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Carbon to be returned to the soil

Biochar may be one of the solutions to reducing emissions of harmful greenhouse gases from agricultural land and to improving soil fertility. These are the research objectives of the EU research project Refertil, which scientists at Aarhus University are participating in.


Biochar is one of the products of the so-called pyrolysis of biomass. Biochar can be added to soil and boost plant growth, increase carbon sequestration and reduce the emission of CO2. Photo: AU

In contrast to miners that dig the coal out of the soil, a new research project supported by the EU will be putting the coal back into the soil.


Biochar is the name for the product of the so-called pyrolysis of biomasses such as straw and woodchip. Biochar has in recent years emerged as an interesting research topic, because the coal may constitute a solution not only for reducing emissions of greenhouse gases that exacerbate climate change but also for increasing the carbon content of soils. The latter will benefit soil fertility as carbon in soil helps to capture nutrients and in that way to halt some of the processes that lead to leaching and gaseous losses of nitrogen.


Lars Elsgaard, lecturer at Aarhus University, is leader of one of the projects of a large EU research project which over the next four years will be looking into whether biochar can be used as a soil amendment product.


-          It would appear that biochar can be used as a soil improver and as a source of stable carbon in the soil that is very recalcitrant. Biochar also has good adsorption properties and this means that it is able to retain the nutrients in the soil so they are available to plants. The good adsorption properties can also delay the conversion of ammonium to nitrate and thus restrict the formation of the powerful greenhouse gas nitrous oxide, he explains.

Side effects

Together with the Knowledge Centre for Agriculture the scientists will be using two different types of biochar and will record yields and greenhouse gas emissions at four different locations in Denmark.


The scientists from Aarhus University will also be looking at possible side effects of biochar and at how biochar may affect the microbial processes in soil, particularly the nitrogen cycle.


-          The pyrolysis process converts biomass to gas, biochar and oil at high temperatures and under anoxic conditions. This means that a number of chemical compounds are formed, depending on how the process progresses. With our partners in the project we will be testing how different types of biochar affect soil microorganisms and we will look at how it behaves in the soil, says Lars Elsgaard.


The scientists from Aarhus University have previously shown that pyrolysed straw and woodchip from Danish sources did not appear to have any harmful effects on microorganisms and they expect to be able to also document this for the types of biochar used in the new EU project.


-          We believe that the levels of harmful substances in biochar would have to be unrealistically high for it to be an impediment to the physiological processes in the microorganisms, explains Lars Elsgaard. And Lars Elsgaard has clear expectations of the final results.


-          I hope that at the end of the project we will be able to document that biochar has a function as a soil improver and that we will be able to measure this in yields. We will also have good documentation for the influence of biochar on the soil ecosystem. And we will finally have found the right technology and biomass for the generation of biochar to help reduce the emission of greenhouse gases.


The REFERTIL (289785) Collaborative project (2011-2015) is co-funded by the European Commission, Directorate General for Research, within the 7th Framework Programme of RTD, Theme 2  - Food, Agriculture and Fisheries, and Biotechnology. The project is coordinated and biochar system key technology designed by Mr. Edward Someus (Swedish environmental engineer, www.3ragrocarbon.com , edward.someus@gmail.com ) / Terra Humana Ltd. Further information is available at the REFERTIL website www.refertil.info


There are 14 partners in the project including a large number of private European companies.


Further information: Lecturer Lars Elsgaard, Department of Agroecology, telephone: +45 8715 7674, e-mail: lars.elsgaard@agrsci.dk


Text: Søren Tobberup Hansen

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