Cropping systems and fertilization have important effects on soil organic carbon (OC) and nitrogen (N) turnover and availability; however, little information exists about the interaction of cropping system and fertilization. Herein, we analyzed the dynamics of soil OC and N in a 31-year experiment in a highland agroecosystem to understand how the effects of fertilization vary with cropping systems. The experiment included different cropping systems, and each system included various fertilization treatments. The cropping systems were continuous alfalfa (Medicago sativa L.), continuous winter wheat (Triticum aestivum L.), and grain-legume rotation of winter wheat + millet (Panicum miliaceum L.) - pea (Pisum sativum L.) - winter wheat. The fertilization treatments were the control (CK), phosphorous (P), P and nitrogen (NP) and NP and manure (NPM). A bare fallow treatment that did not receive any crop and fertilizer was designed to compare the effects of the cropping systems. The soil samples were collected at different times of the experiment. The contents of OC, N, and labile OC were measured, and the carbon management index was calculated. When averaged across the experimental periods, soil OC, N, labile OC and carbon management index were significantly higher in the pure legume (i.e., continuous alfalfa) system than in the bare fallow and nonlegume system (i.e., continuous winter wheat) due to the higher C and N inputs from root biomass. The NP and NPM significantly increased these soil variables, and the effects of NPM were greater than those of NP due to the higher supplying of C and N in NPM treatment than NP treatment. However, the effects of NP or NPM on soil OC and N contents were similar among the cropping systems. The effects of P were greater in the continuous alfalfa system but smaller in the continuous winter wheat system in comparison with those in the grain-legume rotation system. Therefore, at the conditions of our study, legume-included cropping systems with large root biomass and manure combined with chemical fertilizers have the potential to increase OC and N and their availability in highland soils, which could be important strategies for improving soil fertility and quality and sequestrating C in soils. Moreover, P fertilizer was recommended for the legume-included cropping systems.

种植系统和施肥对土壤有机碳 (OC) 和氮 (N) 的周转和有效性具有重要影响；然而，关于种植系统和施肥之间相互作用的信息很少。在此，我们在高原农业生态系统的 31 年实验中分析了土壤 OC 和 N 的动态，以了解施肥的影响如何随耕作系统而变化。实验包括不同的种植系统，每个系统包括不同的施肥处理。种植方式为连作苜蓿（Medicago sativa L.）、连作冬小麦（Triticum aestivum L.）、冬小麦+小米（Panicum miliaceum L.）-豌豆（Pisum sativumL.) - 冬小麦。施肥处理为对照(CK)、磷(P)、磷和氮(NP)和NP和粪肥(NPM)。未接受任何作物和肥料的裸休耕处理旨在比较种植系统的效果。在实验的不同时间收集土壤样品。测定OC、N、不稳定OC的含量，计算碳管理指标。当在整个实验期间取平均值时，纯豆科植物（即连续苜蓿）系统中的土壤 OC、N、不稳定 OC 和碳管理指数显着高于裸休耕和非豆科植物系统（即连续冬小麦），这是由于来自根生物量的更高的 C 和 N 输入。NP 和 NPM 显着增加了这些土壤变量，由于NPM处理比NP处理更高的C和N供给，NPM的影响大于NP的影响。然而，NP 或 NPM 对土壤 OC 和 N 含量的影响在不同的种植系统中是相似的。与谷物-豆类轮作系统相比，连续苜蓿系统中磷的影响更大，但在连续冬小麦系统中的影响较小。因此，在我们研究的条件下，具有大根生物量和粪便的豆科作物系统与化肥相结合有可能增加 OC 和 N 及其在高原土壤中的可用性，这可能是提高土壤肥力和质量的重要策略并在土壤中封存 C。此外，建议将磷肥用于包含豆类的种植系统。