French soil scientists Claude and Lydia Bourguignon survey a 5-foot-deep soil pit at Madroña Vineyards in El Dorado County.
—Internationally known French soil scientists Claude and Lydia Bourguignon made their first visit to the Sierra Foothills this month, spending two days at Madroña Vineyards
in El Dorado County to evaluate soils and collect samples for lab analysis.
The Bourguignons founded the independent Laboratory for the Analysis of Soil Microbiology in 1990. Based near the city of Dijon, it is the only lab in France to offer physical, chemical and biological soil analysis. The pair worked as researchers for the French National Institute for Agricultural Research (INRA.) Although the lab works with clients growing any type of agricultural crop, a major part of the business is vineyard soil analysis, with an international list of clients that include Romanee Conti in Burgundy, Chateau de Beaucastel in Cotes du Rhone and Villa Maria in New Zealand. United States vineyard clients include Harlan Estate
in the Napa Valley and Bonny Doon
in the Central Coast. The lab has worked with a number of organic and Biodynamic farms and vineyards as well as conventional growers.
The Bourguignons have visited more than 30 countries collecting and analyzing soils and have built a database of 12,000 soils worldwide. In addition to specializing in soil microbiology and providing advice about how to maintain and improve soil health, the Bourguignons have a reputation for assessing vineyard soils for the purpose of matching the best grape varieties to the soil type.
The El Dorado-French connection
With an interest in working with different varieties, improving grape/wine quality and expanding the reputation of El Dorado County wines, Madroña’s vineyard manager and winemaker Paul Bush invited the Bourguignons to evaluate soils at Madroña. Bush and his wife Maggie, Madroña’s general manager, met the Bourguignons during a 2011 educational trip they took to the Cahors region in France to learn more about Malbec production, a variety they believe has great potential in El Dorado County. The Bourguignons recently developed their own Malbec vineyard near Cahors with their son Emmanuel, choosing the site based on soil analysis.
During a tasting of Malbecs from throughout the world, Claude Bourguignon tasted a Madroña vintage and told Bush, “This is from acidic soil.” Bush was impressed by the observation. He knew Madroña had acidic soil and felt it contributed to the quality of the winery’s Riesling and other estate wines. After he and Bourguignon talked in more detail, Bush realized a better understanding of Madroña’s soil could be a major benefit. Madroña has been focusing on understanding and improving vineyard health and is converting to organic vineyard practices, although there are no plans for certification.
Bush explained, “We grow 27 varieties on 70 acres, which represents both our strengths and our challenges. We’re always trying to learn more about our mountain vineyards here at 3,000 feet elevation. We have information on what we’ve grown for the past 40 years, but we’re still looking at the potential for other varieties and for what grows best at this location.”
The family-owned and operated Madroña Vineyards and winery (12,000 cases annual production) was founded in 1973 by Dick and Leslie Bush. The second-generation owners, Paul and Maggie, handle most of the day-to-day operations. Paul Bush’s brother David and his wife Sheila own and manage the Sumu-Kaw vineyard in nearby Pleasant Valley, about 5 miles south of Madroña’s original Camino vineyard, with 35 acres of estate vineyards planted in the early 1990s.
Soil pits for evaluation
Dick Bush planted the original Madroña (home) Vineyard adjacent to the winery in 1973. Both white and red varieties were planted on own-rooted vines, as nursery vines grafted onto rootstocks were not available from the nursery source at the time. Most of the original vines remain and continue to produce quality wine. Over the years, different varieties were grafted onto established rootstocks in some locations if they were deemed more site-appropriate or more commercially in demand.
A day prior to the Bourguignons’ arrival, four 5-foot-deep soil pits were dug at different locations, representing both strong and weak areas in the vineyard, and at the sites of four different varieties—Chardonnay, Riesling, Cabernet Franc and Zinfandel. Other varieties in the vineyard include Gewurztraminer, Merlot, Cabernet Sauvignon, Petite Sirah and Malbec.
At each soil pit, the Bourguignons measured the root depths of each indicator vine, made visual observations of soil layers, compaction, soil moisture and permeability. They also performed some basic field chemistry testing for pH and the presence of elements such as iron.
The general soil type at Madroña is weathered volcanic material including volcanic ash and rocks of more solid volcanic tuff that helps with drainage and permeability. Soil samples were taken at different depths, then bagged and labeled to undergo more detailed analysis at the lab in France. Citing the importance of soil biology, Claude Bourguignon explained, “Biological activity is important in the top soil and in deep soil because it gives food to the vine. If the soil does not have good biological activity, you need to add fertilizer. The problem is that fertilizers tend to be the same throughout the world, so the same fertilizer will tend to produce the same type of wine everywhere. If you can retain and develop your site-specific soil microbiology, then it provides a more site-specific terroir
for your wine.”
Generally, the Bourguignons thought the Madroña soils were in good co ndition, with good depth, drainage and biological content. Dick observed, “One reason we decided to plant here was because we knew the soils were good up here based on the vigor of the native vegetation and the quality of the fruit grown in the orchards in the area.” At the weakest area of the vineyard, where Cabernet Franc and Zinfandel vines are less healthy and productive, the Bourguignons discovered the soils had more sandy texture, low moisture content and poor water retention. It was suggested that this area have an individual soil moisture probe and its irrigation be managed differently than the rest of the vineyard. Mulching was also suggested to help with water retention and to improve topsoil nutrients in this weaker location.
The Bourguignons spent the following day at Madroña’s vineyards in Pleasant Valley, where five soil pits were dug—two in two different Zinfandel blocks, one in Nebbiolo, one in Marsanne and one in a block of seven Portuguese varieties used in the winery’s Port program. The vineyards here were planted in the 1990s, when soil cross-ripping was a common practice in vineyard development to break up soils and remove the roots from existing vegetation prior to vine planting. The soils here are also volcanic in origin—but less rocky, except for the Port block. The Bourguignons do not advocate soil ripping, and in this case they thought it disturbed too much of the biological soil components while also contributing to soil compaction in the vine root zone. They recommended planting cover crops of oats, vetch and rye to improve soil nutrition and permeability.
Paul Bush commented, “The wines off of these vineyards do well for us, but we will be replanting one block with virused vines in a weaker part of the vineyard. We’re looking forward to getting the report after they complete the lab analyses to see what they recommend in terms of the best varieties and management practices to employ in the weaker parts of our vineyards.”
Bush hopes to share the information he learns with other El Dorado growers who have similar soils. He summarized, “I like the quality of the wines we have, but I’m excited about the potential for getting more out of our vineyards.” Bush said he feels fortunate that the Bourguignons came to Madroña, and he agrees with their philosophy that some wine regions are destined to make great wines with the right varieties matched to the soils. El Dorado County, with its varied terrain and soils, offers a diversity of microclimates, hillside gradients and directional aspects, and it grows a wider diversity of winegrape varieties than any other county in the Sierra Foothills.
“We believe El Dorado County’s higher elevation vineyards and soils are destined for greatness—it’s just a matter of how to tap into that more than we’re doing now,” Bush said.