Agriculture Reference
In-Depth Information
Modifying the Soil-Vine Environment
Site Potential
Each site has an inherent potential that reflects its suitability for particular varieties
and the likely vigor (relating to vegetative growth) of the vines to be grown. Given
that site potential is determined by geology, soil, topography, climate, and human
influence (if the land form is reconstructed by earth-moving), we can summarize
the broad differences between low- and high-potential sites using a combination
of the soil properties given in table 2.2 and additional geological factors, as shown
in table 2.4.
Additionally, topography influences site potential through soil depth, drain-
age, temperature, and aspect. Soil on steep slopes is prone to erosion and therefore
tends to be shallower than soil on gentle slopes and in valley bottoms. Soil at the
top of slopes is usually better drained than at the bottom. Temperature and aspect
effects were discussed earlier, but for a given suite of cultivars and scion-rootstock
combinations, the interaction between rainfall and soil has a powerful influence
on site potential, as expressed through vine vigor. Deep, well-drained soils that are
naturally fertile and well watered will predispose to “excess vigor.”
Table 2.4
Soil and Geological Features of Low- and High-Potential Site
a
Low-potential sites
High-potential sites
Often on conglomerates, sandstones, or shales
and their metamorphic products, in which
little weatherable mineral remains
Often on igneous rocks, especially basalt,
diabase, and dolerite, relatively unweathered
shales, their metamorphic products, and
alluvium derived from these rocks
Underlying rock is hard and unrippable
Underlying rock is soft and rippable; no
shallow barriers to root growth
Shallow soil (<0.5 m)
Deep soil (>1 m)
Sand to sandy loam, or a high proportion
of gravel and stones; small water-holding
capacity
Clay loam to light clay and <5% stones; large
water-holding capacity
Low pH and exchangeable Al, or high pH and
salinity
pH 5.5-7.5 and no exchangeable Al or salinity
Little organic matter, usually a shallow topsoil
and low mineral nitrogen supply
Plentyoforganicmatter,darkA1horizon
that can be more than 20 cm thick;
potentially high rate of mineralization of
organic nitrogen
Weak soil structure, especially in the subsoil;
aggregates unstable in water
Well-aggregated soil; firm aggregates stable
in water
Poorlydrainedsubsoil(mottledorblue-gray
colors throughout)
Well-drained soil profile (uniform orange to
brick-red colors in subsoil and no mottling)
a
Varieties appropriate for high- and low-potential sites are discussed in chapter 5.
