Unit 3 The interaction between the Vine and the soil

1.3 Read Article : Soils, Vines and Fine Wines

Eastern Winery Exposition workshop explores some of the impacts of soils on wines by Linda Jones McKee
Lancaster, Pa.—
Whether a potential grapegrower has just inherited Grandpa’s farm or decided to plant vines on a newly purchased piece of property, that future grower has hundreds of questions. While the ultimate goal usually is to produce the best quality grapes possible on the land available, many factors and dozens of decisions will determine if a given site can produce the level of quality that a grower has set as his or her ideal. Growers with existing vineyards also look for advice about differences they observe within a given varietal block or vineyard and what they can do when their vineyard has already been planted.

Lucie Morton, a well-known Virginia viticulturist, brought together a team of soil scientists, a geologist, and a winemaker currently making wine in three international locations for an intense, information-packed day-long workshop that addressed the relationships between soils, vines and fine wines. The workshop was held March 8, the first day of this year’s annual Eastern Winery Exposition in Lancaster.

Basic soil information

Alex Blackburn and Ryan Reed, two soil scientists from Blackburn Consulting Services in Berryville, Va., kicked off the workshop with a review of many different aspects of soil. Blackburn provided a basic primer on the wide range of soil and landform characteristics that should be examined in evaluating a vineyard site, including information about soil depth, color, texture, structure and chemistry as well as geomorphology considerations such as ridgetops, streams, concave and convex areas.

Blackburn noted that the Natural Resources Conservation Service at the U.S. Department of Agriculture has a web soil survey available online that provides information about general geology and type of soils. However, he cautioned that the survey “was mapped between 1930 and 1990, and was prepared for farmers who were growing corn, soybeans and wheat.” A detailed, site-specific soil mapping done by an experienced soil scientist would provide more useful information for a proposed vineyard, Blackburn stated. “They would understand the specific soils and help you lay out blocks for uniform management of the vines.”

According to Reed, the physio-chemical properties of soils include the soil organic matter (SOM), texture and mineralogy. The labile pool of SOM is the direct energy, the food source that microbes use to create other nutrient materials for vine roots or other crops, while the stable pool—comprising one-third to one-half of the organic material—helps create structure. If a grower wants (or needs) to improve the organic matter in the soil, Reed stated, “Do it pre-plant if you can. You have to decide if you want to rip the soil or not, because if you rip, it will affect the amount of organic material in the soil. Post-planting, once lost, it’s hard to re-establish the organic matter.”

The empirical approach to soils and terroir

Ernest “Bubba” Beasley, a geologist with HydroGeo Environmental in Charlottesville, Va., has worked with Morton in evaluating a number of different sites for potential and existing vineyards. He reviewed some technological tools for conducting site evaluations including GPS (for slopes), GIS (for geology and aspect maps) and weather data. Both Morton and Beasley believe that on-site visits and testing reveal more useful data than any other evaluation. Morton uses a drone to fly over a site and provide local photos; Beasley conducts electro-magnetic conductivity measurements (EM) that map the soil electrical properties that are affected by the presence of moisture, rocks and soil composition (e.g., clay).
EM by itself yields digital images of the variability in soil electrical conductivity. When EM is combined with a technique Morton refers to as “ground truthing,” which includes drilling auger holes, digging backhoe pits and conducting farmer interviews—information can be gathered about topsoil depth, soil texture, depth to rock, type of clay, nutrient load, land-use history and moisture variations.

Important take-home message

The problem with most laboratory soil analyses, Morton pointed out, is that the sample is usually taken from the first 6 inches of the topsoil, a depth that is fine if farmers are planting row crops such as corn or wheat. However, this doesn’t work as well for permanent crops like fruit trees or grapevines; when vines are planted, the trunk of the plant often goes 8 inches into the ground, and the roots are then even deeper down. Morton and Beasley have demonstrated that the numbers reported for key factors such as potassium are often identified incorrectly as being too low in soil analyses. Laboratories look at two forms of soil potassium—the soil solution potassium and the exchangeable potassium, which may reveal only 2% of the potassium. They do not look at non- exchangeable (fixed) potassium or mineral potassium, located deeper into the soil and extractable over longer periods of time.

In the East, where high-pH wines are common, the standard potassium levels recommended by most viticulturists are much too high, given the amount of potassium that is actually present at the depth where grapevine roots are growing and absorbing nutrients. Morton pointed out what she calls the “potassium paradox:” “The soil analysis shows the potassium to be low and the magnesium is high. But the petiole analysis shows the potassium is OK, and so is the magnesium.” If there is more potassium in the soil, that relates to the excess of potassium in vines, and the amount of potassium in the fruit plays a critical role in the pH of must and wine.

Other factors

In addition to soil amendments, other factors must be considered before a vineyard is planted. Soil amendments—what type, how much, when and where—should be determined, because it is much easier to put something into the soil than it is to take it out. The need for drainage should be determined, and whether cover crops can help with both water and vigor concerns. Variety and rootstock selection, row orientation and vine spacing must be considered. As Morton noted, “You ask for a 25-year headache if you plant where you shouldn’t.”

If a vineyard is already planted, the grapevines can tell a viticulturist a great deal about the soil and nutrition levels, but caution is advised. “Red blotch virus looks a lot like potassium deficiency,” Morton stated. Vines that really are potassium deficient can be supplemented with foliar applications and, in some cases, added through a vineyard drip irrigation system. In addition, backhoe pits next to existing vines can reveal good information about both the soil and the vines, including the type of soil, texture and whether ripping the soil is a good idea or will create vertical compaction.

Soil and wine quality in three locations

Thomas Bachelder is different than most winemakers in that he makes wine from Chardonnay and Pinot Noir in three locations across two continents: Burgundy, Oregon and the Niagara escarpment in Ontario, Canada. In Burgundy, limestone pebbles and small rocks in shallow, poor clay soils give both drainage and minerality to the vines, which are tightly planted on 1 meter by 1 meter spacing and allowed to grow only 1 meter high. The soils in Oregon are mostly sedimentary (sandstone and some basalt/volcanic), while the soils in Ontario are dolomitic limestone, although he sources his Pinot Noir from a vineyard with “red stone” clay.
The vines in Ontario and Oregon are both younger and planted on wider spacing than in Burgundy, and Bachelder believes these factors result in wines with a more fruit-forward character, even after 16 months of barrel age. For him, terroir is a loaded term: It is better to think of it as the relationship of the soil and the vines/cultivars to wine quality. He states, “We use Burgundian techniques and the exact same barrels in all three countries, not to copy Burgundy, but because the Burgundian techniques are themselves revelatory of terroir—and end up best expressing local dirt, aspect and climate.”
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