Preprints
https://doi.org/10.5194/bg-2023-66
https://doi.org/10.5194/bg-2023-66
19 Apr 2023
 | 19 Apr 2023
Status: a revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

Adjustments of the Rock-Eval® thermal analysis for soil organic and inorganic carbon quantification

Joséphine Hazera, David Sebag, Isabelle Kowalewski, Eric Verrecchia, Herman Ravelojaona, and Tiphaine Chevallier

Abstract. Quantifying both soil organic and inorganic carbon (SOC & SIC) is essential to understand carbon (C) dynamics and to assess the atmospheric C sequestration potential in calcareous soils. The procedures usually used to quantify SOC and SIC involve pretreatments (decarbonation, decarbonatation) and calculation of the difference between C contents estimated by elemental analysis on raw and pretreated aliquots. These procedures lead to analytical bias associated to pretreatments, measurement deviations associated to the sample heterogeneity, and cumulative errors associated to calculations. The Rock-Eval® thermal analysis, used in soil sciences since the 2000s, provides two parameters estimating the organic (TOC) and inorganic (MinC) C contents of a non-pretreated aliquot with a single analysis. Nevertheless, the Rock-Eval® protocol has been standardized in the 70s by IFP Energies Nouvelles for studying oil bearing rocks and is, thus, not perfectly suited for soil study. Previous studies suggested statistical corrections of the standard parameters to improve their estimations of C contents assessed by elemental analysis but only few of them focused on the estimation of inorganic C content using the MinC parameter. Moreover, none of them suggested adjustments of the standard Rock-Eval® protocol. This study proposes to adapt this protocol to optimize SOC and SIC quantifications in soil samples. Comparisons between SOC and SIC quantifications by elemental analysis and by Rock-Eval®, with and without statistical corrections of the standard TOC and MinC parameters, were carried out on a soil panel with a wide range of SOC and SIC contents. The results show that the standard Rock-Eval® protocol properly estimates SOC contents once the TOC parameter is corrected. However, it cannot achieve a complete thermal breakdown of SIC amounts > 4 mg leading to an underestimation of high SIC contents by the MinC parameter, even after correcting it. Thus, the final oxidation isotherm is extended to 7 min to complete the thermal breakdown of SIC before the end of the analysis.

Joséphine Hazera et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on bg-2023-66', Yakov Kuzyakov, 14 May 2023
    • AC3: 'Reply on CC1', Joséphine Hazera, 18 Jul 2023
    • AC1: 'Reply on RC1', Joséphine Hazera, 18 Jul 2023
    • AC4: 'Reply on CC1', Joséphine Hazera, 12 Sep 2023
    • AC7: 'Reply on CC1', Joséphine Hazera, 18 Sep 2023
  • RC1: 'Comment on bg-2023-66', Anonymous Referee #1, 06 Jun 2023
    • AC1: 'Reply on RC1', Joséphine Hazera, 18 Jul 2023
    • AC5: 'Reply on RC1', Joséphine Hazera, 12 Sep 2023
    • AC8: 'Reply on RC1', Joséphine Hazera, 18 Sep 2023
  • RC2: 'Comment on bg-2023-66', Anonymous Referee #2, 27 Jun 2023
    • AC2: 'Reply on RC2', Joséphine Hazera, 18 Jul 2023
    • AC6: 'Reply on RC2', Joséphine Hazera, 12 Sep 2023
    • AC9: 'Reply on RC2', Joséphine Hazera, 18 Sep 2023

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on bg-2023-66', Yakov Kuzyakov, 14 May 2023
    • AC3: 'Reply on CC1', Joséphine Hazera, 18 Jul 2023
    • AC1: 'Reply on RC1', Joséphine Hazera, 18 Jul 2023
    • AC4: 'Reply on CC1', Joséphine Hazera, 12 Sep 2023
    • AC7: 'Reply on CC1', Joséphine Hazera, 18 Sep 2023
  • RC1: 'Comment on bg-2023-66', Anonymous Referee #1, 06 Jun 2023
    • AC1: 'Reply on RC1', Joséphine Hazera, 18 Jul 2023
    • AC5: 'Reply on RC1', Joséphine Hazera, 12 Sep 2023
    • AC8: 'Reply on RC1', Joséphine Hazera, 18 Sep 2023
  • RC2: 'Comment on bg-2023-66', Anonymous Referee #2, 27 Jun 2023
    • AC2: 'Reply on RC2', Joséphine Hazera, 18 Jul 2023
    • AC6: 'Reply on RC2', Joséphine Hazera, 12 Sep 2023
    • AC9: 'Reply on RC2', Joséphine Hazera, 18 Sep 2023

Joséphine Hazera et al.

Joséphine Hazera et al.

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Short summary
This study adapts the Rock-Eval® protocol to optimize SOC and SIC quantifications on one aliquot of calcareous soil. The standard protocol properly estimates SOC contents once the TOC parameter is corrected. However, it cannot achieve a complete thermal breakdown of SIC amounts > 4 mg leading to an underestimation of high SIC contents by the MinC parameter, even after correcting it. Thus, the final oxidation isotherm must be extended to 7 min to quantify any amount of SIC.
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