), Dexter (a placid Irish small cattle breed) and indigenous Nguni cattle.
Biodiversity has flourished on the farm with the introduction of various new fauna and flora, including nine previously undocumented mushroom species, numerous new grass species, and dung beetles that have not been seen in the region in decades.
In taking soil samples and using nematodes (microscopic roundworms that feed on plant roots) as bio-indicators of soil health, Joubert found that after the animals were introduced, the nematode diversity increased, the ratio of non-harmful to harmful nematodes improved, and no single group of nematodes dominated.
Regenerative viticulture is not simply about putting ruminants in the vineyard to roam. Joubert says, “Certain rules, practical stuff, needs to happen. It needs to be managed, otherwise you won’t get the results you want. It’s a tool that we use.”
Hartenberg cellarmaster Carl Schultz. (Photo: Supplied)
Winemaker Carl Schultz, a Cape Winemakers Guild member who has been with Hartenberg for 31 harvests, says in the first year since they brought animals into the vineyard, they were impressed by the rapid improvement in the measured soil biodiversity and health.
“The question was: What happens to the grapes from vineyards where cattle graze as opposed to the vineyard without cattle?”
Two years ago, Schultz and Joubert divided a single vineyard parcel into two — a control group and a densely grazed portion — and replicated the process last year in September 2023.
Once harvested, the grapes were handled separately in the cellar, although the winemaking process was the same.
They found that while the control block produced slightly more bunches per vine, the ruminant parcel yielded a noticeably different wine.
“In the ruminant portion, there were slightly fewer bunches per vine and the berries were smaller too. This means production per hectare could be marginally less, but smaller berries naturally result in a greater concentration of fruit,” Schultz explained.
They also achieved physiological ripeness at lower sugar levels.
“If I can achieve physiological ripeness at a Balling (test for sugar content) or two lower, the resultant alcohol will also be lower,” said Joubert.
The grazed portion’s wine is characterised by elegance, freshness, and red fruit profile, while the control wine is heavier, more structured, and may exhibit hints of darker berry fruits and riper aromas.
Indian runner ducks are used for snail and other pest control in the vineyard. (Photo: Supplied)
Regenerative viticulture is viable and cheaper, Schultz says. “Our farmers are unsubsidised — the only sector in the Western world. They’re completely on their own. To farm in this way will save us billions of rands.”
Hartenberg is on track to be the first in South Africa to achieve accreditation from Land to Market — the world’s first regenerative verification for meat, dairy, wool and leather.
Later this year, the results of a multi-year study are expected to be released which is poised to revolutionise our understanding of regenerative viticulture. Led by Dr Cristina Lazcano in the US and funded by various organisations, including Jackson Family Wines, the USDA, and the California Department of Food and Agriculture, the study is examining 12 West Coast vineyards from Oregon to Santa Barbara over five years. Researchers are analysing soil samples from these vineyards to better understand the response of soil microbial life to different combinations of regenerative practices.
While initially focused on soil carbon sequestration, the study’s scope has expanded to include various aspects of soil health, such as nutrient cycling, microbial activity, and water retention. Researchers are also investigating the relationship between carbon cycling indicators and microbial diversity.
The study is a unique opportunity to explore the effects of different combinations of regenerative practices on soil health. By examining various factors like soil type, climate, and specific practices, researchers hope to gain valuable insights into optimising soil health and sustainability in viticulture.
One of the key areas of focus is the soil microbiome: Scientists are increasingly recognising the importance of understanding the below-ground ecosystem, as it plays a crucial role in regulating essential processes like water and carbon cycling. DM