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More Worms the Merrier for Soil E-mail
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Tuesday, 29 May 2007
More Worms the Merrier for Soil and Plant Quality

Daily News; New Plymouth, New Zealand

By Wally Richards 

March 2, 2007

There are 3500 to 4000 species of earthworms and almost 200 have been identified in New Zealand.

The only way to ensure good-quality plants and gardens is to have a healthy soil-food web. That means a soil that is teeming with microbes, beneficial fungi along with many soil creatures including big populations of earthworms.

The easiest way to determine that you have healthy soil is by the number of worms you see when the soil is opened up. No worms, in a moist soil, means you have a problem and, until it is rectified, you will struggle to have healthy plants and gardens.

I say moist soil because, when the soil becomes too dry, too wet or too cold you will be lucky to see any worms, even if you do have good worm populations.

When temperatures drop or soils get too warm or dry, worms know what to do. If it starts getting chilly, they may tunnel deep into the soil before it hardens. They may also coil into a slime-coated ball and go into a sleep-like state called estivation. It's something like a hibernating bear.

Once conditions improve to the worm's liking up they come to work your gardens.

There are 3500 to 4000 species of earthworms and almost 200 have been identified in New Zealand. They are full of calcium, protein, fibre and vitamins, making them a valuable food source for many mammals, reptiles and fish.

Earthworms vary in size, on average from no more than one centimetre to about three metres in length. One of the world's largest earthworms, the Giant Gippsland Earthworm (Megascolides australis), is found in Australia. It has an average length exceeding one metre. However, the longest recorded earthworm was a South African giant specimen (Microchaetus rappi), measuring around seven metres in length. 

An interesting site to find out about worms and other aspects of gardening is hosted by Lincoln University. It notes that pastures commonly support the biggest populations of earthworms because they usually contain large amounts of organic matter and are infrequently disturbed by cultivation.

Numbers of earthworms can commonly range between seven million and 12 million per hectare under a productive pasture in New Zealand. This corresponds to one to three tons of earthworms per hectare and means that the weight of earthworms below a pasture is similar to the weight of the grazing animals supported above ground.

Earthworms are hermaphroditic, which means they each have both male and female organs.

It is an old wives' tale that cutting an earthworm in half will make two earthworms; one part may survive, but it is much more likely that both parts will die. 

The excreta produced by earthworms is known as casts. As soil passes through an earthworm's body, some of the nutrients are converted into forms that are more readily available for plant uptake. So casts are generally rich in plant-available nutrients like nitrogen, phosphorus, and potassium.

As well as consuming soil, earthworms also help to break down and thereby recycle organic materials (such as dead herbage and dung). Scientists have calculated that each year through their activities they are responsible for burying around six tons of pasture litter per hectare.

As they burrow through the soil, earthworms create burrows and channels that help to loosen the soil, allowing air to circulate and roots and water to penetrate the soil more easily.

In New Zealand, 25 to 30 tons of soil per hectare per year has been measured by scientists as being deposited by earthworms in the form of casts. But some worms deposit their cast material both within and upon the soil surface, so the total amount of soil that they turn over in a year is even higher.

Last Updated ( Tuesday, 29 May 2007 )
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