Disappearing earth
The
global threat of soil erosion
Among the soaring pyramids of the Maya in Central
America, or the enigmatic statues of Easter Island lies a mystery
that has long puzzled archaeologists – how did these grand civilisations
fall? But after years of dramatic theories about their fate, it is
beginning to look like many of these fabulous cities were not defeated
by some terrible disaster, but by the same environmental problems
that face our civilisation today.
Lost civilisations
Many scientists, such as Professor Jared Diamond, a physiologist at
the University of California Los Angeles now think the people of many
of these “lost civilisations” engineered their own demise
through poor stewardship of their most important natural resource
– the soil. On Easter Island, where deforestation and soil depletion
devastated the island’s ecology, Professor Diamond says, “society
ended up in cannibalism, the government was overthrown and people
began pulling down each other’s statues.” On other islands,
everyone ended up dead.
Archaeologists
believe a similar fate befell the ancient Maya. The Maya were skilled
stewards of the land, but as their population expanded and more forest
was cleared, they did not notice the gradual erosion and nutrient
depletion of their soil until it was too late. Their inability to
feed themselves led to famine and war; their population crashed by
around 90 per cent. Even today, over one thousand years later, many
of the soils in the around cities such as Tikal, now in Guatemala,
have not fully recovered. The population today is still lower than
during the Maya period. A similar story has developed around the fall
of the ancient civilisations of the fertile crescent, such as Sardis
and Mesopotamia (in modern-day Turkey and Iraq).
But this is more than just an exercise in history.
Professor Diamond says soil erosion poses the same threat to our civilisation,
equal to the danger of climate change, loss of biodiversity and deforestation.
“Perhaps someday New York’s skyscrapers will stand derelict
and overgrown with vegetation, like the temples at Angkor Wat and
Tikal,” he says.
A fragile resource
It takes thousands of years for soils to form from the solid rock
of the earth’s crust. The slow attrition of rainwater, freezing
and thawing, and the action of pioneering plants such as lichen break
down the minerals and mix in organic material, creating a bed of soil
that is stable, fertile and the key to most life on the surface of
the Earth. It provides the nutrients to grow 99% of the world’s
food. It filters rain, preventing flooding and maintaining the quality
of ground and surface water. It is also capable of storing large amounts
of carbon, a crucial factor as the world tries to counteract global
warming.
Yet
soil is a fragile resource. In the most fertile regions, it may only
be a few metres deep. In tropical or semi-arid regions, it is far
thinner and vulnerable to the constant attrition of wind, water and
farming.
A recent study from the Global Assessment of Human-induced
Soil Degradation (GLASOD) estimated that 15 per cent of the Earth’s
ice-free land surface is substantially degraded. Every years, ten
million hectares of cropland are lost as soils are destroyed by erosion
and over cultivation; 300 million hectares – an area about ten
times the size of the UK – is already too degraded to produce
food.
While loss of soil fertility can be overcome in the
short term simply by using more fertilisers, this is not an option
for many poor farmers in the developing world.
A recent UN study of South Asia showed 43 per cent
of its land was substantially degraded, losing it around $10bn (£5.5m)
each year, or 2 per cent of its GDP. In China, the Yangtze River basin
is suffering greatly from erosion. Some 41 per cent of the land is
degraded, losing over 2 billion tons of soil annually. But the worst
affected area of the world is sub-Saharan Africa.
“I
am seriously worried about some parts of Africa and their declining
ability to feed themselves,” says Dr John Boardman of Oxford
University’s Environmental Change Institute. He recently visited
the Karoo, a farming region east of the Cape of South Africa, where
200 years of overgrazing is turning a once fertile land into a desert,
devoid of native grasses and riddled with eroded gullies and badlands.
“I talked to a poor farmer – a woman with probably about
a dozen children,” he says. “She said that 20 years ago
she was getting twenty bags of maize from her fields, now she’s
getting between one and two. If that’s not a catastrophe in
terms of soil quality, I don’t know what is. That woman has
to rely on food aid most years now.” A similar story is repeated
across the continent, bringing hunger to millions.
In the developed world, problems of soil erosion
are less urgent, but equally significant. In the UK, farmlands in
Somerset, Dorset and the Midlands are all badly degraded. The green
pastures of the South Downs are turning white as the soil becomes
thin and the underlying chalk comes to the surface. In centuries past
the soil was several metres deep; now scientists have find a thickness
of only 15 cm on some hillsides. Dr Boardman says that farming may
become impossible there if no action is taken.
However, in most parts of the UK, short-term loss
of fertility can be overcome with increased application of fertilisers.
“The main problem,” says Dr Boardman, “is what we
call off-site impacts – runoff carrying soil flooding houses,
pollution of rivers by soil that is coming off fields and carrying
phosphorus and pesticides.” The end result is silting up of
dams and reservoirs, damage to the spawning grounds of trout and salmon
and higher costs in purifying water for human consumption. A study
by the University of Essex says the cost of these off-site effects
is at least £96 million each year in the UK. Water companies
alone spend £69 million removing soil particles from drinking
water, a cost ultimately met by the consumer.
The sins of modern farming
Most soil erosion is caused by wind and water. Heavy rains can wash
soil out of fields; strong winds can whip up huge clouds of loose
dry soil and carry them great distances. But none of this is new;
soils have always been affected by natural forces, but most have achieved
a stable equilibrium. The sudden acceleration of soil erosion in the
last 50 years is largely down to the radical change in farming methods
that has occurred.
Dr
Boardman says a combination of, “intensification, big machines,
larger fields, removal of hedges and breaking up the soil into bits
all contribute to erosion.” The soil on a modern farm undergoes
far more intense cultivation than ever before. Constant ploughing
breaks the soil into ever smaller pieces and depletes the organic
matter that binds it together, thus making it more susceptible to
the eroding forces of wind and rain. Expanding farms onto land previously
considered unsuitable for cultivation has also increased erosion.
“Growing risky crops on sloping ground is a
big problem,” says Dr Boardman. Cultivating profitable crops
like maize, potatoes and sugar beet on sloping ground can increase
rates of erosion by as much as three times, but economic necessity
usually takes precedence over conservation. “Some farmers are
aware [of soil erosion], but it’s well down their list of priorities.
Their first priority is to earn a damn good living from the crops
they are growing.”
There is also the possibility that climate change
will cause big increases in soil erosion. While there is no consensus
on exactly how our climates will change, some models, such as those
predicting wetter winters and drier summers, could potentially cause
big increases in soil erosion. The American Soil and Water Conservation
Society recently reported that even small increases in mean precipitation,
especially if it comes in more intense storms, could cause much more
damage, reversing any progress made in soil conservation.
The British government is beginning to take the issue
of soil conservation seriously. Earlier this month, the Department
for the Environment Farming and Rural Affairs released its first Soil
Action Plan for England, acknowledging that it was time to start managing
soils as a strategic resource with a view both to “society’s
short term needs and to the interests of future generations”.
While offering few definite measures to counter soil erosion, the
two-year plan seeks to raise awareness in farmers of the importance
of soil as a resource, developing penalties for poor soil management
and rewards for good practices. It also plans to introduce a national
soil monitoring scheme. The National Farmers Union fully supports
the scheme, agreeing that the legislation would, “protect the
water, environment and improve the profitability of farms.”
However, most experts agree that a much more aggressive
approach to the problem is needed, including harsher penalties for
farmers who do not manage their land properly and contaminate waterways
with runoff from their fields. “It would be eminently sensible
to tax the polluters,” says Professor Jules Pretty, and expert
on sustainable farming from the University of Essex, “but we
won’t ever see things like environmental taxes on agriculture,
the government is just not interested in getting into discussion over
that three letter word – tax.” He argues that the current
system of public subsidy needs a radical overhaul if we are to protect
our soils.
“We actually pay three times for our food,”
he says. “Once over the counter; twice, through our taxes, which
are largely used to support one type of farming; and thrice, to clean
up the mess caused by this method.” Each year, British farmers
receive around £3 billion in subsidy from the taxpayer. In addition,
Professor Pretty estimates that the cost of cleaning up environmental
damage caused by agriculture is at least £1.5-2 billion a year.
By shifting the true costs of farming away from those responsible,
he says we are encouraging unsustainable and damaging practices.
“I think radical changes in policy are necessary
everywhere,” he says. “At the 1992 Earth Summit in Rio,
every country that was there signed up to the idea of sustainable
agriculture and rural development. Only three countries in the world
have put the idea of agricultural sustainability at the centre of
their policies – Cuba, Bhutan and Switzerland. That’s
lamentable progress.”
A new agricultural revolution
While few countries are doing enough, there may be the beginnings
of a quiet revolution in farming practices. Professor Pretty says
there are 9 million farmers using sustainable practices that are conserving
the soil of around 29 million hectares of land worldwide. One of the
biggest success stories is Latin America, where many farmers have
reversed 12,000 years of agricultural history and stopped tilling
their soil.
Ploughing
the soil with tractors is seen as one of the most significant factors
in its degradation, especially in tropical regions with thin topsoil.
The technique known as “zero-tillage” removes ploughing
altogether, leaving a permanent cover of leaves and stems from the
previous crop that protects the soil from the sun, wind and rain.
In some cases, seed is simply scattered on the surface; in others,
only a single strip of land is ploughed or the seed is plugged directly
into the ground. Not only is the soil protected from erosion, but
its organic content and retention of water also increases dramatically.
Already some 15 million of hectares of land has been
converted to zero-tillage in southern Brazil, with another 11 million
hectares in Argentina. Farm trials have generally shown yields that
are equal to or higher than conventional practices. On some farms
in Argentina yields have doubled, soil fertility has improved and
costs have lowered, since the time and effort of ploughing the land
is saved. There are some disadvantages, such as the need for herbicides
to control weeds, but its proponents remain enthusiastic. “Applying
no till as an entirely holistic approach enabled us to discover a
new scenery, a system based on emulating nature,” said Robert
Peiretti, chairman of the Argentine farmers’ zero-tillage organisation.
“We clearly see wildlife has increased on our farms, there is
water in the soil and farmers are better off.”
Ultimately, Professor Pretty says we need to change
our relationship with the land; understanding its fragility and treating
seeing it as a form of natural capital that we either spend or save.
“What we’ve done with a lot of our soils is to capitalise
those assets and spend them now,” he says, “rather than
saving them for future generations.”
The ancient civilisations whose ruins litter the
Earth may never have realised they were denying a future to their
children. We, at least, are in a position to do something about it.
