Understanding the stability and movement of biochar in soil is pivotal for its effective use in soil improvement and carbon sequestration projects. Building on a previous study that evaluated the migration of three size fractions of maize biochar carbon (BC) after 4.5 years in a Zambian loamy sand soil using δ13C isotopes, this study compares the results with those using chemothermal oxidation (CTO) and benzene polycarboxylic acid (BPCA) biomarkers. While the δ13C method registered the most BC in the application layer (0–7 cm), it detected less BC in lower layers (7–30 cm, 3.2–7.9 % downward migration), and with a greater variance, than the other two methods. The BPCA method detected relatively more BC in the lower layers (9.1–20.2 % downward migration), particularly for fine-sized biochar. It also detected the most BC in the control soil plot and outside the experimental block, which suggests either its efficiency in fine biochar detection or an issue with false positive detection. The CTO method, though less sensitive in detecting fine biochar particle BC, was strongly correlated with δ13C isotope results, thus representing a cost-effective and simpler alternative to the other BC quantification methods. These findings underscore the necessity of methodological consideration in biochar C quantification to ensure accurate assessment of its distribution and stability. This is a pressing need for correct assignment of climate mitigation credits. More field studies should be carried out involving multiple biochar types and quantification methods to refine our understanding of biochar C dynamics in soil.

中文翻译：

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用于检测热带土壤中生物炭碳迁移的三种定量方法的比较：赞比亚为期 4.5 年的田间实验


了解生物炭在土壤中的稳定性和移动性对于其在土壤改良和碳封存项目中的有效利用至关重要。基于之前的一项研究，该研究使用 δ13C 同位素评估了 4.5 年后玉米生物炭碳 （BC） 在赞比亚壤土中的迁移，本研究将结果与使用化学热氧化 （CTO） 和苯聚羧酸 （BPCA） 生物标志物的结果进行了比较。虽然 δ13C 方法在应用层 （0-7 cm） 中记录的 BC 最多，但它在较低层中检测到的 BC 较少（7-30 cm，向下迁移 3.2-7.9%），并且与其他两种方法相比，差异更大。BPCA 方法在下层检测到相对更多的 BC（向下迁移 9.1-20.2%），特别是对于细粒生物炭。它还在对照土壤样地和实验块外检测到最多的 BC，这表明它在精细生物炭检测方面的效率或存在假阳性检测问题。CTO 方法虽然在检测细小生物炭颗粒 BC 时灵敏度较低，但与 δ13C 同位素结果密切相关，因此是其他 BC 定量方法的一种经济高效且更简单的替代方案。这些发现强调了在生物炭 C 定量中进行方法学考虑的必要性，以确保准确评估其分布和稳定性。这是正确分配气候减缓信用的迫切需求。应该进行更多的田间研究，涉及多种生物炭类型和量化方法，以完善我们对土壤中生物炭 C 动力学的理解。