Confusion persists regarding the potential for no-till (NT) farming to accumulate soil organic C (SOC) and mitigate climate change. This uncertainty could be partly due to shallow sampling (<40 cm soil depth) employed in most previous SOC publications. The specific objective of this study was to gain additional knowledge of SOC accumulated by a wide range of tillage systems in surface and deeper soil profiles in the long term (> 34 yr). We quantified SOC stock (Mg ha⁻¹) on an equivalent mass basis for the 0–60 or 100 cm soil depths for NT, disk, double disk, chisel plow, and moldboard plow under continuous corn and corn-soybean on silt clay loams after 34 yr and 39 yr in the western US Corn Belt. Results showed that NT did not increase SOC stocks near the surface but it did with cumulative depth relative to moldboard plow. No-till accumulated SOC at a rate of 0.68 Mg ha⁻¹ yr^-1 relative to inversion tillage (moldboard plow). However, NT did not store more SOC than common conventional (chisel plow) or reduced (disk) till practices for the whole soil profile. Results indicate that depth of soil sampling can affect conclusions about tillage system impacts on SOC stocks. For example, if we had sampled to 20 cm soil depth only, we would have incompletely concluded that NT does not significantly accumulate more SOC than moldboard plow. Results after 34 and 39 yr of tillage management also indicate that non-inversion tillage, particularly disk, can be as effective as NT for accumulating SOC. Overall, deep soil sampling can tell a different story about NT impacts on SOC stocks from shallow sampling.

关于免耕（NT）农业积累土壤有机碳（SOC）和缓解气候变化的潜力仍然存在困惑。这种不确定性可能部分归因于大多数先前的SOC出版物中采用的浅层采样（土壤深度<40 cm）。这项研究的具体目标是获得长期（> 34年）地表和较深土壤剖面中各种耕作系统积累的SOC的更多知识。我们量化了SOC库存（Mg ha ^-1）以相等的质量为基础，在西部34年和39年后，在连续的玉米和玉米-大豆条件下，在连续的玉米和玉米-大豆壤土下，NT，圆盘，双圆盘，凿子犁和mold土犁的0–60或100 cm土壤深度美国玉米带。结果表明，NT不会增加表层附近的SOC储量，但相对于刮土机犁具，其累积深度却会增加。免耕累积SOC的速率为0.68 Mg ha ^-1 yr ^-1相对于反向耕作（mol刨犁）。但是，在整个土壤状况下，NT不会比普通的传统（凿犁）或减少的（圆盘）存储更多的SOC。结果表明，土壤取样的深度会影响有关耕作制度对SOC储量的影响的结论。例如，如果仅取样到20 cm的土壤深度，我们将无法完全得出结论，NT不会比mold土犁累积更多的SOC。耕作管理的34年和39年后的结果还表明，非反转耕作（尤其是盘状耕作）在累积SOC方面与NT一样有效。总体而言，深层土壤采样可以从浅层采样中得出关于NT对SOC储量的影响的不同说法。