Visualizing Environmental Science

Stephen Aumus/US Dept. of Agriculture/SPL

356 CHAPTER 14 Agriculture and Food Resources

generally equal. Advances by research scientists since then

have dramatically increased food production in highly

developed countries (Figure 14.7). Greater knowledge

of plant nutrition has resulted in production of fertilizers

that promote high yields. The use of pesticides to control

insects, weeds, and disease-causing organisms has also

improved crop yields.

The Green Revolution By the middle of the 20th cen-

tury, serious food shortages occurred in many developing

countries coping with growing populations. The devel-

opment and introduction during the 1960s of high-yield

varieties of wheat and rice to Asian and Latin American

countries gave these nations the chance to provide their

people with adequate supplies of food (Figure 14.8).

But the high-yield varieties required intensive industrial

cultivation methods, including the use of commercial

inorganic fertilizers, pesticides, and mechanized machin-

ery, to realize their potential. These agricultural tech-

nologies were passed from highly developed nations to

developing nations.

Using modern cultivation methods and the high-

yield varieties of certain staple crops to produce more

food per acre of cropland is known as the green revo-

lution. Some of the success stories of the green revolu-

tion are remarkable. During the 1920s, Mexico produced

Global Decline in Domesticated
Plant and Animal Varieties

A global trend is currently under way to replace the many
local varieties of a particular crop or domesticated farm
animal with just a few kinds (Figure 14.6). A traditional
variety is adapted to the climate where it was bred and con-
tains a unique combination of traits conferred by its unique
combination of genes. Modern varieties, which are bred for
uniformity and maximum production, are generally more
susceptible to insect pests and disease and less able to adapt
to environmental changes, including climate change.
When farmers abandon traditional varieties in favor
of more modern ones, the traditional varieties frequently
face extinction. This represents a great loss in genetic
diversity because each variety’s characteristic combina-
tion of genes gives it distinctive nutritional value, size,
color, flavor, resistance to disease, and adaptability to
different climates and soil types.
To preserve older, more diverse varieties of plants and
animals, many countries, includ-
ing the United States, are collect-
ing germplasm: seeds, plants, and
plant tissues of traditional crop
varieties and the sperm and eggs
of traditional livestock breeds.

Increasing Crop Yields

Until the 1940s, agricultural yields among various coun-
tries, whether highly developed or developing, were

germplasm Any

plant or animal

material that may be

used in breeding.

Average U.S. wheat yields, 1950 to 2010

Uʈ}ÕÀiÊ£{°ÇÊ

Each year shown is actually an average of 3 years to minimize the

effects that poor weather conditions might have in a single year.

Similar increases in yield have occurred in other grain crops.

1950 1960 1970

Year

1980 1990 2000 2010

5

10

15

20

25

30

35

40

45

Annual yield (bushels per acre)

50

Based on data from USDA.

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If you eat eggs, they are probably laid
by white leghorn hens, which
produce almost all of the
eggs in the United
States as well as
those in many other
countries. This
breed is prolific at
egg laying, but it
is not particularly
good for meat
production.