Deep Down & Dirty: The Science of Soil

'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

hundreds of others to thrive.

One such animal is so important it's been called an ecosystem engineer.

In this field, there might well be over two million of them.

There are no prizes for guessing which animal I'm seeking out here.

It's one that's inspired generations of horticulturists

and agriculturists.

It is possibly the greatest gardener on earth.

And it's this, the humble earthworm.

As a gardener,

I've long known that worms play an important role in soil.

The great Charles Darwin devoted over 40 years of study

to them, culminating in the publication of his seminal work,

The Formation Of Vegetable Mould Through The Actions Of Worms

With Observations On Their Habits.

You may not have heard of it,

but it sold faster than On The Origin Of Species.

Darwin's studies, lesser known than his work on evolution,

revealed an organism that was essential for the life of the soil.

He became obsessed by them.

He fed them different diets, tested their intelligence

and even tested their senses by playing a bassoon to them.

What is about the earthworms that beguiled Darwin?

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 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

and, below, the various layers or horizons of soil,

each with a different characteristic in terms of colours and textures.

The topsoils, going down into the subsoils with the roots

penetrating, this is what we saw in the forest.

But, as we go further down, the dark organic plant material disappears.

We seem to have left the soil behind.

These deeper layers are mainly

made up of fragments of the underlying rock.

And then further down we're into bedrock.

Collectively, these layers form the foundation of soil development.

Rock fragments permeate the soil

from the bedrock all the way to the surface.

It's mainly this stuff that was left behind

when I burned the plant matter away from the topsoil.

But, though these particles are from lifeless rock,

that doesn't mean they have no purpose.

In fact, they are fundamental to how soil works.

Soil particles are divided into three different categories

depending on the size of the particle.

The largest being sand. There you can see them

just coming into focus, wonderful, rounded particles.

The next size down, well, it's silt.

And there you can start to see the individual silt particles.

And the very smallest are the clays.

Search for the clay. There they are, much smaller.

Relatively speaking, if the sand was the size of a beach ball

then the clay particles would be the size of a pin head.

Incredibly small and flat in their profile.

What's curious about the particles is that the relative

proportions of them in any soil fundamentally affect

how that soil behaves, and, more importantly, how it supports life.

'To see exactly how, I've come to the James Hutton Institute

'in Aberdeen.

'I'm here to meet soil scientist Dr Jason Owen.'

Jason, what will this experiment demonstrate?

What we have here are three cylinders. One with a sand, one

with a silt-dominated soil and one with a clayed soil.

When we pour water in the top what we'll see is the water

percolating through the soil profile.

With the sand it'll go very quickly.

With a clay it'll go very slowly.

And the silt will be somewhere in between.

To me, this is familiar stuff, as it will be to any gardener.

It's the age-old question of drainage. How well water

moves through different types of soil.

With the sand, large particles,

there's quite large gaps, comparatively speaking,

and water can go down through the profile.

With the clay, very small particles, and as a result the gaps

where water can penetrate are exceptionally small.

The silt is somewhere in between the two extremes.

But to really see what's going on inside the soil

we have to look at it in far greater detail.

Here, they're using cutting edge technology to examine soil

on an incredibly small scale.

We're joined by Evelyne Delbos,

operator of the Scanning Electron Microscope at the Hutton Institute.

She's looking at soil magnified 400 times.

I have the three main parts of the soil.

The sand grains here.

On the right is the silt and the clay at the bottom.

Well, you can sort of see with the clay, for example,

it's stacked so tightly together

that you can actually not see discernible gaps between them.

Whereas here we've got these very large sand particles

and even through they're right on top of each other

you can still see the far larger gaps.

That allows air, for aeration of the soil,

and it also allows water movement through the soil.

But there's more going on here than just how the particles

are packed together.

Let's imagine this is a grain of sand.

And the surface area of that grain of sand is that surface,

that surface, that surface, and that's it.

It we take, by comparison, the same volume of clay

then you have that surface plus that surface plus that surface, so you

can imagine already that the surface area is much, much, much larger.

So what does the surface area do to the water?

What's the relationship between those two things?

What's interesting about many clays, it has an electric charge

associated with its surfaces.

Many nutrients that are dissolved within the water can be

attracted to these clay sites, to this large surface area,

and then held,

basically for root systems then to uptake for plant growth.

So clay particles have an electrical charge that can bind nutrients

and water to them.

This allows soil to act as both larder

and reservoir for plants and animals.

Sounds ideal, but there's a catch.

Too much clay and the soil can act like a sponge

and can quickly become waterlogged.

At the other end of the scale, too much sand

and the water can run through too quickly,

washing the nutrients out and leaving behind soil that's dry.

Have we got an image of what a good soil should look like?

Here you can see some grains of sand, they are different sizes.

It's a mixture and you can also have there and there the clay

and the silt all mixed up.

So this is demonstrating the ideal, in terms of soil. It would

be free draining, retain sufficient moisture,

sufficient nutrients, what about microbial activity?

This is a very, very complicated 3D structure

which gives all of the microbiota

within the soil effectively a niche, a home to live, and as a result

the ecosystems that exist in the soil are exceptionally complicated.

This is a classic example where you've got the mix between the

large particles, the clay particles and silt all working together.

So the elements that make up soil come from two very different places.

The chaos of life, and the inert world of rock.

Together, they create an intricate substance that can naturally

feed and water all plant life on earth.

And it makes me wonder just how did this strange

alliance between rock and life begin?

'How did the very first soil come to exist?'

To find out, we need to go back to a time

and place before the first soil appeared on the planet.

That's not quite as difficult as it might sound.

This is Malham Cove, an inland cliff deep in the Yorkshire Dales.

It's a striking landscape, built from limestone

and sculpted by the awesome power of ice.

This place offers a wonderful window into the Earth

billions of years ago, before there was soil.

That's because at the end of the last Ice Age,

as temperatures rose and the ice retreated, it left this

naked rock. Any soil that had been here had been scoured away

and deposited somewhere in that direction.

And as a consequence any soil you see here is relatively new,

in fact, it's still forming.

Making this one of the best places in the country to discover

how we get from this naked rock, to this. Soil that supports life.

I'm joined by Professor Steven Nortcliff from Reading University.

Landscape is fascinating in terms of the soil.

First, I want to know what could possibly start to break up

something as seemingly permanent as rock.

We've got to break it down.

And we've got evidence here in this landscape

of those early stages of breakdown.

We have ice forming in the fissures in the rock and as the ice expands

it forces the rock apart. And that's the first form of disintegration.

When water freezes, it expands.

If that expansion happens within a crack,

it can exert a force strong enough to break rock apart.

And you can witness this in your own freezer at home.

You fill the ice tray and when it freezes there's expansion.

But it seems remarkable that that expansion is powerful enough

to blow rock apart.

Well, you're expanding in a confined space.

It only has one way to expand and that's sideways.

That forces the rock apart and it's the beginning

of the disintegration to give us the soil.

This process is called physical weathering.

It breaks down rock by sheer brute force.

But we're still a long way from soil.

Next comes a different process entirely.

And it starts with rain.

We'll just drop some hydrochloric acid onto limestone.

You can see it fizzing.

You can hear it fizzing. It's really going at it.

What Stephen's showing me

is an exaggerated version of what happens every time it rains.

Rain is slightly acidic and, with limestone,

when this slightly acidic water falls on the surface it weathers it.

And is that what we're seeing here, on the surface of the rock?

That is exactly what we're seeing here.

So rain reacts with the rock, gradually dissolving it. This is

chemical weathering. The second key step towards soil.

Using a stronger acid to speed the process up,

we can see just how powerful it is.

Here, a piece of rock is almost entirely dissolved. Leaving

behind nothing but insoluble, sandy remains known as sediments.

And that's the beginning of the soil.

It's a very small amount of insoluble residue,

but that's where the soil development starts.

But sediment isn't yet soil. There's something fundamental missing.

Life. But look closely, and this rock is not bare.

It's covered in this, lichen.

And this is what causes the final,

almost magical metamorphosis from inert rock, to life-giving soil.

In this environment they are key

because the lichen will attack the rock, very much like the chemical

weathering we saw, but it will break it down, release nutrients.

Lichen is actually two organisms, algae and fungus,

living in one body.

And though it seems almost incredible, the fungus part is able

to break down the rock to release nutrients that it can feed on.

Much as we saw the fungi do with the wood in the forest.

Over time, generations of lichen grow over one another,

the new on top of the dead.

The dead remains form organic matter.

And when this mixes with sediment the result is soil.

And so from an apparently barren limestone pavement up here

we have the complete story of the generation of our soils.

Bare rock through the various weathering processes, the biological

processes and eventually the formation of soil. It is all here.

Condensed into just a few square metres.

Yeah, it's a wonderful example of soil development in motion.

And what we've got is different areas representing different timescales -

some it's just starting,

others it's been going on for a few thousand years.

Soil is the place where the relatively inert world of rock meets

the riot of life above.

It's a complex, staggeringly complex ecosystem,

but it also offers something of a conundrum

because the life creates soil,

breaking down organic matter and

forcing rocks apart, but that life is also dependent upon the soil

for nutrients, moisture, habitat, anchorage, somewhere to live.

That means there's a delicate balance between the life and the soil.

Challenge one and you inevitably challenge the other.

And today that ancient balance between rock and life

is being challenged as never before in history.

A new force has entered the world of the soil. Humankind.

In geological terms,

human civilisation is a mere blink of the eye, at around about

9,000 years. And in that brief moment in time we've arguably done

more to change our soils than in the previous 400 million years.

We've mined it.

Built on it.

Farmed on it.

And, in places like this, drained it.

And our actions have had consequences we never imagined.

East Anglia is famed for its fenland landscape. One of rivers,

marshes and streams.

But what we have left is just a fraction of what was once here.

Largely because this is a habitat that's prone to flooding

and since the 17th century

generation after generation have been progressively draining it.

The great system of canals and ditches have been dug.

To drain the unwanted water into the sea.

Over the past 300 or so years,

the population of the UK has grown rapidly.

This put huge pressure on places like the fens.

To help feed all those extra mouths, we needed to dry out

the waterlogged land to make way for the business of agriculture.

Rivers and lakes were drained and crops planted.

The few people who lived there were thought rough and unfriendly.

Old ways of life and traditional pastimes that had grown up

around the flooding were swept aside.

But this progress came with a sting in the tail.

As the rivers and meres were drained,

something unexpected happened.

The land began to sink.

This is Holm Fen, drained in the 1850s.

It was the home of Whittlesea Mere,

once thought to be the second largest lake in England.

This is all that's left.

Previous experience had demonstrated that if you drain the fens

the land would sink.

So a local landowner here at Holme Fen, William Wells,

decided to measure that process.

He took a post and pushed it into the ground

until the top was completely covered. And that post today?

Well, here it is.

The top of the post was originally ground level.

Since 1850 this whole tract of land

has sunk somewhere in the region of four metres,

making this one of the lowest places in Britain.

There can surely be no clearer indication of the effect

of human interference on soil.

But why did it sink? And what are the consequences?

'I'm joined by Dr Ian Homan.

'He and his colleagues at

'Cranfield University have extensively studied the area.

'We're going to take a look at a rather special type of soil

'found here in the fens.

'This is peat.'

-Pretty good profile.

-It is indeed.

Peat forms in a wetland environment, so the soils are waterlogged.

It's low in oxygen under the surface and it's quite acidic.

So the combination of the waterlogged nature,

the lack of oxygen and acidity slows down the rate of decomposition.

The soil bacteria and the microbiological

components of the soil aren't able to decompose that organic material.

So it accumulates very slowly.

So in peat, instead of being broken down, plant material builds up.

And this has an important effect.

Plants grow using carbon dioxide from the air.

And if they're not broken down when they die

they and the carbon they contain become trapped within the soil.

This is what's known as a carbon sink

and peat bogs are some of the best.

But remove the water, and the balance changes.

Oxygen enters the soil, allowing bacteria and fungi to breathe.

This is what happened when the fens were drained

and it had profound consequences.

That allows the micro-organisms to use the carbon within this peat

as an energy source, converting

the carbon into carbon dioxide and energy.

The fens, we think, are losing about four million cubic metres of

peat soil every year and that equates to an emission of carbon dioxide

of about 1, 1½ million tonnes of carbon dioxide a year.

We've gone from being an environment

that should be storing carbon dioxide into the soil

into an environment now that is emitting carbon dioxide.

So the story of the fens really is that it's the worst possible,

for both ends of the spectrum.

Not only are we losing the carbon sink,

-but the carbon dioxide is being released into the atmosphere.

-Indeed.

So as a result of human activity four metres of peat,

which took thousands of years to form, disappeared in mere decades.

And this old post is a monument to what can happen

when we upset the balance within the soils.

It's a story that's repeated throughout human history.

Archaeological records very clearly demonstrate

that, as our nomadic ancestors began to settle and farm the land,

populations increased dramatically.

And in order to feed the population

the area of land that was turned over to the plough also increased.

Those early farmers tilled and ploughed, fertilised

and irrigated in the best way they knew how.

But, as we've seen,

human interference can have unexpected consequences.

Ploughing and tilling can destroy the soil's structure.

Intensive farming will deplete the soil of nutrients

and over-irrigation can cause high levels of toxicity.

When these factors combine the soil becomes degraded

and prone to erosion from wind and water.

For me, recent history provides a stark warning.

By the 1930s, vast swathes of the North American prairies

were turned over to the plough.

All the way from Canada down to Texas.

But this would lead to catastrophe.

High winds and sun. A country without rivers and with little rain.

Intensive farming techniques had weakened the structure

of the soil till it could no longer hold itself together.

So when a drought came the soil dried out then simply blew away.

Turning the prairies into a huge dustbowl.

The rains failed and the sun baked the light soil.

It affected 100,000,000 acres of land. By 1940,

over 2½ million people had been forced off the prairies.

Their stock choked to death on the barren land.

Their homes nightmares of swirling dust night and day.

Many went to heaven.

It was one of the biggest environmental disasters

in American history.

But today the problem is potentially worse than it ever was.

There are now more than seven billion human beings on the planet.

There are more of us alive today

than there have been up to the 20th century.

So it comes as no surprise more is being taken from the soil.

We're more reliant on the soil than ever before.

In trying to satisfy that need we're cultivating, tilling,

fertilising to keep our soil productive.

In doing so, we're destroying the delicate structural

balance of the soil. That can be hugely costly.

So when we talk about an impending food crisis

what we should actually be talking about is a soil crisis.

And that crisis is being felt as keenly in the UK as anywhere else.

It's brought this farm in Ross-on-Wye to the brink of ruin.

Asparagus farmer John Chinn has seen massive gullies

open up in his fields.

Weakened by farming, the soil was washed away by the rain,

taking his crop with it.

So what is it about the conventional way of managing

a crop like asparagus that was causing that degree of erosion?

It's two sides.

The first is that we have soil exposed the whole time.

Then, secondly, because we didn't want water standing in the crop

we would plant the rows up and down the slope so the water would run off.

Of course, what was happening was that the water was

running off faster and faster and as it went it picked up the soil

because it was just there on the surface. Carried that soil out to

the bottom of the field, maybe into a stream, a road, leaving behind it

a gully that as you came down the slope got deeper and deeper.

We have an amber warning in force for the Somerset Levels.

Water erosion has become a devastating problem in the UK.

Could be another 20mm or perhaps a bit more in this area.

Over the past five years, we've experienced an unusually high

number of storms, culminating in the winter of 2013.

It was the wettest on record.

Vast swathes of the UK suffered rainfall on an almost biblical

scale, leaving many areas like the Somerset Levels deluged for months.

It's this kind of rainfall that was partly to blame

for the destruction of John's asparagus fields.

In desperation,

he sought the advice of soil specialists at Cranfield University.

One of them was Dr Rob Simmons.

'He's investigating the huge problem of water erosion on the smallest

'possible scale.

'By studying the energy within individual raindrops.'

The raindrop has a certain mass and a velocity

which affects its kinetic energy.

When that raindrop with that kinetic energy impacts on the soil surface

it will damage the soil and cause breakdown at the soil surface.

As you start to get extreme rainfall events you get short-duration,

high-energy events with a larger drop size, more kinetic energy

and they're going to cause more damage to your soil surface.

And it's those that we're having more of?

And it's those that we're having more of. Yep.

Rob is testing what happens when rain hits soil.

It's immediately apparent that excess water quickly starts

to flow across the surface, what the scientists call run-off.

Right, what we can see here is that

run-off is being generated almost straight away.

So expanded out onto a large field situation

this could cause major problems.

This is all well and good in a lab,

but is there anything you can do about it out in the field?

Absolutely, but the best thing to do is to go out in the fields.

-Where the sun is shining.

-Where the sun is shining.

By understanding exactly what happens when raindrops hit soil, Rob

has been able to help John make some big changes to the way he farms.

And they're surprisingly low-tech.

Instead of planting straight up and down the hillside,

John now plants his rows on the diagonal.

And he plants grass strips between them.

The combined effect is to slow down the run-off of water,

reducing its power to erode the soil.

But that's only the beginning.

Now Rob's come up with an ingenious new idea to take the energy

'out of the rain itself.

'To test it, he's set up rainfall simulators

'and dug a series of channels, or wheelings.'

We've got two rainfall simulators.

We've got

a wheeling which is bare on the left-hand side. And on the

right-hand side we've got a wheeling which has got straw mulch in it.

What the straw will do is it will absorb the energy of that rainfall.

It will also act as a blanket effectively

and it will absorb some of that water, slow down the run-off.

It seems an incredibly simple solution, basic straw.

Comparing the two scenarios side by side reveals a big difference.

Raindrops hit the bare earth with force and break up the soil.

Run-off water soon begins to flow and carry the soil away.

But here the large drops are broken up before they can hit the ground.

It's the straw, not the soil, that takes the brunt of the impact.

And the run-off is reduced to a trickle.

By having that canopy it absorbs all the energy, you don't have

the detachment, you don't have the run-off and erosion problems.

What's your reaction to the technology which is now being

deployed in the field?

Well, I suppose as a farmer it started off as scepticism,

you know, here's a chap from the university. Yes, he can solve

civil engineering problems, mining quarrying problems, but

this is farming.

And so it's taken a little while, I think, hasn't it, Rob?

You've worked on me, you've shown me that it works. Now that's starting

to snowball. That's going out to other farmers and I think that

in 10 years' time the sort of things were doing now

will become standard practice

and frankly to not do them will become unacceptable.

We have to look after the soil, it's a valuable resource.

To me, it's astonishing that a potentially huge threat to soil

can be averted using something as low-tech as straw.

All it needs is a little thought and a willingness to change.

I believe these are vital if we're to avoid the mistakes of our past

and preserve this most precious of resources.

And research like this and the commitment of farmers

like John give me hope that we'll achieve that.

So, whilst we have a chequered history when it comes to our

relationship with soil,

it does seem at last we're beginning to understand and

appreciate what an amazing substance it is.

'Exploring soil, we've uncovered the secrets of its life-giving force.'

We've revealed an intricate living system, where life meets rock

at the microscopic scale.

Each acting on the other in complex

and surprising ways to form what to me is, without doubt,

the most fascinating and important material on the face of the planet.

So the next time you walk on the grass

give a nod of thanks to the hidden rainforest beneath your feet.