Solutions to Agricultural Problems 361© Pierre Holtz/Reuters/CorbisNG MapsGlobal
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SAHELTANZANIASustainable agriculture is not a single program but
a series of programs adapted for specific soils, climates,
and farming requirements. Some sustainable farmers—
those who practice organic agriculture—use no commer-
cial inorganic fertilizers or pesticides; others use a system
of integrated pest management (IPM), which incorporates
the limited use of pesticides with pest-controlling biologi-
cal and cultivation practices. (See the Case Study at the
end of the chapter for more on organic agriculture.)
In growing recognition of the environmental prob-
lems associated with industrialized agriculture, more
and more mainstream farmers are trying some methods
of sustainable agriculture. These methods cause fewer
environmental problems to the agricultural ecosystem,
or agroecosystem, than industrialized agriculture. This
trend away from using intensive techniques that produce
high yields and toward methods that focus on long-term
sustainability of the soil is sometimes referred to as the
second green revolution.Instead of using large quantities of chemical pesti-
cides, sustainable agriculture controls pests by enhancing
natural predator–prey relationships. Biological diversity is
maintained to minimize pest problems. For example, pro-
viding hedgerows (rows of shrubs) between fields provides
a habitat for birds and other insect predators.
An important goal of sustainable agriculture is to pre-
serve the quality of agricultural soil. Crop rotation, conser-
vation tillage, and contour plowing help control erosion
and maintain soil fertility (see Figures 12.17c and 3.1a).
Sloping hills converted to mixed-grass pastures erode less
than hills planted with field crops, thereby conserving
the soil and supporting livestock.
Animal manure added to soil not only cuts costs but
decreases the need for high levels of commercial inorganic
fertilizers. Legumes such as soybeans, clover, and alfalfa
convert atmospheric nitrogen into a form that plants
can use in a process called biological nitrogen fixation. Thus
legumes also reduce the need for nitrogen fertilizers.
One particular non-insect biological control agent targets
desert locusts, which periodically increase in number and
swarm across the African Sahel, threatening crops across
12 million hectares (30 million acres) located south of the
Sahara Desert (see photo). Extensive swarms can move
well beyond the Sahel, including into southern Africa.
During a major swarm in 1988, African farmers sprayed
massive quantities of pesticides into the environment to
bring the locust population under control. However, many
people were concerned about the adverse ecological and
health effects of using such large quantities of pesticides.
Economists were also concerned about high short-term
costs of using pesticides ($300 million for the 1988 swarm)
as well as long-term economic costs.
After the 1988 swarm, an international team of
scientists worked for 15 years to develop a biological
control for locusts that consists of fungal spores. Called
Green Muscle, it is environmentally safe and very effective.
The use of Green Muscle in Tanzania—the first major
application of the biological control agent— averted much
of the threat from a 2009 locust infestation that could have
impacted crops that feed as many as 15 million people.
EnviroDiscovery
A New Weapon against Locust Swarms
A boy runs through a cloud of locusts
during a 2004 swarm in Senegal, in
the Sahel.