Reliable estimations of soil organic carbon (SOC) deficits in agroecosystems are crucial in evaluating the atmospheric C sequestration potential of agricultural soils and supporting management decisions. Nonetheless, the co-benefit on soil quality resulting from SOC accrual is rarely considered. Here, we assessed SOC saturation and soil physical quality in permanent grasslands (PG) and croplands (CR) by applying the C-saturation concept and the SOC:clay ratio as an indicator of soil physical quality to a set of long-term monitoring sites in western Switzerland. For this goal, we produced a new relationship between the silt + clay (SC) particles and the C stored in the mineral-associated fraction (MAOM_C) and we assessed the assumption that grasslands can be used as C-saturated reference sites. The saturation in PG was not coincidental as it depended on the C accrual history. Hence, PG with the lowest MAOM_C have not reached their C-saturation level and present a potential SOC storage under optimal management. The MAOM_C saturation in CR was low (62 ± 4%) and corresponded to a deficit of −8.8 ± 1.2 mg C g⁻¹ soil as compared to the current level in PG. The saturation was mainly affected by the proportion of temporary grassland in the crop rotation. The relative distribution of C between MAOM (∼80%) and the fine and coarse particulate organic matter (POM) was not affected by land-use types. The MAOM_C saturation in this study (MAOM_C = 0.372 × SC + 4.23) was similar to that reported in the litterature, but discrepancies appeared when the silt and clay contents were considered separately. SC was by far the main factor explaining MAOM_C amount in PG (semi-partial R²: 0.66). In contrast to other studies, the C content of MAOM in PG (43 mg C g⁻¹ SC) was not related to the SC content, suggesting a fixed maximal value in C-saturated soils. Nonetheless, MAOM_C saturation may be underestimated as the least saturated PG might still accumulate MAOM_C. Finally, the SOC:clay ratio was correlated with MAOM_C saturation level in CR, but not in PG suggesting that targeting SOC accrual in CR optimizes the benefits between soil C storage and soil quality.

对农业生态系统中土壤有机碳 (SOC) 缺乏的可靠估计对于评估农业土壤的大气固碳潜力和支持管理决策至关重要。尽管如此，很少考虑 SOC 累积对土壤质量的共同利益。在这里，我们通过将 C 饱和度概念和 SOC:粘土比率作为土壤物理质量的指标应用于一组长期监测站点，评估了永久草地 (PG) 和农田 (CR) 的 SOC 饱和度和土壤物理质量在瑞士西部。为了这个目标，我们在粉砂 + 粘土 (SC) 颗粒和存储在矿物相关部分 (MAOM _C ) 中的 C 之间建立了新的关系) 并且我们评估了草原可以用作碳饱和参考点的假设。PG 的饱和并非巧合，因为它取决于 C 应计历史。因此，具有最低 MAOM _{C 的}PG尚未达到其 C 饱和水平，并在优化管理下呈现出潜在的 SOC 存储。与 PG 中的当前水平相比，CR 中的 MAOM _C饱和度较低 (62 ± 4%)，对应于 -8.8 ± 1.2 mg C g ^-1土壤的不足。饱和度主要受轮作临时草地比例的影响。MAOM (~80%) 与细颗粒和粗颗粒有机物 (POM) 之间 C 的相对分布不受土地利用类型的影响。本研究中的 MAOM _C饱和度 (MAOM_C  = 0.372 × SC + 4.23) 与文献中报道的相似，但在分别考虑粉砂和粘土含量时出现了差异。SC 是迄今为止解释PG 中MAOM _C量的主要因素（半偏 R ²：0.66）。与其他研究相比，PG 中 MAOM 的 C 含量（43 mg C g ^-1 SC）与 SC 含量无关，表明在 C 饱和土壤中具有固定的最大值。尽管如此，MAOM _C饱和度可能会被低估，因为饱和度最低的 PG 可能仍会积累 MAOM _C。最后，SOC：粘土比例与 MAOM _C相关 CR 中的饱和水平，但 PG 中没有，这表明在 CR 中针对 SOC 的增加优化了土壤碳储存和土壤质量之间的好处。