Deep, Down and Dirty: The Science of Soil

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'Every spring,

our planet is transformed.'

A riot of new life

bursting from the ground.

'And it's all made possible by one

rather misunderstood material.'

From early childhood

we're told that this stuff, dirt,

is best avoided.

But as someone with a lifelong

passion for soil and

everything that grows in it, it's a

rule I've always enjoyed breaking.

'I'm Chris Beardshaw. I spend my

life designing and planting gardens.

'Everything I do depends on soil.

'And I'm going to try and convince

you that it's an unrecognised

'wonder of the natural world.'

For billions of years

our land must've looked

pretty much like this.

Bare rock. A barren place.

Apparently devoid of life.

But something transformed it

into a vibrant, living planet.

'And that something was soil.'

But what fascinates me

is where did the soil come from?

What is it composed of

and why is it so essential to life?

So I'm going to get down

and dirty with soil.

I want to investigate its secrets.

And reveal it as you've never seen

it before. An intricate

microscopic landscape...

..teeming with

strange and wonderful life forms.

I'm going to reveal a world

more complex

and fragile than anything that

exists above ground.

A substance so remarkable,

you'll never walk on the grass

in the same way again.

'As a gardener, I spend my life

among plants.

'I see them emerge from the soil.

'But I've never really had

the chance to discover what gives

'soil its amazing, life-giving

force.

'So now I want to find out.

'And I'm starting by doing

what comes naturally.

'I'm going out to dig.'

Ask any gardener and they'll tell

you that the soil

provides their plants with the

nutrients that are needed for life.

And if you grow anything

intensively,

on farms or gardens,

you have to apply fertiliser

to replace and replenish those

nutrients in the soil.

In a natural landscape like this,

all of these trees are being

supported by the nutrients that

are just inherently in the ground.

But we shouldn't take these

nutrients for granted.

Like our fertilisers,

they also need to be replenished.

And how that happens is the first

great mystery of soil.

Even at the end of winter

there's plenty of evidence of life

on the woodland floor, or at least

last season's life.

Leaf litter,

coming from the canopy above.

But this is of no use at all

to the surrounding plants

in its current state.

That's because most plants simply

can't feed on dead leaves and twigs.

They're too tough to break down

and digest.

And this creates a problem.

Any nutrients

they hold are locked in

so the plants can't get at them.

'But hidden beneath the surface

of the soil

'is a very different picture.'

This modified-looking spade is

actually a scientific instrument.

The soil corer gives us

the perfect cross section through

the layers of the topsoil.

At the top we can see here this

unrotted layer of leaf litter.

It's last season's leaves just

sitting on the surface.

But below that is a much darker

layer where the

particles are much more broken down,

much smaller and quite compact.

Beneath that is what

we would recognise as topsoil.

These are described by soil

scientists as different horizons.

'Collectively, the horizons

are known as a soil profile.'

And the deeper down the profile

we go, the smaller

the pieces of leaf and twig become

until they just disappear.

So somehow the tough plant matter

is eventually broken down,

releasing its trapped

nutrients into the soil.

This is one of the most vital

processes in nature.

'And it's begun by a rather

unlikely hero.

'To help track it down,

'I'm joined by Lynne Boddy,

Professor of Mycology

'at Cardiff University.

'We're on the hunt for an organism

that prefers to stay

'out of the light.'

This is a likely-looking candidate,

plenty of moss on the surface.

Let's turn it over gently

and see what we can see.

Look at that.

Oh, it's wonderful, isn't it?

Absolutely covered, it's almost like

a spider's web under here, isn't it?

It is. This is fungus.

The crucial thing about the fungi

is that they release nutrients

which allow plants to

continue to grow.

The main body of the fungus is

called the mycelium, which is

made up of very, very,

very fine filaments,

they're too small to see by the naked

eye. But here they're aggregated

together to form cord- or root-like

structures that we can clearly see.

What do these threads do?

They grow out from this wood

in search of new resources,

so maybe the resources would be dead

leaves, more wood.

When they find them they exude

enzymes that break down the structure

of the wood or the leaves or any

other bits of dead plant material.

It's easy to overlook fungi.

But, to me,

they're true champions

of the natural world.

They begin the process

of breaking down dead wood

and leaves to release

the nutrients trapped inside.

It's an extremely rare ability.

The thing about the wood decay

fungi is that actually

they are the only organism or almost

the only organism that can

actually break down wood on this

planet, and that is one

of the reasons why they're

so important, because otherwise

we'd be up to our armpits in dead

stuff. And, in fact, plants

wouldn't be able to

grow because all the nutrients

on this planet would be locked up

in the dead plant material.

As the fungus breaks down the leaves

and twigs, it produces a rich

substance we call humus that becomes

part of the soil itself.

But the fungus is doing another

crucial job.

It's feeding an entire world

most of us don't even know exists.

Using specialist microphotography,

we can catch a rare glimpse

of an astonishing hidden kingdom...

..teeming with weird,

almost alien-looking life.

Millions of tiny creatures,

all of which are dependent

on nutrients being

released by the fungi.

These are nematodes,

tiny, round worms.

Scientists think there may be up

to half a million

species of these

wriggling in the soil.

There are mites, tiny

relatives of spiders and scorpions.

Tardigrades, often called 'water

bears' due to their cute appearance.

And rotifers, fascinating little

creatures that can propel themselves

through the soil using special hairs

that appear to revolve like a wheel.

This is the first great

secret of the soil. A vast,

living kingdom of tiny animals.

As they move around, eat

and are in turn eaten themselves,

they spread the essential nutrients

released by the fungi.

Helping to make the soil a more

fertile place for growing plants.

'Yet so far

we've only seen how fungi

'begin the process of unlocking

those nutrients.

'Breaking down all the tough remains

of dead plants is too large

'a job for fungi alone.

'But they have a secret ally

underground.

'An animal whose impact on the soil

is greater than any other.'

When it comes to ecosystems,

not all organisms are created equal.

By that, what I mean is the work

of one or two species will allow

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