Agriculture Reference
In-Depth Information
The soils on the lower land of St. Emilion, and most of Pomerol, fall into
three broad categories (van Leeuwen and Merouge 1998):
1. Soils that are gravelly (50-70%) throughout the profile and very well
drained
2. Soils that are sandy in the topsoil (up to 1 m deep), but with increasing silt
and clay content (ca. 20%) in the subsoil
3. Soils that have a sandy to sandy clay texture in the topsoil (30-50 cm
deep), but become very high in silt and clay (
90%) in the subsoil. Often
this subsoil layer is compacted.
There are many variations within these categories, particularly with respect
to the proportions of gravel and coarse sand in the topsoil and the interleaving of
sand and clay “lenses” in the subsoil. Examples of these main profile types are
given in figure 9.3a-c. Soils of type 2 frequently have a permanent water table
within 1 to 2.5 m of the surface. Surprisingly, soils of type 3 do not develop
perched water tables over the clay subsoil. Detailed studies by French scientists at
the University of Bordeaux and INRA have shown that the quality of the grapes
and wine produced is primarily determined by the water supply to the vines (Seguin
1986). On the gravelly and clayey soils (types 1 and 3), the vines showed a grad-
ual increase in water stress from veraison on, which was associated with a higher
fruit sugar concentration, lower malic acid levels, and more concentrated antho-
cyanins and total polyphenols (tannins) at vintage. However, on the sandy soils
with a permanent water table, which remained within reach of the roots during
the entire growing season, the vines did not show any water stress. Berry weights
were high and favorable indices, such as anthocyanin and tannin concentrations,
were low. The results of these measurements are summarized in table 9.2. The
wine made from the grapes was ranked by tasters in the order type 3
type 1
type 2, and a number of vineyards on type 3 soils produce wines that are Grands
Crus Classés.
The overriding influence of soil type on the personality and quality of wines
in St. Emilion-Pomerol is through the regulation of the water supply to the vines,
especially in the post-veraison period. For this reason, drainage with pipes at 80-
cm depth and 10-m spacing is used to remove excess water from clay subsoils,
and groundwater pumping is used to control the water table in the deep sandy
clays.
The Médoc
. The Médoc is a long strip of land protected in the west from
Bay of Biscay winds by extensive pine forests, and adjoining the estuary of the
Gironde in the east. The soils are formed on Quaternary alluvial and glaciofluvial
deposits that are deep and gravelly in the south (Haut-Médoc) and increase in
clay content to the north (Central and Bas-Médoc). The vines are planted at
10,000 per ha, with the best vineyards situated on well-drained soils and facing
east or northeast (where they “see the river”). A number of châteaus are classed as
Premier Cru (First Growth) in Margaux in Haut-Médoc and as First and Second
Growths in the communes of St. Estephe, Pauillac, and St. Julien in the Central
Médoc.
Because the soils were formed on alluvial deposits, the soil texture is highly
variable over short distances, both laterally and vertically, and drainage is very de-
pendent on local relief. Records from the seventeenth and eighteenth centuries of
Château Latour in Pauillac reveal that the land was originally divided into parcels
of 1-5 ha according to soil type, particularly the proportion of gravel in the pro-
