American Vineyard – March 1999
By Joe Traynor, Scientific Ag Company
I visited the wine country of France last summer to get an idea of the vineyard inputs that cause the French to brag about their wines. As an agricultural consultant specializing in soil fertility and plant nutrition, I was particularly interested in their soils, their fertilizer programs, and their irrigation schedules. The trip was quite informative and often surprising.
The predominant characteristic of vineyard soils in France conformed with what I had previously read: the soils were very calcareous, i.e., they contained much lime (calcium carbonate). What I learned about fertilizing and irrigating French vineyards surprised me: French vineyardists don’t fertilize and don’t irrigate, not because they don’t want to, but because the state forbids it; violators are subject to stringent penalties.
The reason for such draconian restrictions is two-fold: it keeps production down and it keeps quality up, with both contributing to higher prices for French wine. French growers are allowed to apply fertilizer to their vineyards at the time of planting, but nothing else for the life of the vineyard. As a result, vineyards are loaded up with nutrients on the front end. I took a soil sample from a vineyard near Chinon (in the Loire Valley of France) and compared the amount of 3 major vineyard nutrients with a composite of a number of samples I had taken in California. The results are shown in Table A.
Soil nutrient levels
Because none of the 3 major vineyard nutrients leaches readily, their levels in the French soil (see table) should be sufficient for the life of the vineyard (nitrogen does leach and will be discussed later). Certainly nutrient levels in other French soils will vary from the sample shown just as they do in California soils, but the soil analysis does give an indication that French vineyards are well supplied with nutrients.
The nutrient levels found in French soil far exceed levels one would expect from a virgin soil, making it obvious that significant amounts of fertilizer were applied to the vineyards prior to planting. Plant analysis confirmed the findings of the soil analysis and showed that the Chinon vineyard did not suffer from a lack of nutrients, including nitrogen (N), although N was a little lower than N levels normally found in California plant tissue (soil tests for nitrogen are not a good indicator of N status). A visual check of numerous French vineyards showed healthy plants with no signs of nutrient deficiencies.
Comparison of Soil Nutrient Levels in Vineyards
|Nutrient||Chinon, France||Composite, California||Levels that are
|Phosphorus, P||49 ppm||10 ppm||over 10 ppm|
|Potassium, K||300 ppm||150 ppm||over 150 ppm|
|Zinc, Zn||11 ppm||1 ppm||over 1 ppm|
Nitrogen is different from other plant nutrients because it is usually applied annually to avoid leaching losses. Grapes have a relatively low N requirement (about 60 lbs. per acre annually) and their extensive root system can forage efficiently for N. Significant N is returned to the vineyard each year from decomposed leaves; a bit more is returned if prunings are shredded and left in the vineyard. Eliminating irrigation will lower the N requirement for any crop since the resulting reduced growth will require less N.
On many orchard crops, it has been shown that high N fertilization rates reduce fruit quality. This is partly due to increased vegetative growth depriving the fruit of calcium but it is also due to the deleterious effects of N itself on fruit quality. The zero-N regime used by French vineyardists (not counting contributions from leguminous cover crops) undoubtedly contributes to grape quality and probably to wine quality.
The French fertilizer-irrigation program (or lack thereof) supports what most Napa Valley growers already believe: that making vines suffer produces lower yields of higher quality wines. San Joaquin Valley grape growers do not subscribe to this belief because climatic limitations (mainly warm nights) have a depressing effect on wine quality that cannot be overcome by withholding water and/or nitrogen.
Shorting vines on nutrients other than nitrogen probably does nothing to improve grape or wine quality. As discussed previously, French vineyards likely have an ample supply of nutrients other than nitrogen.
Having good calcium reserves in the soil, as French soils do, probably contributes to grape and wine quality. Most California vineyards are well supplied with calcium, especially those on the high-lime soils of the southern San Joaquin Valley. California growers on soils with little or no natural lime often apply gypsum (calcium sulfate), thus assuring a good supply of calcium for their vines. All in all, the calcium status of California vineyards is probably close to that of French vineyards.
As for irrigation, the long hot summers in California preclude going to a no-irrigation regime. French vineyardists can get away with such a program because of a shorter growing season, more spring-summer rain and relatively mild summer temperatures (due in good part to France’s higher latitude which is equivalent to that of Washington state). At the time of year I visited France (late June), it had been quite a while since their last rain and the vines were showing signs of stress for water. A timely rain while I was there alleviated this stress; however, in some years prolonged dry spells in the summer must lower yields significantly.
It is unlikely that French soils or French management practices are the major reason for the excellent reputation enjoyed by French wines, although zero-N fertilization and no irrigation are undoubtedly contributing factors. It is likely, as others have concluded, that climate, and climate alone, is the major reason for French wine quality. Longer summer days (a component of climate) due to France’s higher latitude (compared to California) likely also contribute to wine quality. The French have also done an excellent job of matching individual varieties with areas best suited to those varieties.
The mystique about the superiority of French wine is in good part a placebo effect that lingers on in spite of the fact that it was unmasked during the French-California blind tastings of 1976. Because Washington has calcareous soils and is the same latitude as France, California winemakers might feel more threatened by Washington wine than by French imports.