Answer to the earth’s problems could lie in the soil...

8:32am Wednesday 30th April 2008

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The large number of wind turbines in Spain was a highlight on a recent rail trip through that country to Morocco, but it was the landscape between Tangiers and Casablanca that really caught my attention - mile after mile of plantations of coppiced trees and smouldering charcoal kilns.

The fuel for much of the cooking in this mainly rural country is charcoal, from eucalyptus trees, and that is a very positive way of reducing the contribution of CO2 to the atmosphere.

Instead of cooking with coal or gas, fossil fuels from millions of years ago, the trees absorb CO2 from the air and then return it when the charcoal is burned, and so the impact is neutral.

This benefit from charcoal only happens when more trees are grown and reused to make even more charcoal.

When trees are just cleared and burned and not replaced, the CO2 builds up. Such deforestation is responsible for a third of man-made emissions.

Recent work on fertile black soils in the Amazon rainforest has discovered that charcoal may be even more important as it can reduce the amount of CO2 by storing it in the soil for long periods. These soils get their colour from very high levels of carbon that has remained in the soil for thousands of years.

This is the exciting bit because dead wood decays and gives off its CO2 in a handful of years. As charcoal it can last for millennia and this means that CO2 in the atmosphere can be captured and locked away in the soil until alternatives to fossil fuels are developed.

It gets even better as this charcoal, called biochar, has a very positive effect on the soil. Trials show greatly improved crop yields for soils with increased carbon levels.

Biochar holds water and oxygen and increases microbial activity, as well as attracting trace minerals that can be washed away. It also binds the soil together while at the same time improving the way that nitrogen is fixed from the air.

It is best made by heating woody material at about 400 deg C in a closed boiler that keeps out oxygen. The result is a variety of gases and liquids that can be made into biofuel as well as producing about 50 per cent solid carbon.

If the latter is used on farmland, not only will it reduce the amount of CO2 in the atmosphere, but it will increase crop yields significantly. It also seems to reduce the amount of two other serious climate change gases given off from soils, methane and nitrous oxide.

It is suggested that if combined with the production of biofuel from waste materials, carbon-rich soils could store up to nine billion tonnes of carbon a year by the end of the century - more than man manages to contribute with all the electricity production, car driving and flying.