Agriculture Reference
In-Depth Information
pore space for gas diffusion) and temperatures are greater than 12°C. After fumi-
gation, a cover crop is sown to protect the soil during winter, until the vines are
planted in spring. Fertilizers can be applied with the cover crop, although if rock
phosphates are used, as with lime or gypsum, they should be incorporated along
the vine row when the soil is ripped. If the topsoil is shallow, the soil in the vine
row may be hilled to increase the depth and improve drainage.
Cover Crops
The use of cover crops for soil protection and stabilization of structure is referred
to in section 7.5.4. The physical and biological basis for the beneficial effect of
plant roots, especially grass roots, on soil structure is outlined in section 3.1.1.
The species commonly used in cover crops and their management are discussed
in section 7.3.1, where their role in controlling vine vigor is also indicated.
8.4.1.2
Site Potential and Planting Density
Preliminary survey data on geology, topography, mesoclimate, and soil are used
to evaluate
site potential
, primarily to assess the likely vigor of the vines to be
grown. Vigor depends on the interaction among the rootstock and scion, vine-
yard management, soil, and the environment. Of the soil factors that affect vigor,
the main ones are soil depth,
AWC
per m depth, drainage, and soil fertility, pri-
marily N.
Although there are various ways in which these factors can be modified by
management (e.g., deep ripping, irrigation, including
RDI
and
PRD
, cover crops,
and fertilizer management), the value of these factors at vineyard establishment
indicates the site potential (table 8.3). Depending on this potential, the vine spac-
ing can then be chosen to satisfy the dual objectives of
highest quality fruit
from
each vine and
optimum yield per ha
of this fruit. Another consideration is that the
vineyard should be easy to manage with whatever machinery is necessary.
The general principles for vine spacing, derived largely from research in Cal-
ifornia, Australia, New Zealand, and South Africa (Smart and Robinson 1991,
Weber 1992) are summarized here:
8.4.2
Characteristics of Low- and High-Potential Sites
Table 8.3
Low-potential Sites
High-potential Sites
Impervious rock underlying
Shallow soil depth (
No impervious rock or other shallow barriers
Deep soil (
0.5 m)
Sandy to sandy loam texture, or high
proportion of stones (
1.5 m)
Clay loam to light clay texture;
5% stones
2-mm diameter)
Low organic matter content (
by volume
High organic matter content (
1% C)
2% C), well
humified
Well-aggregated soil; aggregates stable in
water
Well-drained soil throughout the soil profile
(uniform orange to red-brown colors in
subsoil)
Weak soil structure, especially in the subsoil
Poorly drained subsoil (grey gley colors and
orange-red mottles)
