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Do Vineyard Soils Really Matter?

How soil composition affects the flavor of wine.

May 1, 2007

A new look at the terroir issue and how things like soil composition and climate affect the character of wine.

Terroir is the term usually used to describe a particular vineyard location, particularly with respect to its soil composition, sun exposure, and climate. It's a proven fact that certain areas even within the same vineyard can produce measurably different results.

The French have long argued that their particular soil compositions are the foundation of clear quality differences in their wines. Clos Vougeot in Burgundy, for example, had 16 different owners/viticulturists at last count, each producing a version of Clos Vougeot with different characteristics. It's differences in the soil, say the French.

Not so, says viticultural guru Dr. Richard Smart, who declared the notion of vines taking up any kind of specific flavors from the soil "absolute nonsense." And professor Jean-Claude Davidian of the Ecole Nationale Supériere Agronomique in Montpellier, France, echoes the sentiment, saying "Nobody has been objectively able to show any links between the soil mineral composition and the flavor or fragrance of the wines."

Yet New World viticulturists continue to try to replicate the soils of famous Old World vineyards. The owners of Chateau de Beaucastel in Chateauneuf-du-Pape purchased vineyard property in west Paso Robles a decade or so ago because of the "similar limestone soil composition to the native soils of the southern Rhône Valley." The famous Côte d'Or in Burgundy is also known for its limestone soils. So should New World Pinot Noir, Chardonnay, Syrah, and Grenache be planted on limestone soils?

The notion purported by Jamie Goode in his 2005 book The Science of Wine is that vines take up only water and dissolved mineral ions from the soil; and that the operative element in soil composition is texture. A loose soil will allow grapevines to send roots down to 40 feet. Some have said 100 feet. These soils are typically found on slopes and ridges where soils are eroding and decomposing. Vines planted on these soils are often dry-farmed, meaning that they receive little or no irrigation. Valley soils are typically more fertile and denser, being composed of finer textural elements. They hold water better, but roots are often too shallow to allow dry farming and contaminants in commercial water supplies can affect growth characteristics as any home gardener is reminded of after a rainstorm restores fresh verdure to his garden. When these valley soils allow deep penetration of root systems they lead to excessive growth at the expense of concentrated flavors.

An interesting side note is the plethora of high quality vineyard areas in California that lie on or near earthquake faults. Earthquake faults continually disrupt the physical composition of soils, both by shaking them up and by importing soils from other locations in the case of transverse faults such as the famous San Andreas. Major faults permeate California's Central Coast region as well as Napa Valley and regions of Sonoma County.

The San Andreas moves earth regularly at an average rate of 2" a year from the Mexican border to Pt. Arena in northern California. Along this fault may be found the premium winegrowing areas of Temecula, Cucamonga, Cienega Valley, the Santa Cruz Mountains and Sonoma Coast- all areas of prime viticulture.

Pietra Santa Winery in San Benito County, famous for its Sangiovese, lies directly on top of the fault, and Calera, famous for distinctive Pinot Noir, lies high above it on uplifted mountains.

Could it be that the movement of faults breaks up the soil at deep levels, permitting better penetration by vine roots? And could it be that California's earthquakes are at least partly responsible for the overwhelming success of its viticulture?

The copyright of the article Do Vineyard Soils Really Matter? in New World Wine is owned by Alan Boehmer. Permission to republish Do Vineyard Soils Really Matter? in print or online must be granted by the author in writing.

Comments

Aug 2, 2007 4:55 AM

Thomas J. Rice :

To Alan Boehmer:

You need to do some more reading about earthquakes and the consequent rate of land movement in California. There is no relation between soil disturbance caused by earthquakes and grape vine growth. Earthquake movement is simply too slow and too intermittent to have any real effect on soil disturbance and mixing.

The important relationship to vine growth results from the soil physical properties, especially soil texture and its effect on water supplying capacity to the vines. The more clay and organic matter a soil has, the higher its water holding capacity.

There has been no research study that shows a direct relationship of the soil chemical properties to wine quality and flavor, with the exception of potassium (K). However, there are several published studies that show a relationship between soil depth & soil texture and their effects on soil water holding capacity. Also, there has been shown that soils with high water holding capacities can supply more water to the grape vine and can stimulate increased vegetative growth.

In California, the management of irrigation water relative to soil texture influences vine growth and subsequently can influence ultimate wine quality and flavor. In parts of the world where natural precipitation (rainfall) occurs during the growing season, viticulturists have less control over the water supplied to the vines. In areas where it is dry during the growing season, like California, we can more easily control fruit and vine growth and consequently can influence wine quality better than in the more humid regions of the world.

Dr. Richard Smart states that soil physical properties (texture, water holding capacity, depth, etc.) influence wine quality. He agrees that we has never seen any definitive study that shows a direct effect of a soil chemical property on wine quality. The one exception is that high potassium (K) levels in the soil and in the vines has been shown to cause elevated grape pH levels (to over pH 4.0). If the grape pH levels rise to over about 3.8 at time of harvest, this will have a detrimental effect on wine quality by inhibiting fermentation. This has been well documented in several scientific studies.

I suggest that you read the section on "soils and wine quality" in the "Oxford Companion to Wine" by Jancis Robinson.

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