When Polly and I were in Bordeaux a few years ago, we visited Damien Bielle, technical director at Château La Gaffelière. La Gaffelière is a Premier Grand Cru Classé estate that lies on the descending slope below St. Émilion’s famed limestone plateau. It’s adjacent to Château Ausone, one of only four class A château in the most recent St. Émilion classification. La Gaffelière is one of 14 Premier Grand Cru Classé B château.
As we looked up the hill, Damien explained how the special soil of the plateau and the hillside location had produced many of the region’s great wines. When we turned to return to the cellar, we could see Château Pavie, also Class A, to the southeast at the base of the slope where the soil becomes more alluvial and sandy, where one might think the soils would be less likely to produce the stunning wines of the plateau. When we asked Damien how Pavie achieved its status despite the presumed challenges of its site, Damien’s response was matter of fact and utilitarian. “They know how to farm it,” he said.
It turns out that the four St. Émilion class A chateau – Ausone, Angelus, Cheval Blanc, and Pavie –each have very different soils from one another, and even within their vineyards, there is considerable variation. The key is that the wine growers at each site intimately understand their soils, and they adapt their viticultural and winemaking methods accordingly.
How are soils classified?
Because soils across the world differ, the United Nations Food and Agricultural Organization has created a comprehensive taxonomy that characterizes soils based on their characteristics and suitability for agriculture. There are six taxonomical levels. The highest, most general level is the soil order; the most specific is the series. There are 12 orders and more than 15,000 series. With so many series, the characteristics of the soils within each are very similar.
There is no dominant soil order among the world’s wine growing regions, let alone specific series that are associated with the best wines. This fact alone leads to the conclusion that high quality wine grapes can be grown on different types of soils. Inceptisols are the most common soil order in Bordeaux, alfisols in Burgundy and the Loire, and mollisols in northern Italy, California, Oregon, and Washington, and the ancient wine regions of Armenia. Alfisols, which are good for many agricultural uses, are also found in Maryland and Virginia west of the fall line.
Dodon’s soils substantially differ from those in other wine growing regions. Termed Marr-Dodon complex soils, they are described as fine-loamy (meaning smallish particle size), siliceous (rich in silica that warms the soil), semiactive (modest cation exchange associated with low fertility), mesic (medium temperature), aquic (Dodon series) or typic (Marr series) (aquic soils retain more water than typic) hapludults (derived from sandstone).
Hapludults belong to the ultisols, an order found in humid climates and characterized by high degrees of weathering, mineral leaching, and acidity. They age very rapidly, leading to rapid turnover in rock and mineral content. With relatively low fertility, they are marginal agricultural soils that require significant inputs for most crops, but these characteristics make them good candidates for viticulture. Ultisols have a well-developed reddish clay horizon (horizons are the distinctive layers that can be seen at various depths below the surface) associated with weathered sandstones and resulting in their common name “red clays” in the southeastern United States.
Dodon’s distinctive soils represent a considerable opportunity to make wine that will differ from those produced in other regions, even when the climate and grape variety are the same. The process of discovering what the final wines will be like adds enormously to the excitement and pleasure of our project. I often wonder whether Dodon Merlots will exhibit the power found in Pavie, the finesse in Cheval Blanc, the minerality in Angelus, some combination, or none of these. While we have some early hints, each vintage brings new learning. What we do know is that understanding the nuances of the vineyard soils and farming them with care and precision are essential to the process of discovery.
How do we study soil?
We started by understanding what we mean by soil, which usually depends on whom we are talking with. Engineers, concerned chiefly with the stability of buildings, roads, and other structures, define soil broadly as any material that can excavated without systematic drilling or blasting. In other words, to an engineer, soil is everything above bedrock, which is about 3,000 feet below the surface at Dodon.
Soil scientists and farmers take a narrower view of soil, defining it as a medium that can support rooted plants. Soils that meet this definition vary in depth, mineral and rock composition, and hydrology. Since most agricultural plants are relatively shallow rooted, only surface soils have been surveyed by the United States Department of Agriculture. Dodon series soils have been characterized to a depth of 72 inches. Because grape vines can send roots more than 200 feet below the surface, they are influenced by soils well below typical agricultural assessments.
Even though soils within a series (Dodon series, for example), have very similar characteristics, there can be, and usually is, significant variation on any given parcel. At Dodon, geologist Bubba Beasley documented this variation using electromagnetic induction imaging to identify plots that differ according to water holding capacity, mineral content, and texture. The resulting image represents a rich mosaic of individual plots, each created hundreds of millions of years ago and transported to Maryland’s western shore uplands. (I’ll describe the origins of Dodon’s soil in a subsequent post.)
How do we use our understanding?
We used the information from the survey to lay out the vineyard in ways that would maximize our chances of creating complex, balanced wine. For example, Merlot grown on clay soils tends to have more structure and intensity than those grown on sandy soils, where the wines are often described as elegant and finessed. Because we think of Merlot as foundational for Dodon wines, most of our Merlot is planted on plots with more clay where we hope it will have good intensity and structure.
The information from our survey allows us to precisely farm each plot. For example, areas of the vineyard dominated by sand and gravel have less water holding capacity than areas with more clay. We are a bit quicker to irrigate those parts of vineyard. Because of the leaching, we include calcium and magnesium in our nutrient management program, providing small amounts of these essential elements to thicken grape skins and provide both more flavor and better disease resistance.
Bubba found that some parts of the vineyard were nearly “dead,” with compacted grey soil that lacked microbial and insect life, undoubtedly the result of fifty years of “conventional” agriculture characterized by excessive use of herbicide and inorganic fertilizers, and by compaction associated with use of heavy equipment. The wines from these areas of the vineyard are weak, lacking the structure and fatness that we want for Dungannon and Oronoco. To restore life to these plots, we’ve been using deep tillage, adding compost and compost teas, and strategically planting deep rooted cover crops to create better soil structure and allow oxygen to enter the soil.
It’s all, of course, a bit of an experiment, with educated guesses dominating our hypotheses. Because the soils differ from those in other parts of the wine growing world, we can’t merely duplicate their methods. And even after hundreds, or even thousands, of years, the Bordelais are still learning. A winemaker from Pomerol recently told us that he had been working for 43 years to improve one plot of Cabernet Franc that consistently ripened a week or two after the others in his vineyard. His last experiment involved adding river gravel to the soil. Even though he added only a small amount, the result was higher sugar levels but also green notes in the final wine, making him worse off than he had been. If the Bordelais don’t have all the answers for their plots after thousands of years of experience, we can’t really know after just ten how to optimize the wine from any given plot at Dodon. And so we've started on a long and interesting journey of discovery and learning.