Agriculture Reference
In-Depth Information
Figure 6.5
Old bush vines on a schistose soil of pH 4 in the Coteaux du Languedoc region,
France. (White, 2003)
induces a distinctive wine character (discussed later), nutritional stress imposed
by a very acid soil may be responsible for the so-called “flinty” taste of wines pro-
duced, for example, on the very acid soils of the Rangen region in Alsace, France.
An aspect of soil chemistry that is not directly nutritional concerns salts: a
high concentration of soluble salts is undesirable. The electrical conductivity
of a soil's saturation extract (
EC
e
) is a surrogate for the concentration of soluble
salts and is easily measured. As discussed in “Salt, Drought, and pH Tolerance,”
chapter 5, the threshold value of
EC
e
is 1.8 dS/m for own-rooted vines, which is
approximately equivalent to 3.6 dS/m in the soil solution in the lower root zone.
If irrigation is used, the aim should be to keep the soil solution
EC
below the
threshold (which can be higher for some rootstocks), because the salt concentra-
tion in the root zone increases over time. In soils in which vines can root deeply,
groundwater should not occur within 2 m of the surface because dissolved salts
can rise into the root zone by capillary action.
Soil Organisms and Organic Matter
Ideally, a soil should have a diversity of organisms, ranging from bacteria and
fungi to arthropods and earthworms, which interactively decompose organic
residues. Most of these organisms are saprophytes (i.e., they feed on dead organic
matter) and are therefore crucial to nutrient cycling. Some, such as earthworms,
burrow through the soil and improve aeration and drainage; others, such as
