Deep, Down and Dirty: The Science of Soil Page #3

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Just why are they so important?

Well, first of all the sheer

scale of the worm operation.

As they tunnel into the ground

in their millions,

their burrows permeate the earth

like a vast ventilation system,

providing essential supplies of air

to everything else that

lives in the soil.

But that's not the earthworms'

only talent.

They also continue

what the fungi began.

They eat and digest dead leaves

underground,

unlocking their trapped nutrients.

The way they do this reveals

one of the most fundamental

secrets of soil.

But it's hard to see.

'So I've come to meet

Mark Hodson, Professor

'of Environmental Science

at York University.'

I find they're very fun creatures,

you see them a lot.

If you walk around after the rain

you see them crawling around.

'He's spent years studying what

and how worms eat.'

They go up and down.

During the day, they stay in

the bottom of their burrows.

At night they come out onto

the surface, they look round,

sort of, sometimes they keep their

tails anchored in their burrows.

They sort of stretch out

and eat or grab organic material,

they pull it down into their

burrows to eat later on.

And the undigested material gets

squirted out of the back end and that

helps make all of this black, browny

stuff which is the soil.

Nothing is quicker at breaking down

dead leaves than an earthworm.

It's thought that in the average

field the worms get through

a staggering one and a half

tonnes of plant matter every year.

They're like leaf-processing

factories,

operating on an industrial scale.

Yet they look nothing more than

a simple, fleshy tube.

So what's going on inside?

To help answer that, Mark has been

doing a rather unsavoury experiment.

This Petri dish contains

a sample of plain soil.

And this one was made using earth

that has passed through

an earthworm.

In other words, worm poo.

Mark's been comparing the two

and he's uncovered

evidence of a hidden army of secret

agents at work within the worm.

Bacteria.

So each of these spots is

a bacterial colony. You can see

there are far more growing here

from the material that's just

come out of the earthworm gut.

So the earthworm ingests the soil,

there are bacteria in there already,

and the earthworm gut environment

is good for bacteria.

It's moist, its got the right pH,

the earthworm is secreting mucous

full of polysaccharide sugars,

which the bacteria love to eat.

So it's bacteria

that finish the job of breaking down

dead plant matter.

There are billions of them

naturally present in the ground,

like workers on a production line

turning dead plants into new soil.

But inside the earthworm

this activity is magnified to levels

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