Crop straw return is being widely applied as a sustainable soil management practice to improve soil organic carbon (SOC) storage in intensive agricultural ecosystems. However, the dynamics and chemical composition of SOC under long-term straw return are not fully understood. Based on a 15-year field experiment with soybean (Glycine max (L.) Merrill.)–maize (Zea mays L.) cropping system, we studied SOC temporal dynamics under no fertilization (NF), mineral fertilizers (NPK) and mineral fertilizers with straw return (NPKS). Meanwhile, we determined five labile carbon (C) pools, i.e., microbial biomass C (MBC), water-soluble organic C (WSOC), light fraction C (LFC), readily oxidizable organic C (ROC), and particulate organic C (POC), as well as δ¹³C values and organic functional groups of soil organic matter (SOM). After 15-year application of continuous straw return with mineral fertilizer application, SOC content increased by 14.2%. The δ¹³C values of SOC increased with time under all treatments, and its positive relationship with cumulative maize C input indicated a larger C contribution to SOC from maize than soybean residues. The NPKS treatment significantly increased the contents of MBC, WSOC, LFC, ROC, and POC and their proportion in SOC, compared with the NF treatment. The aliphatic and aromatic relative peak areas were significantly affected by straw return, with an increasing relative peak area at 2930 cm⁻¹ and decreasing at 1620 cm⁻¹, respectively. Our results demonstrate that straw return could continuously increase SOC in an inter-annual rotation of soybean and maize cropping system in Mollisol. Meanwhile, long-term fertilization can alter SOM chemical composition, with lower humification degree under the combined application of straw and mineral NPK fertilizers.

农作物秸秆还田作为一种可持续的土壤管理实践被广泛应用，以改善集约化农业生态系统中土壤有机碳 (SOC) 的储存。然而，长期秸秆还田下 SOC 的动态和化学成分尚不完全清楚。基于对大豆（Glycine max (L.) Merrill.）-玉米（Zea mays L.）种植系统进行的 15 年田间试验，我们研究了在不施肥 (NF)、矿物肥料 (NPK) 和矿物秸秆还田肥料 (NPKS)。同时，我们确定了五个不稳定碳 (C) 库，即微生物生物量 C (MBC)、水溶性有机 C (WSOC)、轻质组分 C (LFC)、易氧化有机 C (ROC) 和颗粒有机 C ( POC)，以及 δ ¹³土壤有机质 (SOM) 的 C 值和有机官能团。连续施用秸秆还田并施矿肥15年后，SOC含量增加了14.2%。在所有处理下，SOC的δ ¹³ C 值随时间增加，其与累积玉米 C 输入的正相关表明玉米对 SOC 的 C 贡献大于大豆残留物。与NF处理相比，NPKS处理显着增加了MBC、WSOC、LFC、ROC和POC的含量及其在SOC中的比例。秸秆还田对脂肪族和芳香族相对峰面积的影响显着，2930 cm ^-1处相对峰面积增大，1620 cm ^-1处相对峰面积减小， 分别。我们的结果表明，在 Mollisol 的大豆和玉米种植系统的年际轮作中，秸秆还田可以持续增加 SOC。同时，长期施肥会改变SOM的化学成分，在秸秆和矿物NPK肥料的配合下，腐殖化程度较低。