Cover crops are widely advocated for increasing soil organic carbon (SOC) levels, thereby benefiting soil health improvement and climate change mitigation. Few regional-scale studies have robustly explored SOC stocks under cover cropping, due to limited long-term experiments. We used the unique experimental data from the North American Project to Evaluate Soil Health Measurements conducted in 2019 to address this issue. This study included 19 agricultural research sites with 36 pairs of cover cropping established between 1896 and 2014. Explanatory variables related to site-specific environmental conditions and management practices were collected to identify and prioritize contributing factors that affect SOC stocks with cover crops, by coupling the Boruta algorithm and structural equation modeling. Overall, cover crops significantly (P < 0.05) improved several indicators of soil health, including greater SOC (concentration: +8%; stock: +7%), total nitrogen (+8%), water-stable aggregates (+15%), and potential carbon mineralization (+34%), on average, compared to no cover crop control. Likewise, on average, cover crops sequestered SOC 3.55 Mg C ha^-1 (0–15 cm depth), with a sequestration rate of 0.24 Mg C ha^-1 yr^-1. In addition, we found climate (Hargreaves climatic moisture deficit) was important in explaining the variation of SOC stocks with cover crops, followed by soil properties (e.g., soil clay content). In terms of management practices, cover crop type had a significant positive (0.36) effect on SOC stocks, with non-legumes showing a greater impact, compared to legumes and mixtures. Crop rotational diversity also had a positive (0.28) effect on SOC accumulation. Our findings suggested that integrating non-legume cover crops into diverse crop rotation is likely to be a promising strategy to maximize SOC stocks with cover crops across North America.

覆盖作物被广泛提倡用于增加土壤有机碳 (SOC) 水平，从而有利于改善土壤健康和减缓气候变化。由于长期实验有限，很少有区域规模的研究对覆盖种植下的 SOC 储量进行有力探索。我们使用了 2019 年进行的北美项目评估土壤健康测量的独特实验数据来解决这个问题。这项研究包括 19 个农业研究地点，在 1896 年至 2014 年间建立了 36 对覆盖作物。收集了与特定地点的环境条件和管理实践相关的解释变量，以通过耦合Boruta算法和结构方程建模。总体而言，覆盖作物显着（P  < 0.05）改善了土壤健康的几个指标，包括更高的 SOC（浓度：+8%；存量：+7%）、总氮 (+8%)、水稳性聚集体 (+15%) 和潜在碳矿化(+34%)，平均而言，与无覆盖作物控制相比。同样，平均而言，覆盖作物固存 SOC 3.55 Mg C ha ^-1（0–15 cm 深度），固存率为 0.24 Mg C ha ^-1 yr ^-1. 此外，我们发现气候（Hargreaves 气候水分亏缺）对于解释覆盖作物的 SOC 储量变化很重要，其次是土壤特性（例如，土壤粘土含量）。在管理实践方面，覆盖作物类型对 SOC 库存有显着的积极影响 (0.36)，与豆科植物和混合物相比，非豆科植物的影响更大。作物轮作多样性也对 SOC 积累有积极影响 (0.28)。我们的研究结果表明，将非豆科植物覆盖作物整合到多样化的作物轮作中可能是一种有前途的策略，可以最大限度地提高北美覆盖作物的 SOC 储量。