Possibilities to improve soil aggregate stability using biochars derived from various biomasses through slow pyrolysis, hydrothermal carbonization, or torrefaction

Jaakko Heikkinen (Corresponding Author), Riikka Keskinen, Helena Soinne, Jari Hyväluoma, Johanna Nikama, Hanne Wikberg, Anssi Källi, Virpi Siipola, Thierry Melkior, Capucine Dupont, Matthieu Campargue, Sylvia H. Larsson, Markus Hannula, Kimmo Rasa

    Research output: Contribution to journalArticleScientificpeer-review

    56 Citations (Scopus)


    Various thermochemical conversion technologies can be applied in producing biochar from a wide range of raw materials. We studied the chemical quality of 10 different biochars produced via torrefaction (TOR), slow pyrolysis (SP), or hydrothermal carbonization (HTC), in order to assess their potential in improving clay soil aggregate stability and thus contribute to mitigation of erosion from agricultural soils. X-ray tomography was used to visualize soil aggregates in some selected biochar treatments. Feedstock type had a major influence on the properties of the biochar, but in general biochars derived through SP were alkaline and exhibited higher electrical conductivity and ash content and lower surface activity than acidic HTC and TOR biochars. Alkyl peak areas determined from FTIR spectra were higher in biochars produced by TOR and HTC than in SP biochars, which indicates a higher degree of hydrophobicity in the former. Significantly higher aggregate stability and reduced colloid detachment were achieved with HTC biochars, most likely due to hydrophobicity reducing wetting rate and aggregate slaking. When mixed with initially aggregated soil, the biochar particles settled in inter-aggregate voids. According to image analysis, the internal porosity of soil aggregates was not affected by biochar addition, i.e., biochar did not enter the aggregates during the short incubation period. Addition of hydrophobic HTC biochar decreased the soil water content at field capacity, whereas more inert SP chars tended to increase it. The overall effect of biochar hydrophobicity on soil functions needs to be explored prior to wider use of biochar as a soil amendment.
    Original languageEnglish
    Pages (from-to)40-49
    Publication statusPublished - 7 Mar 2019
    MoE publication typeA1 Journal article-refereed


    This project received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 637020 −MOBILE FLIP. ANR (French Agency for research) is acknowledged for partial funding of the GENEPI biomass research platform of CEA (Grenoble, France) within the framework of the investments of future (ANR-11-EQPX-0019). We thank Bio4Energy, a Strategic Research Environment appointed by the Swedish government, for supporting this work.


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