Geoscience Reference
In-Depth Information
Global distribution of Andisols
(a)
(c)
Figure 11.35 Andisols. (a) Generalized map of Andisols on
Earth. These soils are associated with volcanic regions and occur
on about 1% of Earth's ice-free land area. ( Source: U.S. Depart-
ment of Agriculture.) (b) Typical Andisol landscape in Hawaii. The
Hawaiian Islands are covered in most places with volcanic sedi-
ments. (c) Andisol in Hawaii. Note the banding in this soil, which
reflects periodic deposition of new volcanic parent material.
(b)
important issue there because Oxisols and Ultisols are heavily leached
of their nutrients by the abundant rainfall. As a result, subsistence
farmers clear their land and burn the forest residue (Figure10.29) to
temporarily increase soil fertility. Soil fertility is also a major concern
in the agricultural regions of the United States, such as the Midwest
and California's Central Valley. These regions are very important in
the United States because they provide much of the food Americans
consume. Substantial amounts of food are also exported from these
regions to countries around the world. As you will see in Chapter
20, the Central Valley of California is known as the nation's “salad
bowl” because most of our vegetables are grown there. In a similar
vein, the Midwest is the location of the important corn and wheat belts
(Figure 10.33) that provide much of our food. A large part of this zone
overlaps with the fertile Mollisols (as well as some Alfisols) shown
in Figure 11.22. If you consider that the average American consumes
over 55 kg ( 125 lb) of wheat per year, as well as over 23 kg (50 lb)
of corn, it is easy to see why soils in this region are heavily farmed.
Given the intense pressure on the nation's agricultural soils,
it is essential to maintain high levels of fertility to insure sustain-
able levels of inexpensive food and to meet increased demand
as population grows. During the commercial agricultural era,
which intensified in the United States after World War II, the
primary way to increase fertility and crop yields has been to
apply commercial fertilizers loaded with calcium, magnesium,
potassium, and nitrogen (Figure 11.37a). Another technique
used to raise fertility is the application of animal manure. Such
Figure 11.36 Soils and agriculture. (a) Workers harvesting
lettuce near Yuma, Arizona. In order to produce food efficiently,
farmers must have a keen understanding of the character and
variability of soils.
 
 
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