Biochar May Also Sequester Carbon Dioxide

'Biochar' is the name for charcoal when it is used as a soil amendment. People add charcoal to land in order to increase soil fertility and agricultural productivity.  Water holding capacity in soils is also usually increased.

In addition to these benefits, researchers are now saying that biochar has potential to mitigate climate change as it can help sequester carbon and thus cut our greenhouse gas emissions.

Sean Case, a PhD student at the US NERC's Centre for Ecology and Hydrology (CEH) and lead author of the study says: "We've shown that adding biochar suppresses CO2 emissions very significantly over several years... Previous studies have found this effect in the lab and over short periods, but this is the first time anyone has looked at bioenergy crops in the field, and at the effects of biochar over a long period."

Results of the study show that by applying biochar before planting energy crops, soil greenhouse-gas emissions can be cut by around a third.

Researchers studied a plantation of miscanthus, a perennial grass which is harvested for fuel. They monitored how much CO2, nitrous oxide and methane came from the plot's soil over two years. They also monitored soil emissions under controlled conditions in the lab.

The plots that had been treated with charcoal emitted 37% less greenhouse gases than neighbouring plots that hadn't, while in the lab the impact was 55%. Most of this came from cutting CO2 emissions, with methane playing no significant role and only a small nitrous oxide component.

"There's a lot of interest at the moment in the potential of bioenergy crops to sequester carbon in the soil, because unlike arable land these crops aren't ploughed every year so the carbon is not being regularly disturbed," says co-author Dr Jeanette Whitaker of CEH. "Biochar contains a lot of carbon in its own right, so adding it to the soil is already having an immediate sequestration effect, but our research suggests that it also reduces the CO2 emitted by soil respiration, which makes the case for using it even stronger. It's about maximising the sustainability benefits of bioenergy crops."

Whitaker explains that in the long term, it is unlikely people will use wood as biochar. Instead, biochar can be made out of anything from municipal waste to chicken manure.

Different regions will have different availability of feedstock products, with crop residuals common.