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Earthworms are most active during the winter months, as, unless
the soil is irrigated, it generally becomes too hot and dry for
them during the summer. Some species may even appear to die out
altogether in the summer, but they will have left their eggs behind
ready to hatch when the conditions become suitable for them. Other
species burrow down to a cooler spot in the soil and tie themselves
up into a small knot ready to aestivate for the summer (a similar
process to hibernation where they are completely inactive for long
periods). Once the conditions are suitable these earthworms will
become active again.
A recent study in Canterbury has shown that earthworms can remain
active throughout the summer under irrigated conditions. Earthworm
populations were able to be maintained above 300 m2 in
irrigated plots throughout the summer, but populations were reduced
to almost zero in mid-summer where no irrigation was used.
The use of irrigation can increase the productivity of crops or
pastures, which results in greater inputs of organic matter to the
soil, thereby providing earthworms with additional food supplies.
Excessive water inputs can however have an adverse effect upon
earthworms, mainly due to the conditions of poor aeration that accompany
high soil moisture. After heavy rainfalls, for example, earthworms
often come up to the soil surface in search of air.
For more information contact:
Dr Trish Fraser
Agricultural practices and earthworm
population
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