The Dirty Truth Soil Health Plays In Wine

Walking through Joseph Cattin’s Le Clos Madelon Alsatian vineyard, it’s hard to imagine it once being a World War I battleground.

The fully covered ground is soft, sponge-like under foot. Chickens forage freely through the vineyard. Indiscriminately extracted plugs of earth reveals moist, living soil teeming with microbial life.

By stark contrast, an adjoining vineyard contains bare, dry, cracked earth. A monocrop of vines growing in perceptively dead soil.

Terroir, a wine’s “somewhereness”, includes tradition, climate, terrain, and soil. Until recently, soil equals type, such as limestone, calcareous, or volcanic.

Modern scientific advancements expand beyond soil type, revealing a vast microbial world exists within living soil. Research indicates this world is vital in producing high quality agricultural products, like wine, and, when properly managed, offers potential in combating climate change. This world, known as soil biome, is small but mighty.

Underground Ecosystem

Utilizing native flora as ground cover between the vines, as well as abstaining from synthetic herbicides and pesticides, Le Clos Madelon vineyard is rich with organic nutrients and water retention, both vital for a healthy vineyard.

What’s visible above ground feeds the invisible community below ground. As single-cell organism, alone soil microbes cannot accomplish much. Therefore, they live in communities, or according to Anne Biklé, biologist and co-author of The Hidden Half of Nature: The Microbial Roots of Life and Health, guilds.

A stationary vine has little protection against pathogens. However, through an evolutionary quid pro quo the vine and the microbes live in a mutually beneficial relationship.

“Because of their mobility, mycorrhizal fungi, aka fetching fungi, and bacteria, aka nitrogen nabbers, acquire and deliver nutrients the plant otherwise cannot get a hold of,” says Biklé.

Conversely, through photosynthesis the vine turns CO₂ into microbial food in the form of exudates. The beneficial microorganisms stay close to the vine for their food, while simultaneously providing protection against pathogens. Furthermore, this exchange naturally sequesters carbon dioxide from the atmosphere and stores it in the soil.

“It’s a Star Trek type forcefield. This is what the bacteria bodyguard do – they give the pathogen absolutely no place to get a toe-hold on the vine,” says Biklé.

Stressors to this delicate ecosystem—heat, drought, synthetic chemicals, tilling the soil, and erosion—prove harmful to the vine, forcing it to choose between producing less fruit, lower quality fruit, or death.

A New Horizon

Soil is divided into six horizons, like the layers of flora in a mountain ecosystem, only inversed.

The uppermost layer of the earth’s surface is known as topsoil. Science believes it to host the highest level of organic matter and concentration of active microorganisms. It is where water is absorbed and where sunlight aids in the plant’s growth.

Ninety-five percent of the world’s food is grown in this layer, but in the last 150 years, half the earth’s topsoil has been lost. One culprit is tilling—digging into and turning over the first six to ten inches of soil.

Natural order dictates the forest layers of alpine mountains and soil horizons. Tilling the soil pulverizes the delicate microbial community, adding stress such as loss of water absorption, opening the door to lurking pathogens, and potentially jeopardizing the quality of fruit and life of the vine.

Modern Science Meets Ancient Farming Practices

“The foundation for a lot of concern about soil life from my end as a geologist has been the amount that has been degraded over time. The fertility of the soil has been impacted by the long-term way we have farmed. Winemaking is not immune to this,” says David R. Montgomery, professor of geomorphology at the University of Washington and author of Growing a Revolution: Bringing Our Soil Back to Life.

Scientific understanding of the soil biome is in its infancy. But what is known points to old-world solutions for maintaining or rebuilding healthy soil.

First, keep soil disturbance to a minimum, avoid tilling. Second, “maintain a diversity of plants and constant cover crops—don’t have bare earth—keeping exudates flowing, introducing carbon and organic matter into the soil which helps feed the microbes and helps prevent erosion,” says Montgomery.

Healthy Soil, High Quality Wine

“Some of the worst soil Anne and I have seen in the last few years was on a vineyard in Sonoma County. The soil was beaten to hell between the vines,” shares Montgomery.

He and Biklé were conducting research at a nearby farm when they observed the vineyard. “The soil between the vine rows was heavily tilled and looked like moon powder,” he adds.

For these two scientists, dry, dusty vineyard soil is counterintuitive to what is needed in drought-stricken northern California. They recommend moist, fertile, undisturbed soil blanketed with cover crop year-round for maximum water retention.

Wine Is Made In The Vineyard

In my research winemakers routinely proclaim: “Wine is made in the vineyard.” I cannot help but wonder about the wine quality produced from that Sonoma vineyard.

When visiting a vineyard, pay close attention to the condition of the soil. Does it feel like walking on a sponge or cement? Is the ground between the vines and rows bare, or covered with plants? Is the soil cracked, dry, baren or rich and moist? Is the vineyard a monocrop of vines or biodiverse? Does its appearance suggest high-quality, chemical-free grapes? Ask the winemaker or viticulturalist about farming practices and philosophy. Then ask yourself, what type of vineyard practices matter in the wine you consume.

The good news is dedication to right practices and patience can transform a “moon powder” vineyard into fertile, living soil brimming with microbial life producing high quality fruit, while also sequestering carbon from the atmosphere.

“Some of the best wines we have enjoyed has been from vineyards where they have restored healthy, fertile soil,” says Montgomery. “Turning mediocre wine into stellar wine.”