The Need for Sustainable Food Production Systems - Agroecology: The Ecology of Sustainable Food Systems - page 13

wastes converts to ammonia and enters the atmosphere,
where it combines with water droplets to form ammonium
ions. As a result, the rainwater downwind of livestock feed-
ing operations often has extremely high concentrations of
ammonium ions. Although most treated animal waste is
ultimately applied to fields as fertilizer, the phosphorus and
nitrogen it contains is beyond useful levels for most crops.
Furthermore, factory farms often have so much waste to
get rid of that they apply more treated waste to fields than
the soil can accommodate, and do so year-round, even at
times in the crop cycle when fields and crops are unable to
absorb it. The excess nitrogen and phosphorus finds its way
into streams, rivers, and the local drinking water supply.
Through all these various avenues, tons of nitrogen and
phosphorus from animal waste and inorganic fertilizer make
their way into lakes and rivers and then into the oceans,
creating large “dead zones” near river mouths. More than
50 of these dead zones exist seasonally around the world,
with some of the largest — in the Chesapeake Bay, Puget
Sound, and Gulf of Mexico — off the coast of the U.S.

adapted traits through selective breeding, and by contin-
ually recruiting wild species and their genes into the pool
of domesticated organisms. In the last 100 years or so,
however, the overall genetic diversity of domesticated
plants and animals has declined. Many varieties of plants
and breeds of animals have become extinct, and a great
many others are heading in that direction. About 75% of
the genetic diversity that existed in crop plants in 1900
has been lost (Nierenberg and Halweil, 2004). The United
Nations Food and Agriculture Organization estimates that
as many as two domesticated animal breeds are being lost
each week worldwide (FAO, 1998).
In the meantime, the genetic bases of most major crops
and livestock species have become increasingly uniform.
Only six varieties of corn, for example, account for more
than 70% of the world's corn crop, and 99% of the turkeys
raised in the U.S. belong to a single breed (FAO, 1998).
The loss of genetic diversity has occurred mainly
because of conventional agriculture's emphasis on short-
term productivity gains. When highly productive varieties
and breeds are developed, they tend to be adopted in favor
of others, even when the varieties they displace have many
desirable and potentially desirable traits. Genetic homo-
geneity among crops and livestock is also consistent with
the maximization of productive efficiency because it
allows standardization of management practices.
For crop plants, a major problem with increasing
genetic uniformity is that it leaves each crop as a whole
more vulnerable to attack by pests and pathogens that
acquire resistance to pesticides and to the plants' own
defensive compounds; it also makes crops more vulnera-
ble to changes in climate and other environmental factors.
These are not insignificant or hypothetical threats. Every
year, crop pests and pathogens destroy an estimated 30 to
40% of potential yield. Plant pathogens can evolve rapidly
to overcome a crop's defenses, and global commerce and
genetically uniform farm fields allow these new virulent
strains to spread rapidly from field to field and continent
to continent. In a report on crop diversity and disease
threats released in 2005, researchers identified four dis-
eases with the potential to devastate the U.S. corn crop,
five that could threaten potatoes, and three with the poten-
tial to harm U.S.-grown wheat (Qualset and Shands,
2005). In late 2004, for example, a new soybean rust
(a type of fungus) appeared in the southern U.S. and began
to attack the soybean crop. None of the commercial soy-
bean varieties planted in the U.S. are resistant to it, and
scientists are concerned about the potential impact on the
U.S.$18 billion soybean harvest as the rust spreads north.
Throughout the history of agriculture, farmers — and
more recently, plant scientists — have responded to out-
breaks of disease by finding and planting resistant varieties
of the affected crop. But as the size of each crop's genetic
reservoir declines, there are fewer and fewer varieties from
which to draw resistant or adaptive genes. The importance

D EPENDENCE ON E XTERNAL I NPUTS

Conventional agriculture has achieved its high yields
mainly by increasing agricultural inputs. These inputs
comprise material substances such as irrigation water, fer-
tilizer, pesticides, and processed feed and antibiotics; the
energy used to manufacture these substances, to run farm
machinery and irrigation pumps, and to climate-control
animal factories; and technology in the form of hybrid and
transgenic seeds, new farm machinery, and new agro-
chemicals. These inputs all come from outside the agro-
ecosystem itself; their extensive use has consequences for
farmers' profits, use of nonrenewable resources, and the
locus of control of agricultural production.
The longer conventional practices are used on farmland,
the more the system becomes dependent on external inputs.
As intensive tillage and monoculture degrade the soil,
continued fertility depends more and more on the input of
fossil-fuel-derived nitrogen fertilizer and other nutrients.
Agriculture cannot be sustained as long as this depen-
dence on inputs remains. First, the natural resources from
which many of the inputs are derived are nonrenewable and
their supplies finite. Second, dependence on external inputs
leaves farmers, regions, and whole countries vulnerable to
supply shortages, market fluctuations, and price increases.
In addition, excessive use of inputs has multiple negative
off-farm and downstream impacts, as noted above.

L OSS OF G ENETIC D IVERSITY

Throughout most of the history of agriculture, humans
have increased the genetic diversity of crop plants and
livestock worldwide. We have been able to do this both
by selecting for a variety of specific and often locally