Agriculture Reference
In-Depth Information
vineyards close to centers of population, as in the Napa and Willamette Valleys,
operate under the watchful eyes of environmentally aware communities. In the
production of wine, soil and water must be used in such a way that they are not
degraded and off-site effects are minimized. To achieve this goal, the vignerons as
well as the community must be better educated about soil—its productive po-
tential, its role as a reserve of biodiversity, and as a foundation for stable land-
scapes.
Thus, a responsible approach to soil use recognizes soil as a
natural body
,
clearly distinguished from inert rock by (1) the presence of plant and animal life,
(2) a structural organization that reflects the action of pedogenic processes, and
(3) a capacity to respond to inputs and changes in the environment, which alter
the balance between gains and losses in the profile and determine the formation
of a different soil in dynamic equilibrium with new conditions. The third point
indicates that soil has no fixed inheritance because it depends on the conditions
prevailing during its formation. Nor is it possible to unambiguously define the
boundaries of the soil body. The soil air is continuous with the air above the
ground. Many organisms can live as well on the soil surface as they can in the soil,
and the litter layer usually merges gradually with soil organic matter. Likewise,
the boundary between soil and parent material is difficult to demarcate. It is com-
mon, therefore, to speak of the soil as
a three-dimensional body that is continuously
variable in time and space.
We discuss the scale at which soil variability occurs and
its effect on the expression of
terroir
in chapter 9.
Components of the Soil
The soil is a porous body comprising about 50% solid matter by volume, with
water and gases competing for the remaining pore space. The relative proportions
of the four major components—
mineral matter, organic matter, water, and air
—
generally lie within the ranges shown in figure 1.13. Soil water contains dissolved
organic and inorganic solutes, and is called the soil solution. Although the soil air
consists primarily of nitrogen gas (78% by volume), oxygen (21%), and argon
(0.9%), it also contains higher concentrations of carbon dioxide (
0.1%) than
1.4.2
Figure 1.13
Proportions of the main soil components by
volume (White 1997). Reproduced with
permission of Blackwell Science Ltd.
Mineral matter
(40-60%)
Air
(10-25%)
Organic
Water
(20-50%)
