Biochar is a carbon-rich product derived from the slow pyrolysis of organic materials under oxygen limited conditions. It is usually used as a soil amendment to increase soil fertility, boost agricultural productivity, and provide protection against some foliar and soil-borne diseases.

Scientists have been studying biochar as an approach to carbon sequestration and thus help mitigate climate change via reducing soil greenhouse gas emission. However, a group of Chinese scientists recently found that during the freeze-thaw cycles period, biochar addition in soil may stimulate soil emission of carbon dioxide (CO₂) while reduce that of methane (CH₄).

Their study was published in the recent issue of Plant, Soil and Environment entitled "Effects of biochar addition on CO₂ and CH4 emissions from a cultivated sandy loam soil during freeze-thaw cycles".

Previous studies have shown that soil N₂O emissions decreased by 61% during freeze-thaw cycles through biochar addition. But what will that do to the emission of Carbon dioxide and methane, two of the major greenhouse gases that play a key role in global climate change?

To answer this question, LI Lanhai and his team from the Xinjiang Institute of Ecology and Geography simulate the freeze-thaw cycles in their lab. They hope to examine the effects of biochar additions on soil carbon dioxide and methane emissions during freeze-thaw cycles.

Their study showed that soil CO₂ emissions were stimulated by both freeze-thaw cycles and biochar addition. In the meantime, the biochar addition promoted the intake of CH₄, especially under freeze-thaw conditions.

"Although there are some limitations in this study, the results still indicate that the effects of biochar additions on soil C emissions may be different between control and freeze-thaw conditions," said LI.

More in-situ observations are expected in further studies to make systematic evaluations on the effects of biochar on greenhouse gas emissions during the freeze-thaw cycles, according to the researchers.