Mollisols contain a high amount of soil organic carbon (SOC) that is highly susceptible to tillage practices. Conservation tillage (CT) could improve soil aggregate stability, but the predominant factor controlling this stability remains debatable. This study reports on a tillage management experiment established in 2004 to explore the influences of tillage practices on the content and chemical composition of labile and recalcitrant OC fractions, plus with the aggregate stability change and potential mechanisms. CT without straw mulching, reduced tillage (RT), and no tillage (NT) (zero tillage) with straw mulching were set up. Compared with CT, 15-year RT significantly increased SOC content (by 11.4%) in the surface (0–10 cm) by increasing the amount of aromatic compounds. Simultaneously, RT and NT promoted soil aggregate stability, as verified by the increase in mean weight diameter (MWD) and geometric mean diameter (GMD) of 7%–71.3% at 0–30 cm soil depth. Of importance, RT and NT increased aromatic compound amount of silt + clay fractions (by 12.6%–27.2%) within macroaggregates (>0.25 mm) but decreased that (by 15.6%–32.9%) within free microaggregates (0.053–0.25 mm) than CT at 0–30 cm soil depth. Collectively, conservation tillage controls the SOC stability in Mollisols by regulating the MWD and GMD values and further affects the amount of aromatic compounds in silt + clay fractions within aggregates. Rather than physical and biochemical protection, chemical protection through a mineral association could be the crucial mechanism for aggregate stability under long-term conservation tillage in Mollisols.

中文翻译：

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十五年的保护性耕作通过改变软土中有机碳组分的含量和化学成分来提高土壤团聚体的稳定性

软土含有大量土壤有机碳 (SOC)，对耕作非常敏感。保护性耕作 (CT) 可以提高土壤团聚体稳定性，但控制这种稳定性的主要因素仍有争议。本研究报告了 2004 年建立的耕作管理实验，以探索耕作方式对不稳定和顽固 OC 级分的含量和化学组成的影响，以及总体稳定性变化和潜在机制。设置了秸秆覆盖CT、减耕(RT)和秸秆覆盖免耕(NT)(零耕)。与 CT 相比，15 年 RT 通过增加芳香族化合物的量，显着增加了表面（0-10 cm）的 SOC 含量（增加了 11.4%）。同时，RT 和 NT 促进了土壤团聚体的稳定性，正如在 0-30 cm 土壤深度处平均重量直径 (MWD) 和几何平均直径 (GMD) 增加 7%-71.3% 所证实的那样。重要的是，RT 和 NT 增加了大骨料 (>0.25 mm) 内粉砂 + 粘土部分的芳香族化合物量（增加 12.6%–27.2%），但在游离微骨料 (0.053–0.25 mm) 内减少了（减少了 15.6%–32.9%）在 0-30 cm 土壤深度比 CT。总的来说，保护性耕作通过调节 MWD 和 GMD 值来控制 Mollisols 的 SOC 稳定性，并进一步影响聚集体中淤泥 + 粘土部分中芳香族化合物的量。与物理和生化保护不同，通过矿物组合的化学保护可能是在 Mollisols 长期保护性耕作下聚集体稳定性的关键机制。