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SOIL is the world’s most important resource. Stripping away forests
often leads to a loss of soil but still the forests are stripped – as is
so evident in Nigeria. The reasons for clearance – a growing population,
government policy and the high price of crops – are the same whether in
Nigeria or another country. Contrary to the popular view, even countries
such as Britain, with its gentle rainfall, have suffered serious loss of
soil. Yet, while developed countries preach to the Third World, they do
little to stop their own erosion. Small wonder, then, that many Third World
countries fail to see the need to conserve their soil.

When Britain’s population swelled rapidly in the past, it went through
the same sequence of events as Nigeria is now going through.

Much of Britain was wooded until about 5000 years ago, when the first
clearances began. Removing pockets of woodland by axe and fire was often
accompanied by erosion, but in the humid, temperate climate of Britain,
vegetation soon covered the bare soil and erosion stopped.

As the neolithic population grew, people began to clear much greater
areas of the chalklands of southeast England to grow crops. Erosion was
widespread. The clearances spread and soil began to wash from the slopes
and fill the valleys.

During the Roman occupation, the population grew rapidly to about 4
million. Farmers began to add manure and marl to the soil, which had begun
to lose fertility. Many were growing winter wheat, which encourages erosion.
When the Romans left, the population fell to around half a million and erosion
more or less stopped.

As people began to settle the country again, so they cleared the woods
and erosion started again. By the time of the Black Death, in the mid-1300s,
little forest remained. Medieval farmers had problems maintaining the fertility
of their soil: one of their solutions was to leave land fallow, allowing
it to recuperate. But, unless the fallow land is vegetated quickly it is
very vulnerable to erosion – there is widespread evidence of such erosion
in the Middle Ages.

The Black Death almost halved Britain’s population of 4 or 5 million,
and it took almost three centuries to recover. Only after 1500 did the population
begin to expand rapidly again. And after 1750 it grew on the sort of scale
we see in the Third World today.

Despite the huge increase, the land was protected from erosion by the
farming practices of the time. Much land was protected as grazing, rather
than fallow, and additions of manure and crop rotations helped to maintain
fertility.

Soil loss increased again in the 1920s when the Ministry of Agriculture
encouraged farmers to grow sugar beet, a crop that makes land vulnerable
to erosion. It has grown much worse since the 1960s, when agriculture became
more intensive.

By the 1970s erosion by water was obvious and widespread. Before this,
the main problem had been wind erosion, in local areas – the sandlands of
Nottinghamshire and the fens of East Anglia, for instance. The Ministry
of Agriculture made some attempt to stop wind erosion, not to prevent the
loss of soil but to stop the loss of crops and fertiliser. Only the most
valuable crops, including sugar beet, onions and carrots, received much
attention.

The sudden increase in water erosion was the result of sowing much greater
areas with autumn cereals, which produce higher yields – and bigger profits
– than older varieties. Improved technology allowed farmers to grow these
crops in areas that were never thought suitable before. Autumn cereals leave
the soil vulnerable in winter, when the vegetation provides little cover
and the soil is saturated with water.

The problem even spread to Scotland, where it had always been rare,
as farmers in the lowlands of the south and east began to plant cereals.
By the mid-1980s, cereals, and erosion, had reached Aberdeen.

Since the first woodlands were cleared, the chalklands and sandlands
have lost between 15 and 25 centimetres of soil. Elsewhere between 5 and
10 centimetres have disappeared. Many of these soils are shallow (less than
80 centimetres deep) and have lost a considerable proportion of their potential
productivity.

Robert Evans lectures in the geography department at the University
of Cambridge.