Deep, Down and Dirty: The Science of Soil Page #5

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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, 1 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 2 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

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