Agriculture Reference
In-Depth Information
By contrast, in other regions where the land surface has been exposed for
much longer (10
5
-10
6
years), the attainment of steady state by a soil-plant ecosys-
tem is more problematic. In such old landscapes, the effect of time is confounded
by changes in other factors: climate, parent material, and relief. If the rate of min-
eral weathering is faster than in cool temperate regions, and if leaching is more
severe, then weathering occurs to a much greater depth. The deep horizons are
less influenced by surface organic matter. Clay minerals break down mainly to
iron and aluminum oxides, with the release of SiO
2
and basic cations (chapter 4).
Silica not removed in solution remains as resistant quartz grains or hardened lay-
ers of silcrete. Under such conditions, climate exerts less influence than parent
material and relief on the end product of soil formation.
Soil as a Natural Body
1.4
Current Attitudes about Soil
During the twentieth century, the predominant attitude regarding soil use was
one of exploitation. Exploitation of soil for production has accelerated since the
1940s with the introduction of greater mechanization, expansion of irrigation, and
increased use of chemical fertilizers. Although this intensification of agriculture
has had the very desirable benefit of enabling world food production to more than
keep pace with the increase in population (now greater than 6 billion), there have
been costs in the form of worsening soil and water degradation (table 1.1).
Viticulture has the potential to degrade soil and water resources because many
vineyards are clean-cultivated and situated on slopes that are sometimes very steep.
Soil eroded in runoff can be transported to streams and rivers. But in the Old
World, a tradition of nourishing the soil to nurture the vine has developed over
centuries, as in Bordeaux and Burgundy (chapter 9). Also, in the New World,
1.4.1
Causes, Extent, and Severity of Land Degradation Globally
Table 1.1
Area
(Million ha)
a
Process
Reversibility
Off-site Effects
Water erosion
Wind erosion
Loss of nutrients
Loss of organic
matter
Soil acidification
Salinization
Pollution
Physical damage
700
280
135
General
Difficult
Difficult
Easy
b
Easy
b
Important
Important
Possibly important
Negligible to
possibly important
Negligible
Possibly important
Possibly important
Possibly important
10
80
20
60
Easy
b
Difficult
Difficult
Difficult
a
Total area of arable land is ca. 1500 million ha.
b
Provided the necessary inputs are available and are economically justified
Source:
Data from Greenland et al. (1998)
