Environmental Engineering Reference
In-Depth Information
(a)
Terracing
(b)
Contour planting and strip cropping
(c)
Alley cropping
(d)
Windbreaks
Figure 10-16
Solutions:
In addition to conservation tillage, soil conservation methods include (a) terracing,
(b) contour planting and strip cropping, (c) alley cropping or agroforestry, and (d) windbreaks.
Crops such as corn, tobacco, and cotton can de-
plete nutrients (especially nitrogen) in the topsoil if
they are planted on the same land several years in a
row.
Crop rotation
provides one way to reduce these
losses. Farmers plant areas or strips with nutrient-
depleting crops one year. The next year, they plant the
same areas with legumes whose root nodules add ni-
trogen to the soil. In addition to helping restore soil
nutrients, this method reduces erosion by keeping the
soil covered with vegetation.
tilizers can run off the land and pollute nearby bodies
of water.
These fertilizers can replace depleted inorganic
nutrients, but they do not replace organic matter.
Thus, for healthy soil, both inorganic and organic fer-
tilizers should be used.
10-4 FOOD PRODUCTION, NUTRITION,
AND ENVIRONMENTAL EFFECTS
Science: Inorganic Fertilizers
Inorganic fertilizers can help restore soil fertility if
they are used with organic fertilizers and if their
harmful environmental effects are controlled.
Many farmers (especially in developed countries) rely
on
commercial inorganic fertilizers.
The active ingredi-
ents typically are inorganic compounds that contain
nitrogen, phosphorus,
and
potassium.
Other plant nutri-
ents may be present in low or trace amounts. These
fertilizers account for about one-fourth of the world's
crop yield. However, without careful control these fer-
Science: Global Grain Production
After increasing significantly since 1950, global grain
production has mostly leveled off since 1985, and per
capita grain production has declined since 1978.
After almost tripling between 1950 and 1985, world
grain production has essentially slowed down (Fig-
ure 10-17, left, p. 218). Also, after rising by about 36%
between 1950 and 1978, per capita food production
has declined (Figure 10-17, right). The sharpest drop
in per capita food production has occurred in Africa
since 1970.
