Soil and the Environment - Soils for Fine Wines - page 13

Wind moves rock fragments by rolling, saltation, and aerial suspension. Ma-
terial swept from dry periglacial regions during the Pleistocene has formed de-
posits called loess in the central United States, central Europe, northern China,
and Argentina. These deposits are many meters thick in places and form the par-
ent material of highly productive soils. Similar windblown deposits called parna
are common in parts of the southern Murray-Darling Basin in Australia. Where
the parna cover is relatively thin, the underlying buried soils, typically Red Brown
Earths or Red Earths, may be revealed. Soils on shallow and deep parna are used
for irrigated viticulture along rivers in the Griffith, Sunraysia, and Riverland dis-
tricts of the Murray-Darling Basin.
Gravity produces colluvial deposits as fragments of weathered rock slide down
steep slopes in mountainous regions. Less obvious, but widespread under
periglacial conditions, are solifluction deposits at the foot of slopes. These deposits
are formed when frozen soil thaws from the surface downward and the saturated
soil mass slips over the frozen ground beneath. Many vineyards are planted on so-
lifluction deposits in valleys and on escarpment slopes in France, Italy, and Ger-
many, as, for example, the vines growing on colluvial deposits derived from lime-
stone in the Côte d'Or. Slips and larger earth flows can occur on steep slopes on
unstable parent materials when forest vegetation is cleared and replaced by vine-
yards.

Climate
Climate has a major effect on soil formation and is also an important determi-
nant of terroir in wine growing. Various climatic classifications have been devel-
oped to indicate regions most suitable for particular grape varieties. These have
been reviewed by Gladstones (1992). Smart and Robinson (1991) recognize three
levels of climate:
1. Macroclimate or regional climate: usually applicable over tens of kilometers,
depending on topography and the distance from moderating influences,
such as the sea
2. Mesoclimate or site climate: more local than a macroclimate, determined by
altitude, slope, and aspect, such as, for example, the south-facing steep
slopes in the Mosel Valley in Germany. In California, the macroclimate of
the Lodi District in the Central Valley is different from the macroclimate
of the Napa Valley, but within each region, there are several mesoclimates
based on distance from San Francisco Bay, closeness to the mountains, and
elevation.
3. Microclimate or canopy climate: the climate within and immediately
around the vine canopy
The key components of climate for soil formation are water and temperature .

1.3.2

Water
The effectiveness of water in soil formation depends on the form and intensity of
the precipitation, its seasonal variability, the evaporation rate (from vegetation and
soil, see chapter 6), land slope, and permeability of the parent material.
Leaching . In wet or humid climates, there is a net downward movement of
water in the soil most of the year. This downward flow or drainage usually results

1.3.2.1