Photos Imperfect Carbon Storage
But authors of another paper published today in Science find that char can trigger microbial activity when mixed with other soil components, enhancing carbon release from soil humus and offsetting some of char's potential benefits. David Wardle and colleagues at the Swedish University of Agricultural Sciences in Umeå, Sweden put mesh bags filled with charcoal, humus, and with a half of each at three different sites in a Swedish forest and left them there for a decade. They found that after 10 years, the amount of carbon and mass lost from the bags was greater in the mixture than expected based on the losses from the individual components. About 23 percent of the carbon was lost from the mixture, Wardle said, compared with the predicted loss of 15 percent. Charcoal has a large surface area and absorbs organic molecules well, he explained, creating an environment that boosts microbial degradation of the humus. "I wouldn't dispute that charcoal may have a lot of potential," Wardle said, "But I think we have to acknowledge that it doesn't just sit there." "It will be very important to look at the implications of that for natural black carbon cycles and for the approach of adding biochar to the soil as a means for carbon sequestration," Lehmann said. "However, I don't see any evidence that would alarm me too much that the approach of putting biochar in soil will increase carbon losses from the soil." Lehmann notes that the boreal forest environment found in Sweden has a rich layer of organic matter for bacteria to eat while agricultural soils, where char would likely be added, have far less. Related Links: Discovery News blog: Earth Impacts |
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