Geography Reference
In-Depth Information
Climatic conditions.
Soil fertility tends to be best where the climate is not too hot,
not too cold, not too wet, or not too dry. High heat speeds up organic decay, basically
wasting a high volume of nutrients before soil can make them available to plants. Low
temperatures slow down decay, and again render nutrients unavailable to plants. Very
wet conditions flush away nutrients in soil (a process called
leaching
), while very dry cli-
mates produce very little “soup” to surround soil particles. In contrast, climatic moderation
(such as occurs in the middle latitudes) encourages nutrient accumulation and retention
in soil, and thereby enhances fertility.
Profile depth.
This is the vertical distance from surface to bedrock — “thickness,”
in other words. Thick is preferable for the simple reason that more soil is present. As is
the case with other factors, thickness varies geographically. Soft-parent material may be
responsible for locally thick soils, and so, too, the process of deposition, as when a silt-
laden river overflows its banks and adds a new layer of sediments to the flooded coun-
tryside (also, see “Deposition” in this chapter).
Plant cover.
Organic matter contributes greatly to the quality of topsoil. Thus, plant
cover is an important determinant of the geography of soil fertility. Generally, grasslands
are best because their fine roots and root hairs readily decompose and are in the soil to
begin with. Leaf-fall from trees has good nutrient potential, but these are deposited on top
of the ground and therefore are dependent on climatic factors (rainfall and temperature)
to mix with topsoil.
Wasting away
Mass wasting
is the movement of particles that are products of weathering. Thus, it's the as-
pect of gradation that is most directly concerned with creation and alteration of landforms and
has two discrete components:
Erosion:
This is the removal of
particulate matter
(pieces of soil and rock) from a par-
ticular location. Thinking back to the Grand Canyon, running water removed — or
eroded
—
material from the space now occupied by the canyon. Of course, those eroded pieces didn't
just disappear. Instead, they went someplace else.
