Abstract

The climate change mitigation benefits of biochar systems arise largely from carbon storage in biochar. However, while biochar is increasingly recognized as a carbon dioxide removal technology, there are on-going scientific discussions on how to estimate the persistence of biochar carbon when biochar is used in soils. Estimates vary from decades to millennia, building on different modelling approaches and evidence. Here, we revisited the persistence estimates derived from extrapolation of biochar incubation experiments, with the aims of making incubation data available, modelling choices transparent, and results reproducible. An extensive dataset of biochar incubations, including 129 biochar decomposition time series, was compiled and is made available alongside code for its analysis. Biochar persistence correlations were sensitive to data selection procedures and to the curve fitting modelling step, while soil temperature adjustments methods had less impact. Biochar H/C ratio remained the main predictor of biochar persistence, in line with previous research, regardless of the extrapo-lation assumptions (multi-pool exponential functions or power function) used in curve fitting. The relation be-tween H/C and percentage of biochar carbon remaining after 100 years (BC100) was better explained by a power model than a linear model, with R-2 values between 0.5 and 0.9. Using multi-pool exponential functions, esti-mated BC100 varied between 90 % and 60 % for H/C from 0 to 0.7. However, using power functions, BC100 was constrained between 90 % and 80 % for the same H/C range. Additional information about the biochar, the pyrolysis conditions or the environmental incubation conditions did not significantly increase explained vari-ance. Notably, the dataset lacks observations at H/C ratios below 0.2, of biochar made from manure and bio-solids, biochar from processes other than slow pyrolysis, field studies, and incubation temperatures below 10( degrees)C, which should guide future experimental work. The detailed analysis performed in this study does not cast doubts on the longevity of biochar carbon storage; rather, it confirms previous knowledge by critically examining the modelling, elucidating the assumptions and limitations, and making the analysis fully reproducible. There is a need for further interdisciplinary work on integration of various theories and approaches to biochar persistence, ultimately leading to the formulation of policy-relevant conclusions.

Keywords

Biochar persistence; Biochar carbon modelling; Durability; Soil carbon sequestration; Temperature sensitivity (Q (10) )

Published in

Geoderma
2024, Volume: 441, article number: 116761

SLU Authors

• Azzi, Elias

  • Department of Energy and Technology, Swedish University of Agricultural Sciences
    

• Li, Haichao

  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    

• Cederlund, Harald

  • Department of Molecular Sciences, Swedish University of Agricultural Sciences
    

• Karltun, Erik

  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    

• Sundberg, Cecilia

  • Department of Energy and Technology, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Soil Science


Publication identifier

DOI: https://doi.org/10.1016/j.geoderma.2023.116761

Permanent link to this page (URI)

https://res.slu.se/id/publ/128967