In agricultural ecosystems, soil organic carbon (SOC) which is affected by management practices, is important for soil health, food security, and climate change mitigation. However, accurately assessing the influence of agricultural management practices on SOC storage is a challenge, due in part to the uncertainty of calculation approaches used to estimate SOC stocks. Although equivalent soil mass (ESM) is widely recommended over the fixed depth (FD) approach, few field studies directly compare FD with different ESM approaches. Hence, the magnitude of potential difference in estimated SOC stocks among different approaches is not well known. Here, we collected soil cores (0–60 cm depth) from a 24-yr experiment (Ridgetown, Ontario, Canada) to investigate (1) the effect of two tillage systems (conventional tillage: CT, moldboard plowing to ∼20 cm deep; no-tillage with zone tillage: NT/ZT) on different SOC estimates (n=448), including concentration and stocks estimated by FD and ESM (cubic spline interpolation model: ESM_cubic__spline, linear interpolation model: ESM_linear, and non-modeling fit: ESM_{non_model}); and (2) the relative difference of SOC stocks estimated by FD and ESM under NT/ZT system. The tillage effect on SOC stock was more pronounced than SOC concentration (P<0.05; except for 0–5 cm depth), indicating that using SOC concentration alone appears to be unreliable for evaluating tillage system effects on carbon sequestration. Furthermore, FD overestimated SOC stocks under NT/ZT (P<0.05), mainly due to greater soil bulk density than CT (P<0.05). Specifically, in the 0–60 cm depth, FD overestimated about 15% (or 30.6 Mg ha⁻¹) of cumulative SOC stocks than ESM_cubic__spline. However, the differences in SOC stocks estimated among three ESM approaches (ESM_cubic__spline, ESM_linear, and ESM_{non_model}) were negligible (P>0.05; Cohen’s d<0.2), suggesting that these approaches may work equally well when soil depth increment is small (< 10 cm). Overall, we recommend using the ESM approach to calculate SOC stock, especially when comparing treatments where soil bulk density varies. Our findings may help to guide policy decision-making towards more accurately quantifying SOC stock when considering climate change mitigation practices.

在农业生态系统中，受管理实践影响的土壤有机碳（SOC）对于土壤健康、粮食安全和减缓气候变化非常重要。然而，准确评估农业管理实践对 SOC 储存的影响是一项挑战，部分原因是用于估计 SOC 储量的计算方法的不确定性。尽管等效土体质量 (ESM) 比固定深度 (FD) 方法更被广泛推荐，但很少有现场研究直接将 FD 与不同的 ESM 方法进行比较。因此，不同方法估计的 SOC 储量潜在差异的大小尚不清楚。在这里，我们从一项为期 24 年的实验（加拿大安大略省里奇敦）收集了土芯（0-60 厘米深），以研究 (1) 两种耕作系统的效果（传统耕作：CT、犁耕至约 20 厘米深） ；免耕与区域耕作：NT/ZT）在不同的 SOC 估计值（n=448）上，包括通过 FD 和 ESM 估计的浓度和储量（三次样条插值模型：ESM __样条，线性插值模型：ESM_线性，以及非建模拟合：ESM _{non_model} ); (2)NT/ZT系统下FD和ESM估算的SOC储量的相对差异。耕作对 SOC 储量的影响比 SOC 浓度的影响更显着（P <0.05；0-5 cm 深度除外），表明单独使用 SOC 浓度来评估耕作系统对碳固存的影响似乎并不可靠。此外，FD 高估了 NT/ZT 下的 SOC 储量（P <0.05），主要是由于土壤容重大于 CT（P <0.05）。具体来说，在0-60 cm深度，FD比ESM_三次__{样条高估了约15%（或30.6 Mg ha} ^-1）的累积SOC库。_{然而，三种 ESM 方法（ESM三次}样_条、ESM_线性和 ESM _{non_model} ）估计的 SOC 储量差异可以忽略不计（P >0.05；Cohen's d<0.2），这表明当土壤深度增加时，这些方法可能同样有效。很小（< 10 厘米）。总体而言，我们建议使用 ESM 方法来计算 SOC 库，特别是在比较土壤容重变化的处理时。我们的研究结果可能有助于指导政策决策，在考虑减缓气候变化的做法时更准确地量化 SOC 存量。