Agricultural waste can be made into biochar, which serves to raise soil fertility and fix carbon (C). When biochar is added to soil, a small part of biochar could be transformed into soil organic C in a short time to promote soil fertility. However, it is still unknown how much biochar can be stored in the soil as stable C and whether it plays a role in C sequestration. In this study, a 540-day incubation experiment was conducted to evaluate the transformation of maize straw biochar into humus fractions using a ¹³C isotopic labelling technique. The treatments were CK (no biochar applied) and AB (21.3 g kg^-1 of biochar + CK). The results showed that: 1) Compared with those in the CK treatment, the concentrations of organic and humus C in the bulk soil were significantly higher under the AB treatment. 2) The δ¹³C values of soil humus C were higher (ranging between 0% and 23.45%) in the AB treatment than those in the CK treatment. 3) The proportions of biochar transformed into humic acid (HA), fulvic acid (FA), water-soluble substances (WSS), and water floating substances (WFS) were 2.66–4.30%, 1.11–1.57%, 0.49–0.88%, and 0.68–1.40%, respectively. The remaining biochar (59.44–98.00%) remained in the crude humin form, retaining the inert nature of the biochar itself. Although biochar is relatively stable, approximately 4.22–5.40% of biochar was transformed into extracted humic substances (HA+FA). We concluded that a relatively small amount of biochar could be transformed into soil organic matter under short-term (540 days) incubation conditions.

农业废弃物可制成生物炭，用于提高土壤肥力和固碳 (C)。在土壤中加入生物炭后，一小部分生物炭可在短时间内转化为土壤有机碳，促进土壤肥力。然而，尚不清楚有多少生物炭可以作为稳定的 C 储存在土壤中，以及它是否在 C 封存中发挥作用。在这项研究中，进行了 540 天的孵化实验，以使用¹³ C 同位素标记技术评估玉米秸秆生物炭向腐殖质部分的转化。处理为 CK（未应用生物炭）和 AB（21.3 g kg ^-1biochar + CK）。结果表明：1）与CK处理相比，AB处理下大块土壤有机质和腐殖质C含量显着升高。2) δ ¹³AB 处理土壤腐殖质 C 的 C 值高于 CK 处理（范围在 0% 和 23.45% 之间）。3）生物炭转化为腐植酸（HA）、富里酸（FA）、水溶性物质（WSS）和水浮性物质（WFS）的比例分别为2.66-4.30%、1.11-1.57%、0.49-0.88% , 和 0.68–1.40%, 分别。剩余的 biochar (59.44–98.00%) 保持原始腐殖质形式，保留 biochar 本身的惰性性质。尽管生物炭相对稳定，但大约 4.22-5.40% 的生物炭转化为提取的腐殖质 (HA+FA)。我们得出的结论是，在短期（540 天）培养条件下，相对少量的生物炭可以转化为土壤有机质。