Biochar: looking better all the time

By Bryan Walker 05/08/2010

Interesting biochar research is reported in a news release from the American Society of Agronomy.  An Australian research team has been testing the effects of biochar on nitrous oxide emission and nitrogen leaching from two different soil varieties. Their results are reported (no charge for this month) in the Journal of Environmental Quality.

The study demonstrates that biochar, applied to soils to capture and store carbon, can reduce emissions of the potent greenhouse gas nitrous oxide and inorganic nitrogen runoff from agriculture settings.

It apparently takes time for the biochar to interact with the soil in this way. The scientists subjected soils samples to three wetting-drying cycles, to simulate a range of soil moistures during the five-month study period, and measured nitrous oxide emissions and nitrogen runoff. Initially the effects were inconsistent. Several early samples produced greater nitrous oxide emissions and nitrate leaching than the control samples. However, during the third wetting—drying cycle, four months after biochar application, all biochars reduced nitrous oxide emissions by up to 73%, and reduced ammonium leaching by up to 94%. The researchers suggest that reductions in nitrous oxide emissions and nitrogen leaching over time were due to ’ageing’ of the biochars in soil.

Senior author Bhupinder Pal Singh comments:

’The impacts of biochars on nitrous oxide emissions from soil are of interest because even small reductions in nitrous oxide emissions can considerably enhance the greenhouse mitigation value of biochar, which is already proven to be a highly stable carbon pool in the soil environment.’

Research is on-going to investigate the causes of the reductions in nitrous oxide emissions, especially under field conditions, and to determine optimal rate and timing of biochar and fertiliser applications to agricultural soils to maximize the greenhouse mitigation value.

The effect of biochar on nitrous oxide emissions is not a new discovery. A Hot Topic post eighteen months ago mentioned early indications that biochar appeared to cause the soils in which it was buried to give off less carbon dioxide than normal and much reduced levels of nitrous oxide. Geoff Bertram and Simon Terry in The Carbon Challenge, in arguing that farmers have means for reducing greenhouse gas emissions, mention biochar both for its carbon sequestration value and also for its reported suppression of nitrous oxide emissions. The research reported here appears a confirmation of this, especially if it proves robust over time. Longer testing will be needed, but the signs seem promising.