Agriculture Reference
In-Depth Information
Calcrete layer
Figure 1.4
A Terra Rossa soil formed on calcrete-capped porous limestone in the
Coonawarra region, Australia. Vines are in the background. See color insert.
Sauvignon fruit. The limited soil volume offered by these soils exerts a control on
the vigor of the vines.
Box 1.2 gives a summary of the ages of rocks. Note that although the geologi-
cal time scale extends back many millions of years, the present-day soil need not
necessarily be very old because in most instances the parent rock has undergone
many cycles of weathering, erosion, and deposition in an ever-changing land-
scape. Older soils will have been buried (see box 1.1), and current soil formation
may have proceeded for only a few thousand years or less.
Soils on Transported Materials
As exposed rocks weather, some of the weathered material remains in place,
but much can be transported elsewhere by gravity, water, ice, or wind. On
steep slopes, especially in cold or very dry climates where vegetation is sparse,
rock fragments tumble downslope under the influence of gravity to form col-
luvial deposits at the footslopes. Such colluvial deposits in the shadow of the
Mayacamus Mountains of the Napa region, California, where they are called
benches (e.g., Rutherford, Oakville, and St. Helena), comprise some of the best
vineyard sites in the valley because of their low fertility, good drainage, and
favorable local climate. Elsewhere, the steep slopes themselves are extensively
used for vineyards as in the Valais and Vaud regions of Switzerland (figure 1.5)
