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 CO signal from the oxidation stage (COoxi) 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 (Corg), may be tricky for heterogeneous surface areas and soil profiles. In the latter context, both protocols 1 and 2 are alternative methods to quantify Corg 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 COoxi, 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.

中文翻译：

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耕地中生物炭的定量：基于 Rock-Eval® 热分析的新方法


热解碳（PyC）构成重要的土壤有机碳库，可能在土壤中保留数千年。其在土壤中的准确定量对于监测土壤碳储量和通量的演变是必要的。本研究使用基于 Rock-Eval® 热法的三种协议测试了量化土壤中 PyC 富集的新直接方法。将六种工业生物炭和四种栽培土壤以 0.05% 至 1%（w/w）之间的五种不同生物炭/土壤比例混合。可以在 410 °C 至 610 °C 之间氧化阶段 (COoxi) 的 CO 信号中识别生物炭-C 排放，与原始未改良土壤中的碳和碳酸盐含量无关。基于该信号并使用参考样品，方案 3 可以很好地估计相对于参考样品的 PyC 富集度。因此，该协议非常适合监测农业土壤中生物炭的添加。然而，对于异质表面区域和土壤剖面，选择具有最低耐热有机碳 (Corg) 值的样品作为参考样品的使用可能会很棘手。在后一种情况下，方案 1 和 2 都是量化生物炭和土壤中的 Corg 的替代方法，无需参考样品，尽管不如方案 3 准确。方案 2，基于对生物炭衍生峰的更精确识别COoxi 的值比方案 1 更准确。然而，当生物炭衍生的峰很容易与原始未改良土壤中存在的耐热 SOM 和 PyC 衍生的峰区分开时，使用方案 2 是合适的。 总之，Rock-Eval® 热方法被证明是量化耕种土壤中生物炭-C 的良好工具，并且完全适用于现场实验（其中控制生物炭的初始含量），旨在破译潜在效益生物炭对土壤功能和相关生态系统服务的影响。