This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Biochar can store carbon in the soil and reduce the amount of carbon dioxide in the atmosphere—yet we still know too little about how long the biochar will persist. Now, researchers from the Swedish University of Agricultural Sciences have found a new way to measure this, using wood from the 1960s that was affected by nuclear weapons testing.
The paper is published in the journal Radiocarbon. There is currently great interest in using biochar—the type of carbon we use in barbecues—to improve the cultivation properties of agricultural land. Tilling biochar into the soil is also viewed as a method for the long-term storage of significant amounts of carbon, thereby helping to combat climate change.
This form of carbon is considered so stable that, in practice, it does not return to the atmosphere. Estimates suggest that, on a global scale, it might be possible to store enough carbon in the soil to offset 6%–16% of annual human-caused carbon dioxide emissions. Erik Karltun is a soil scientist at the Swedish University of Agricultural Sciences and has worked extensively with biochar.
"There is great potential here, but a concern for us is that we still know too little about the long-term stability of biochar incorporated into soil and how it affects the turnover of other carbon present in soil organic matter. However, it is difficult to study the decomposition of a material that breaks down much more slowly than other plant residues in the soil. We have therefore thought about how to design an experiment that makes it possible to distinguish carbon dioxide originating from decomposed biochar from that coming from other soil carbon." More than 20 years ago, Karltun participated in a study where so-called "bomb carbon" provided interesting insights into carbon turnover in forest soils.
Bomb carbon refers to radioactive carbon (carbon-14) created by the hundreds of nuclear tests conducted after World War II; these tests nearly doubled the level of radioactive carbon in the atmosphere before above-ground testing was eventually banned. Levels peaked in the mid-1960s, and traces remain in biological material formed during that period, such as wood and bone. The idea of utilizing bomb carbon in other types of studies had been brewing in Karltun's mind ever since, and eventually, he found a research question for which this material would be ideally suited.
"Wood formed during the peak years contains significantly elevated levels of carbon-14, and it struck me that biochar produced from such wood would possess a 'carbon-14 profile' clearly distinct from that of soil carbon," says Karltun. The studies he has now conducted alongside colleagues Haichao Li and Harald Cederlund confirmed his hypothesis. It proved possible to produce biochar with a sufficiently high proportion of radioactive carbon to investigate the fate of biochar incorporated into the soil.
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