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Frequent cultivation of soil favours the breakdown of the soil
organic matter and therefore reduces the food supplies available
to earthworms. As a result of this reduction in food and also due
to direct mechanical damage, numbers of earthworms in the soil decline
following cultivation. Continual cultivation results in degradation
of the soil physical conditions, which can also be detrimental to
earthworm activity.
Different types of implements also have different effects on earthworms.
For example, the greater soil disturbance caused by rotary hoeing
compared to mould board or disc ploughs has a more damaging effect
on earthworm populations.
Deeper ploughs favour earthworms more than surface scraping ones,
because there is less disturbance of the surface soil.
The time of cultivation can also be important. Following cultivation,
the earthworms can become exposed at the soil surface and may desiccate
very rapidly, particularly if the soil is already dry. Earthworms
exposed at the soil surface may also be eaten by birds, but it is
estimated that birds only eat a small proportion (around 3-4%) of
the earthworms in the soil following cultivation.
Tillage method (direct drilling versus conventional cultivation)
also has a large effect on earthworm population size and composition
in arable soils. Earthworm populations can be up to three times
higher under direct drilling than conventional cultivation. The
reasons for the populations being higher under direct drilling include:
- the soil is not disturbed several times a year by cultivation,
organic litter material is available over a longer period since
it breaks down more slowly at the soil surface than when incorporated,
- the soil is generally more moist over the summer period under
direct drilling due to the surface mulch of litter,
the mulch also insulates the soil from extremes of temperature,
which can have very detrimental effects upon earthworms.
For more information contact:
Dr Trish Fraser
Agricultural practices and earthworm
populations
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