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Biochar slashes bioenergy soil emissions

29 March 2013, by Tom Marshall

Adding charcoal to land used to grow bioenergy crops can greatly increase their overall benefit in helping cut our greenhouse-gas emissions, scientists have shown.

Harvesting biomass

Applying so-called 'biochar' before planting energy crops can cut soil greenhouse-gas emissions by around a third. Soils are among the biggest sources of UK emissions, and this study adds to a growing body of evidence that charcoal could be part of the answer.

'We've shown that adding biochar suppresses CO2 emissions very significantly over several years,' says Sean Case, a PhD student at NERC's Centre for Ecology & Hydrology (CEH) and lead author of the paper. '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.'

The main point of growing bioenergy crops like miscanthus or coppiced willow is to generate energy without burning fossil fuels; such energy crops are vital if we're to meet the EU's target of a fifth of energy coming from renewable sources by 2020.

Bales of miscanthus

Bales of miscanthus.

But this study strengthens the idea that there could be other benefits arising from carbon being stabilised and stored by bioenergy soils, and that biochar could add to them. Biochar seems to alter microbial activity in the soil, reducing soil respiration (CO2 emissions) and reducing the conversion of N fertiliser to nitrous oxide that would otherwise go into the air as greenhouse gases. The hope is that it can help the land accumulate and store much more carbon over time than it already does.

'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.'

It's about maximising the sustainability benefits of bioenergy crops.
Dr Jeanette Whitaker, CEH

The researchers looked at a plantation of miscanthus, a tough, perennial grass whose woody stems can be regularly harvested for fuel. They monitored how much of three greenhouse gases - CO2, nitrous oxide and methane - came from the plot's soil over two years. To check their results weren't being distorted by unusual weather or other conditions in the field, they also monitored soil emissions under controlled conditions in the lab.

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

Charcoal added to a miscanthus field after harvesting

Charcoal added to a miscanthus field after harvesting.

Case says this is probably because miscanthus soil doesn't usually produce much nitrous oxide anyway, as it doesn't need a lot of nitrogen fertiliser. It could be a different story on land that receives large amounts of fertiliser, such as that used to grow many food crops, as this increases nitrous oxide emissions. He's now doing research on this topic, and says early results from lab experiments suggest that adding biochar reduces nitrous oxide from arable land by 90 to 95 per cent, or around 40 per cent of overall greenhouse-gas emissions.

At present, bioenergy crops are generally burned for energy, so the charcoal used for the study came from wood harvested elsewhere. But this could change over the next few years. New, more efficient ways of turning biomass into energy exist. These often involve using a process called pyrolysis that heats organic material without burning it, to produce both charcoal and liquid or gas fuel. In the future the fuel could be used in vehicles or to generate power, while the charcoal can be returned to the soil.

'In the long term it's unlikely people will be making biochar out of wood,' says Whitaker. 'You can make it out of anything from municipal waste to chicken manure. Ultimately there's a much stronger argument for using an approach based on pyrolysis, as it means you can produce charcoal for carbon sequestration as well as energy.' But she says that more research on these technologies' overall impact is needed before they can be applied on a large scale.

This research is part of a wider body of work at CEH looking at a range of sustainability issues regarding UK bioenergy.

The paper appears in Global Change Biology Bioenergy.


Case, S. D. C., McNamara, N. P., Reay, D. S. and Whitaker, J. (2013), Can biochar reduce soil greenhouse gas emissions from a Miscanthus bioenergy crop?. GCB Bioenergy. doi: 10.1111/gcbb.12052


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Your comments

that's a excellent idea thant fixes carbon dioxide and make energy at the same time

lianer_10070, china
Monday, 1 April 2013 - 04:14

This study should be of deep interest to Coolplanet biofuels. They plan on using "Freedom" Miscanthus in production of bio-gasoline.

The wider applications of Biochar, use as a feed additive and nutrient management tool, Please review my presentation for the USBI Biochar conference in Sonoma California.
Carbon Conservation for Home, Health, Energy & Climate

CoolPlanet Biofuels, guided by Google's Ethos and funding, along with GE, BP and Conoco, have reactors that convert 1 ton of biomass to 75 gallons of bio-gasoline and 1/3 ton Biochar for soil carbon sequestration.
http://www.youtube.com/watch?v=zkYVlZ9v_0o

To review other developments in cleanburning cook stoves, pyrolytic home heating stoves etc. Please review my Sonoma Biochar Conference Report

Erich j Knight, McGaheysville, VA.
Tuesday, 2 April 2013 - 02:03

And what sort of acreage are we looking at to make any difference 10, 100 1000, 10,000, 100,000 taking land from food to growing charcoal?
Plus what Co2 in to Co2 out, on a small scale this may work but to make a difference we would be better to just grow the trees for timber, house building and the like.

Jon Nemo, Tumble, Llanelli
Wednesday, 3 April 2013 - 11:30

Fair points. Some of the benefit of crops like miscanthus and willow is that they grow on much less productive land than many food crops need, so they don't necessarily interfere that much with food production compared to (eg) growing maize to turn into ethanol.

But it does seem likely that bioenergy crops are only going to be part of the answer as we can't spare enough land for them to provide all the energy we need. This study does suggest, though, that as we're going to be growing these crops a fair bit anyway, we may as well take advantage of the ability of charcoal to increase carbon sequestration. Adele wrote a story a couple of years ago about a study that looked at some of these questions, showing that using currently marginal land for bioenergy could make a significant difference. I haven't seen any papers comparing bioenergy to timber; I imagine the economics of the two crops are very different - I'll have a look.

Tom Marshall, Planet Earth Online
Wednesday, 3 April 2013 - 15:01

How does this differ from the terra preta technology practiced by natives in the Amazon before 1500 AD?

Charles Scouten, Warrenville, IL
Wednesday, 3 April 2013 - 22:58

It differs dramatically from terra preta because the ancient Amazonians were adding a lot more than just biochar to their soil - they added manure, fish bones, food waste, pottery sherds....and not to mention the unique suite of microorganisms that co-occur with terra preta. That all said, I think this is a good first step toward that direction.

Trisha Jackson, Brookings, SD
Thursday, 4 April 2013 - 17:45

Tom, the marginal land you talk about is the last refuge for most of our wild life so to take that away from them will bring a greater disaster to our dwindling wildlife.
And as these crops are cut annually they offer nothing for them from food to nest sites.

Jon Nemo, Tumble, Llanelli
Friday, 5 April 2013 - 13:11

2011 Son of 1G ton Study
ORNL projected that the US would have 1.1 and 1.6 billion tons of available, sustainable biomass for industrial bioprocessing by 2030. a highlight of the "2011 U.S. Billion-Ton Study"

Colleagues working with Agave on marginal lands in Mexico & US southwest, estimate that such marginal lands have the potential of another 1.5 Gt of biomass production. Then the potential of new genetically hybridized, perennial biomass energy crops, triple cropping in the tropics, etc. can double the current biomass crop yields of about 10 tons per acre. [1]

No projections consider the integrated nutrient management and cascading values when char is used sequentially in real farming situations, as demonstrated in Europe. the potential of methane abatement from Biochar fed livestock or the 50% nitrogen retention composting with Biochar, This is solid data in such a study would be touting food security not food insecurity.[3]

Erich j Knight, usa, VA.
Monday, 8 April 2013 - 03:09

[1]
Borland et al.
Exploiting the potential of plants with crassulacean acid metabolism for bioenergy production on marginal lands
"The substantial biomass increases reported for CAM species under elevated CO2 on marginal lands indicate that serious consideration should be directed towards exploring the potential of CAM plants as a low-input source of bioenergy
http://jxb.oxfordjournals.org/content/60/10/2879.full

[2]
In the EU, 90% of the Biochar produced is passed through livestock before composting and field application. On Swiss Farms they have eliminated manure odor and closed the nutrient loop by retaining N in the Char/Composting process.

C. Steiner, showing a 52% reduction of NH3 loss when char is used as a composting accelerator.
http://www.ibi2010.org/wp-content/uploads/BiocharPoultrySteiner.pdf

55 Uses of Biochar
by Hans-Peter Schmidt;
http://www.ithaka-journal.net/55-anwendungen-von-pflanzenkohle?lang=en

Erich j Knight, usa, VA.
Monday, 8 April 2013 - 03:15

Thanks for the links Erich - interesting. We had an article by Andrew Leitch, Theodosios Korakianitis and Manuel Robert in late 2010 on agave's potential for bioenergy.

Tom Marshall, Planet Earth Online
Monday, 8 April 2013 - 11:01

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