Experiments led by Jim Amonette at the Department of Energy's Pacific Northwest National Laboratory in Richland, Wash., and reported today at the American Chemical Society national meeting, show that maintaining a proper alkalinity plus frequent wetting and drying cycles can coax soil to retain more carbon.
"Globally, soils contain four times as much carbon as the atmosphere, and half of the soil carbon is in the form of organic matter," said Amonette, a PNNL senior research scientist. Until about 30 years ago, soil tillage released more carbon dioxide to the atmosphere than burning of fossil fuels. Some agricultural soils have lost a third of their carbon from tillage.
"These carbon-depleted soils are a tremendous potential reservoir for carbon that can help slow the increase in atmospheric carbon dioxide," Amonette said. "The amount of carbon added to soil in a year is incredible. Today, 99 percent of it comes out the top as carbon dioxide. If we can increase the fraction that is retained in soil by even a small amount, it will make a huge difference."
Amonette's experiments promoted the activity of tyrosinase, a common enzyme that catalyzes soil's natural "humification" process. This process involves the gradual incorporation of carbon from dead plants and microbes into stable organic matter called humus, which is responsible for the dark color in many soils. Tyrosinase increases the reaction rate between oxygen and humus precursors, such as phenols and hydroxybenzoic acids, to form quinones. The quinones react with amino acids released by soil microbes to form complex, durable molecules called humic polymers.