Page 248 - Environment: The Science Behind the Stories

Figure 9.17 No-till farming is practiced on 24% of U.S. farmland. (a) Other forms
of conservation tillage are practiced on 18% of land, while “reduced tillage” (15–30% crop
residue left on ground after harvest) takes place on 21%, and conventional farming (0–15%
residue left on ground) occurs on 37%. Across the United States (b), red and orange colors
on this county map show where no-till methods are practiced most. Data are for 2008 (a) and
2004 (b), from Conservation Technology Information Center, National Crop Residue Management Survey.

Can you find your county on
this map? What percentage of
its farming is no-till? How about your Iowa
state—what percentages does it show?

No-till farming
Conventional (65.0 million acres)
(intensive)
tillage
(101.3 million
acres) Other
conservation Percent no-till
tillage
(48.8 million 0–10%
Reduced acres)
tillage 10–25%
(59.0 million acres) 25–50%
50–100%
(a) Types of tillage in (b) Distribution of no-till farming in United States, and in Iowa
United States

reduced too much. In cultivating trees through the practice
of forestry, methods such as clear-cutting—the removal of
all trees from an area at once (p. 335)—can lead to severe
erosion, but alternative methods that remove fewer trees
over longer periods of time help to minimize soil loss. When
banks along creeks and roadsides erode, we plant plants to
anchor the soil. China has embarked on the world’s larg-
est tree-planting program to slow its soil loss (Figure 9.18).
Although such “reforestation” efforts help slow erosion, they
do not at the same time produce ecologically functioning
forests, because tree species are selected only for their fast
growth and are planted in monocultures.

Overgrazing can degrade soil

Raising livestock has impacts on soils and ecosystems. When CHAPTER 9 • So I l AN d A gr I culT ure
sheep, goats, cattle, or other livestock graze on the open range,
they feed primarily on grasses. As long as livestock popula-
tions do not exceed the rangeland’s carrying capacity (pp.
85–86) and do not consume grass faster than it can regrow,
grazing may be sustainable. Moreover, human use of range- Figure 9.18 Vast swaths of countryside in northern and
land does not necessarily exclude its use by wildlife or its western China have been planted with fast-growing trees
continued functioning as a grassland ecosystem. However, such as poplars. These simple tree plantations do not create
when too many livestock destroy too much of the plant cover, ecologically functional forests, but they do reduce soil erosion.
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