Scientists dispute virtues of ‘black gold’


London : The virtues of biochar — or “black gold” — in the soil, which was being touted as a possible carbon sink to counteract global warming, has been disputed by scientists.

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A new study suggests that the supposed benefits of biochar (charcoal derived from wood) may be exaggerated. When charcoal was mixed with humus, there was a substantial increase in soil micro-organisms (bacteria and fungi), the study found.

These microbes carry out decomposition of organic matter (carbon) in the soil. And consistent with this, they found that charcoal caused greatly increased losses of native soil organic matter, and soil carbon, for each of the three forest stands.

Much of this lost soil carbon would be released as carbon dioxide, a greenhouse gas.

Therefore, while it is true that charcoal represents a long-term sink of carbon because of its persistence, this effect is at least partially offset by the capacity of charcoal to greatly promote the loss of that carbon already present in the soil.

The study also suggested that the effect of biochar on the loss of carbon already in the soil needs to be better understood before it can be effectively applied as a tool to mitigate human-induced increases in carbon-based greenhouse gases.

These findings by David Wardle, Marie-Charlotte Nilsson and Olle Zackrisson of Swedish University of Agricultural Sciences, Umeå, was published in the latest issue of the jounral Science