The Need for Sustainable Food Production Systems - Agroecology: The Ecology of Sustainable Food Systems - page 4

but now farmers are far more likely to specialize, growing
corn for livestock feed, for example, or raising hogs. In
crop agriculture, specialization means monoculture —
growing only one crop in a field, often on a very extensive
scale. Monoculture allows more efficient use of farm
machinery for cultivation, sowing, weed control, and har-
vest, and can create economies of scale with regard to
purchase of seeds, fertilizer, and pesticides. Monoculture
is a natural outgrowth of an industrial approach to agri-
culture, where labor inputs are minimized and technology-
based inputs are maximized in order to increase productive
efficiency. Monoculture techniques mesh well with the
other practices of modern agriculture: monoculture tends
to favor intensive cultivation, application of inorganic
fertilizer, irrigation, chemical control of pests, and special-
ized plant varieties. The link with chemical pesticides is
particularly strong; vast fields of the same plant are more
susceptible to devastating attack by specific pests and
diseases and require protection by pesticides.

diverted rivers has been key to increasing overall yield
and the amount of land that can be farmed. Although only
18% of the world's crop land is irrigated (FAOSTAT,
2005), this land produces 40% of the world's food
(Serageldin, 1995; FAO, 2002). Currently, there are more
than 44 ha of irrigated land per 1000 people in the world
(FAOSTAT, 2005).
All sectors of society have placed rapidly increasing
demands on fresh water supplies over the past half-century,
but agricultural purposes account for the lion's share of
the demand — about 70% of water use worldwide (Postel
and Vickers, 2004). Unfortunately, agriculture is such a
prodigious user of water that in many areas where land is
irrigated for farming, irrigation has a significant effect on
regional hydrology. One problem is that groundwater is
often pumped faster than it is renewed by rainfall. This
overdraft can cause land subsidence, and near the coast it
can lead to saltwater intrusion. In addition, overdrafting
groundwater is essentially borrowing water from the future.
Where water for irrigation is drawn from rivers, agriculture
is often competing for water with water-dependent wild-
life and urban areas. Where dams have been built to hold
water supplies, there are usually dramatic effects down-
stream on the ecology of rivers. Irrigation has another type
of impact as well: it increases the likelihood that fertilizers
will be leached from fields and into local streams and
rivers, and it can greatly increase the rate of soil erosion.

A PPLICATION OF S YNTHETIC F ERTILIZER

The spectacular increases in yields in the second half of
the 20th century were due in large part to the widespread
and intensive use of synthetic chemical fertilizers. In the
U.S., the amount of fertilizer applied to fields each year
increased rapidly after World War II, from 9 million tons
in 1940 to more than 47 million tons in 1980. Worldwide,
the use of fertilizer increased tenfold between 1950 and
1992; since then, the increase has moderated, but in 2002,
the total world consumption of fertilizers was estimated
to be 141.6 million metric tons (FAOSTAT, 2005).
Produced in large quantities at relatively low cost
using fossil fuels and mined mineral deposits, fertilizers
can be applied easily and uniformly to crops to supply
them with ample amounts of the most essential plant nutri-
ents. Because they meet plants' nutrient needs for the short
term, fertilizers have allowed farmers to ignore long-term
soil fertility and the processes by which it is maintained.
The mineral components of synthetic fertilizers, how-
ever, are easily leached out of the soil. In irrigated systems,
the leaching problem may be particularly acute; a large
amount of the fertilizer applied to fields actually ends up
in streams, lakes, and rivers, where it causes eutrophica-
tion (excessive growth of oxygen-depleting plant and algal
life). Fertilizer can also be leached into groundwater used
for drinking, where it poses a significant health hazard.
Furthermore, the cost of fertilizer is a variable over which
farmers have no control since it rises with increases in the
cost of petroleum.

C HEMICAL P EST AND W EED C ONTROL

After World War II, chemical pesticides were widely
touted as the new, scientific weapon in humankind's war
against plant pests and pathogens. These chemical agents
had the appeal of offering farmers a way to rid their fields
once and for all of organisms that continually threatened
their crops and literally ate up their profits. But this prom-
ise has proven to be false. Pesticides can dramatically
lower pest populations in the short term, but because they
also kill pests' natural predators, pest populations can
often quickly rebound and reach even greater numbers
than before. The farmer is then forced to use even more
of the chemical agents. The dependence on pesticide use
that results has been called the “pesticide treadmill.” Aug-
menting the dependence problem is the phenomenon of
increased resistance: pest populations continually exposed
to pesticides are subjected to intense natural selection for
pesticide resistance. When resistance among the pests
increases, farmers are forced to apply larger amounts of
pesticide or to use different pesticides, further contributing
to the conditions that promote even greater resistance.
Although the problem of pesticide dependence is
widely recognized, many farmers — especially those in
developing nations — do not use other options. Even
in the U.S., the amount of pesticides applied to major field
crops, fruits, and vegetables each year remains at twice

I RRIGATION

An adequate supply of water is the limiting factor for food
production in many parts of the world. Thus supplying
water to fields from underground aquifers, reservoirs, and