It’s a process that is as old as humankind taming fire and growing crops. The practice of returning carbon to the soil through charcoal (called “biochar” when put into the ground) from fires has been known for centuries to have a positive effect on plant growth.

Now, thanks to some work done at the Canadian Light Source in Saskatoon, advocates of using biochar know the reason why charcoal works so well in capturing and releasing nutrients such as nitrogen and phosphorus slowly into the soil to improve crop yields over an entire growing season and beyond. The findings could lead to the creation of an organic slow release fertilizer with significantly better performance than current agricultural management practices.

Nikolas Hagemann

The answer researchers from Europe got in a trip to the CLS beamlines was not the one that everyone had previously presumed.  Instead of the old assumption that oxidization of biochar enabled the storage and release of nutrients for crops, team leader Nikolas Hagemann says the CLS allowed researchers to see the actual pathway.  Martin Obst, one of Hagemann’s collaborators and frequent user of the CLS, used the soft X-ray spectromicroscopy beamline to get a picture at the molecular level so they could see how other nutrients such as composted manure clung to the biochar due to size and shape of the carbon molecules. Incorporated into soil, the biochar is slow to give up the nutrients clinging to it.

Hagemann, an environmental scientist based in Switzerland, worked with a team of researchers from several European, American and Australian institutes who are part of a worldwide effort to apply a more rigorous scientific approach to the use of biochar. 

Martin Obst

They see this form of carbon having the potential to improve crop yields in both developed and developing countries, especially in tropical soils in Africa and South America where historically fire pit residues and other forms of biochar were proven to boost crop yields.

“Prior to this, we had no real idea of what happens in the soil with biochar,” Hagemann explained.

“It turns out the driving factor is absorption by the plant root system thanks to an organic coating which is the result of co-composting manure with the biochar. The roots of the plant like the biochar because it slowly releases the nitrogen in the manure.”

Biochar is the scientific name for something that most everybody has experienced if they have stared into a campfire at night. Hagemann says you can see the blue flames of gases in wood burning off in the combustion process.  But inside the wood where the oxygen can’t get to, the wood cellulose is turned into a hard carbon as it heats up without oxygen. 

The result for the environment is a simple but valuable form of carbon sequestration through agriculture in a process that can be either high tech or low tech.  In high tech production of biochar, the carbon char is what remains after external heat drives off a gas such as methane.  In low tech applications, the biochar is left over from simple household cooking processes once used in Europe and North America and still in use in the developing world. 

Hagemann says advocates of biochar know that composting the biochar along with organics such as cow manure can also take place in an enclosed vessel or in a less technical composting system. A paper published late this year following the team’s visit to the CLS points out that farmers can gain benefits in yield even if the application of manure-infused biochar is as low as half a tonne per hectare.

Hagemann is particularly interested in a project that the Ithaka Institute is doing in Nepal with 60 local farmers using biochar in more than 140 different test fields, substantially improving yields. 

In a practical sense, the European researcher is hoping what was learned at the CLS will result in new ways of creating biochar-based fertilizers that exploit the mechanism by which biochar releases other nutrients over time into soil.

“We want to continue this work on the technical side of things to create this organic fertilizer and work to bring down what is now a very expensive process,” he said.

The article, “Organic coating on biochar explains its nutrient retention and stimulation of soil fertility,” was published in Nature Communications.

Hagemann, Nikolas, Stephen Joseph, Hans-Peter Schmidt, Claudia I. Kammann, Johannes Harter, Thomas Borch, Robert B. Young et al. "Organic coating on biochar explains its nutrient retention and stimulation of soil fertility." Nature Communications 8, no. 1 (2017): 1089. DOI: 10.1038/s41467-017-01123-0

Story by Murray Lyons

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