Geoscience Reference
In-Depth Information
Global distribution of Inceptisols
(a)
(c)
Figure 11.34 Inceptisols. (a) Generalized map of Inceptisols
on Earth. These soils occur on about 10% of Earth's ice-free
land area. ( Source: U.S. Department of Agriculture.) (b) An Incep-
tisol landscape. Soils on these steep slopes within the Appa-
lachian Mountains have weakly developed horizons because
they are easily eroded. (c) An Inceptisol in Wisconsin. Note the
weak E horizon (arrow) that indicates some eluviation of iron has
occurred.
(b)
thing that lies beneath the ground on which we walk. This lack of
awareness is due in large part to major demographic changes in
the country over the past 200 years. In 1800 approximately 90%
of the labor force was farmers intimately familiar with the soil
because they worked with it every day. By 1900 the percentage of
the labor force devoted to agriculture had dropped to about 38%.
Today, farmers comprise less than 2% of the American workforce.
In contrast, over 80% of Americans live in urban environments
where soils are rarely considered by the average person.
In spite of the indifference most people have toward the
ground beneath them, the fact is that soils are very important to
everyone. In terms of agriculture, understanding the character
of soil is essential for a variety of reasons directly related to
crop yields and food production (Figure 11.36). For example,
the texture of soil is important because it influences how rapidly
water drains through the soil. In general, farmers desire loamy-
textured soils like a silt-rich Mollisol because they hold draining
water long enough (but not too long) for crops to be consistently
well watered. Likewise, soils with good structure are usually
preferred because they have higher porosity and better aeration,
and crop roots can spread easily through the ground.
Another important factor that farmers consider relating to soils
is their fertility. As we have seen in tropical regions, soil fertility is an
Andisols Andisols are soils that form in parent material that is
more than half volcanic ash. Like Entisols and Inceptisols, Andi-
sols occur at scattered places on Earth, occupying about 1% of
Earth's ice-free landmass (Figure 11.35a). Most of Hawaii, for
example, lies within areas classified as Andisols (FigureĀ 11.35b).
Given their volcanic origin, it is accurate to say that the most
important soil-forming factor associated with Andisols is par-
ent material because fresh deposits of volcanic ash are deposited
on the landscape following a volcanic eruption. These deposits
consist mostly of glass-like shards that frequently contain a high
proportion of carbon. As a result, these soils are usually dark in
color (Figure 11.35c) and quite fertile. Given the high frequency
of volcanic eruptions in some areas, Andisols may be poorly de-
veloped because the soils have had insufficient time to develop.
Human Interactions with Soils
Throughout much of recorded history, soil has been a key environ-
mental factor around which human societies revolved. For most
people living in the United States today, however, soil is a vague
Andisols Soils formed in parent material that is at least 50%
volcanic ash.
 
 
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