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Fertiliser applications are usually made to soils in order to maintain
or improve crop or pasture growth and yields. The increased plant
material produced by fertilisers results in increased returns of
organic material to the soil in the form of decaying roots, litter
and crop residues. Indirectly, applications of superphosphate and
nitrogen fertilisers in particular have been shown to have long-term
beneficial effects on earthworm populations.
Sometimes, however, where very high rates of inorganic fertilisers
are applied (especially ammonia based fertilisers), earthworm numbers
may decline due to the short term changes in soil pH.
Since most earthworm species prefer a soil pH of around 7, the
addition of lime to soil often encourages earthworm populations.
The continued use of ammonium-containing or forming fertilisers
is potentially damaging to earthworm populations since they can
cause soil to become too acidic for the earthworms. For this reason,
ammonium sulfate has often been reported to have harmful effects
on earthworms and is commonly applied to the greens on golf courses
to stop earthworm activity.
Other forms of fertiliser, such as manures and sewage sludges have
also been found to increase earthworm populations as these fertilisers
provide additional organic matter – again providing an extra
food source for the earthworms.
For more information contact:
Dr Trish Fraser
Agricultural practices and
earthworm populations
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