Agriculture Reference
In-Depth Information
Selected Wine Regions of Southeastern Australia
9.7
As indicated in section 1.1, soil is generally not considered to be an important
component of
terroir
in Australia. Summarizing Australian opinion, Halliday
(1993) considered that no link had been established between soil mineral com-
position and grape quality or wine character, with two exceptions: a certain amount
of N is essential, and excess K can be a problem, especially in warmer regions. In
this, Halliday was also echoing the conclusions of Seguin (1986, p. 871) who
wrote, “in the Bordeaux area the chemical properties of soils . . . do not have a
definite influence on the quality of harvests and wines. The quality of terroirs is
perhaps better explained by considering the physical properties . . . and their con-
sequences for root development and on the regulation of water supply to the vine.”
With this background, it is no surprise that there is little knowledge of the
specific role of soil in the
terroir
of Australian wine regions. However, for the pur-
poses of marketing and identifying an exclusive GI, there are regions that now
claim a distinctive influence of the local soil on the character of the wines. Three
of the more important such regions are briefly discussed next.
The Coonawarra Region of South Australia
The Coonawarra Region is flat, with an elevation of 55-60 m above sea level. The
annual rainfall is ca. 650 mm, with a marked winter incidence. Summers are hot
and dry, and there is a significant temperature gradient from south to north (grapes
ripen two weeks earlier in the north). Nevertheless, temperature extremes are mod-
erated by proximity to the cool Southern Ocean. Here, soil and climate have com-
bined to create a
terroir
that confers a distinctive character on quality wines. To-
day, Coonawarra makes much of the influence of its “unique” Terra Rossa soil
on its superpremium and premium red wines (51% Cabernet Sauvignon and 21%
Shiraz).
The Terra Rossa soil has formed on a sandy, porous limestone laid down dur-
ing the Miocene epoch (22 M yr B.P.). During the Pleistocene, fluctuations in
sea level associated with the glacial and interglacial periods led to a succession of
sandy beaches being formed over limestone ridges. These have subsequently been
exposed as the land was uplifted, and the sea has retreated to the west. The lower-
lying areas between the ridges are poorly drained and swampy, in contrast to the
higher ridges, which are well drained. Although the boundaries of the much-prized
Coonawarra GI are still in dispute, the region is currently a cigar-shaped strip of
land, about 20 km long and 5 km across at its widest point, between the towns
of Coonawarra and Penola in the southeast of South Australia. Grapes are grown
on other outcrops of limestone with similar soil in the wider region, so that the
whole GI Zone is called the Limestone Coast.
A catena of soils (section 1.3.4.1) has formed on the limestone ridges and old
beaches. During the last glacial period, silt-size particles of clay, quartz, and lime-
stone were blown from the dry lake beds and shoreline to accumulate on the
ridges. With weathering of the limestone by dissolution in Recent time, this loes-
sal material has accumulated and given rise to the sequence of soils shown in fig-
ure 9.10. Lowest in the sequence are very poorly drained Black Earths, which are
used only for pasture. Next come the Groundwater Rendzinas on which vineyards
9.7.1
