Quantification of biochar in arable land : A new approach based on Rock-Eval® thermal analysis
Résumé
Pyrogenic carbon (PyC) constitutes an important pool of soil organic carbon and may remain in soil over
millennia. Its accurate quantification in soil is necessary to monitor the evolution of soil carbon stocks and fluxes.
This study tested new direct approaches to quantify PyC enrichment in soil, using three protocols based on the
Rock-Eval® thermal method. Six industrial biochars and four cultivated soils were mixed at five different biochar/soil ratios from 0.05 % to 1 % (w/w). Biochar-C emissions could be identified in the CO2 signal from the
oxidation stage (CO2oxi) between 410 ◦C and 610 ◦C, independently from carbon and carbonate contents from
the original unamended soil. Based on this signal and using a reference sample, the protocol 3 allowed for a good
estimation of the PyC enrichment relatively to the reference sample. This protocol is thus well adapted to monitor
biochar addition in agricultural soils. However, the use of a reference sample, chosen as the sample with the
lowest value of thermo-resistant organic carbon (CorgTR), may be tricky for heterogeneous surface areas and soil
profiles. In the latter context, both protocols 1 and 2 are alternative methods to quantify CorgTR from biochar and
soil without the need of a reference sample, although less accurate than protocol 3. Protocol 2, based on a more
precise identification of the biochar-derived peak of CO2oxi, resulted in more accurate values than protocol 1.
However, the use of protocol 2 is suitable when the biochar-derived peak is easily distinguishable from the peaks
derived from both thermo-resistant SOM and PyC present in the original unamended soil. In conclusion, the
Rock-Eval® thermal method turns out to be a good tool to quantify biochar-C in cultivated soil and is fully
adapted in field experiments – in which, the initial content in biochar is controlled – aiming to decipher the
potential benefits of biochar on soil functioning and related ecosystem services.
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QuantificationOfBiochar.pdf (3.16 Mo)
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Annexe1_QuantificationOfBiochar.pdf (432.16 Ko)
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