Agriculture Reference
In-Depth Information
bacteria and fungi, contribute to aggregate formation and stabilization through
the secretion of gums and mucilage. An adequate content of organic matter,
as indicated earlier in “Soil Structure and Water Supply,” is a prerequisite for a
healthy soil biota. Box 5.3 in chapter 5 describes some simple field tests to deter-
mine whether a soil is biologically healthy; table 5.7 lists laboratory tests that can
be used to benchmark a soil's biological condition.
A healthy soil biota implies a population of organisms whose activities
are mutually beneficial, that can suppress undesirable organisms that may be
pathogenic, and that are themselves not harmful to plants. This concept is one
of the underlying premises of organic (including biodynamic) viticulture—
a fast-growing movement in viticulture globally. However, there is no evidence
that an organic/biodynamic vineyard is any better than a well-managed conven-
tional vineyard in suppressing parasitic nematodes and phylloxera. Hence in new
and replant situations, the soil should be tested for these pests and grafted vines
used as a preventative measure (see “The Function of Rootstocks,” chapter 5).
Furthermore, a regular input of organic residues through a cover crop, mulch,
compost, or manure in conventional viticulture also encourages a diversified and
metabolically active soil biota.
Managing Soil for Specific Winemaking Objectives
There is no doubt that wine grapes can be grown on a range of soils and that some
soils such as deep red and brown loams and alluvial soils will provide a better
growing medium for vines than others such as shallow soils on slate, schist, or hard
limestone. Nevertheless, the optimum growing conditions and soil property val-
ues will inevitably be different according to the style of wine to be produced. Thus
winegrowers should manage the soil in a way that enables them to achieve their
specific objectives of wine style and market price point. Soil amelioration, fertil-
izers, water management, and biological tools can be used to modify soil behavior
and the vines' response to it.
In setting objectives, the question arises: Is the wine to be an expression of place
(
terroir
), or is it to conform to a brand image or “house style” that is consistent from
year to year? In the former case, soil variability occurring over distances of tens of
meters is a potential boon, with subtle differences in soil properties conferring typ-
icity on the wine produced from different blocks. This approach is more likely to
be followed by small winegrowers who produce distinctive wines of one variety or
another from blocks of 2 to 3 ha or less. Winegrowers in the Mornington Peninsula
region, Victoria, Australia, provide a good example from the New World of a con-
scious effort being made to relate their Pinot Noir wines to subtle differences in the
soil and mesoclimate (figure 6.6). Although the distribution of soil orders in this
region has been mapped at a broad scale (see figure 1.14, chapter 1), soil differences
