土壤有机碳（SOC）由于其在调节气候，保持土壤肥力和恢复力方面的核心作用而成为研究的重点。方法上,从整个土壤C测量值转移到特定的SOC分数增加了检测巨大SOC存储中的小变化的可能性，增强了SOC稳定性的估计。然而,SOC分馏方案是众多且可变的。在这项研究中,通过将土壤分离成粗土（0.25-2毫米），比较了去离子水和六偏磷酸钠（SHMP）在土壤分散中的分布，中等（0.063-0.25毫米）和细（<0.063毫米）尺寸的部分。通过密度（1.8gcm-3）进一步分离前两个级分，以获得游离的颗粒状有机C（POC）和矿物缔合的有机C（MOC）。该方法适用于有或没有木质纤维污泥改良剂的粘土和淤泥壤土，以遵循添加的C。与水相比，SHMP增强了骨料的破坏，但是效果很小，使用SHMP降低了SOC的恢复，因此，水是首选。在这两种土壤中，5-10%的SOC发生为粗POC，1-3%作为粗MOC，5%作为培养基POC，10%作为培养基MOC，和70-85%的罚款MOC。添加的C存在于POC级分中，表明粘土土壤中的细MOC有少量积累。尽管MOC储量的饱和可能会阻碍细粒含量低的粉质壤土的积累，但需要更长的时间范围重复添加C才能增加稳定的MOC储量。
Soil organic carbon (SOC) is in the focus of research due to its central role in regulating climate and maintaining fertility and resilience of soils. Methodologically, shifting from whole soil C measurements to specific SOC fractions increases possibility to detect small changes in the vast SOC storage, and enhances estimation of SOC stability. However, SOC fractionation schemes are numerous and variable. In this study, deionized water and sodium hexametaphosphate (SHMP) were compared in soil dispersion by separating soils into coarse (0.25-2 mm), medium (0.063-0.25 mm) and fine (<0.063 mm) size fractions. The first two fractions were further separated by density (1.8 g cm-3) to obtain free particulate organic C (POC) and mineral associated organic C (MOC). The approach was applied to a clay and a silt loam soil with and without wood fiber sludge amendment to follow the added C. Aggregate disruption was enhanced with SHMP in comparison to water, but the effect was small and the use of SHMP decreased recovery of SOC, wherefore water was preferred. In both soils, 5-10 % of SOC occurred as coarse POC, 1-3% as coarse MOC, 5 % as medium POC, 10 % as medium MOC, and 70-85 % as fine MOC. The added C resided in the POC fractions with an indication of minor accumulation to the fine MOC in the clay soil. Longer time frame with repeated C additions would be needed to increase the stable MOC storages though saturation of the MOC reserve may hinder accumulation in the silt loam low in fines.
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