Grounded Grapegrowing


Celebrating the Soil That Gives Us Wine

December 2011
by Glenn McGourty
With a sigh of relief, most of us are enjoying the end of another harvest following the challenges of a late start, untimely rain and all the other issues that make winegrowing both fun and frustrating. It is time to reflect, pay the bills, put away the tools, clean up the debris and catch our breath before we get out our pruning shears and another season begins. We should find a moment to celebrate, too, and reflect on all that makes winegrowing possible. What most of us don’t think about very much is the miraculous substance beneath our vines and our feet: the soil.

Honor thy soil profile
The Earth and soil itself doesn’t always get the honor and respect that it deserves. My father, who was born in Ireland, wrote a brief autobiography toward the end of his life. He was not a touchy-feely kind of guy, yet he wrote that “he came from the soil” on the border of Cavan and Leitrim. My father understood his connection with that spot on the planet, even though he rarely talked about his Irish ancestry (unfortunately, his childhood home in New York had a much more profound influence on his personality!) And it was true—all of the elements that made up his young body came from the food, water and air on a small patch of rocky ground that my grandfather tended. I visited his birthplace recently with my daughter Carolyn. The ruined cottage was in a lovely place situated on rolling hills covered with grass and sheep, while heather, blue bells and irises grew in the hedgerows. Ultimately the little farm with its rocky, shallow soil couldn’t feed my grandfather’s young family, so they packed up and emigrated to North America.

In those days, most people in the world were locavores by default, so their principal mineral stream was right off their local real estate. Our modern supermarkets, with their vast arrays of numerous products available any season for very reasonable prices, have changed all that. Yet wine remains one of the few things that can be treasured for its origin and the soil from which it came.

Soil and the cosmos
Soil does have an extraordinary cosmic connection in that its origins are outside this solar system. Our sun can only generate hydrogen and helium, which leaves about 90 other elements that have their origins from the cosmos. We are literally stardust, as Joni Mitchell and William Bryant Logan (author of “Dirt: The Ecstatic Skin of the Earth”) have asserted. The Earth coalesced from blown apart stars some 4 billion years ago, and it has taken a long time for our ecosystem to evolve and thrive. You are made up of elements that have been recycled many times. Soil is the substrate on which life itself is converted from the inanimate and dark to the living when light and warmth are provided. Our ancestors were in awe of this, and they celebrated the cycle of life emerging and returning from the earth in spring, flourishing in the summer and then retreating once again into darkness and cold.

Soil, a key ingredient of terroir
As someone trained in soil science, I am happy that I work with an industry that recognizes the soil as an important influence on the quality and flavor of wine. As winegrowers, we often choose places to plant our vines that other agriculturists have no interest in. Soil can be a naturally regulating system for vine balance and fruit quality. We cherish the locations where the climate is right, the vines grow enough to ripen modest amounts of fruit and the fruit ripens without stress producing balanced wines that need little intervention on their way to the bottle. Places like the Cote d’Or in Burgundy (a calcareous, rocky slope in a sea of clay), the gravelly soils of Bordeaux (low-fertility but deep gravel coated with clay), Mendocino’s Red Vine soils (weathered sand stones that are low fertility, but friable with good water-holding capacity) and New Zealand’s Hawkes Bay Gimlet gravels (gravelly and deep like Bordeaux, but not particularly fertile) are examples of soils that help self-regulate the vines to produce superior fruit and world-class wines. Planted to the right varieties, tended by knowledgeable winegrowers and processed by caring winemakers, these spots create the kind of wines that we treasure and look forward to drinking year after year.

Every place is different
In much of coastal California, there is an incredible array of soils and climates that allow considerable latitude in what we choose to grow. Presently, I am working on a project to identify the top 10 viticultural soils of Mendocino County. We will use this information as both a marketing tool and a planning tool (since our county planning department tends to protect only Class 1 soils, of which we have very little in the county.) We have used GIS soils maps to determine which soils have the most vineyard area planted on them. Working with soil scientists from the Natural Resource Conservation Service, we are excavating down 6 feet and photographing the soil profile, verifying that it is indeed the soil that it is supposed to be (soil mapping isn’t an exact science.) This information will be added to the Mendocino Winegrape and Wine Commission’s website. Growers can advertise fruit that they have for sale and, if requested, their vineyard will be linked to soil descriptions.

We are working in a relatively small geographic area in the Upper Russian River Watershed to conserve time and money. The diversity of what is below the surface of the soil is striking. In some of these sites, the soil has been carried in by the river and dropped in place. Since the valley is relatively narrow, the river has meandered numerous times. Soils literally change every 100 feet or so depending on where you are in this part of the Russian River flood plain. These soils are quite young—some of them so recently deposited that there are not distinct soil horizons but mixes of sand, clay and gravel. Others show definite profile layers of sand, gravel and loam. Still others are quite uniform, loamy and deep, and are superb agricultural soils (these soils tend to be in the backwater areas where fine textured particles are deposited.) Trying to plant a large vineyard across this landscape becomes a challenge if you want uniform growth. In general, white varieties are well suited to these locations, and that is why Chardonnay and Sauvignon Blanc dominate the vineyard plantings in our alluvial soils along the Russian River.

As we move up the slope from the flood plain, the soils and the landscape become much ol der. The alluvial fans coming down from the mouth of the many canyons can also have very mixed soils, somewhat similar to the flood plain, but are often older than soils lower on the landscape. On the face of the slopes and ridges, the soils here usually have more well-defined horizons, as they were formed in place as uplifted rocks weathered (mostly sandstones, but also shale and other Franciscan rock associations.) If not too steeply sloped or unstable, they make some of our best locations for red varieties. Limited water-holding capacity and fertility control vine growth and help to create fruit that is intense in flavor and color. These soils need some real thought to plant (ease and safety of farming), manage (variability of fertility and available water) and protect the soil from erosion.

Protecting a resource, making an investment
I am heartened that the winegrowing industry has made great strides in valuing soils as an important part of their production package. Most growers take the time to protect their soil from erosion by planting cover crops, hardening water conveyances and practicing stewardship that will sustain the soil resource. Additionally, many are learning how to manage soil’s organic matter, which has tremendous potential to improve nutrient availability, improve water infiltration and water holding capacity. Building soil organic matter is also a fabulous way to recycle carbon dioxide from the atmosphere. The soil has the potential to hold five times as much carbon as the atmosphere, and since we have depleted so much soil carbon during the past 100 years (along with the top soil itself), there is plenty of capacity to regenerate soil carbon through the use of cover crops and compost.

In our study looking at some of the vineyard soils, one stood out. It had been conventionally managed for at least 80 years, and while the soil had many positive attributes, years of conventional tillage had taken its toll. It was rather hard and bricklike in the upper surfaces and surprisingly dry in the lower horizons. The soil scientist working with us commented that this vineyard could really benefit from humus-forming cover crops. Regardless, the vineyard still produces very nice Zinfandel, especially since it is dry farmed. But if cover crops and compost were applied, soil quality would improve and late-season stresses would be less. Quite possibly, yields would increase, too. At least in recent years, the grower has protected this site from erosion using strategic placement of straw and cover cropping in the areas most prone to erosion.

Finally, the Regional Water Quality Control Boards are looking at non-point source pollution all over the state of California. Movement of sediment off your vineyard site won’t be tolerated, and increasingly, water quality planning is going to be a reality for most winegrowing operations. The good news is that the techniques to prevent erosion and protect water quality are fairly well understood. Technical support from UC Cooperative Extension and the USDA Natural Resource Conservation Service are easily accessible to address many water quality issues.

I hope you find time to celebrate the end of one harvest and the beginning of the next farming cycle. Raise a glass of wine with your friends, and don’t be afraid to thank the soil that helps to bring everything to life. Soil is truly the miracle of our universe, and we wouldn’t be here without it. We are stardust, and so is our soil.

Glenn McGourty is the UC Cooperative Extension winegrowing and plant science advisor for Lake and Mendocino counties. He also tends a 1-acre vineyard of the aromatic Italian winegrape variety Arneis on his property along the Russian River near Ukiah, Calif.

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