Environmental Engineering Reference
In-Depth Information
17% of total U.S.
commercial
energy use
4%
2%
6%
5%
Crops
Livestock
Food processing
Food distribution and preparation
Food production
Figure 10-7
In the United States, industrialized agriculture uses about 17% of all commercial energy.
Food travels an average 2,400 kilometers (1,500 miles) from farm to table. (Data from David Pimentel
and Worldwatch Institute)
needed to produce a unit of food has fallen consider-
ably, so that today most plant crops in the United States
provide more food energy than the energy used to
grow them.
Energy efficiency is much lower if we look at the
whole U.S. food system. Considering the energy used
to grow, store, process, package, transport, refrigerate,
and cook all plant and animal food,
about 10 units of
nonrenewable fossil fuel energy are needed to put 1 unit of
food energy on the table.
By comparison, every unit of
energy from human labor in traditional subsistence
farming provides at least 1 unit of food energy and as
many as 10 units of food energy using traditional in-
tensive farming.
are planted together. Low-input polyculture offers a
number of advantages. There is less need for fertilizer
and water because root systems at different depths in
the soil capture nutrients and moisture efficiently. This
practice provides more protection from wind and wa-
ter erosion because the soil is covered with crops year-
round. Insecticides are rarely needed because multiple
habitats are created for natural predators of crop-
eating insects. Also, there is little or no need for herbi-
cides because weeds have trouble competing with the
multitude of crop plants. The diversity of crops raised
provides insurance against bad weather. Polyculture is
a way of growing food by copying nature.
Recent ecological research has shown that, on av-
erage, low-input polyculture produces higher yields
per hectare of land than high-input monoculture. For
example, a 2001 study by ecologists Peter Reich and
David Tilman found that carefully controlled polycul-
ture plots with 16 different species of plants consis-
tently outproduced plots with 9, 4, or only 1 type of
plant species.
Global Outlook: Traditional Agriculture
Many traditional farmers in developing countries use
low-input agriculture to produce a variety of crops on
each plot of land.
Traditional farmers in developing countries today
grow about one-fifth of the world's food on about
three-fourths of its cultivated land. Many traditional
farmers grow several crops on the same plot simulta-
neously, a practice known as
interplanting.
Such crop
diversity reduces the chance of losing most or all of the
year's food supply to pests, bad weather, and other
misfortunes.
Interplanting strategies vary.
Polyvarietal cultiva-
tion
involves planting a plot with several genetic vari-
eties of the same crop. In
intercropping,
two or more
different crops are grown at the same time on a plot—
for example, a carbohydrate-rich grain that uses soil
nitrogen and a nitrogen-fixing plant (legume) that puts
it back. In
agroforestry,
or
alley cropping,
crops and
trees are grown together.
A fourth type of interplanting is
polyculture,
in
which many different plants maturing at various times
10-2 SOIL EROSION
AND DEGRADATION
Science: Causes of Soil Erosion
Water, wind, and people cause soil erosion.
Most people in developed countries get their food
from grocery stores, fast-food chains, and restaurants.
But ultimately
all food comes from the earth or soil
—the
base of life. This explains why preserving the world's
topsoil (Figure 3-21, p. 51) is the key to producing
enough food to feed the world's growing population.
Land degradation
occurs when natural or human-
induced processes decrease the ability of land to sup-
port crops, livestock, or wild species in the future. One
