Deep, Down and Dirty: The Science of Soil Page #4

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that are truly mind-blowing.

If you do counts on the soil

in earthworm guts

you can have 1,000 times more active

bacteria in that soil

than the bulk soil

surrounding the earthworm.

What it's proving is

the earthworms have ramped up

the bacterial activity in the soil.

And it's this army of bacteria,

hidden in the guts of earthworms,

that completes the vital cycle.

Unlocking all

the nutrients from dead leaves

and releasing them

back into the soil.

We very often think of soil as being

brown, solid, inert stuff.

But there's more life within in it

than flies, swims or walks above it.

And, far from being a haphazard

array of organisms,

this is a complex

range of interconnected structures

that support the life above.

As we've seen, it takes

a combination of plants, fungi,

animals and bacteria all working

together to keep nutrients

flowing from the dead to the living.

In the process, new soil is created

which in turn supports

even more life, making a cycle that

keeps the soil fertile.

Yet so far we've only scratched

the surface of the soil.

Everything we've seen happens within

just the topmost layers.

'Look deeper and there's

far more to soil than this.

'To reveal just how much,

I first need a bit of heat.'

What I have here is dried topsoil.

I want to find out

how much of this is

derived from plants by setting

fire to it.

If it's 100% plant material,

there should be nothing left.

So I'm starting with 100g.

'Let's see how much remains.'

As this is burning away, the soil is

completely transforming colour.

It's going from a soft brown

to almost a carbon colour.

Very similar to the

embers in a barbecue.

The soil particles are fracturing,

breaking apart. The organic matter

binding them together is burning

away and the soil particles are

just falling to pieces.

'The plant matter is turning

into gases like carbon dioxide

'that are lost into the air.

'After about 15 minutes of intense

heat, I'm going to weigh it again.'

See how much we've lost?

We started off with about 100,

it's now down to 70.

So about 30% of this original soil

was plant based.

It's burnt away.

Clearly, there's more to soil than

just plant material.

To see what that is, we need to get

beneath the topsoil

and look deeper down.

'This is Scolly's Cross

in Aberdeenshire, where

'a landslide has exposed the layers

of soil beneath the pine forest.

'It's something we rarely

get to see,

'as all this is usually hidden

underground.'

In a landslip situation like this

we get to examine perfectly

the soil profile, the horizons or

layers of various materials.

At the top we've got the vegetation

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