SOILS could become as important a 鈥渟ink鈥� for atmospheric carbon dioxide as
forests. A paper by the North American Society for Water and Soil Conservation
(NASWSC) suggests that modern techniques of soil conservation could soak up
enough carbon to meet a sixth of the American and Canadian targets for reducing
emissions of greenhouse gases over the next 20 years.
The organic carbon in soils accounts for an estimated three-quarters of the
carbon stored in ecosystems on land鈥攎uch more than that in forest timber.
But Don Reicosky from the US government鈥檚 Soil Conservation Research Laboratory
in Minnesota says that soils on the US prairies 鈥渉ave lost between 30 and 50 per
cent of the carbon they held when they were first cultivated鈥�.
Reicosky blames deep ploughing for releasing carbon by encouraging soil
erosion and by introducing oxygen, which speeds the microbial processes that
break down organic matter. It is 鈥渢he equivalent of setting a match to soil
organic matter鈥�.
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The NASWSC estimates that, in 50 years, farmers could recover half the carbon
lost from soil through ploughing. That is 20 to 30 billion tonnes of carbon, or
about four years鈥� worth of world fossil-fuel emissions.
Some soil scientists are more cautious. The movement of carbon between soil
and air has only recently begun to be measured. And the soil conservation
methods being proposed here, notably by agribusiness companies such as Monsanto,
involve the heavy use of pesticides and fertilisers.
Nonetheless, there is growing pressure to include soil conservation among
projects recognised under the Kyoto Protocol which aim to expand natural carbon
sinks.
