Fertile ground for waste

Excess CO2 generation could be a solution rather than a problem, according to a team at the US Department of Energy's Pacific Northwest National Laboratory in Richland, Washington.

Researchers led by Jim Amonette have found that treating soil with furnace waste can increase its ability to absorb carbon-containing molecules.

Carbon depletion in soil is becoming widespread, especially in the US. 'Globally, soils contain four times as much carbon as the atmosphere, and half the soil carbon is in the form of organic matter,' says Amonette. Tilling the soil releases the carbon - and putting it back is more difficult than it seems, Amonette says.

Amonette's research looks for ways to promote the activity of tyrosinase, an enzyme which catalyses the reaction between oxygen and organic molecules derived from dead plants, such as phenols and hydroxybenzoic acids, to form quinones. These react with amino acids in the soil to form stable molecules known as humic polymers.

This process is known as humification, and is important in maintaining soil fertility. The rate of humification depends on factors such as moisture, alkalinity and microbial population. Amonette has devised an apparatus which can control all of these.

The system sandwiches soil samples between a pair of watertight but gas permeable tubes. The whole assembly is then placed inside another tube which controls moisture levels in the sample.

Amonette has found that another waste material might help the process. Fly ash from coal combustion promotes the reaction of quinones with amino acids, and provides small pores to protect humic polymers, he says.

Wetting and drying the soil develops a population of microbes which break down plant molecules into simpler precursors. 'Today, 99% of the carbon added to soil in a year comes out the top as carbon dioxide,' says Amonette. 'If we can increase the fraction that is retained in soil by even a small amount, it will make a huge difference.'