Abstract Increasing soil organic carbon (SOC) in agroecosystems enables to address simultaneously multiple goals such as climate change adaptation and mitigation as well as food security. As croplands are depleted in SOC, they offer a great potential to sequester atmospheric carbon (C). Nonetheless, croplands are still losing SOC under most of the current agricultural systems. Although many factors driving SOC dynamics have already been identified, their relative importance has not been quantified yet. Using one of the densest European soil monitoring networks with 250 sites established in western Switzerland, in the present study we (i) assessed long-term (over 30 years) SOC dynamics in croplands (CR), permanent grasslands (PG) and mountain pastures (MP), and (ii) prioritized the importance of land use, soil characteristics and sites conditions in driving SOC dynamics. The SOC levels in PG and MP were similar when clay content was accounted for, whereas CR were depleted in SOC by 3.9 mg C mg−1 clay as compared to PG. The majority (61 %) of CR had SOC:clay ratio below 1:10, but only 16 % of PG and MP sites reached this threshold. By contrast, soil organic matter stoichiometry (C:N:Porg ratios) was similar in CR and PG for comparable SOC content. The increase of C:Porg ratio with SOC content (dilution effect) and the high total P in CR and PG (legacy effect) indicate the possibility to sequester atmospheric C at reduced nutrient sequestration costs. SOC changes ranged from -0.61 to 1.32 mg g-1 soil yr−1 and were the highest in sites that experienced land-use changes. No PG were losing SOC, while CR sites exhibited both SOC gains and losses. Because of the predominance of the initial SOC content on SOC dynamics, land-use history must be accounted for when assessing the effect of management practices. The main manageable factors driving SOC dynamics were the time under temporary or permanent grasslands along with the soil total P. As PG already are rich in SOC and total P, organic amendments should be partly redirected to CR.

中文翻译：

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温带农田-草地系统中长期土壤有机碳动态

摘要 在农业生态系统中增加土壤有机碳 (SOC) 能够同时实现多个目标，如气候变化适应和减缓以及粮食安全。由于农田的 SOC 耗尽，它们为封存大气碳 (C) 提供了巨大的潜力。尽管如此，在目前的大多数农业系统下，农田仍在失去 SOC。尽管已经确定了许多驱动 SOC 动态的因素，但它们的相对重要性尚未量化。使用在瑞士西部建立的 250 个站点的最密集的欧洲土壤监测网络之一，在本研究中，我们 (i) 评估了农田 (CR)、永久性草地 (PG) 和山地牧场的长期（超过 30 年）SOC 动态(MP) 和 (ii) 优先考虑土地利用的重要性，土壤特征和场地条件在驱动 SOC 动态。当考虑粘土含量时，PG 和 MP 中的 SOC 水平相似，而与 PG 相比，SOC 中的 CR 消耗了 3.9 mg C mg-1 粘土。大多数 (61%) CR 的 SOC:粘土比例低于 1:10，但只有 16% 的 PG 和 MP 站点达到此阈值。相比之下，对于可比的 SOC 含量，CR 和 PG 的土壤有机质化学计量（C:N:Porg 比率）相似。C:Porg 比率随 SOC 含量的增加（稀释效应）以及 CR 和 PG 中的高总磷（遗留效应）表明有可能以降低的养分封存成本封存大气 C。SOC 变化范围为 -0.61 至 1.32 mg g-1 土壤 yr-1，并且在经历土地利用变化的地点中最高。没有 PG 失去 SOC，而 CR 站点表现出 SOC 增加和损失。由于初始 SOC 含量对 SOC 动态的主导作用，在评估管理实践的影响时必须考虑土地利用历史。驱动 SOC 动态的主要可管理因素是临时或永久草地下的时间以及土壤总磷。由于 PG 已经富含 SOC 和总磷，有机添加物应部分重定向到 CR。