Environmental Engineering Reference
In-Depth Information
Scientists also point out that continuing to in-
crease fertilizer, water, and pesticide inputs eventually
produces no additional increase in crop yields. For
example, grain yields rose about 2.1% per year be-
tween 1950 and 1990, but then growth dropped to 1.1%
per year between 1990 and 2000 and to 0.5% between
1997 and 2004. No one knows whether this downward
trend will continue.
There is also concern that crop yields in some
areas may decline as soil erodes and loses fertility, irri-
gated soil becomes salty and waterlogged, under-
ground and surface water supplies become depleted
and polluted with pesticides and nitrates from fertiliz-
ers, and populations of rapidly breeding pests de-
velop genetic immunity to widely used pesticides. We
do not know how close we are to such environmental
limits.
Also, according to Indian economist Vandana
Shiva, overall gains in crop yields from new green and
gene revolution varieties may be much lower than
claimed. The yields are based on comparisons be-
tween the output per hectare of old and new
monocul-
ture
varieties rather than between the even higher
yields per hectare for
polyculture
cropping systems and
the new monoculture varieties that often replace poly-
culture crops.
There is also concern that the projected increased
loss of biodiversity might limit the genetic raw mater-
ial needed for future green and gene revolutions. The
FAO estimates that two-thirds of all seeds planted in
developing countries belong to uniform strains. Such
genetic uniformity increases the vulnerability of food
crops to pests, diseases, and harsh weather.
Science: Cultivating More Land—Another
Limited Solution
Significant expansion of cropland is unlikely over the
next few decades because of poor soils, limited water,
high costs, and harmful environmental effects.
Theoretically, clearing tropical forests and irrigating
arid land could more than double the world's crop-
land. In reality, much of this area is
marginal land
with
poor soil fertility, steep slopes, or both. Cultivation of
such land is unlikely to be sustainable.
Much of the world's potentially cultivable land lies
in dry areas, especially in Australia and Africa. Large-
scale irrigation in these areas would require expensive
dam projects, use large inputs of fossil fuel to pump
water over long distances, and deplete groundwater
supplies by removing water faster than it is replen-
ished. It would also require expensive efforts to prevent
erosion, groundwater contamination, salinization, and
waterlogging, all of which reduce crop productivity.
Furthermore, these potential increases in cropland
would not offset the projected loss of almost one-third
of today's cultivated cropland caused by erosion, over-
grazing, waterlogging, salinization, and urbanization.
Such cropland expansion would also reduce wildlife
habitats and thus the world's biodiversity. Bottom line:
Significant expansion of cropland is unlikely over the next
few decades.
Find out how much of the world's land is suitable for
farming and how that land is now used at Environmental
ScienceNow.
Science: Producing More Meat
Meat and meat products are important sources of
protein, but meat production has many harmful
environmental effects.
Meat and meat products are good sources of high-
quality protein. Between 1950 and 2004, world meat
production increased more than fivefold, and per
capita meat production more than doubled. It is likely
to more than double again by 2050 as affluence rises in
middle-income developing countries (such as China
and India) and people begin consuming more meat.
Some analysts expect most future increases in
meat production to come from densely populated
feed-
lots,
where animals are fattened for slaughter by feed-
ing on grain grown on cropland or meal produced
from fish. Feedlots account for about 43% of the
world's beef production, half of pork production, and
almost three-fourths of poultry production.
In the United States, most production of cattle,
pigs, and poultry is concentrated in increasingly large,
Science: Increasing Irrigation—
A Limited Solution
The amount of irrigated land per person has been
declining since 1978 and is projected to fall much
more during the next few decades.
Approximately 40% of the world's food production
comes from the 20% of the world's cropland that is ir-
rigated. Between 1950 and 2004, the world's irrigated
area tripled, with most of the growth occurring from
1950 to 1978.
However, the amount of irrigated land per person
has been declining since 1978 and is projected to fall
much more between 2005 and 2050. One reason is that
since 1978, the world's population has grown faster
than irrigated agriculture. Other factors are depletion
of underground water supplies (aquifers), inefficient
use of irrigation water, and salt buildup in soil on irri-
gated cropland. In addition, the majority of the
world's farmers do not have enough money to irrigate
their crops.
