Preprints
https://doi.org/10.5194/egusphere-2022-1130
https://doi.org/10.5194/egusphere-2022-1130
 
03 Nov 2022
03 Nov 2022
Status: this preprint is open for discussion.

Elemental stoichiometry and Rock-Eval® thermal stability of organic matter in French topsoils

Amicie A. Delahaie1, Pierre Barré1, François Baudin2, Dominique Arrouays3, Antonio Bispo3, Line Boulonne3, Claire Chenu4, Claudy Jolivet3, Manuel P. Martin3, Céline Ratié3, Nicolas P. A. Saby3, Florence Savignac2, and Lauric Cécillon1 Amicie A. Delahaie et al.
  • 1Laboratoire de Géologie, École normale supérieure, CNRS, PSL Univ., IPSL, Paris, France
  • 2UMR 7193 ISTeP, Sorbonne Université, Paris, France
  • 3INRAE, US1106, InfoSol, F-45075 Orléans, France
  • 4UMR ECOSYS, Université Paris Saclay, INRAE, AgroParisTech, 91120 Palaiseau, France

Abstract. The quality and quantity of soil organic matter (SOM) are key elements of soil health and climate regulation by soils. The Rock-Eval® thermal analysis technique is increasingly used as it represents a powerful method for SOM characterization by providing insights on bulk SOM chemistry and thermal stability. In this study, we applied this technique on a large soil sample set from the first campaign (2000–2009) of the French monitoring network of soil quality: RMQS. Based on our analyses on ca. 2000 composite surface (0–30 cm) samples taken all over mainland France, we observed a significant impact of land cover on both SOM thermal stability and elemental stoichiometry. Cropland soils had a lower mean value of hydrogen index (a proxy for SOM H / C ratio) and a higher thermal stability than grasslands and forests. Regarding the oxygen index (a proxy for SOM O / C ratio), we observed significant differences in values for croplands, grasslands and forests. Positive correlations between the temperature parameters on the one hand and the clay content and pH on the other hand highlight the protective effect of clay on organic matter and the impact of pH on microorganisms mineralization activity. Surprisingly, we found weak effects of climatic parameters on the thermal stability and stoichiometry of SOM. Our data suggest that topsoil SOM is on average more oxidized and biogeochemically stable in croplands. More generally, the high number and even repartition of data on the whole French territory allow to build a national interpretative referential for these indicators in surface soils.

Amicie A. Delahaie et al.

Status: open (until 09 Jan 2023)

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Amicie A. Delahaie et al.

Amicie A. Delahaie et al.

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Short summary
We characterized organic matter in French soils by analyzing the samples of the French RMQS using Rock-Eval thermal analysis. This study demonstrates that thermal analysis is appropriate to characterize large set of samples (~2000) and provides interpretation references for Rock-Eval parameter values. It shows that organic matter in managed soils is on average more oxidized and more thermally stable and that some Rock-Eval parameters are good proxies of organic matter biogeochemical stability.