Claude Bourguignon and Lydia Gabbucci L.A.M.S., 21120 Marey-Sur-Tille, France
E-mail: [email protected]
Introduction
If the agronomists have managed to prove the role played by the climate conditions and topography in the expression of the "Terroir", they have brought only superficial scien- tific explanations on the part taken by the soil. This is due to the fact that they had only a physical-chemical approach of the soil, and through this they have ignored its biologi- cal aspect.
The soil fauna is responsible for the soil porosity and therefore of the circulation of oxygen and water in the soil depths.
The microflora is responsible for the formation of negative elements assimilable for the plants, like the nitrates: NO3-, the phosphates: PO42-, the sulphates: SO42-.
Those elements, which are oxides, can be formed only if the soil is well aerated, by the actions of the fauna, which will be found only if the plant roots are present (i.e.: same depth).
So if we destroy the soil fauna with pesticides, by compacting the soil with ever more heavy machinery, it is easy to understand that we are stopping the soil aeration along with the microbial activity.
Wine roots creep up to the surface in order to breathe and we are substituting the work of the microbes with the same fertilisers.
So we tend to get an uniformisation of wines and slowly we are switching from a wine of "Terroir" to a wine of "cepage" (vine variety). By disregarding the soil’s biology, the winemaking profession has standardised its wine. It is now easy to reproduce those wines, this is making them vulnerable to foreign competitors.
For 4 years, our Laboratory has been working to define the physical, chemical and bio- logical characteristics of the vineyard soils especially the one of Burgundy. If we can define the part played by the soil in the wine typicality, we would not be limited to the climate, the topography, the "cepage" and the wine fermentation.
Those 4 criteria are relatively easy to copy by other countries. On the other hand the soil diversity along with fundamental relations that unify soil, microbes and plants reach such a high complexity that its is impossible to copy it. These assure the wine makers that their wines are unique and original.
• To define the physical, chemical and biological criteria in the definition of "Ter- roir".
• To develop new cultivation techniques, that respect those characteristics. In or- der to illustrate our idea we have chosen the Burgundy region, because of its "monocepage" and its constant geology (Jurassic calcareous).
In this area, the difference in taste observed between two wines of the same appellation can be due only by the soil, especially if those two wines are produced by the same wine maker.
Physical characteristics of the soil of a "Terroir" Texture
Classical granulometric approaches have never showed correlation with the "Terroir". In Burgundy, for example, two "clos" can have the same granulometry and give two very different wines: ie "Latriciere" and "Chapelle Chambertin".
On the other hand, soils have an unusual characteristic, the specific surface of clays. This is the total surface area of the clay layers in 1 gram of soil.
The studies we carried out on the "Côtes de Nuits" and ‘Côtes de Beaune" seem to indi- cate 3 things:
• The soil of each vintage is characterised by a unique specific clay surface.
• Soils with a high clay surface are good for red wines while the ones with a lower specific clay surface are suited for white wines.
• The smaller the specific clay surfaces, the better and finer the white wines will be.
On the hill of Puligny-Montrachet we observed for example: - AOC Village: "Les Houlières": 375 m2 / g - First vintage: "Clavaillon: 233 m2 / g - Vintage: "Le Montrachet": 176 m2 / g. Those results can be checked out in other French regions.
The smallest specific clay surface that we have ever encountered was 57 m2 /g in the "Coulée de Serrant". The highest 550 m2 / g was found in the plot of "Richebourg". Since we have a linear relation between the specific clay surface and its C.E.C we can bring forward the hypothesis that each type of clay will nourish its wine in a specific way. This is the first level of typicality due to the soil, the one of the specific clay sur- face and their C.E.C.
Structure
The great "Terroirs" are characterised by a strong porosity in the surface and in depth. Those porosities can be from physical origins like the one of surface in gravel soils or alluvial pebble soils. (I.e.: Bordelais, Côtes du Rhônes or Val de Loire) or the one of depth for the cracked calcareous soils of Burgundy and Alsace.
Those porosities are also from biological origins (galleries, faeces of the soil fauna). This is the case for porosity of deep clays in "Bordelais" and "Val de Loire" and the porosity of surface in the calcareous soils of Burgundy and the chalk of "Champagne". Those strong porosities of surface and at depth allow a quick drainage of soils after the rain, and a quick warm-up of the soil surface, which is necessary for the good ripening of the grape, and a good oxygenation of the deep roots.
The water flow at depth enables the wine to have a constant availability of water during the summer. By stopping the work of the soil and by killing the soil fauna through ex- cess of pesticides, the wine makers have stopped the water flow through the soil and instead promoted the flow of water horizontally increasing the erosion. Then the oxygen cannot flow down in the soil and the roots become shallow.
The chemical characteristics of the "Terroirs"
No content of key assimilable elements could be correlated with the typicality of terroir. On the other hand, high contents of some assimilable oligo-elements seem to character- ise some "Terroirs". "Coulée de Serrant", "Le Morgon" and "Montrachet” are all high in magnesium.
The wine can assimilate those oligo elements of the "Terroir" only if the soil microflora is active. The activity of the microflora can be stopped by massive input of pesticides. Another interesting characteristic is the type of calcareous soils. Our observations under microscopes show that depending of the water circulation, there are two types of cal- careous soil:
• Originated from the rocks.
• Originated from the recarbonation by microbes.
It is on the first type that the red wine are found and the white on the second type. Curiously soils with a rich content of microbial calcareous are poor in freely available Fe++ which is necessary for the synthesis of the "anthocyanes".
The biologic characteristic of "Terroirs"
The biologic characteristic of "Terroirs" is found at three different levels: roots, soil fauna, and microbes.
I. Characteristics of root’s depth.
All the vintages we worked for had wines deeply rooted. When the root’s depth is important the taste of "Terroir" is stronger.
After the war, productive stocks were commonly used, they were exploiting the in- put of fertiliser very efficiently and promoted shallow roots. SO4 is an example of those stocks.
We have the same type of problems with the deep soils present in "Herault", "Aude", "Côte d’Or" (below the national road) because they are too rich in nutri- ents, and badly aerated at depth, and those factors give a taste of "Cepage".
The deeper the roots, the better they are at extracting the elements of the "Terroir" and they give a protection to the wine against drought.
II. Characteristic of the soil fauna.
In the vintage we have always observed, in the clays at depth or on the parent mate- rial rock, a concentration of dead roots. This mass is the primary source of food for a fauna called "endogenous Fauna" (acarids, earth worms etc.). The multiplication of this fauna along with its activity increases the porosity at depth (galleries) and increases the biological activity, against the rock. This activity allows the formation of assimilable elements distinctive of the "Terroir".
III. Microbiological characteristics.
Our microscopic observations show that the dominant micro flora changes depen- ding the soils. Some are dominated by fungi other by bacteria. Some bacterial groups can be very abundant like the sidero bacteria in the soils of "Bordeaux", or calcareous bacteria in "Champagne", "Chablis". Our measures of microbial activity shows that the activity is link to the specific internal surface of clays, the type and content in carbonates of calcium, the quantity and quality of the soil humus.
of microbial activity, in the soils of "Terroir". In some soils, we have observed acti- vities lower than in Sahara soils. At the opposite, vineyards that switched to organic techniques, we have noticed an increase in those activities, along with a better depth of roots. It is in the "Terroirs" practising “biodynamic agriculture”, where we have observed elements of the deep soil.
Conclusion
This quick presentation the role-played by the soil in the characteristics of "Terroir" is a proof that the soil is not a myth but real and important.
The role of the soil in the typicality is found on the physical of level: types of clays, their C.E.C. which will have different effect on providing the wine with nutrients. The superficial and deep structure of the soil is important in the terms of porosity to allow a good circulation of O2 and the good flow of water towards the roots.
This action of the soil is showed by the soil biology because it is the microbes of the "Terroir" that produce the assimilable oxides. The porosity is made by the action of the fauna.
It is by integrating and by applying those new know ledges of soil biology, that we can improve our understanding of "Terroirs" and develop new viticulture practices able to respect it.
Wine fermentation is not the limiting factor anymore, to improve the quality of the wine, but the soil is.
We have to respect it, to improve the "Terroirs".
"Less chemicals and more life in our wine soils" must be leitmotif of the future wine makers.