Black carbon estimation in French calcareous soils using chemo‐thermal oxidation method |
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| Authors: | G Caria D Arrouays E Dubromel C Jolivet C Ratié M Bernoux B G Barthès D Brunet C Grinand |
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| Institution: | 1. Institut National de la Recherche Agronomique, INRA, U.S.010, Laboratoire d’analyses des sols, 273 rue de Cambrai, 62000 Arras, France;2. Institut National de la Recherche Agronomique, INRA, U.S.1106, Infosol, 2163 avenue de la Pomme de Pin, CS 40001, Ardon, 45075 Orléans Cédex 2, France;3. Institut de Recherche et de Développement, IRD, UMR Eco&Sols (INRA‐IRD‐Montpellier SupAgro), 2 place Viala, Bat. 12, 34060 Montpellier Cedex 2, France |
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| Abstract: | We studied the black carbon (BC) content of ca. 405 samples from French topsoil and artificial soil and carbonate mixtures. Our protocol involved three main steps: (i) decarbonation by HCl, (ii) elimination of non‐pyrogenic organic carbon in a furnace at 375 °C, and (iii) quantification of residual carbon by CHN analysis. BC content increased for calcareous soils according to their carbonates content. Subsequent analyses confirmed the existence of a methodological artefact for BC determination only in calcareous soils. Decarbonation changes the thermal properties of organic matter, creating more recalcitrant carbon than in the initial sample. Higher CaCO3 and organic carbon content results in a more pronounced artefact. The reversal of the first two steps of the chemo‐thermal oxidation method (i.e. thermal oxidation before soil decarbonation) eliminates this artefact. Overall, our results suggest that BC content may have been overestimated in a large number of studies on calcareous soils. |
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| Keywords: | Black carbon calcareous soils CTO methods decarbonation thermal oxidation artefact |
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