Article (Scientific journals)
Accumulation of century-old biochar contributes to carbon storage and stabilization in the subsoil
Fouché, Julien; Burgeon, Victor; Meersmans, Jeroen et al.
2023In Geoderma, 440, p. 116717
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Keywords :
Differential scanning calorimetry; Dissolved organic carbon; Mineral-associated organic matter; PARAFAC modeling; Particulate organic matter; Biochar; Carbon concentrations; Dissolved organic matters; Mineral phasis; Organics; PARAFAC; Particulate organic matters; Soil Science
Abstract :
[en] Soil organic carbon (C) is a key component of the global C budget. As soil organic C turnover rates decrease with depth, agricultural practices favoring deep organic C storage will gain importance as long-term climate change mitigation strategies. In addition, amendment of pyrogenic organic matter (biochar) is considered a promising practice for sequestering C in croplands. However, so far the >30 cm depth soil organic C pool, and subsoil biochar dynamics in particular, has been understudied. To address this, we focused on leftovers from pre-industrial charcoal kilns as a proxy to study the accrual of century-old biochar in the subsoil (30–100 cm) in comparison to adjacent control soil. Using thermal and elemental analyses as well as size and density fractionations (i.e., separating particulate and mineral-associated organic matter), we determined the distribution of pyrogenic organic C within the soil profile and investigated its stabilization in depth. We measured the dissolved organic carbon (DOC) concentrations as well as absorbance and fluorescence properties of dissolved organic matter (DOM) at different depths to characterize the effects of century-old biochar accumulation on the current leaching of DOM. Our results showed that the presence of century-old biochar resulted in an increase of 53.8 ± 25.1 t C ha−1 in 0–100 cm, and 12 % of the pyrogenic organic C was stored in 30–60 cm. No difference in C stocks was observed in 60–100 cm between kiln sites and reference soils. Most of the pyrogenic organic C has been translocated as particulate organic matter, either free or occluded, to subsoils. This led to a change in the dominant fraction of organic matter in the E horizon; in reference soils 64.7 % of the total C was associated with mineral phases as opposed to only 42.3 % in soils enriched with biochar. The thermal analysis of the mineral-associated organic matter revealed that pyrogenic organic C was associated with mineral phases. With depth, DOC concentrations decreased and the relative contribution of microbial byproducts to fluorescent DOM increased. The soils enriched with century-old biochar displayed lower DOC concentrations and more aromatic DOM in the Ap horizon, which suggests biochar dissolution is still an on-going process. Our results suggest that the vertical transfers of century-old biochar mainly occurred as particle leaching in macroporosity and bioturbation but continuous dissolution has also contributed in these fine-textured cropland soils. In conclusion, the association of pyrogenic organic C with mineral phases as well as its migration in subsoil horizons promoted its physical disconnection from abiotic and biotic degrading agents, which likely contribute to the long-term stability of biochar.
Disciplines :
Environmental sciences & ecology
Author, co-author :
Fouché, Julien ;  LISAH, Univ Montpellier, INRAE, IRD, Institut Agro, AgroParisTech, Montpellier, France
Burgeon, Victor ;  Université de Liège - ULiège > Département GxABT > Echanges Eau - Sol - Plantes
Meersmans, Jeroen  ;  Université de Liège - ULiège > TERRA Research Centre > Echanges Eau - Sol - Plantes
Leifeld, Jens ;  Climate and Agriculture Group, Agroscope, Zurich, Switzerland
Cornelis, Jean-Thomas  ;  Université de Liège - ULiège > Département GxABT > Echanges Eau - Sol - Plantes ; Faculty of Land and Food Systems, The University of British Columbia, Vancouver, Canada
Language :
English
Title :
Accumulation of century-old biochar contributes to carbon storage and stabilization in the subsoil
Publication date :
December 2023
Journal title :
Geoderma
ISSN :
0016-7061
eISSN :
1872-6259
Publisher :
Elsevier B.V.
Volume :
440
Pages :
116717
Peer reviewed :
Peer Reviewed verified by ORBi
Funding text :
We would like to thank colleagues from the water-soil-plant exchange lab for their advice during the set-up of the field work and in particular Thomas Rochereau for his precious work in the lab. A special thanks goes to Alexandre Godfrind owner and farmer of the experimental site for his help in the field. We warmly thank the two anonymous reviewers for their supportive contributions and constructive comments which improved the quality of the manuscript. This research was funded through the Concerted Research Action grant 17/21-03 within the CHAR project framework by the French Community of Belgium .
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