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Long-term application of chemical fertilizers has both positive and negative
impacts on soil and the environment. Chemical fertilizers fertilize the soil and
increase crop yields but they modify microbial functions involved in bioremediation
and organic matter processing. As a consequence soils become unproductive. In
the 1960s the Ismani area was the major growing zone of maize in Tanzania. From
the 1960s to early 1990s this area attracted more people to invest in maize production.
People immigrated in the area because of soil fertility where they grew maize
to curb food insecurity and poverty. In 1976 Ismani contributed over 10% of the
total maize in the National Milling Corporation. Subsequently, in 1983 Ismani produced
250,000 tons of maize. This production was mainly catalyzed by the application
of chemical fertilizers. However, in 1990s the production trend started to
diminish rapidly. The major reason for this downfall was acidification of the soils
due to increasing soil pH. Long-term chemical fertilization was the major reason for
this. Acidic soil limited the availability of plant nutrients and raised the concentration
of toxic metals in the soil. Subsequently, this situation impaired the life of
micro-organism such as earthworms, which forms humus useful for crop
production. |
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