Abstract. No-till (NT) cropping systems have been proposed as a strategy to combat soil degradation by storing soil organic carbon (SOC) and total nitrogen (TN). We quantified the impacts of NT cropping systems on the changes in SOC and TN stocks and in particulate and mineral-associated organic matter fractions (POM and MAOM), to 100 cm depth, from three 13-year-old experiments in a tropical red Oxisol in Cambodia using diachronic and equivalent soil mass approaches. Established in 2009 and arranged in a randomized complete-block design with triplicates, the experiments included maize (MaiEx)-, soybean (SoyEx)-, and cassava (CasEx)-based cropping systems. Each experiment comprised three treatments: (1) mono-cropping of main crops (maize, soybean, and cassava) under conventional tillage (CTM); (2) mono-cropping of main crops under NT systems with the use of cover crops (NTM); and (3) bi-annual rotation of main crops under NT systems with the use of cover crops (NTR), with both crops being presented every year and represented by NTR1 and NTR2. Soil samples were collected in 2021, 10 years after the last sampling. All the NT systems significantly (p<0.05) increased SOC stock in the topsoil in SoyEx and MaiEx and down to 40 cm in CasEx. Considering the whole profile (0–100 cm), the SOC accumulation rates ranged from 0.86 to 1.47 and from 0.70 to 1.07 Mg C ha−1 yr−1 in MaiEx and CasEx, respectively. Although SOC stock significantly increased in CTM at 0–20 cm in MaiEx and CasEx, it remained stable at 0–100 cm in all the experiments. At 0–5 cm, NTR systems significantly increased TN stock in all the experiments, while, in NTM systems, it was only significant in MaiEx and SoyEx. At 0–100 cm, TN stock in all the experiments remained stable under NTR systems, whereas a significant decrease was observed under NTM systems in SoyEx and CasEx. Although C-POM stock significantly increased under all NT systems limited to 0–10 cm in MaiEx and SoyEx, all the NT systems significantly increased C-MAOM stock in the 0–10 cm layer in MaiEx and SoyEx and down to 40 cm in CasEx. All the NT systems significantly increased N-POM stock at 0–10 cm in MaiEx and SoyEx, while a significant decreased in N-MAOM stock was observed below 5 cm in CasEx and below 40 cm in MaiEx and SoyEx. Our findings showed that long-term NT systems with crop species diversification accumulated SOC not only on the surface but also in the whole profile by increasing SOC in both the POM and MAOM, even in the cassava-based system. This study highlights the potential of NT systems for storing SOC over time but raises questions about soil N dynamics.

中文翻译：

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柬埔寨热带高地长期免耕耕作制度下土壤有机碳氮动态的历时评估


摘要。免耕 （NT） 种植系统已被提议作为一种通过储存土壤有机碳 （SOC） 和总氮 （TN） 来对抗土壤退化的策略。我们量化了 NT 种植系统对 SOC 和 TN 储量以及颗粒和矿物相关有机物组分（POM 和 MAOM）变化的影响，来自柬埔寨热带红 Oxisol 的三个 13 年实验，使用历时和等效土壤质量方法。成立于 2009 年，采用一式三份的随机完整区组设计排列，实验包括基于玉米 （MaiEx）、大豆 （SoyEx） 和木薯 （CasEx） 的种植系统。每个试验包括 3 个处理：（1） 常规耕作 （CTM） 下主要作物（玉米、大豆和木薯）的单季种植;（2） 在 NT 系统下使用覆盖作物 （NTM） 对主要作物进行单作种植;（3） 在 NT 系统下，主要作物每年半年轮作，使用覆盖作物 （NTR），两种作物每年展示一次，以 NTR1 和 NTR2 表示。土壤样本是在 2021 年收集的，距离上次采样已经过去了 10 年。所有 NT 系统均显著 （p<0.05） 增加了 SoyEx 和 MaiEx 表层土壤中的 SOC 储量，而 CasEx 的土壤有机碳储量下降到 40 cm。考虑到整个剖面 （0-100 cm），MaiEx 和 CasEx 的 SOC 积累率分别为 0.86 至 1.47 和 0.70 至 1.07 Mg C ha-1 yr-1。尽管 MaiEx 和 CasEx 中 0-20 cm 的 CTM 中 SOC 储量显著增加，但在所有实验中，SOC 储量在 0-100 cm 处保持稳定。在 0-5 cm 处，NTR 系统在所有实验中均显著增加 TN 原液，而在 NTM 系统中，仅在 MaiEx 和 SoyEx 中显著增加。 在 0–100 cm 处，所有实验中的 TN 原液在 NTR 系统下保持稳定，而在 SoyEx 和 CasEx 中，在 NTM 系统下观察到显著减少。尽管在所有 NT 系统下，C-POM 储量在 MaiEx 和 SoyEx 中均限于 0-10 cm，但所有 NT 系统均显著增加 MaiEx 和 SoyEx 中 0-10 cm 层的 C-MAOM 储量，在 CasEx 中降至 40 cm。所有 NT 系统在 MaiEx 和 SoyEx 中均显著增加了 0-10 cm 处的 N-POM 储量，而在 CasEx 中观察到 N-MAOM 储量低于 5 cm，在 MaiEx 和 SoyEx 中观察到低于 40 cm 的 N-MAOM 储量显著减少。我们的研究结果表明，具有作物物种多样化的长期 NT 系统不仅在表面积累了 SOC，而且通过增加 POM 和 MAOM 中的 SOC，甚至在基于木薯的系统中，也在整个剖面中积累了 SOC。这项研究强调了 NT 系统随时间储存 SOC 的潜力，但提出了关于土壤氮动力学的问题。